High-Order Adaptive Optics Design Requirements · High-Order Adaptive Optics Design Requirements...

Project Documentation Document SPEC-0146

Revision A

High-Order Adaptive Optics Design Requirements

Luke Johnson, Keith Cummings, Mark Drobilek, Scott Gregory, Erik Johansson, Kit Richards, Friedrich

Wöger

WFC Group

April 2018

Name Date

Released By: Rob Hubbard

Systems Engineer 30-April-2018


SPEC-0146, Revision A Page ii

REVISION SUMMARY:

1. Date: August 2016 Revision: Draft Changes: First draft of the requirements.

2. Date: April 2018 Revision: A Changes: Significant updates. Initial revision-controlled release for CDR.

3.


SPEC-0146, Revision A Page iii

Table of Contents

1. Overview .............................................................................................................. 1

1.1 Document Scope ................................................................................................ 1

1.2 Related Documents ............................................................................................ 1

1.3 Interface Control Documents ............................................................................ 1

1.4 Verification Methods .......................................................................................... 1

1.5 Specific Definitions and Terminology .............................................................. 2

2. General Requirements ........................................................................................ 4

2.1 WFC general requirements ................................................................................ 4

3. HOAO Optical Requirements .............................................................................. 5

3.1 M5 Optical Requirements .................................................................................. 5

3.2 M10 Optical Requirements................................................................................. 5

3.3 HOWFS Optical Requirements .......................................................................... 5

3.3.1 Optical Interface ........................................................................................................... 5

3.3.2 Optical Design .............................................................................................................. 5

3.3.3 Optical Performance .................................................................................................... 8

3.3.4 HOWFS Field steering mirror....................................................................................... 9

3.3.5 Lenses ........................................................................................................................... 9

3.3.6 Microlens array ............................................................................................................19

3.4 NCP Wavefront Sensor .................................................................................... 20

3.4.1 Beam expansion optics...............................................................................................20

3.4.2 PA&C reflective sphere ...............................................................................................20

3.4.3 NCP reference flat .......................................................................................................21

4. HOAO Mechanical Requirements .................................................................... 22

4.1 M5 Assembly ..................................................................................................... 22

4.1.1 Mount positioning: resolution ....................................................................................22

4.1.2 M5 dummy ...................................................................................................................22

4.1.3 Uniformity between M5 Assembly and M5 dummy ...................................................22

4.1.4 Mechanical Performance ............................................................................................23

4.2 DM Assembly .................................................................................................... 23

4.2.1 M10 dummy..................................................................................................................23

4.2.2 Uniformity between M10 Assembly and M10 dummy ...............................................23

4.2.3 Mechanical Performance ............................................................................................23


SPEC-0146, Revision A Page iv

4.3 HOWFS Stages and Mechanisms .................................................................... 23

4.3.1 Locking mechanisms ..................................................................................................23

4.3.2 Field Steering mirror ...................................................................................................24

4.3.3 Objective lens assembly .............................................................................................24

4.3.4 Field stop mount assembly ........................................................................................25

4.3.5 Pupil lens mount assembly ........................................................................................26

4.3.6 Lenslet array mount assembly ...................................................................................26

4.3.7 Relay lens #1 mount assembly ...................................................................................27

4.3.8 Relay lens #2 mount assembly ...................................................................................28

4.3.9 Camera mount assembly ............................................................................................29

4.4 HOWFS Optics mount stability ........................................................................ 29

4.5 HOWFS Camera ................................................................................................ 30

4.5.1 Format ..........................................................................................................................30

4.5.2 Pixel size ......................................................................................................................30

4.5.3 Quantum efficiency .....................................................................................................30

4.5.4 Fill factor ......................................................................................................................30

4.5.5 Full Well .......................................................................................................................30

4.5.6 Linearity .......................................................................................................................31

4.5.7 Artifacts ........................................................................................................................31

4.5.8 Frame Rate ...................................................................................................................31

4.5.9 Flexible Integration time .............................................................................................31

4.5.10 Read Noise ...................................................................................................................31

4.5.11 Internal Noise ...............................................................................................................31

4.5.12 Bias Frame Stability ....................................................................................................32

4.5.13 Pixel Gain Stability ......................................................................................................32

4.5.14 Digitization ...................................................................................................................32

4.5.15 Faint Image Tracking ...................................................................................................32

4.5.16 Granulation tracking ...................................................................................................32

4.5.17 Streaming readout .......................................................................................................32

4.5.18 Read latency ................................................................................................................33

4.5.19 Full-frame read time ....................................................................................................33

4.5.20 Simultaneous readout .................................................................................................33

4.5.21 Power dissipation ........................................................................................................33

4.5.22 Heat management........................................................................................................33


SPEC-0146, Revision A Page v

4.6 HOAO calibration sources ............................................................................... 33

4.6.1 HOAO GOS pinhole .....................................................................................................33

4.6.2 GOS calibration lamp ..................................................................................................35

4.6.3 GOS reflective sphere .................................................................................................35

5. HOAO Algorithm Functionality REQUIREMENTS ........................................... 36

5.1 Extract multiple Regions of Interest from Full Frame ................................... 36

5.2 Dark Calibration ................................................................................................ 36

5.3 Gain Calibration ................................................................................................ 36

5.4 Calibration of subaperture images ................................................................. 37

5.5 Subaperture Shift Measurement ..................................................................... 37

5.5.1 Cross-correlation algorithm .......................................................................................37

5.5.2 Computation of image displacements to subpixel accuracy ...................................38

5.6 Wavefront Reconstruction ............................................................................... 38

5.7 PI Servo Loop ................................................................................................... 38

5.8 Tip-Tilt Derotation ............................................................................................. 39

5.9 Fast Tip-Tilt Offload to Mount .......................................................................... 39

5.10 R0 calculation .................................................................................................... 40

5.11 Residual error calculation................................................................................ 40

5.12 DM rms calculation ........................................................................................... 41

5.13 HOAO Modal Coefficient Computation from Subaperture Shifts ................. 41

5.14 HOAO Modal Coefficient Computation from Actuator Commands .............. 42

5.15 HOAO Modal Coefficient Confidence ............................................................. 42

5.16 DM Interactuator Voltage Limitation ............................................................... 43

5.17 OOB Subaperture Shift Detection ................................................................... 43

5.18 DM Interaction Matrix Calibration ................................................................... 44

5.19 HOAO Automatic Gain and Reconstruction Matrix Optimization ................. 44

5.20 Mitigation of Bad Seeing or Loop Instability .................................................. 44

5.21 HOWFS Automatic exposure time adjustment .............................................. 46

5.22 HOWFS Pupil position measurement ............................................................. 46

5.23 Absolute Error after Calibration ...................................................................... 47

5.23.1 Total wavefront error ...................................................................................................47

5.23.2 HOAO error budget .....................................................................................................47

6. HOAO Software Requirements ......................................................................... 48


SPEC-0146, Revision A Page vi

6.1 General Requirements ..................................................................................... 48

6.1.1 Division of software tasks ..........................................................................................48

6.2 HOAO System Settings Requirements ........................................................... 48

6.2.1 WFC mode ...................................................................................................................48

6.2.2 r0 Calculation Period ...................................................................................................48

6.2.3 r0 Calculation Frameskip .............................................................................................49

6.2.4 aO Engine Event Period ..............................................................................................49

6.2.5 aO Engine Event Basis ...............................................................................................49

6.2.6 aO Engine Event Frameskip .......................................................................................50

6.2.7 HOAO Frame Rate .......................................................................................................50

6.2.8 HOAO Camera Exposure Control Method .................................................................50

6.2.9 HOAO Camera Exposure Time ...................................................................................51

6.2.10 HOAO Minimum Flux per Exposure ...........................................................................51

6.2.11 HOAO Maximum Flux per Exposure ..........................................................................51

6.2.12 HOAO Exposure Time Update Period ........................................................................52

6.2.13 Load High-Order Reconstruction Matrix ....................................................................52

6.2.14 Load Low-Order Shift Reconstruction Matrix ............................................................52

6.2.15 Load Low-Order Actuator Reconstruction Matrix .....................................................53

6.2.16 Servo Gain Update period ...........................................................................................53

6.2.17 High-Order Servo Loop DM Gain Control Method .....................................................53

6.2.18 High-Order Servo Loop DM Gains ..............................................................................54

6.2.19 High-Order Servo Loop FTT Gain Control Method ....................................................54

6.2.20 High-Order Servo Loop FTT Gains .............................................................................54

6.2.21 Load Actuator Gains Array .........................................................................................55

6.2.22 Load Actuator Offsets Array .......................................................................................55

6.2.23 Reference Subaperture ID ...........................................................................................55

6.2.24 Reference Image Update Method ...............................................................................55

6.2.25 Reference Image Update Period .................................................................................56

6.2.26 Reference Image Tolerance Threshold ......................................................................56

6.2.27 Reference Image Contrast Threshold ........................................................................56

6.2.28 Get New Reference on Lock .......................................................................................57

6.2.29 Get Immediate Reference ............................................................................................57

6.2.30 Get Tolerance Reference ............................................................................................57

6.2.31 Apply DM Actuator Map ..............................................................................................58


SPEC-0146, Revision A Page vii

6.2.32 Apply DM Modal Coefficients .....................................................................................58

6.2.33 DM Out of Bounds Threshold .....................................................................................58

6.2.34 DM OOB Gain Increment .............................................................................................59

6.2.35 DM OOB recovery period ............................................................................................59

6.2.36 FTT Out of Bounds Threshold ....................................................................................59

6.2.37 FTT Out of Bounds Gain Increment ...........................................................................60

6.2.38 FTT OOB recovery period ...........................................................................................60

6.2.39 FTT Range Offload Threshold ....................................................................................60

6.2.40 FTT Offload Period ......................................................................................................61

6.2.41 FTT Offload Gain .........................................................................................................61

6.2.42 Pupil Motion Subaperture Selection ..........................................................................61

6.2.43 Pupil Motion Measurement Period .............................................................................62

6.2.44 Number of Images to Accumulate ..............................................................................62

6.2.45 Load DM registration pattern ......................................................................................63

6.3 HOAO System Mode Requirements ................................................................ 63

6.3.1 Off .................................................................................................................................63

6.3.2 Idle ................................................................................................................................63

6.3.3 Calibrate .......................................................................................................................63

6.3.4 WFC-OPM1: Diffraction limited on-disk .....................................................................67

6.3.5 WFC-OPM2: Seeing limited on-disk ...........................................................................68

6.3.6 WFC-OPM3: Seeing limited coronal ...........................................................................68

6.3.7 WFC-OPM4: Limb occulting with image stabilization ...............................................69

6.4 Mechanism Control Requirements ................................................................. 69

6.4.1 Field Steering Mirror Postion......................................................................................69

6.4.2 Objective Lens Look-up Table ....................................................................................69

6.4.3 Objective Lens Position ..............................................................................................69

6.4.4 Active Field Stop Assembly Aperture .............................. Error! Bookmark not defined.

6.4.5 Microlens Array Position ............................................................................................70

6.4.6 Relay Lens #1 Position ...............................................................................................70

6.4.7 Relay Lens #2 Position ...............................................................................................70

6.4.8 Camera Mount Position...............................................................................................70

6.4.9 Camera Relay Optics Assembly Position ..................................................................71

6.5 Interface Requirements .................................................................................... 71

6.5.1 WCCS interface ...........................................................................................................71


SPEC-0146, Revision A Page viii

6.5.2 Engineering user interface .........................................................................................71

6.5.3 HOAO status screen ....................................................................................................71

6.6 Real-Time system requirements ..................................................................... 72

6.6.1 Compute time ..............................................................................................................72

6.6.2 FPGA firmware ............................................................................................................72

6.7 HOAO telemetry data products ....................................................................... 72

6.7.1 Telemetry latency ........................................................................................................72

6.7.2 Telemetry data format .................................................................................................73

6.7.3 Header Data .................................................................................................................73


SPEC-0146, Revision A Page 1 of 73

1. Overview

1.1 Document Scope

The High-Order Adaptive Optics (HOAO) Design Requirements Document (DRD) details all

requirements used to guide the design of the HOAO component of the Wavefront Correction (WFC)

system.

1.2 Related Documents

SPEC-0001, Science Requirements Document

SPEC-0005, Software and Controls Requirement

SPEC-0012, DKIST Acronym List and Glossary

SPEC-0013, Software Concepts Definitions

SPEC-0014, Software Design

SPEC-0022, Common Services Framework Reference Design

SPEC-0058, Wavefront Correction System Specifications Document

SPEC-0063, Interconnects and Services

SPEC-0061, Hazard Analysis Plan

SPEC-0068, M5 Tip Tilt Module Specification

SPEC-0070, DKIST Standard Environmental Conditions

SPEC-0109, M5 Tip Tilt Mirror Specification

SPEC-0111, M10 Deformable Mirror Specification

SPEC-0125, High Order Adaptive Optics Real Time FPGA Firmware Specification

SPEC-0129, Wavefront Correction Operational Concepts Model

SPEC-0147, High Order Adaptive Optics Critical Design Document

SPEC-0149, Haleakala Environmental Design Specification

SPEC-0174, WFC Generic Requirements

[1] Generic Criteria for Vibration-Sensitive Equipment, Colin G. Gordon, Proc. SPIE 1619, 1991.

1.3 Interface Control Documents

ICD 1.2-2.3 M1 Assembly to Wavefront Correction Control System

ICD 1.3-2.3 Top End Optical Assembly to Wavefront Correction Control System

ICD 1.5-2.3 Feed Optics to Wavefront Correction Control System

ICD 2.1-2.3 Wavefront Correction Coudé to Wavefront Correction Control System

ICD 2.3-4.4 Wavefront Correction Control System to Telescope Control System

1.4 Verification Methods

Included in each major numbered specification listed in this document is a requirement verification

method. These verification methods specify the minimum standards of verification required to ensure that

the individual requirements and specifications are met.

Examples of verification methods include:

Design Review. Verification by design review means that it is shown during an appropriate

design review that the system meets specification by way of its intrinsic design and configuration.

Analysis. Verification by analysis demonstrates that the design meets the specification through

use of performance modeling metrics.



Test. Verification by test and/or measurement means that it is demonstrated that the as-built

system meets the specification through measurements of its operation performance. Testing is

performed during acceptance testing and/or as part of a pre-ship readiness review.

Inspection. Verification by inspection means that visual inspection verifies that the specification

has been achieved on the as-built system during preassembly and/or during Site assembly.

1.5 Specific Definitions and Terminology

Daniel K. Inouye

HOAO

K-L

High Order Adaptive Optics

Abbreviation Meaning

α

β

γ

aO

CDD

CSF

CV

DIQ

DKIST

Slow rotation about the local x-axis

Slow rotation about the local y-axis

Slow rotation about the local z-axis

Active Optics

Critical Design Document

Common Services Framework

Context Viewer

Delivered Image Quality

Daniel K. Inouye Solar Telescope

DM

DRD

Deformable Mirror

Design Requirements Document

FOV

FTT

GOS

HOAO

HOWFS

IT&C

K-L

LOWFS

LT

LUT

M1CS

ms

NCP

nm

Field-of-view

Fast Tip-Tilt

Gregorian Optical Station

High-Order Adaptive Optics

High-Order Wavefront Sensor

Integration, Testing, and Commissioning

Karhunen-Loéve (modal basis)

Low Order Wavefront Sensor

Limb Tracker

Lookup Table

M1 Control System

millisecond, 10-3 second

Non-Common Path

nanometer, 10-9 meter

OCD Operational Concepts Definition

OCS

OOB

QSA

RTC

SRD

TCS

TEOACS

TMA

VC-B

Observatory Control System

Out-of-box, shifts that are larger than the subaperture capture range

Quasi-Static Alignment

Real-Time Controller

Science Requirements Document

Telescope Control System

Top End Optical Assembly Control System

Telescope Mount Assembly

Vibration Criterion, class B (25 µm/sec rms)



WBS

WCCS

WFC

Work Breakdown Structure

Wavefront Correction Control System

Wavefront Correction System



2. General Requirements

High Order Adaptive Optics (HOAO) requirements flow down from top-level Wavefront Correction

(WFC) science and operational requirements as well as general facility requirements for DKIST. In some

instances, the flowdown is explained in more detail in the HOAO Critical Design Document (CDD), in

which case the HOAO CDD will be referenced as a secondary origin of the requirement.

2.1 WFC general requirements

The WFC HOAO shall meet all applicable WFC Generic requirements. These requirements shall be

tracked in the HOAO Compliance Matrix (CMX-0007) and assigned numbers prefixed with the HOAO

WBS number, 2.1.1.

Verification: Varies

Requirement Origin: Science, Engineering, Operations, Safety (SPEC-0174)



3. HOAO Optical Requirements

3.1 M5 Optical Requirements

M5 optical requirements are contained in SPEC-0109. The compliance matrix associated with these

requirements appears in the L3/Brashear contract documents.

3.2 M10 Optical Requirements

M10 optical requirements are contained in SPEC-0111. The compliance matrix associated with these

requirements appears in the AOA Xinetics contract documents.

3.3 HOWFS Optical Requirements

3.3.1 Optical Interface

REQ# 2.1.1-1000

The HOWFS optical interface shall be defined by the reflective surface of the HOWFS/CV beamsplitter.

Verification: Design Review

Requirement Origin: Engineering

3.3.2 Optical Design

The Optical Design Requirements that appear in this section are those used to drive the optical design of

the HOWFS. After completion of the design, requirements on optical components were created based on

the accepted final optical design. Many of the component-level requirements in following sections

supersede the requirements in this section. However, the requirements in this section remain to justify the

decisions made during the HOWFS optical design process.

3.3.2.1 Sensor Type

REQ# 2.1.1-1005

The HOWFS shall be a Shack-Hartmann wavefront sensor.

Verification: Design Review, & Inspection

Requirement Origin: Science (SPEC-0058, 2.1.1-0010)

3.3.2.2 Pupil imaging capability

REQ# 2.1.1-1010

The HOWFS shall be able to be reconfigured so that the pupil-plane lenslet array is imaged on the

detector, with the full pupil diameter not exceeding the active sensor length or width, but extending at

least 80% across the smaller of active sensor length and width. The steps required to achieve this

configuration shall be automated through the use of translating stages.

Verification: Design Review, Inspection, & Test

Requirement Origin: Engineering (SPEC-0129, 4.3.6)



3.3.2.3 HOWFS Off-Pointing

REQ# 2.1.1-1015

The HOWFS shall be able to adjust its pointing so that the center of the HOWFS field of view is

displaced from the telescope boresight by 20 arcseconds in any direction.

Verification: Design Review, Analysis & Test


3.3.2.4 Subaperture count

REQ# 2.1.1-1020

The HOWFS shall contain 43 fully-illuminated subapertures across the pupil diameter, with a total of

1405 fully-illuminated subapertures.

Note: For purposes of this requirement, a fully-illuminated subaperture is defined as a subaperture whose

active lenslet area is ≥ 90% filled by the telescope pupil.

Verification: Design Review & Analysis

Requirement Origin: Engineering (SPEC-0111, DMS-REQ-0004)

3.3.2.5 Subaperture Field of View

REQ# 2.1.1-1025

Each subaperture of the HOWFS shall have a FoV of 10 0.5 arcseconds.


Requirement Origin: Science (SPEC-0058, 2.1.1-0025; SPEC-0147)

3.3.2.6 Pupil Size

REQ# 2.1.1-1030

The pupil diameter on the HOWFS lenslet array shall be larger than 16.0 mm and smaller than 25.0 mm.

Verification: Design Review, Analysis & Inspection

Requirement Origin: Engineering (SPEC-0147)

3.3.2.7 Pupil Adjustability

REQ# 2.1.1-1035

The pupil size on the HOWFS lenslet array shall be adjustable to at least 15% of its nominal value.

Note: This adjustability is to allow for compensation of manufacturing defects during alignment.


Requirement Origin: Science (SPEC-0058, 2.0-0015, SPEC-0147)

3.3.2.8 Lenslet focal length

REQ# 2.1.1-1040

The focal length of the lenslets in the HOWFS lenslet array shall be greater than or equal to 25 mm and

less than or equal to 100 mm.



Verification: Design Review & Test


3.3.2.9 Subaperture image separation

REQ# 2.1.1-1045

Subaperture images at the detector plane of the HOWFS shall not overlap each other, nor shall any two

adjacent subaperture images be separated by more than one pixel (11.5 microns).

Verification: Design Review & Inspection


3.3.2.10 Plate Scale

REQ# 2.1.1-1050

The final focal plane of the HOWFS shall have a plate scale of 43.48 2.17 arcseconds per mm.

Note: the HOWFS camera is required to have 11.5 micron square pixels (REQ# 2.1.1-2155) and each

subaperture has a 10 arcsecond square field of view. To obtain 20 pixels across each subaperture, the final

plate scale must be (100.5)/(20 *11.5e-3) = 43.48 2.17 arcseconds/mm


Requirement Origin: Science (SPEC-0058, 2.1.1-0025; SPEC-0147)

3.3.2.11 Plate Scale Adjustability

REQ# 2.1.1-1055

The plate scale at the final focal plane of the HOWFS shall be adjustable to at least 15% of its nominal

value.

Note: This adjustability is to compensate for manufacturing defects during alignment.


Requirement Origin: Science (SPEC-0058, 2.0-0015, SPEC-0147)

3.3.2.12 HOWFS total length

REQ# 2.1.1-1060

The final detector plane of the HOWFS shall be no more than 1.5 meters from the HOWFS field stop.



3.3.2.13 Wavelength

REQ# 2.1.1-1065

The HOWFS shall be optimized for operation at a wavelength of 525 nm with a bandpass of 100 nm.

Note: The HOWFS is expected to use a Schott VG-9 filter or equivalent.





3.3.3 Optical Performance

3.3.3.1 Dynamic Refocus

REQ# 2.1.1-1070

When off-pointing, the HOWFS shall use a lookup table to automatically move the objective lens to

compensate for mean field curvature.

Note: It is expected that gradual image quality degradation will occur when pointing off-axis. Dynamic

refocus will compensate for much of the image degradation but the Strehl requirement is only specified

on-axis.


Requirement Origin: Science (SPEC-0058, 2.0-0015)

3.3.3.2 Pupil Distortion

REQ# 2.1.1-1075

Maximum distortion between the M10 pupil and the pupil at the HOWFS lenslet array shall be less than

5% of a HOWFS subaperture.



3.3.3.3 Image Distortion

REQ# 2.1.1-1080

Maximum distortion between the lenslet array focal plane and the detector focal plane shall be less than

11.5 microns (one pixel).



3.3.3.4 Image Quality over central FOV

REQ# 2.1.1-1085

As designed, mean Strehl over the on-axis 10 arcsecond field of view shall be greater than 0.96 when

measured at the HOWFS field stop.

Verification: Design Review, Analysis

Requirement Origin:Science (SPEC-0058, 2.0-0015), Engineering (SPEC-0147)

3.3.3.5 HOWFS Lens Manufacturing Tolerances

REQ# 2.1.1-1090

Including manufacturing error, the final mean Strehl in every subaperture shall be greater than or equal to

0.90 over the on-axis 10 arcsecond HOWFS field of view.


Requirement Origin: Engineering (SPEC-0058, 2.0-0015), Engineering (SPEC-0147)



3.3.4 HOWFS Field steering mirror

REQ# 2.1.1-1095


Requirement Origin: Engineering (SPEC-0146, 2.1.1-1085)

3.3.5 Lenses

The HOAO lenses shall have properties within the tolerances specified in the lens drawings below



3.3.5.1 Objective lens

REQ# 2.1.1-1100





3.3.5.2 Pupil lens, element #1

REQ# 2.1.1-1105






REQ# 2.1.1-1110






REQ# 2.1.1-1115





3.3.5.5 Relay lens 1, element #1

REQ# 2.1.1-1120






REQ# 2.1.1-1125






REQ# 2.1.1-1130






REQ# 2.1.1-1135






REQ# 2.1.1-1140






REQ# 2.1.1-1145



3.3.6 Microlens array

3.3.6.1 Array dimensions

REQ# 2.1.1-1150

The HOWFS microlens array shall have a clear aperture that is a minimum of 21.5 mm in diameter and

contains at least 43 complete subapertures across its diameter. The array shall be 1.5 0.1 mm thick.



3.3.6.2 Focal length

REQ# 2.1.1-1155

All microlenses within the clear aperture of the HOWFS microlens array shall have focal length equal to

56 0.5 mm.





3.3.6.3 Pitch

REQ# 2.1.1-1160

The HOWFS microlens array shall consist of square microlenses with lateral dimensions equal to 0.500

0.005 mm.



3.3.6.4 Optical quality

REQ# 2.1.1-1165

Each microlens within the clear aperture of the HOWFS microlens array shall introduce a maximum of

/10 P-V wavefront distortion @ = 633 nm.



3.4 NCP Wavefront Sensor

REQ# 2.1.1-1170

The NCP wavefront sensor shall consist of an interferometer, beam expansion optics, a reflective sphere

at the GOS, a stabilized laser, and a reference flat. The NCP wavefront sensor shall be able to be inserted

and removed without perturbing any DKIST optics.


Requirement Origin: Science (SPEC-0058, 2.0-0015; SPEC-0009, Case1a)

3.4.1 Beam expansion optics

REQ# 2.1.1-1175

The NCP wavefront sensor beam expansion optics shall be insertable into the optical path of the science

light just past BS1. The NCP wavefront sensor shall be capable of measuring the wavefront over the

diameter of the full telescope pupil at that point. The beam expansion optics shall add less than 20 nm rms

wavefront aberration to the interferometer measurement and any aberrations shall be known and

repeatable to within 5 nm rms wavefront.

Note: The beam exiting BS1 is approximately 222 mm in diameter.

Verification: Design Review& Test


3.4.2 PA&C reflective sphere

REQ# 2.1.1-1185

The PA&C shall provide a reflective sphere as a selectable target at the Gregorian (second) focus of the

telescope. The sphere shall be positioned at the center of the telescope FoV, have a surface figure that

deviates from a perfect sphere by less than 20 nm rms over the surface illuminated by the laser source.



Note: Further requirements for the reflective sphere, including mechanical drawings, are in the PA&C

DRD.



3.4.3 NCP reference flat

REQ# 2.1.1-1190

The NCP wavefront sensor shall have a reference flat that serves as an absolute wavefront reference. This

flat shall have a maximum deviation from flatness of 7.0 nm rms wavefront (3.5 nm rms surface figure).

Note: This requirement is the equivalent of a /20 flat assuming = 632.8 nm





4. HOAO Mechanical Requirements

This section contains the requirements for mechanical stages, mounts, motors, and other HOAO

mechanisms. Requirements in this section can be traced through the HOAO compliance matrix to their

justifications in the CDD or higher-level documents.

4.1 M5 Assembly

4.1.1 Mount positioning: resolution

REQ# 2.1.1-2000

The mount for the M5 Assembly shall allow the mirror surface to be manually adjustable to within the

following resolutions:

x translation: 0.5 mm

y translation: 0.5 mm

z translation: 0.5 mm

x-tilt: 5 arcseconds (24.2 microradians)

y-tilt: 5 arcseconds (24.2 microradians)



4.1.2 M5 dummy

REQ# 2.1.1-2005

The M5 FTT module and mirror shall be replaceable by a “dummy” mirror and module in order to allow

testing or repair of the M5 FTT mirror and/or module. The dummy mirror shall meet all non-dynamic

requirements of the M5 mirror as described in SPEC-0109. The M5 dummy module shall be a static

mount that meets all requirements in SPEC-0068 except those that deal with dynamic motion or

adjustability.



4.1.3 Uniformity between M5 Assembly and M5 dummy

REQ# 2.1.1-2010

When exchanging the M5 assembly with the M5 dummy or vice-versa, any resulting misalignment of the

optical surface shall be less than the following:

x translation: 1 mm

y translation: 1 mm






Note: Manual realignment is allowed to achieve this requirement, however, any necessary manual

alignment must be easily done without sunlight and require less than 30 minutes to perform.



4.1.4 Mechanical Performance

M5 module mechanical performance requirements are contained in SPEC-0068. A full compliance matrix

is contained in the M5 assembly contract documents.

4.2 DM Assembly

4.2.1 M10 dummy

REQ# 2.1.1-2015

The M10 assembly shall be replaceable by a “dummy” mirror in order to allow testing or repair. The

dummy mirror shall meet all non-dynamic requirements of the DM as described in SPEC-0111.



4.2.2 Uniformity between M10 Assembly and M10 dummy

REQ# 2.1.1-2020

When exchanging the M10 assembly with the M10 dummy or vice-versa, any resulting misalignment of

the optical surface shall be less than the following:

x translation: 1 mm

y translation: 1 mm




Note: Manual realignment is allowed to achieve this requirement, however, any necessary manual

alignment must be easily done without sunlight and require less than 30 minutes to perform.



4.2.3 Mechanical Performance

M10 assembly mechanical performance requirements are contained in SPEC-0111. A full compliance

matrix is contained in the M10 FDR documentation.

4.3 HOWFS Stages and Mechanisms

4.3.1 Locking mechanisms

REQ# 2.1.1-2021



All manually-adjustable HOWFS stages and mechanisms shall have locking mechanisms that allow them

to be manually locked in place. Engaging the locking mechanism shall not change the position of the

optic by more than the mechanism’s repeatability requirement.


Requirement Origin: Operations (SPEC-0129, 4.3), Engineering (SPEC-0147)

4.3.2 Field Steering mirror

4.3.2.1 Field Steering mirror: automation

REQ# 2.1.1-2025

The HOWFS field steering mirror shall be motorized so that it can be automatically controlled in α and β

rotation.


Requirement Origin: Science (SPEC-0058, 2.1.1-0125, 2.1.1-0070)

4.3.2.2 Field Steering mirror: automated positioning

REQ# 2.1.1-2030

The HOWFS field steering mirror assembly shall have a minimum resolution of 1 arcseconds (4.8 µrad)

in α and β rotation, a minimum accuracy of 10 arcseconds (48 µrad), and repeatability to within 2

arcseconds (9.7 µrad). The HOWFS field steering mirror shall also have a range of at least 1.0 degrees

in α and β rotation. The α and β rotation velocity shall be greater than or equal to 5 degrees per second in

each axis.


Requirement Origin: Science (SPEC-0058, 2.1.1-0125), Engineering (SPEC-0147)

4.3.3 Objective lens assembly

4.3.3.1 Objective lens assembly: automation

REQ# 2.1.1-2035

The HOWFS objective lens assembly shall be motorized so that it can be automatically controlled in z

translation for focus adjustment.



4.3.3.2 Objective lens assembly: automated positioning

REQ# 2.1.1-2040

The HOWFS objective lens assembly shall have a resolution of less than or equal to 5 µm, accuracy of

within 25 µm, and repeatability to within 10 µm in z-translation. Its range in z-translation shall be greater

than 20 mm. The z-translation velocity of the objective lens assembly shall be greater than or equal to 10

mm per second.





4.3.4 Field stop mount assembly

4.3.4.1 Field stop mount assembly: automation

REQ# 2.1.1-2045

The HOWFS field stop mount assembly shall be motorized so that it can be remotely commanded to

insert a field stop, dark slide or pinhole at the focal plane of the objective lens.


Requirement Origin: Operations (SPEC-0129, 4.2.3, 4.3.1)

4.3.4.2 Field stop mount assembly: field stop size and adjustability

REQ# 2.1.1-2050

The HOWFS field stop shall be a square stop centered on the optical axis with a default size of 3.142

0.157 mm per side and be adjustable to, at minimum, 15% from the default size.



4.3.4.3 Field stop mount assembly: pinhole size

REQ# 2.1.1-2055

The HOWFS field stop mount assembly pinhole shall be a circular hole with diameter equal to 0.500

0.050 mm.


Requirement Origin: Operations (SPEC-0129, 4.2.3)

4.3.4.4 Field stop mount assembly: pinhole positioning

REQ# 2.1.1-2060

The HOWFS field stop mount assembly pinhole mechanism shall have a y-translation resolution of 25

µm with a repeatability of 25 µm and an accuracy of 50 µm. It shall have a minimum range of 10 mm.

Note: The minimum range requirement ensures that the assembly can be out of the beam during normal

operation, insert the pinhole at the center of the field for calibration, and block the beam entirely for dark

calibration.



4.3.4.5 Field stop mount assembly: manual positioning

REQ# 2.1.1-2065

The HOWFS field stop mount assembly shall be manually adjustable in x and y translation with an

adjustment resolution of 100 µm and a minimum range of 2 mm in each axis. The HOWFS field stop

mount assembly shall also be adjustable in γ rotation with resolution of 30 arcseconds and a minimum

range of 2 degrees.


Requirement Origin: Operations (SPEC-0129, 4.3.7.2)



4.3.5 Pupil lens mount assembly

4.3.5.1 Pupil lens mount assembly: manual positioning in x and y

REQ# 2.1.1-2070

The HOWFS pupil lens mount assembly shall be manually adjustable in x and y translation with position

resolution of 5 µm and a minimum range 1.0 mm in each axis.



4.3.5.2 Pupil lens mount assembly: manual positioning in z

REQ# 2.1.1-2075

The HOWFS pupil lens mount assembly shall be manually adjustable in z translation with position

resolution of 5 µm and a minimum range of 40 mm.



4.3.5.3 Pupil lens mount assembly: lens element adjustability

REQ# 2.1.1-2080

Each of the three lens elements of the HOWFS pupil lens shall be manually adjustable in x, y, and z

translation and α and β rotation. X and y translation adjustments shall have a position resolution of 5

µm and a minimum range of 1 mm. Z translation adjustments shall have a position resolution of 5 µm

and adjustment ranges that allow the pupil lens assembly to be configured for any numerical aperture

between 0.0266 and 0.0360, as shown in Table 1. Rotation adjustments in α and β shall have a position

resolution of 10 arcseconds (48.5 µrad) and a minimum range of 5arcminutes (1.45 mrad).

Table 1: Airgap values for full range of pupil lens adjustment

Numerical Aperture 0.0266 0.0313 0.0360

Airgap L1 to L2 (mm) 4.28 27.06 43.07

Airgap L2 to L3 (mm) 43.96 30.86 3.89



4.3.6 Lenslet array mount assembly

4.3.6.1 Lenslet array mount assembly: automation

REQ# 2.1.1-2085

The HOWFS lenslet array mount assembly shall be motorized so that it can be remotely commanded in x

and y translation.





4.3.6.2 Lenslet array mount assembly: automated positioning

REQ# 2.1.1-2090

The HOWFS lenslet array mount assembly shall have maximum x and y-axis resolution of 1 µm with

maximum repeatability of 1 µm and accuracy of 5 µm. Its range in x and y translation shall be a minimum

of 1 mm. The x and y translation velocities of the lenslet array mount assembly shall be a minimum of 1

mm per second.


Requirement Origin: Science (SPEC-0058, 2.1.1-0110), Operations (SPEC-0129, 4.3.7.5)

4.3.6.3 Lenslet array mount assembly: manual positioning

REQ# 2.1.1-2095

The HOWFS lenslet array mount assembly shall be manually adjustable in γ-rotation with a maximum

position resolution of 22 arcseconds and a minimum range of 4 degrees.



4.3.7 Relay lens #1 mount assembly

4.3.7.1 Relay lens #1 mount assembly: automation

REQ# 2.1.1-2100

The HOWFS relay lens #1 mount assembly shall be motorized so that it can be remotely commanded in z

translation.



4.3.7.2 Relay lens #1 mount assembly: automated positioning

REQ# 2.1.1-2105

The HOWFS relay lens #1 mount assembly shall have maximum z-translation resolution of 5 µm with

maximum repeatability of 10 µm and accuracy of 10 µm. Its range in z translation shall be a minimum of

2 mm. The z-translation velocity of the mount assembly shall be minimum 0.2 mm per second.



4.3.7.3 Relay lens #1 mount assembly: manual positioning

REQ# 2.1.1-2110

The HOWFS relay lens #1 mount assembly shall be manually adjustable in x and y translation with

minimum resolution of 10 µm and minimum range 1 mm.





4.3.8 Relay lens #2 mount assembly

4.3.8.1 Relay lens #2 mount assembly: automation

REQ# 2.1.1-2115

The HOWFS relay lens #2 mount assembly shall be motorized so that it can be remotely commanded in z

translation.



4.3.8.2 Relay lens #2 mount assembly: automated positioning

REQ# 2.1.1-2120

The HOWFS relay lens #2 mount assembly shall have maximum z-translation resolution of 5 µm with

maximum repeatability of 10 µm and accuracy of 10 µm. Its range in z translation shall be a minimum of

20 mm. The z-translation velocity of the mount assembly shall be a minimum of 0.2 mm per second.



4.3.8.3 Relay lens #2 mount assembly: manual positioning

REQ# 2.1.1-2125

The HOWFS relay lens #2 mount assembly shall be manually adjustable in x and y translation with

minimum resolution of 10 µm and minimum range 1 mm.



4.3.8.4 Relay lens #2 mount assembly: lens element adjustability

REQ# 2.1.1-2130

Each of the three lens elements of the HOWFS relay lens #2 shall be manually adjustable in x, y, and z

translation and α and β rotation. X and y translation adjustments shall have a position resolution of 10

µm and a minimum range of 1 mm. Z translation adjustments shall have a position resolution of 5

µm and adjustment ranges that allow the pupil lens assembly to be configured for any magnification

between -0.391 and -0.529, as shown in Table 2. Rotation adjustments in α and β shall have a position

resolution of 20 arcseconds (87.0 µrad) and a minimum range of 5arcminutes (1.45 mrad).

Table 2: Airgap values for full range of plate scale adjustments

Magnification -0.391 -0.46 -0.529

Airgap T2 L1 to T2 L2 (mm) 6.15 3.30 2.48

Airgap T2 L2 to T2 L3 (mm) 5.03 4.76 4.22





4.3.9 Camera mount assembly

4.3.9.1 Camera mount assembly: automation

REQ# 2.1.1-2135

The HOWFS camera mount assembly shall be motorized so that it can be remotely commanded in x, y,

and z translation. When moving in z-translation, the two relay lenses and the filter shall move with the

camera.


Requirement Origin: Science (SPEC-0058, 2.1.1-0110), Engineering (SPEC-0146, 2.1.1-1010)

4.3.9.2 Camera mount assembly: automated positioning

REQ# 2.1.1-2140

The HOWFS camera mount assembly shall have x and y translation resolution of 10 µm or less with a

repeatability of 20 µm and an accuracy of 20 µm. Its range in x and y translation shall be greater than 1

mm in each axis. Its z translation resolution shall be maximum 5 µm with maximum repeatability of 10

µm and maximum accuracy of 10 µm. Its minimum range in z translation shall 100 mm. Minimum x and

y translation velocities of the camera mount assembly shall be 1 mm per second in each axis. Minimum z

translation velocity of the camera mount assembly shall be 25 mm per second.



4.4 HOWFS Optics mount stability

REQ# 2.1.1-2145

All HOWFS optical elements shall be mounted so that the total optical surface error and centering error

meet requirements shown in Table 3 when subjected to a VC-B vibration spectrum, a standardized

generic vibration spectrum with max level equal to 25 µm per second rms[1].

Table 3: Mounting requirements for HOWFS optics

Optic Surface error,

defocus only

(nm P-V)

Surface error,

focus removed

(nm rms)

Centering Error

(um)

Field Steering Mirror 25.32 25.32 N/A

Objective Lens (triplet) 949.5 24.80 250

Pupil lens, element #1 949.5 31.65 25



Microlens array 949.5 63.30 25

Relay lens #1, element #1 949.5 63.30 50









Requirement Origin: Science (SPEC-0058, 2.1-0015; SPEC-0009)

4.5 HOWFS Camera

4.5.1 Format

REQ# 2.1.1-2150

The HOWFS camera shall have a minimum 860 x 860 pixel area in which all pixels meet noise, linearity,

and well depth requirements.



4.5.2 Pixel size

REQ# 2.1.1-2155

The HOWFS camera shall have 11.5 x 11.5 0.05 micron square pixels.



4.5.3 Quantum efficiency

REQ# 2.1.1-2160

The HOWFS camera shall have a quantum efficiency of greater than 0.22 over the wavelengths specified

for HOWFS performance (475-575 nm).



4.5.4 Fill factor

REQ# 2.1.1-2165

The HOWFS camera shall have an optical fill factor of greater than or equal to 60%.



4.5.5 Full Well

REQ# 2.1.1-2170

The HOWFS camera shall have a minimum linear well depth of 30,000 electrons per pixel.

Verification: Design Review, Analysis, & Test




4.5.6 Linearity

REQ# 2.1.1-2175

Pixels of the HOWFS camera shall have a response that is linear to within 2% for a range greater than or

equal to the minimum required full well depth.



4.5.7 Artifacts

REQ# 2.1.1-2180

Any time variant noise or image artifacts shall cause a maximum of 3 nm rms wavefront reconstruction

error.



4.5.8 Frame Rate

REQ# 2.1.1-2185

The HOWFS camera shall be able to read out an 860 x 860 pixel region at a minimum rate of 2 kHz.


Requirement Origin: Science (SPEC-0058, 2.0-0015; SPEC-0009 Case 1a)

4.5.9 Flexible Integration time

REQ# 2.1.1-2190

The HOWFS camera exposure time shall be adjustable independent of the frame rate setting.



4.5.10 Read Noise

REQ# 2.1.1-2195

The HOWFS camera shall have a maximum of 30 e- rms read noise per frame.



4.5.11 Internal Noise

REQ# 2.1.1-2200

When imaging at greater than 50% of the linear well depth, total measurable image noise shall be a

maximum of 110% of the expected photon noise.





4.5.12 Bias Frame Stability

REQ# 2.1.1-2205

The HOWFS camera bias frame shall be stable to within 1 DN rms over a period of four hours.



4.5.13 Pixel Gain Stability

REQ# 2.1.1-2210

The camera gain correction shall be stable to 0.5% residual rms contrast over a period of four hours. Rms

contrast is defined as the standard deviation of the signal divided by the mean signal.


Requirement Origin: Science (SPEC-0058, 2.1.1-0070), Operations (SPEC-0129, 4.3.2)

4.5.14 Digitization

REQ# 2.1.1-2215

The HOWFS camera shall have greyscale resolution of 10-bit or greater.


Requirement Origin: Science (SPEC-0058 , 2.1.1-0025)

4.5.15 Faint Image Tracking

REQ# 2.1.1-2220

The HOWFS camera shall be able to track 1.5% rms contrast targets in a controlled laboratory

experiment.



4.5.16 Granulation tracking

REQ# 2.1.1-2225

The HOWFS camera shall be able to track solar granulation in good seeing conditions.

Note: In good seeing, supaperture images of solar granulation images have rms image contrast values of

approximately 1.5-2.0%.



4.5.17 Streaming readout

REQ# 2.1.1-2230

The HOWFS camera shall be capable of streaming data, in real time, to the HOAO RTC.





4.5.18 Read latency

REQ# 2.1.1-2235

The latency between the end of an exposure and the beginning of RTC data processing shall be 20

microseconds or less.



4.5.19 Full-frame read time

REQ# 2.1.1-2240

The HOWFS camera shall be capable of copying a full 860 x 860 pixel image into the real-time system

within 500 microseconds from the end of the exposure.



4.5.20 Simultaneous readout

REQ# 2.1.1-2245

The HOWFS camera shall be capable of taking an exposure while reading out the previous image.



4.5.21 Power dissipation

REQ# 2.1.1-2250

The HOWFS camera shall dissipate less than 20 W of heat into the coudé environment during operation.


Requirement Origin: Environmental (SPEC-0063, 4.4a)

4.5.22 Heat management

REQ# 2.1.1-2255

Any surfaces of the HOWFS camera that interact directly with the surrounding coudé environment shall

be cooled to within +1.5/-3.0 C of the ambient temperature.


Requirement Origin: Environmental (SPEC-0063, 4.4b)

4.6 HOAO calibration sources

4.6.1 HOAO GOS pinhole

REQ# 2.1.1-2260

The PA&C assembly shall contain a pinhole sized for the HOAO, hereafter referred to as the HOAO GOS

pinhole. The HOAO pinhole and LOWFS pinhole may be combined into a single WFS GOS pinhole,



provided the WFS GOS pinhole meets all requirements for both the HOAO GOS pinhole and the LOWFS

GOS pinhole.



4.6.1.1 HOAO GOS pinhole size

REQ# 2.1.1-2265

The HOAO GOS pinhole shall provide a spot on the HOAO that is 3-6 pixels in diameter

Note: The HOAO pixel scale is 0.5 arcseconds /pixel



4.6.1.2 HOAO GOS pinhole shape

REQ# 2.1.1-2270

The HOAO GOS pinhole shall deviate from a perfect circle by a maximum of 5% of its diameter.



4.6.1.3 HOAO GOS pinhole stability

REQ# 2.1.1-2275

The HOAO GOS pinhole shall be stable to within 0.05 arcseconds in the x-y plane and to within 100

microns along the z-axis over any 12 minute window of time.


Requirement Origin: Operations (SPEC-0129, 4.3)

4.6.1.4 HOAO GOS pinhole accuracy

REQ# 2.1.1-2280

The HOAO GOS pinhole shall match the position of the GOS inverse pinhole to within 0.15 arcseconds.



4.6.1.5 HOAO GOS pinhole repeatability

REQ# 2.1.1-2285

The HOAO GOS pinhole shall have a minimum positioning repeatability of 0.05 arcseconds.





4.6.2 GOS calibration lamp

4.6.2.1 GOS calibration lamp power

REQ# 2.1.1-2290

The PA&C assembly shall contain a calibration lamp which emits a minimum of 3.53 x 10-5 Watts per

square arcsecond, measured as emitted power integrated between 475 and 575 nm wavelengths.

Verification: Design Review, Test

Requirement Origin: Operations (SPEC-0129, 4.2.8), Engineering (SPEC-0147)

4.6.3 GOS reflective sphere

REQ# 2.1.1-2300

The PA&C assembly shall contain a reflective sphere target that can be used in the sample arm of the

HOAO NCP interferometer.

Note: Dimensions of the GOS reflective sphere are shown in DKIST project drawing ATST-DWG-0309.



4.6.3.1 GOS reflective sphere mounting

REQ# 2.1.1-2305

The GOS reflective sphere shall be mounted so that the reflective sphere is facing optically downstream,

with the sphere centered on the gut ray of the telescope and the base perpendicular to the gut ray of the

telescope. All light between 300 and 1000 nm from upstream of the GOS image plane will be blocked to a

minimum level of 99.999%.



4.6.3.2 GOS reflective sphere perpendicularity

REQ# 2.1.1-2310

The GOS reflective sphere shall be mounted so that the base of the sphere mount is perpendicular to the

gut ray of the telescope to within 0.1 degrees at the GOS focal plane.



4.6.3.3 GOS reflective sphere positioning accuracy

REQ# 2.1.1-2315

The center of the GOS reflective sphere shall match the optical center of mass of the GOS inverse pinhole

to within 12.7 microns over any 12-minute period of time.





5. HOAO Algorithm Functionality REQUIREMENTS

5.1 Extract multiple Regions of Interest from Full Frame

REQ# 2.1.1-3000

The HOAO shall be capable of extracting multiple regions of interest (ROI), each corresponding to a

HOWFS subaperture image, from a full HOWFS camera frame.


Origin: Engineering

5.2 Dark Calibration

REQ# 2.1.1-3005

The HOAO shall be capable of computing an image suitable for correction of the pixel offset value in the

acquired subfield data. It shall have the following functionality:

capability to interpret the HOAO camera configuration to ascertain relevant image information

such as date/time, number of frames, number of pixels, camera & software ROI, etc

capability to ingest all HOAO camera data corresponding to the WFC dark calibration

capability to generate a set of K Dark Calibration Images ��(𝑥, 𝑦, 𝑘), k ≤ K, where K is the total

number of active HOAO subapertures, from a set of ingested dark frames, 𝐷𝑖(𝑥, 𝑦, 𝑘):

��(𝑥, 𝑦, 𝑘) =1

𝑁∑𝐷𝑖(𝑥, 𝑦, 𝑘),

𝑁

𝑖=1

∀𝑥, 𝑦, 𝑘 ≤ 𝐾

where N is the total number of frames taken in the dark calibration

capability to verify that the Dark Calibration Images contain values within the expected range of

dark values and notify the user if they do not.

capability to store the K generated Dark Calibration Images ��(𝑥, 𝑦, 𝑘), k ≤ K


Origin: Operations (SPEC-0129, 4.3.1)

5.3 Gain Calibration

REQ# 2.1.1-3010

The HOAO shall be capable of computing a set of K images suitable for correction of - among others -

image defects in the acquired data. It shall have the following functionality:


such as date/time, number of frames, number of pixels, camera ROI, etc

capability to retrieve the latest relevant Dark Calibration Images (see Section 5.2) matching the

current HOAO camera configuration (number of pixels, camera and software ROI, etc)

capability to ingest all HOAO camera data corresponding to the WFC gain calibration mode

capability to generate a set of K Gain Calibration Images 𝐹(𝑥, 𝑦, 𝑘), k ≤ K, from a set of ingested

gain frames, one for each HOAO subaperture ROI, using the following procedure:

Step 1 - Averaging:

𝐹(𝑥, 𝑦, 𝑘) = ∑𝐹𝑖(𝑥, 𝑦, 𝑘) − ��(𝑥, 𝑦, 𝑘), ∀𝑥, 𝑦, 𝑘

𝑁

𝑖=1



where N is the total number of frames taken in the gain calibration

Step 2 - Normalization:

𝐺(𝑥, 𝑦, 𝑘) =1

𝑋 ∙ 𝑌(∑ 𝐹(𝑥, 𝑦, 𝑘)𝑥,𝑦

𝐹(𝑥, 𝑦, 𝑘)⁄ ), ∀𝑥, 𝑦, 𝑘

where X and Y are the total number of pixels per subaperture in the x and y directions,

respectively.

capability to store the K generated Gain Calibration Images 𝐺(𝑥, 𝑦, 𝑘), k ≤ K


Origin: Operations (SPEC-0129, 4.3.2)

5.4 Calibration of subaperture images

REQ# 2.1.1-3015

The HOAO shall be capable of calibrating the set of K HOAO subaperture images for each full HOAO

camera frame. It shall have the following functionality:


such as date/time, number of frames per frameset, number of pixels, ROI, etc

capability to retrieve latest relevant Calibration Images (see Section 5.2 and 5.3) matching the

current HOAO camera settings (number of pixels, camera and software ROI, etc)

capability to compute a set of K calibrated images, 𝐶(𝑥, 𝑦, 𝑘), over the K subapertures for each

HOAO camera frame received, in the following way,

𝐶(𝑥, 𝑦, 𝑘) = (𝐼(𝑥, 𝑦, 𝑘) − ��(𝑥, 𝑦, 𝑘)) ∙ ��(𝑥, 𝑦, 𝑘), ∀(𝑥, 𝑦, 𝑘)

where 𝐼(𝑥, 𝑦, 𝑘) is the raw image for subaperture k (see above for the definitions of D and G)

capability to output the set of K calibrated images 𝐶(𝑥, 𝑦, 𝑘), ∀k ≤ K, for further internal

processing


Origin: Science (SPEC-0058, 2.1.1-0025)

5.5 Subaperture Shift Measurement

REQ# 2.1.1-3020

For each HOWFS camera frame, HOAO shall compute shifts between the reference image and all active

HOAO subaperture images using the following algorithms for cross-correlation and subpixel

interpolation.



5.5.1 Cross-correlation algorithm

The HOAO shall compute 2-dimensional cross-correlations between

a single reference subaperture image, 𝐶𝑟𝑒𝑓(𝑥, 𝑦) and

each of the K subaperture images in a captured HOAO camera frame, 𝐶(𝑥, 𝑦, 𝑘), k ≤ K, as

follows:



𝐶𝐶(𝑝, 𝑞, 𝑘) = ∑ ∑ 𝐶(𝑥, 𝑦, 𝑘) ∗ 𝐶𝑟𝑒𝑓(𝑥 + 𝑝, 𝑦 + 𝑞)

𝑌

𝑦=1

𝑋

𝑥=1

where K is the total number of subapertures, X and Y are the total number of pixels per subaperture in the

x and y directions, p and q are each integers on the interval [-3, 3], and * represents element by element

multiplication of arrays. The shift of Cref in this calculation is a circular shift.

The p and q indices of the location where 𝐶𝐶(𝑝, 𝑞, 𝑘) is at its maximum correspond to the integer shift

between image 𝐶(𝑥, 𝑦, 𝑘) and the reference image.

5.5.2 Computation of image displacements to subpixel accuracy

The HOAO shall be capable of computing image displacements between each of the K HOAO

subaperture images and the selected reference HOAO subaperture image to subpixel accuracy.

For this computation, the HOAO shall use the K 2-dimensional cross-correlation arrays and the following

formula:

𝑆𝑥𝑘 = (𝑥𝑚𝑎𝑥 − 1

2⁄ ) +𝐶𝐶(𝑥𝑚𝑎𝑥, 𝑦𝑚𝑎𝑥, 𝑘) − 𝐶𝐶(𝑥𝑚𝑎𝑥 − 1, 𝑦𝑚𝑎𝑥, 𝑘)

2𝐶𝐶(𝑥𝑚𝑎𝑥, 𝑦𝑚𝑎𝑥 , 𝑘) − 𝐶𝐶(𝑥𝑚𝑎𝑥 − 1, 𝑦𝑚𝑎𝑥, 𝑘) − 𝐶𝐶(𝑥𝑚𝑎𝑥 + 1, 𝑦𝑚𝑎𝑥, 𝑘)

𝑆𝑦𝑘 = (𝑦𝑚𝑎𝑥 − 1

2⁄ ) +𝐶𝐶(𝑥𝑚𝑎𝑥, 𝑦𝑚𝑎𝑥 , 𝑘) − 𝐶𝐶(𝑥𝑚𝑎𝑥, 𝑦𝑚𝑎𝑥 − 1, 𝑘)

2𝐶𝐶(𝑥𝑚𝑎𝑥, 𝑦𝑚𝑎𝑥, 𝑘) − 𝐶𝐶(𝑥𝑚𝑎𝑥 , 𝑦𝑚𝑎𝑥 − 1, 𝑘) − 𝐶𝐶(𝑥𝑚𝑎𝑥, 𝑦𝑚𝑎𝑥 + 1, 𝑘)

where 𝑥𝑚𝑎𝑥 and 𝑦𝑚𝑎𝑥 are the integer pixel positions for which 𝐶𝐶(𝑥, 𝑦, 𝑘) is maximal for a particular

k ≤ K.

5.6 Wavefront Reconstruction

REQ# 2.1.1-3025

HOAO shall be capable of wavefront reconstruction via a vector-matrix multiply that generates FTT and

DM actuator commands from wavefront sensor residual shift measurements.

𝑎𝑟𝑒𝑠 = 𝑅𝑠

where 𝑎𝑟𝑒𝑠 is a vector of DM and FTT actuator commands, s is a vector of residual x and y shift

measurements, and R is the selected reconstruction matrix.



5.7 PI Servo Loop

REQ# 2.1.1-3030

HOAO shall apply gains to the proportional and integral residual wavefront actuator commands produced

by wavefront reconstruction (section 5.6).

𝑎𝐷𝑀,𝑖[𝑘] = 𝐾𝑃,𝐷𝑀𝑎𝑟𝑒𝑠,𝑖 + 𝐾𝐼,𝐷𝑀 ∑ 𝛼𝐷𝑀𝑘−𝜏𝑎𝑟𝑒𝑠,𝑖[𝜏]

𝑘

𝜏=𝑘0,𝐷𝑀

, ∀𝑖 ∈ [1, 𝑁𝑎𝑐𝑡]

and



𝑎𝑇𝑇,𝑖−𝑁𝑎𝑐𝑡[𝑘] = 𝐾𝑃,𝑇𝑇𝑎𝑟𝑒𝑠,𝑖 + 𝐾𝐼,𝑇𝑇 ∑ 𝑎𝑟𝑒𝑠,𝑖[𝜏]

𝑘

𝜏=𝑘0,𝑇𝑇

, ∀𝑖 ∈ [𝑁𝑎𝑐𝑡 + 1,𝑁𝑎𝑐𝑡 + 2]

where 𝑎𝐷𝑀,𝑖[𝑘] is the ith element of the DM actuator command vector at timestep k, 𝐾𝑃,𝐷𝑀 is the

proportional gain for the DM servo loop, 𝐾𝐼,𝐷𝑀 is the integral gain for the DM servo loop, 𝛼𝐷𝑀 is the DM

leak factor, and 𝑘0,𝐷𝑀 is the timestep when the DM integrator was last reset. Similarly, 𝑎𝑇𝑇,𝑖[𝑘] is the ith

element of the FTT actuator command vector at timestep k, 𝐾𝑃,𝑇𝑇 is the proportional gain for the FTT

servo loop, 𝐾𝐼,𝑇𝑇 is the integral gain for the FTT servo loop, and 𝑘0,𝑇𝑇 is the timestep when the FTT

integrator was last reset. This notation assumes that the 𝑎𝑟𝑒𝑠 vector is ordered so that its first Nact elements

are DM actuator commands and its last two elements are FTT actuator commands.



5.8 Tip-Tilt Derotation

REQ# 2.1.1-3035

HOAO shall rotate the FTT actuator commands from the WFC coordinate plane to the M5 FTT

coordinate plane before sending them to the M5 FTT module.

𝑎𝑀5𝑇𝑇[k] = [cos 𝜃𝑟𝑜𝑡 −sin 𝜃𝑟𝑜𝑡

sin 𝜃𝑟𝑜𝑡 cos 𝜃𝑟𝑜𝑡] 𝑎𝑇𝑇[𝑘]

where

𝜃𝑟𝑜𝑡 = −𝜃𝑎𝑧 − 𝜃𝑐𝑜𝑢𝑑é + 𝐶𝑀5

and 𝜃𝑐𝑜𝑢𝑑é is the coudé rotation angle, 𝜃𝑎𝑧 is the azimuth rotation angle, and 𝐶𝑀5 is a constant offset to

adjust the zeropoint of the M5 rotation angle.


Origin: Engineering (SPEC-0147)

5.9 Fast Tip-Tilt Offload to Mount

REQ# 2.1.1-3040

HOAO shall offload M5 travel to the TCS if the average position of the M5 FTT module, over the user-

set offload period, exceeds the user-set offload range threshold.

In order to offload in the correct basis, the M5 FTT Module axes must be transformed into the TCS

altitude and azimuth coordinate system. This will be done in the following way,

∆𝛉mount = k ∗ 𝐑∅𝐒M5∆𝛉M5

where ∆𝛉mount = [∆θalt, ∆θaz]T is the change in altitude and azimuth angle to be sent to the TCS, 𝐒M5 is

the M5 sensitivity matrix, ∆𝛉M5 is the angular tip-tilt offload desired, and k is a gain factor used to

prevent system stability issues. 𝐑∅ is a rotation matrix that accounts for image rotation due to the altitude

angle of the telescope,

𝐑∅ = [𝐜𝐨𝐬∅ −𝐬𝐢𝐧∅𝐬𝐢𝐧∅ 𝐜𝐨𝐬 ∅

]

∅ = −θalt + C.



where θalt is the current altitude angle of the telescope and C is a constant offset determine by calibration.

Initially, 𝐒M5 will be determined by ZEMAX models of the telescope but will be updated based on

calibrations during IT&C.



5.10 R0 calculation

REQ# 2.1.1-3045

HOAO shall be capable of computing an estimate of the mean atmospheric r0 value over a user-defined

time period (default 1 second). The r0 estimate shall be computed by using a linear influence function

model of the DM to estimate the total atmospheric wavefront at each control-loop iteration.

Once the wavefronts have been collected over the desired time-period, they will be converted into

Karhunen-Loéve (K-L) modal coefficients. The sample variances of the K-L coefficients will be fit to the

expected Kolmogorov variance of K-L functions, using a least-squares fit, to find the value of r0 that best

fits the observed data.

The expected variance of K-L functions shall be a user-defined array which can be edited to change

which K-L functions are used for the r0 calculation.



5.11 Residual error calculation

REQ# 2.1.1-3050

The HOAO shall be capable of computing the mean tilt-removed rms residual wavefront error as

measured by the HOWFS over a period of one second.

The rms mean-subtracted residual wavefront error shall be computed from the array of wavefront sensor

actuator residuals.

𝛔res[𝑘] = 𝑐𝐷𝑀√��[𝑘]𝑇��[𝑘]

𝑁𝑎𝑐𝑡

with �� defined as the actuator residual error vector with the mean piston and tilt terms removed, 𝛔res[𝑘] is the rms residual wavefront shape in nanometers at timestep k, Nact is the total number of active DM

actuators, and cDM is a constant that converts actuator commands from digital numbers to nanometers

wavefront.

The HOAO shall monitor 𝛔res[𝑘] and record its mean value over one second,

𝛔res =1

𝐾∑ 𝛔res[𝑘 ∗ 𝑛𝑠𝑘𝑖𝑝]

𝐾

𝑘=1

with

𝐾 = ⌈𝑓𝐻𝑂𝐴𝑂

𝑛𝑠𝑘𝑖𝑝 + 1⌉

where fHOAO is the HOAO frame rate, nskip is the user-defined frameskip setting, and ⌈∙⌉ signifies the

ceiling function.




Origin: Operations (SPEC-0129. 5.2.1)

5.12 DM rms calculation

REQ# 2.1.1-3055

The HOAO shall be capable of computing the mean rms wavefront correction provided by the DM over

one second.

The DM mean-subtracted rms shape shall be computed from the array of DM actuator commands

immediately following servo loop application and interactuator limitation but before individual actuator

gains and offsets are applied.

𝛔DM[𝑘] = 𝑐𝐷𝑀√��DM[𝑘]𝑇��DM[𝑘]

𝑁𝑎𝑐𝑡

with ��DM defined by

��DM[𝑘] = 𝐚DM[𝑘] − 𝐚DM [𝑘]

and

𝐚DM [𝑘] =1

𝑁𝑎𝑐𝑡∑ 𝐚DM,i[𝑘]

𝑁𝑎𝑐𝑡

𝑖=1

where 𝛔DM[𝑘] is the rms wavefront shape in nanometers due to the DM at timestep k, aDM,i[k] is the ith

element of a column vector containing all DM actuator commands at timestep k, 𝐚DM [𝑘] is the mean of

aDM[k], Nact is the total number of DM actuators, and cDM is a constant that converts actuator commands

from device units to nanometers wavefront.

The HOAO shall monitor 𝛔DM[𝑘] and record its mean value over one second,

𝛔DM =1

𝐾∑ 𝛔DM[𝑘 ∗ 𝑛𝑠𝑘𝑖𝑝]

𝐾

𝑘=1

with

𝐾 = ⌈𝑓𝐻𝑂𝐴𝑂

𝑛𝑠𝑘𝑖𝑝 + 1⌉

where fHOAO is the HOAO frame rate, nskip is the user-defined frameskip setting and ⌈∙⌉ signifies the ceiling

function.


Origin: Operations (SPEC-0129. 5.2.1)

5.13 HOAO Modal Coefficient Computation from Subaperture Shifts

REQ# 2.1.1-3060



The HOAO shall be capable of computing 20 Zernike or M1 natural mode coefficients from the set of

subaperture shift measurements.

If Ts is a matrix reconstructing either Zernike or natural modes from the wavefront gradient (represented

by the measured subpixel accuracy image displacements as reported in the telemetry data), the formula to

calculate the modes shall be the matrix multiplication:

�� (𝑡) = 𝐓s𝑠 (t)

where 𝑠 = (… , 𝑠𝑥𝑘−1, 𝑠𝑦

𝑘−1, 𝑠𝑥𝑘 , 𝑠𝑦

𝑘, 𝑠𝑥𝑘+1, 𝑠𝑦

𝑘+1, … ) is the vector with the subpixel accuracy displacements

as elements.

Note: A matrix 𝐓s will be provided, but it must be possible to load different matrices 𝐓s while HOAO is

operational.

HOAO shall average the modal coefficients over a user-defined time period and shall use a CSF event to

report the average modal coefficients, along with their associated confidence coefficients (section 5.15).



5.14 HOAO Modal Coefficient Computation from Actuator Commands

REQ# 2.1.1-3065

The HOAO shall be capable of computing 20 Zernike or M1 natural mode coefficients from the set of

DM actuator commands.

If 𝐓act is a matrix reconstructing either Zernike or natural modes from the DM actuator commands (as

reported in the telemetry data), the formula to calculate the modes shall be the matrix multiplication:

�� (𝑡) = 𝐓act�� (𝑡)

where �� (𝑡) is a column vector of the DM actuator commands at time t.

Note: A matrix 𝐓act will be provided, but it must be possible to load different matrices 𝐓act while the

HOAO is operational.

HOAO shall average the modal coefficients over a user-defined time period and shall use a CSF event to

report the average modal coefficients, along with their associated confidence coefficients (section 5.15).



5.15 HOAO Modal Coefficient Confidence

REQ# 2.1.1-3070

HOAO shall calculate the confidence of each modal coefficient in sections 5.13 and 5.14 and report these

confidence values in each of the respective CSF events. The confidence of each modal coefficient is equal

to the inverse of that coefficient’s measured variance,

𝐶𝑖 =1

𝜎𝑖2

where



𝜎𝑖2 =

1

𝐾 − 1∑(𝑚𝑖[𝑘 ∗ 𝑛𝑠𝑘𝑖𝑝] − ��𝑖)

2𝐾

𝑘=1

and

��𝑖 =1

𝐾∑ 𝑚𝑖[𝑘 ∗ 𝑛𝑠𝑘𝑖𝑝]

𝐾

𝑘=1

for

𝐾 = ⌈𝑓𝐻𝑂𝐴𝑂 ∗ 𝑇𝑚𝑜𝑑𝑒

𝑛𝑠𝑘𝑖𝑝⌉

with 𝑓𝐻𝑂𝐴𝑂 equal to the HOAO frame rate, 𝑇𝑚𝑜𝑑𝑒 is the user-set averaging period for reporting the modal

coefficients, 𝑛𝑠𝑘𝑖𝑝 is the frameskip setting for the relevant modal computation, ⌈∙⌉ signifies the ceiling

function, 𝑚𝑖 is the ith modal coefficient, and 𝐶𝑖 is the confidence of the ith modal coefficient over the user-

defined time period.

If 𝜎𝑖2 ≤ 0.01 then 𝐶𝑖 = 100

Confidence will be calculated and reported in CSF events for both the modal coefficients from the shift

calculations and the modal coefficients from DM actuators. Each of the two modal coefficient

calculations will have their own independent values for 𝑇𝑚𝑜𝑑𝑒 and 𝑛𝑠𝑘𝑖𝑝.



5.16 DM Interactuator Voltage Limitation

REQ# 2.1.1-3075

The HOAO shall limit voltage between adjacent actuators so that commands sent to the DM drive

electronics do not over-drive adjacent actuators.

The Xinetics DM is expected to operate its actuators at voltages between 20-80V with a bias voltage of

50V. It is expected that the interactuator voltage limit will be 30V.

The interactuator limiting algorithm shall prioritize safety of the DM facesheet above all performance

concerns. The interactuator limiting algorithm shall be demonstrated in simulation to be 100% effective in

eliminating interactuator violations from a minimum of one million consecutive DM shapes created by

driving the actuators using white noise with standard deviation equal to half the interactuator limit.

Additionally, the RTC will be run while disconnected from the DM for one million cycles on pure noise

inputs and monitored to ensure that it does not generate any DM patterns that violate the interactuator

stroke limit.

Only once these tests have been successfully completed shall the DM be driven by the HOAO RTC.



5.17 OOB Subaperture Shift Detection

REQ# 2.1.1-3080



HOAO shall monitor the HOWFS subaperture shift measurement results in real-time for out-of-bounds

(OOB) measurements. An OOB measurement is a shift measurement that is equal to the maximum

measureable shift in any direction, before subaperture shift references are subtracted. HOAO shall record

the total number of OOB shift measurements in each HOWFS frame and report the OOB statistics as

required.



5.18 DM Interaction Matrix Calibration

REQ# 2.1.1-3085

HOAO shall support calibration of the DM interaction matrix using a user-provided matrix of test

patterns, V, where each ith column of the matrix, Vi, represents a vector of DM actuator commands.

To perform the calibration, HOAO shall apply each Vi to the DM and measure the resulting shifts, Si, to

construct the sensor matrix, S = [S1|S2|…]. If there are m active HOWFS subapertures, Nact DM actuators,

and Ntest total test patterns to apply then V is of dimension Nact by Ntest and S is of dimension 2m by Ntest.

It is expected that Ntest will be equal to Nact but HOAO shall be able to accommodate any value for Ntest on

the interval [Nact, 3Nact].

Note: The full matrix construction may be done by a higher level controller (WCCS) instead of at the

HOAO level, provided the time constraint can be met. In this case the only functionality required by

HOAO is the ability to accept a DM command, apply it to the DM, and return the resulting shift

measurements.



5.19 HOAO Automatic Gain and Reconstruction Matrix Optimization

REQ# 2.1.1-3090

HOAO shall be capable of estimating the noise in the HOAO reference subaperture and automatically

adjusting proportional and integral gains of its servo loop to minimize residual wavefront error. HOAO

shall also optimize its reconstruction matrix for current seeing conditions and measurement noise.

This shall be accomplished by maintaining a lookup table that uses the current r0 and reference

subaperture noise estimate to set the optimal servo gains and number of K-L modes reconstructed. HOAO

shall use this lookup table to update the gains and reconstruction matrix at a minimum rate of 1 Hz.



5.20 Mitigation of Bad Seeing or Loop Instability

REQ# 2.1.1-3095

HOAO shall be capable of automatically adjusting system parameters to compensate for poor seeing or

control loop instability. It will do so by monitoring the number of OOB subapertures and reducing the

control loop gains and number of modal basis functions reconstructed if the OOB subapertures exceed the

user-set thresholds for the DM and FTT.

Separate thresholds and gain offsets will be maintained for the DM and FTT control loops. If the HOAO

controller detects a number of OOB counts in a given frame that exceed the DM OOB threshold, it shall



increment the level of the DM gain offset. When incrementing the level of the DM gain offset, the HOAO

controller shall change the control loop gains of the DM loop such that,

𝑘𝐷𝑀,𝐼𝑚 = (1 − 𝑚𝐷𝑀 ∙ 𝑙𝐷𝑀)𝑘𝐷𝑀,𝐼

0

𝑘𝐷𝑀,𝑃𝑚 = (1 − 𝑚𝐷𝑀 ∙ 𝑙𝐷𝑀)𝑘𝐷𝑀,𝑃

0

where 𝑘𝐷𝑀,𝐼0 is the integral gain, set by either manual user input or the automated gain optimization

(depending on whether gains are set manually or automatically), 𝑚𝐷𝑀 is the level of the current DM gain

offset, 𝑙𝐷𝑀 is the DM OOB increment, and 𝑘𝐷𝑀,𝐼𝑚 is the integral gain setting for offset level 𝑚𝐷𝑀.

Similarly, 𝑘𝐷𝑀,𝑃0 is the proportional gain, set by either manual user input or the automated gain

optimization, and 𝑘𝐷𝑀,𝑃𝑚 is the proportional gain setting for offset level 𝑚𝐷𝑀.

Whenever the HOAO controller increases the level of the DM gain offset, it shall zero the DM control

loop accumulators and change the control matrix to the control matrix 𝑚 levels below the one currently

indicated by either manual user input or the automated gain optimization. If the desired reconstruction

matrix is below the lowest level matrix loaded into RTC memory or the gains reach zero then the DM

shall be disabled until the recovery criteria are met.

The FTT OOB threshold will function similarly to the DM OOB threshold. If the HOAO controller

detects a number of OOB counts in a given frame that exceed the FTT OOB threshold, it shall increment

the level of the FTT gain offset. When incrementing the level of the FTT gain offset, the HOAO

controller shall clear the FTT accumulators and change the control loop gains of the FTT loop such that,

𝑘𝐹𝑇𝑇,𝐼𝑚 = (1 − 𝑚𝐹𝑇𝑇 ∙ 𝑙𝐹𝑇𝑇)𝑘𝐹𝑇𝑇,𝐼

0

𝑘𝐹𝑇𝑇,𝑃𝑚 = (1 − 𝑚𝐹𝑇𝑇 ∙ 𝑙𝐹𝑇𝑇)𝑘𝐹𝑇𝑇,𝑃

0

where 𝑘𝐹𝑇𝑇,𝐼0 is the integral gain set by either manual user input or the automated gain optimization, 𝑚𝐹𝑇𝑇

is the level of the current FTT gain offset, 𝑙𝐹𝑇𝑇 is the FTT OOB increment, and 𝑘𝐹𝑇𝑇,𝐼𝑚 is the integral gain

setting for offset level 𝑚𝐹𝑇𝑇. Similarly, 𝑘𝐹𝑇𝑇,𝑃0 is the proportional gain set by either manual user input or

the automated gain optimization and 𝑘𝐹𝑇𝑇,𝑃𝑚 is the proportional gain setting for offset level 𝑚𝐹𝑇𝑇. If the

offset level causes the gains to reach zero then the FTT loop shall be disabled until the recovery criteria

are met.

Recovery from DM or FTT gain offsets shall be done incrementally by decreasing the offset levels

whenever the recovery criteria are met. The recovery criteria are met by observing a number of

consecutive frames equal to the user-set DM and FTT recovery thresholds.

Whenever the DM or FTT recovery periods are met, their respective offsets will be decreased by one

level. For the DM this means the loop gains will be increased and the reconstruction matrix will be

changed to the next highest number of modal basis functions. For the FTT loop, the gains will be

increased. The DM and FTT loop shall never be offset to a level less than zero, i.e. the gains and number

of modes reconstructed will never exceed those set by the user or the automated optimization process.

One of the top-level HOAO controllers, either the Real-Time Manager or Telemetry Processor, shall

monitor the status of the offsets applied to the DM gains and reconstruction matrices due to OOB count

violations. If offsets are applied continuously for longer than a user-set time period (default 3 seconds),

the HOAO health shall be set to ill. Health shall be set back to good if ten continuous seconds are

observed with no applied offsets.


Origin: Science (SPEC-0058, 2.1.1-0040), Engineering (SPEC-0147)



5.21 HOWFS Automatic exposure time adjustment

REQ# 2.1.1-3100

HOAO shall be capable of automatically adjusting the HOWFS camera exposure time based on the flux

level in a selected subaperture. When automatic exposure time adjustment is enabled, it will use the

following algorithm.

Parameters required: Minimum intensity threshold (Tmin), Maximum intensity threshold (Tmax), number of

frames between updates (nframes), current exposure time (texp), maximum exposure time based on current

frame rate (texp, max), subaperture selected for intensity monitoring (aref).

Steps:

Collect a sequence of nframes raw images from the chosen subaperture (Iraw(x,y,i) for i =[1, nframes])

and average them:

I𝑚𝑒𝑎𝑛(𝑥, 𝑦) =1

𝑛𝑓𝑟𝑎𝑚𝑒𝑠∑ 𝐼𝑟𝑎𝑤(𝑥, 𝑦, 𝑖)

𝑛𝑓𝑟𝑎𝑚𝑒𝑠

𝑖=1

Find the maximum intensity value of the mean subaperture image:

𝐼𝑚𝑎𝑥 = 𝑎𝑟𝑔𝑚𝑎𝑥{𝐼𝑚𝑒𝑎𝑛(𝑥, 𝑦)}

If Imax > Tmin and Imax < Tmax then do nothing. Else:

o Adjust exposure time

𝑡𝑒𝑥𝑝 =𝑇𝑚𝑎𝑥

𝐼𝑚𝑎𝑥∗ 𝑡𝑒𝑥𝑝

o Check that new exposure time does not exceed max exposure time

If texp > texp, max then texp = texp, max

o Set texp as HOWFS camera exposure time

The exposure time update shall happen at a maximum update rate of 1 Hz.



5.22 HOWFS Pupil position measurement

REQ# 2.1.1-3105

HOAO shall be capable of measuring mean intensities in edge subapertures of the HOWFS lenslet array

using the following algorithm. The subaperture intensities will be sent to the aO Engine where it will use

them to estimate the pupil position on the HOWFS lenslet array.

Parameters required: Four selected partially-illuminated subapertures (a1 = si, a2 = sj, a3 = sk, a4 = sm,

where i < j < k < m, si represents subaperture number i and subapertures are numbered in increasing order

from top left to bottom right). Number of images per measurement (nimages)

Steps:

Record initial telescope position (Altitude, Azimuth, Coude rotation)

Collect nimages raw images from each selected subaperture and find the mean intensity of each

image:



𝐼𝑚𝑒𝑎𝑛(𝑢) =1

𝑋∗𝑌∗𝑛𝑖𝑚𝑎𝑔𝑒𝑠∑ ∑ ∑ 𝑎𝑢(𝑥, 𝑦, 𝑛)𝑋

𝑥=1𝑌𝑦=1

𝑛𝑖𝑚𝑎𝑔𝑒𝑠

𝑛=1 , 𝑢 ∈ {1,2,3,4}

where X and Y are the total number of pixels in a subaperture image in the x and y directions

Record final telescope position

Report the mean subaperture intensities and initial and final telescope positions to the aO engine



5.23 Absolute Error after Calibration

5.23.1 Total wavefront error

REQ# 2.1.1-3110

After all calibration steps have been successfully completed, quasi-static telescope wavefront error due to

all error sources within the HOAO shall be less than or equal to the DIQ case 1 error budget allocation for

“Adaptive Optics Error”.


Origin: Science (SPEC-0058,2.0-0015; SPEC-0009)

5.23.2 HOAO error budget

REQ# 2.1.1-3115

The WFC team shall maintain an internal error budget that tracks all significant contributions to telescope

wavefront error due to HOAO sources. Error budget allocations shall be updated with the latest estimates

based on testing and analytic methods.

Note: The HOAO Error budget will be recorded in the HOAO CDD (SPEC-0147).





6. HOAO Software Requirements

6.1 General Requirements

6.1.1 Division of software tasks

REQ# 2.1.1-4260

The HOAO software shall be divided into three main components. One software component, the Real-

Time Manager (RTM) shall handle configuration management, scripting, CSF tasks, and other non-real-

time computations necessary for maintaining the state of the HOAO. The HOAO Real-Time Controller

(RTC) shall handle all real-time processing tasks. The HOAO telemetry processor shall ingest the raw

telemetry output from the RTC and perform the necessary computations and formatting required for the

final telemetry data products to be transmitted via the BDT.

Note: This division ensures that critical real-time computations are not interrupted by configuration and

management activities.


Source: Engineering (SPEC-0147)

6.2 HOAO System Settings Requirements

This section contains requirements for the HOAO subsystem settings. The requirements for each setting

will include a brief description of the functionality the setting will drive, what level it can be changed at,

the range of possible values, the default value, and associated validation rules, where applicable.

System settings can be managed at two levels: user level and engineering level.

User level settings consist of those settings that are needed for setting up routine WFC operation. These

settings are available to the operator or general user. Engineering level settings are settings used during

calibration and alignment procedures or during special operations. These settings require the permission

and assistance of the WFC specialist or designee.

6.2.1 WFC mode

REQ# 2.1.1-4265

HOAO requires the WFC mode to be sent from the WCCS. This mode specifies the overall operation

mode of the WFC system.

Setting details:

Level: User

Range of Values: off, idle, calibrate, diffractionLimited, seeingLimitedOnDisk,

seeingLimitedCoronal, limbTracking

Default Value: idle


Source: Science (SPEC-0058, 2.0-0005), Operations (SPEC-0129, 3.1.1)

6.2.2 r0 Calculation Period

REQ# 2.1.1-4269



HOAO shall allow the WFC specialist to set the period of time over which r0 is calculated.

Setting details:

Level: Engineering

Format: float

Range of Values: [0, 60] seconds

Default Value: 1


Source: Science (SPEC-0058, 2.1.1-0055), Engineering (SPEC-0129, 5.2.1)

6.2.3 r0 Calculation Frameskip

REQ# 2.1.1-4270

HOAO shall allow the WFC specialist to set the frameskip parameter for averaging r0 calculations.

Note: When calculating the data products used in estimating r0, HOAO will skip this many frames

between measurements.

Setting details:

Level: Engineering

Format: integer

Range of Values: 0-400

Default Value: TBD



6.2.4 aO Engine Event Period

REQ# 2.1.1-4275

HOAO shall allow the WFC specialist to set the period of time for averaging low-order DM corrections

and WFS measurements for offload to the aO engine. The period, HOAO frame rate, and frameskip

settings determine the number of frames averaged for each event that is sent.

Setting details:

Level: Engineering

Format: float

Range of Values: 1-600 seconds

Default Value: 45



6.2.5 aO Engine Event Basis

REQ# 2.1.1-4280

HOAO shall allow the WFC specialist to select the modal basis used for the modal coefficients sent to the

aO engine.



Note: In operational use cases, the WFC modal basis is controlled by the WCCS. Manual setting of the

WFC modal basis at the subsystem level is for debugging and engineering operations only.

Setting details:

Level: Engineering

Format: string

Range of Values: Zernike, mirrorModes

Default Value: Zernike


Source: Operations (SPEC-0129)

6.2.6 aO Engine Event Frameskip

REQ# 2.1.1-4285

HOAO shall allow the WFC specialist to set the number of frames to skip between updates of DM and

WFS offload measurements.

Setting details:

Level: Engineering

Format: integer

Range of Values: [0, 2000]

Default Value: 0



6.2.7 HOAO Frame Rate

REQ# 2.1.1-4290

HOAO shall allow the WFC specialist to set the operating rate of the HOAO real-time system.

Setting details:

Level: Engineering

Format: float

Range of Values: 1 – 2000+ Hz

Default Value: 2000 Hz

Note: The HOAO frame rate constrains the maximum exposure time for the HOAO camera.

Note 2: The maximum value will be determined during assembly and testing, it will be at least 2000 Hz.



6.2.8 HOAO Camera Exposure Control Method

REQ# 2.1.1-4295

HOAO shall allow the User to set the method used for controlling the HOAO camera exposure time.

Setting details:

Level: User



Format: string

Range of Values: auto, manual

Default Value: auto

Note: If value is manual, HOAO exposure time must have a valid value. If auto then HOAO minimum

flux threshold, HOAO maximum flux threshold, and HOAO exposure time update period must all have

valid values.



6.2.9 HOAO Camera Exposure Time

REQ# 2.1.1-4300

HOAO shall allow the User to set exposure time of the HOAO camera.

Setting details:

Level: User

Format: integer

Range of Values: [2, 1,000,000

𝑓𝑟𝑎𝑚𝑒 𝑟𝑎𝑡𝑒− 5] microseconds

Default Value: 350 microseconds

Other Verifications:

Maximum exposure time is set by the frame rate. For the nominal frame rate of 2000 Hz, the

maximum exposure time is 495 microseconds.



6.2.10 HOAO Minimum Flux per Exposure

REQ# 2.1.1-4305

HOAO shall allow the WFC Specialist to set the minimum flux threshold for adjusting to longer exposure

times.

Setting details:

Level: Engineering

Format: integer

Range of Values: [0, 1022] DN

Default Value: 512 DN

Other Verifications: Required when exposure control method = auto. Must be less than the maximum flux

per exposure.


Source: Engineering (SPEC-0146, 2.1.1-3100)

6.2.11 HOAO Maximum Flux per Exposure

REQ# 2.1.1-4310

HOAO shall allow the WFC Specialist to set the maximum flux threshold for adjusting to shorter

exposure times.



Setting details:

Level: Engineering

Format: integer

Range of Values: [1-1023] DN

Default Value: 818 DN

Other Verifications: Required when exposure control method = auto. Must be greater than the minimum

flux per exposure.



6.2.12 HOAO Exposure Time Update Period

REQ# 2.1.1-4315

HOAO shall allow the WFC Specialist to set the time between updates for automatic exposure time

control.

Setting details:

Level: Engineering

Format: float

Range of Values: [1-300] seconds

Default Value: 10

Other Verifications: Required when exposure control method is set to auto.



6.2.13 Load High-Order Reconstruction Matrix

REQ# 2.1.1-4320

HOAO shall allow the WFC specialist to select a high-order reconstruction matrix to load from the

parameter database or via file upload. The reconstruction matrix shall be loaded into the HOAO Real-

Time Processor memory.

Setting details:

Level: Engineering

Format: string

Range of Values: TBD

Default Value: N/A


Source: Science (SPEC-0058, 2.1.1-0045)

6.2.14 Load Low-Order Shift Reconstruction Matrix

REQ# 2.1.1-4325

HOAO shall allow the WFC specialist to select a low-order shift reconstruction matrix to load from the

parameter database or via file upload. The reconstruction matrix shall be loaded into memory where it

will be used for calculating low-order modal coefficients from residual shift measurements, as in 5.13.



Setting details:

Level: Engineering

Format: string


Default Value: N/A



6.2.15 Load Low-Order Actuator Reconstruction Matrix

REQ# 2.1.1-4330

HOAO shall allow the WFC specialist to select a low-order actuator reconstruction matrix to load from

the parameter database or via file upload. The reconstruction matrix shall be loaded into memory where it

will be used for calculating low-order modal coefficients from DM actuator commands, as in 5.14.

Setting details:

Level: Engineering

Format: string


Default Value: N/A



6.2.16 Servo Gain Update period

REQ# 2.1.1-4335

HOAO shall allow the WFC specialist set the period of time for automatic updates to HOAO servo gains.

This update period will also control the rate at which high-order reconstruction matrices are updated.

Setting details:

Level: Engineering

Format: float

Range of Values: [0.01, 100] seconds

Default Value: 1



6.2.17 High-Order Servo Loop DM Gain Control Method

REQ# 2.1.1-4340

HOAO shall allow the User to set the method used to control DM servo loop gains. If set to auto, the

high-order reconstruction matrix will also be updated automatically.

Setting details:

Level: User

Format: string

Range of Values: manual, auto

Default Value: auto



Other Validations:

If set to manual, DM servo gains must be valid; if auto, gain update period must be valid.



6.2.18 High-Order Servo Loop DM Gains

REQ# 2.1.1-4345

HOAO shall allow the User to set the leak factor and proportional and integral gains used in the DM

servo loop.

Setting details:

Level: User

Format: float[3]


Default Value: TBD



6.2.19 High-Order Servo Loop FTT Gain Control Method

REQ# 2.1.1-4350

HOAO shall allow the User to set the method used to control FTT servo loop gains.

Setting details:

Level: User

Format: string

Range of Values: manual, auto

Default Value: auto

Other validations:

If set to manual, FTT servo gains must be valid; if auto, gain update period must be valid.



6.2.20 High-Order Servo Loop FTT Gains

REQ# 2.1.1-4355

HOAO shall allow the User to set the proportional and integral gains used in the FTT servo loop.

Setting details:

Level: User

Format: float[2]


Default Value: TBD





6.2.21 Load Actuator Gains Array

REQ# 2.1.1-4360

HOAO shall allow the WFC specialist to load an array of actuator gains from the parameter database or

via file upload.

Setting details:

Level: Engineering

Format: string


Default Value: TBD



6.2.22 Load Actuator Offsets Array

REQ# 2.1.1-4365

HOAO shall allow the WFC specialist to load an array of actuator offsets from the parameter database or

via file upload.

Setting details:

Level: Engineering

Format: string


Default Value: TBD



6.2.23 Reference Subaperture ID

REQ# 2.1.1-4370

HOAO shall allow the WFC specialist to select which subaperture to use as a reference for calculation of

image shifts and exposure times.

Setting details:

Level: Engineering

Format: integer

Range of Values: [1, 2304?]

Default Value: TBD



6.2.24 Reference Image Update Method

REQ# 2.1.1-4375

HOAO shall allow the user to set the update method for the HOAO subaperture reference image.

Setting details:



Level: User

Format: string

Range of Values: auto, manual

Default Value: auto

Other Validations:

Reference image tolerance threshold and reference image contrast threshold must have valid

values.



6.2.25 Reference Image Update Period

REQ# 2.1.1-4380

HOAO shall allow the user to set the period of time between reference image updates.

Setting details:

Level: User

Format: float


Default Value: 30

Other Validations:

Reference image tolerance threshold and reference image contrast threshold must have valid

values.



6.2.26 Reference Image Tolerance Threshold

REQ# 2.1.1-4385

HOAO shall allow the user to set the tolerance threshold for the reference image. When selecting a new

reference image from a set of potential reference images, the tolerance threshold sets the maximum

difference allowed between the shift of the chosen reference image and the mean shift of all potential

images.

Setting details:

Level: User

Format: float

Range of Values: [0.001, 0.5] pixels

Default Value: 0.05



6.2.27 Reference Image Contrast Threshold

REQ# 2.1.1-4390

HOAO shall allow the user to set the contrast threshold for the reference image.



Setting details:

Level: User

Format: float

Range of Values: [0, 100] percent

Default Value: 2

Note: The contrast of the reference subaperture is given in percent rms:

𝐶𝑟𝑚𝑠 =√𝑁 ∑ (𝐼(𝑖) − 𝐼)2𝑁

𝑖=1

∑ 𝐼𝑁𝑖=1 (𝑖)

∗ 100

where I is a vector containing all pixel intensity values of the reference subaperture, N is the total number

of pixels in the reference subaperture, and 𝐼 is the mean pixel value, 𝐼 =1

𝑁∑ 𝐼(𝑖)𝑁

𝑖=1 .



6.2.28 Get New Reference on Lock

REQ# 2.1.1-4395

HOAO shall allow the WFC specialist to select whether or not HOAO will automatically acquire a new

subaperture reference image upon receiving a request to lock the AO control loop.

Setting details:

Level: Engineering

Format: boolean

Range of Values: yes, no

Default Value: yes



6.2.29 Get Immediate Reference

REQ# 2.1.1-4400

HOAO shall allow the WFC specialist to request an immediate reference image. HOAO will save the next

subaperture image as the reference.

Setting details:

Level: User

Format: TBD

Range of Values: N/A

Default Value: N/A



6.2.30 Get Tolerance Reference

REQ# 2.1.1-4405



HOAO shall allow the user to request a tolerance reference image. HOAO will select a new subaperture

reference image based on tolerance and contrast settings.

Note: When selecting a tolerance reference, HOAO takes a number of consecutive images from the

chosen reference subaperture and measures their shifts relative to the first image if the DM loop is

unlocked or relative to the current reference image if the DM loop is locked. It then chooses an image,

with contrast above the contrast threshold and whose shift difference from the mean is less than the

tolerance threshold, to be the new reference image.

Setting details:

Level: User

Format: TBD

Range of Values: N/A

Default Value: N/A

Other Validations: tolerance threshold and contrast threshold must have valid values.



6.2.31 Apply DM Actuator Map

REQ# 2.1.1-4410

HOAO shall allow the WFC specialist to apply a given array of actuator values to the DM.

Setting details:

Level: Engineering

Format: integer[1600]

Range of Values: [-32768, 32767]

Default Value: N/A



6.2.32 Apply DM Modal Coefficients

REQ# 2.1.1-4415

HOAO shall allow the WFC specialist to apply a given array of modal coefficients to the DM. The

coefficients given are in the Fringe Zernike basis.

Setting details:

Level: Engineering

Format: float[37]

Range of Values: [-2500, 2500]

Default Value: N/A



6.2.33 DM Out of Bounds Threshold

REQ# 2.1.1-4417



HOAO shall allow the WFC specialist to set the threshold which, if exceeded, causes the HOAO

controller to reduce the DM gains and number of modes reconstructed by the DM.

Setting details:

Level: Engineering

Format: integer


Default Value: TBD



6.2.34 DM OOB Gain Increment

REQ# 2.1.1-4419

HOAO shall allow the WFC specialist to set the increment by which the DM gains are reduced when the

DM OOB threshold is exceeded.

Setting details:

Level: Engineering

Format: float


Default Value: 0.1



6.2.35 DM OOB recovery period

REQ# 2.1.1-4420

HOAO shall allow the WFC specialist to set the number of consecutive frames for which OOB shift

counts must be below the DM OOB threshold before HOAO will increase the DM gains and number of

modes reconstructed.

Note: The gains and reconstruction matrices will never be increased beyond those indicated by the

optimization lookup tables.

Setting details:

Level: Engineering

Format: integer

Range of Values: [1, 10,000] frames

Default Value: 10



6.2.36 FTT Out of Bounds Threshold

REQ# 2.1.1-4423

HOAO shall allow the WFC specialist to set the threshold which, if exceeded, causes the HOAO

controller to reduce the FTT gains.



Setting details:

Level: Engineering

Format: integer


Default Value: TBD



6.2.37 FTT Out of Bounds Gain Increment

REQ# 2.1.1-4425

HOAO shall allow the WFC specialist to set the increment by which the FTT gains are reduced when the

FTT OOB threshold is exceeded.

Setting details:

Level: Engineering

Format: float


Default Value: 0.1



6.2.38 FTT OOB recovery period

REQ# 2.1.1-4427

HOAO shall allow the WFC specialist to set the number of consecutive frames for which OOB shift

counts must be below the FTT OOB threshold before HOAO will increase the FTT gains.

Note: The gains will never be increased beyond those indicated by the optimization lookup tables.

Setting details:

Level: Engineering

Format: float

Range of Values: [1, 10,000] frames

Default Value: 10



6.2.39 FTT Range Offload Threshold

REQ# 2.1.1-4430

HOAO shall allow the WFC specialist to set the threshold which, if exceeded, causes HOAO to offload

the mean FTT mirror position to the TMA.

Setting details:

Level: Engineering



Format: float

Range of Values: [0.10, 1.00] fraction of FTT mirror full range

Default Value: 0.33



6.2.40 FTT Offload Period

REQ# 2.1.1-4435

HOAO shall allow the WFC specialist to set period of time over which the FTT module position will be

averaged when evaluating whether or not the FTT range threshold has been exceeded.

Setting details:

Level: Engineering

Format: float


Default Value: 30



6.2.41 FTT Offload Gain

REQ# 2.1.1-4440

HOAO shall allow the WFC specialist to set the fraction of total FTT mirror position will be offloaded

when the FTT offload range threshold is exceeded.

Setting details:

Level: Engineering

Format: float

Range of Values: [0, 2.00]

Default Value: 0.50



6.2.42 Pupil Motion Subaperture Selection

REQ# 2.1.1-4445

HOAO shall allow the WFC specialist to select which four HOAO subapertures to use for measuring

pupil motion.

Setting details:

Level: Engineering

Format: integer[4]


Default Value: TBD

Other validations: Subapertures must be in correct order (ordering TBD) and the same subaperture may

not be used twice.





6.2.43 Pupil Motion Measurement Period

REQ# 2.1.1-4450

HOAO shall allow the WFC specialist to select the period of time between broadcast of pupil motion

measurements. Subaperture intensity measurements update at a fixed rate (10 Hz) so this parameter sets

the number of frames that are averaged for each measurement.

Setting details:

Level: Engineering

Format: float

Range of Values: [0.1, 300] seconds

Default Value: 3



6.2.44 Number of Images to Accumulate

REQ# 2.1.1-4455

HOAO shall allow the WFC specialist to set the number of images to accumulate for dark and gain

calibrations.

Setting details:

Level: Engineering

Format: integer

Range of Values: [1-20,000]

Default Value: 1000


Source: Engineering (SPEC-0146, 2.1.1-3005, 2.1.1-3010)

6.2.45 Active Field Stop Assembly Aperture

REQ# 2.1.1-4457

HOAO shall allow the WFC specialist to select an aperture in the field stop assembly.

Setting details:

Level: Engineering

Format: string

Range of Values: fieldstop, pinhole, shutter

Default Value: fieldstop

Other Validations: Values “pinhole” or “shutter” require the WFC mode to be “calibrate”.




Source: Operations (SPEC-0129, 4.2.3)

6.2.46 Load DM registration pattern

REQ# 2.1.1-4459

HOAO shall allow the WFC specialist to select a DM registration pattern from an online database or via

file upload.

Setting details:

Level: Engineering

Format: string (filename)


Default Value: N/A



6.3 HOAO System Mode Requirements

HOAO system modes reflect the overall WFC configuration as controlled by the WCCS. Specific

requirements for HOAO subsystem performance in each mode are contained in SPEC-0129.

6.3.1 Off

REQ# 2.1.1-4460

HOAO shall allow the user or WFC specialist to send shutdown and power off commands.

Settings used:

N/A



6.3.2 Idle

REQ# 2.1.1-4465

HOAO shall be ready to act on configurations received from WCCS or the HOAO engineering GUI.

Settings used:

N/A



6.3.3 Calibrate

REQ# 2.1.1-4470

HOAO shall allow the user or WFC specialist to command it to perform calibration activites.

Calibrations available:

Dark



Gain

Center steering mirror

Focus

DM registration

Subaperture offset internal calibration

Subaperture offset NCP calibration

DM-assisted alignment

Pupil stabilization

Manual

Field sizing and rotation



6.3.3.1 Calibrate: dark

REQ# 2.1.1-4475

HOAO shall allow the user or WFC specialist to command it to perform a dark calibration.

Settings used:

HOAO camera exposure time

Number of frames to average

Active field stop assembly aperture

Note: The reason why the exposure time can be fixed and is not tied to ‘auto’ is that the dark current/bias

in the HOWFS camera was found to be constant for all exposure times within those expected during

operational use.

An issue might be that there could be stray light that is recorded in a dark, and subtracted during the

calibration – of course in that case, the dark data will depend on the exposure time.



6.3.3.2 Calibrate: gain

REQ# 2.1.1-4480

HOAO shall allow the user or WFC specialist to command it to perform a camera gain calibration. If the

telescope is not in a random pointing mode, the HOWFS field steering mirror will provide the random

pointing needed for gain calibration. Random pointing can be achieved using a WCCS-level script.

Settings used:


Active field stop assembly aperture = fieldstop

Number of frames to average

Note: The gain calibration assumes camera linearity over the range of expected exposure times set by the

auto adjust method.





6.3.3.3 Calibrate: center steering mirror

REQ# 2.1.1-4485

HOAO shall allow the user or WFC specialist to center the HOAO field steering mirror. This automated

calibration procedure shall return the calibration status (pass, fail, error) along with the final centering

error in units of detector pixels.

Settings used:

Active field stop assembly aperture = fieldstop

HOAO camera exposure method


Source: Operations (SPEC-0129, 4.3.7.3)

6.3.3.4 Calibrate: field sizing and rotation

REQ# 2.1.1-4486

HOAO shall allow the user or WFC specialist to command it to verify the field sizing and rotation of the

HOWFS.

Settings used:


Active field stop assembly aperture = open




6.3.3.5 Calibrate: focus

REQ# 2.1.1-4490

HOAO shall allow the user or WFC specialist to command it to perform a focus calibration. This

automated calibration procedure shall focus on a point source reference at GOS by moving the HOWFS

objective lens until the Zernike focus term from HOWFS shifts is minimized. The calibration shall return

the calibration status (pass, fail, error) along with the final Zernike focus error.

Settings used:


aO Engine event period

aO Engine event modal basis

aO Engine event frameskip



6.3.3.6 Calibrate: DM registration

REQ# 2.1.1-4495

HOAO shall allow the user or WFC specialist to command it to perform DM registration. This automated

calibration shall poke the DM actuators in a pre-determined pattern or set of patterns and analyze the

resulting shift measurements to determine the registration between the DM and HOWFS. On completion,



this calibration shall return the calibration status (pass, fail, error) and the measured registration error (x

shift, y shift, rotation, scaling).

Settings used:


DM registration pattern



6.3.3.7 Calibrate: internal offsets

REQ# 2.1.1-4500

HOAO shall allow the user or WFC specialist to command it to perform internal offset calibration.

Settings used:




6.3.3.8 Calibrate: NCP offsets

REQ# 2.1.1-4505

HOAO shall allow the user or WFC specialist to command it to perform NCP offset calibration.

Settings used:




6.3.3.9 Calibrate: DM-assisted alignment

REQ# 2.1.1-4510

HOAO shall allow the user or WFC specialist to command it to perform DM-assisted alignment.

Settings used:

HOAO frame rate

HOAO camera exposure control method

Reference subaperture ID

Get new reference on lock

DM Out of bounds threshold

FTT Out of bounds threshold

Field steering mirror position

Field steering mirror LUT





6.3.3.10 Calibrate: Pupil stabilization

REQ# 2.1.1-4515

HOAO shall allow the user or WFC specialist to command it to perform pupil stabilization in order to

assist calibrations of other instruments.

Settings used:

HOAO frame rate


Pupil motion subaperture selection

Pupil motion measurement period



6.3.3.11 Calibrate: manual

REQ# 2.1.1-4520

HOAO shall allow the user or WFC specialist to command it to allow manual calibration through the

engineering GUI.

Settings used:

N/A


Source: Operations (SPEC-0129, 4.3)

6.3.4 WFC-OPM1: Diffraction limited on-disk

REQ# 2.1.1-4525

HOAO shall allow the user or WFC specialist to command it to close the DM and FTT loops, send low-

order DM modal coefficients as events, and report pupil position measurements as events.

Settings used:

DM gain control method

FTT gain control method

aO engine event period

aO engine event basis

aO engine event frameskip

r0 calculation period

r0 calculation frameskip

HOAO frame rate



Reference image update method


DM out of bounds threshold

DM OOB gain increment

DM OOB recovery period

FTT out of bounds threshold

FTT OOB gain increment



FTT OOB recovery period

FTT range offload threshold

FTT offload period







6.3.5 WFC-OPM2: Seeing limited on-disk

REQ# 2.1.1-4530

HOAO shall allow the user or WFC specialist to command it to close the FTT loop and report pupil

position measurements as events.

Settings used:

FTT gain control method

r0 calculation period

r0 calculation frameskip

HOAO frame rate



Reference image update method


FTT out of bounds threshold

FTT OOB gain increment

FTT OOB recovery period

FTT range offload threshold

FTT offload period







6.3.6 WFC-OPM3: Seeing limited coronal

REQ# 2.1.1-4535

This mode shall be identical to idle.

Settings used:

N/A





6.3.7 WFC-OPM4: Limb occulting with image stabilization

REQ# 2.1.1-4540

This mode shall be identical to idle.

Settings used:

N/A



6.4 Mechanism Control Requirements

6.4.1 Field Steering Mirror Position

REQ# 2.1.1-4545

HOAO shall allow the user to adjust the position of the HOAO FSM. Units for HOAO FSM motion are

arcseconds in the telescope focal plane.

Setting details:

Level: User

Format: float[2] or string

Range of Values: [-30, +30] arcseconds or named position

Default Value: default (named position)



6.4.2 Objective Lens Look-up Table

REQ# 2.1.1-4550

HOAO shall allow the WFC specialist to select a look-up table for use with the Field Steering Mirror

(FSM) defocus correction.

Setting details:

Level: Engineering

Format: string


Default Value: N/A


Source: Operations (SPEC-0147, 2.1.1-1070)

6.4.3 Objective Lens Position

REQ# 2.1.1-4555

HOAO shall allow the WFC specialist to adjust the HOWFS objective lens assembly set position along

the z-axis.

Setting details:

Level: Engineering



Format: float or string





6.4.4 Microlens Array Position

REQ# 2.1.1-4565

HOAO shall allow the WFC specialist to position the microlens array assembly along the x and y-axes.

Setting details:

Level: Engineering






6.4.5 Relay Lens #1 Position

REQ# 2.1.1-4570

HOAO shall allow the WFC specialist to position the relay lens #1 assembly along the z-axis.

Setting details:

Level: Engineering






6.4.6 Relay Lens #2 Position

REQ# 2.1.1-4575

HOAO shall allow the WFC specialist to position the relay lens #2 assembly along the z-axis.

Setting details:

Level: Engineering






6.4.7 Camera Mount Position

REQ# 2.1.1-4580



HOAO shall allow the WFC specialist to position the camera mount assembly along the x and y-axes.

Setting details:

Level: Engineering






6.4.8 Camera Relay Optics Assembly Position

REQ# 2.1.1-4585

HOAO shall allow the WFC specialist to position the camera relay optics assembly along the z-axis.

Setting details:

Level: Engineering






6.5 Interface Requirements

6.5.1 WCCS interface

REQ# 2.1.1-4590

HOAO shall provide an interface to the higher-level WCCS control software, as defined by the WCCS

design documentation. This interface shall allow the WCCS to control the configuration of HOAO.


Source: Engineering (SPEC-0129, 3.2)

6.5.2 Engineering user interface

REQ# 2.1.1-4595

HOAO shall provide an engineering user interface that implements all functional operations of the HOAO

system. The engineering user interface shall be based upon the DKIST CSF JES tool and shall be

operable from computers on the DKIST control network.



6.5.3 HOAO status screen

REQ# 2.1.1-4600

HOAO shall provide a status screen that displays information on HOAO system operation that is

sufficient to determine the operating mode(s) of HOAO, system performance, and diagnostic information



necessary for efficient and accurate operation. The status screen shall display the following information:

HOAO correction mode, HOWFS subaperture images, subaperture shift measurements, DM and FTT

actuator commands, modal aberration spectra (Zernike, both instantaneous and time-averaged), OOB

statistics, residual wavefront error, modal coefficient offloads, r0 graph display, servo loop gains, and

active reconstruction matrix. The status screen shall also be able to calculate and display the temporal

power spectrum of a user-selected DM actuator or wavefront sensor subaperture with a lookback time of

1 second or more. Additionally, the status screen should be able to display the averaged temporal power

spectra of multiple DM actuators overplotted with the averaged residual wavefront error power spectra of

those same actuators.


Source: Science (SPEC-0058, 2.1.1-0080), Operations (SPEC-0129, 3.3.1)

6.6 Real-Time system requirements

6.6.1 Compute time

REQ# 2.1.1-4605

The HOAO real-time system shall have a compute latency of less than 450 microseconds. The compute

latency is defined as the time elapsed between when the real-time system receives the final HOWFS

image pixel and the time at which actuator commands are sent to the DM drive electronics.


Source: Science (SPEC-0058, 2.1.1-0015; SPEC-0009)

6.6.2 FPGA firmware

REQ# 2.1.1-4610

Firmware within the HOAO FPGA real-time processing unit shall meet all requirements in SPEC-0125:

High Order Adaptive Optics Real Time FPGA Firmware Specification.



6.7 HOAO telemetry data products

6.7.1 Telemetry latency

REQ# 2.1.1-4615

The HOAO telemetry data shall be streamed to the DHS over the BDT. The total elapsed time allowed

between the end of a HOAO control cycle and the time at which all telemetry data associated with that

cycle is available to other instruments is 100 milliseconds.

Note: The DHS is not designed to handle high frame-rate (2kHz) data so the HOAO telemetry must be

buffered into multi-frame blocks and transmitted at a lower rate. The 100 millisecond requirement is the

amount of delay time that the VBI team estimates to be tolerable before the speckle-processing code is

impacted.





6.7.2 Telemetry data format

REQ# 2.1.1-4620

The HOAO telemetry data shall generate the following data products for access by DHS Processing

Plugins (SPEC-0016).

At minimum, but not limited to, the following data shall be published in a DHS Processing Plugin

readable hardware and software format:

Stream Data Product:

Shifts

Residual actuator commands for TT and DM

Final Actuator commands for TT and DM

Stream Data Header:

Time stamp

Frame number

Lock status

WFS RMID

Out-of-bounds count

Interactuator stroke violations

Name of actuator-to-KL transformation matrix

Every Shift/Actuator Command frame shall be published. This data shall be published at a maximum rate

of 2 kHz.

Note: For a full description of the HOAO telemetry data and its formatting, see ICD 2.3-4.3 WCCS to

DHS.



6.7.3 Header Data

REQ# 2.1.1-4625

The HOAO control system shall generate metadata in accordance with SPEC-0122 (Data Model).

Note: HOAO metadata are both important for the interpretation of its own Data Products as well as

instrument Data Products.



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