Post on 11-Jan-2016
description
Drag and Atmospheric Neutral Density Explorer
Colorado Space Grant Consortium and
CU Aerospace Engineering Sciences
Meeting of the NADIR MURIOctober 21st, 2008Boulder, Colorado
2
DANDE - NADIR Seminar
Overview
1. Introduction2. Science3. Instruments4. The DANDE Spacecraft5. Program Status
3I - Introduction
The University Nanosat Program
• University Nanosat – The National Championships of Spacecraft Design– 2 year program in its fifth iteration– 10 out of 30 university proposals selected based on Air
Force Relevance– $85k initial seed funding for hardware and student
support– In January 2009, one school wins additional $85k, I&T at
Kirtland, and flight to Orbit• CU Nanosat Entry
– Has involved a core team of graduate students and expanded into 40 graduate and undergraduate students
– Many aspects of the ASEN Graduate Projects but organized as independent research and MS research
– Has leveraged over $240k from University, Department, DoD, and COSGC Funds
4I - Introduction
Nanosat V Program at CU
DANDE will improve atmospheric models and calibrate near real-time models by measuring the following
•Deceleration
•Atmospheric composition
•Horizontal Winds
DANDE is spherically shaped to minimize biases resulting from estimation of the drag coefficient
5I - Objectives and Requirements
DANDE – NADIR Synergies
• Provide the information to improve empirical models of neutral density• Determine the relationship between neutral density structure and satellite
drag• Understand the physical processes driving the variability of neutral
atmospheric density
6I - Introduction
Background and Motivation
Scientific understanding hindered by lack of neutral density, composition, and wind measurements
Precise orbit prediction depends on accurate knowledge of atmospheric density and in particular excursions from the mean state
drag induced drift
Relative Orbit of Two Separating Spacecraft
Storm response of CHAMP E/W winds
77
DANDE Science
wV
a
TV
ρ – density
Asc – projected area
Msc – s/c mass
CD – drag coefficient
scV
wV
a
TV
ρ – density
Asc – projected area
Msc – s/c mass
CD – drag coefficient
scV
8II - DANDE Science
Mission Statement
Mission StatementExplore the spatial and temporal variability of the
neutral thermosphere at altitudes of 350 - 200 km, and investigate how wind and density variability translate to
drag forces on satellites.
DRAG and
ATMOSPHERIC
NEUTRAL
DENSITY
EXPLORER
9II - DANDE Science
Objectives and Compelling Science Questions Addressed by DANDE
PO1relationship between total mass density, composition, and winds
Q1: What are the global relationships between density, composition and winds?
Q2: How do density, composition and winds vary with respect to each other locally?
Q3: How well do current empirical and first principles models emulate variations in density, composition and winds?
PO2relative contributions of density and winds to satellite drag
Q5: Under what conditions do winds have a non-negligible effect on satellite drag?
Q6: What is the relationship between spatial variability of density and winds, and the integrated drag on a satellite?
PO3key technologies
Q7: Can the in-situ density-measurement concept be employed effectively for aeronomic research within the framework of the University Nanosatellite Program?
PO4variation in coefficient of drag
Q8: How does the coefficient of drag vary when transitioning between free molecular flow and slip flow?
10II - DANDE Science
Objective Requirements
Measure in-situ density and composition (O:N2 ratio) during at least 5 sudden geomagnetic storms and 4 periods of quiet geomagnetic conditions in an altitude of at most 350 km and covering a minimum latitude of at least 54 degrees
Calibration and validation of models. Goal: also estimate the coefficient of drag in orbit at 350 - 100 km altitude.
Measure neutral winds at an altitude of up to 250 km and below and at latitudes of at least 54 degrees during 5 sudden geomagnetic storms and 4 periods of quiet geomagnetic conditions. Provide the wind data with a spatial resolution of at least 500 km (goal: 100 km).
Measure large-scale horizontal variations with in-situ density data over the course of at least 5 geomagnetic storms and 4 periods of quiet geomagnetic conditions
Develop a low-cost system to make in-situ measurements of the neutral atmosphere and adhere to Nanosat Program Requirements. Finish the proto-qualification unit on time and on budget.
11II - DANDE Science
Refs Requirement Precision(1-sigma)
Accuracy
absolute percent* absolute percent*
1.SYS2, 1.SYS52 Density 2x10-13 kg/m3 2% 1.0x10-12 kg/m3 10%
1.SYS6, 1.SYS7 In-Track Wind 100 m/s 20%** 100 m/s 20%
1.SYS56,1.SYS57 Cross-Track W. 100 m/s 10% 100 m/s 10%
1.SYS21
Composition Densities (O & N2) 7x1013 m-3 2% 5.3x1014 m-3 15%
1.SYS52,1.SYS72 Coefficient of Drag 0.1 5% 0.2 10%
*percent value based on average conditions during solar maximum, vernal equinox
**assuming a wind velocity of 1 km/s, storm conditions
Minimum Measurement Requirements
1.SYS26 , composition measurements with resolution of 1.5 m/Δm. Driven by 0.SYS1 and 1.SYS21(where m/Δm = half peak width at mass m)
horizontal resolution of 500km (~64s)
12II - DANDE Science
Wind and Density Requirement Relationship
Requirement
Goal
13II - DANDE Science 13
How Measurements are Made
• Identifying all components of the constituents of the drag equation.• With a near-spherical shape, an a-priori physical drag coefficient may be calculated and a physical density can
be obtained from the measurements
atmosphere
ρ - densityV
A
FD
CD
VW
aMVVACF WDD 2
2
1
accelerometersWTS sensor
a priori knowledge
tracking
a priori knowledge
a priori knowledge/ comparison
solutionmeasured
a priori
solution
solved
1414
DANDE Science Instruments
15III - DANDE Science Instruments
Accelerometers
Method to reduce this drift• Flip one accelerometer in positive and negative directions and remove bias• Modulate measurement to 6 μHz - 1 Hz range• 6 reduces the noise through averaging independent measurements by 0.41 (1/√6)• Provides redundancy
STAR accelerometer
Cost ~$3,000,000Precision 30 ngBandwidth 10 mHz – 100mHz
Cost ~$3,000Precision ng*Bandwidth 6 μHz – 10 KHz****must be able to reject the larger noise outside of 6 μHz - 1 Hz to achieve 79 ng
QA-2000 accelerometer
x 6
16III - DANDE Science Instruments
Accelerometer Measurement System
ANALOG FILTERING
A/D CONVERSION
LEAST SQUARES
70 ng1x100 1x1021x10-31x10-5
1.6x10-10
4.0x10-15
Frequency [Hz]
PS
D [
g2 /
Hz]
1.0x10-12
1x100 1x1021x10-31x10-5
1.6x10-10
4.0x10-15
Frequency [Hz]
PS
D [
g2 /
Hz]
1.0x10-12
spin rate
Low frequency bias
17III - DANDE Science Instruments
R
T
Problem Description: Measurement System
ACC-4
ACC-6
ACC-3 ACC-
2
ACC-
5
ACC-1
FD
PROCESS & AVERAGE
ω
AC
C-6
AC
C-2
AC
C-5
AC
C-1
AC
C-3
AC
C-4
ω = π/3 [rad/sec]
18III - DANDE Science Instruments
Accelerometer AnalysisLatitude [deg]
0∘ 82∘ -82∘0∘ 0∘ 82∘ -82∘0∘ 0∘ 82∘ -82∘0∘ 0∘ 82∘ -82∘0∘
19III - DANDE Science Instruments 19
Wind and Temperature Spectrometer
CO
LLIM
AT
OR
ION
SO
UR
CE
DE
TE
CT
OR
AN
AL
YZ
ER
NMS302 POWER BOARD
NM
S303
DE
TE
CT
OR
BO
AR
D
-167 V
-100 V
e-
-3000V
T
NMS304 CONTROLLER BOARDNMS304 CONTROLLER BOARDNMS304 CONTROLLER BOARD
0V – 5V SCAN
5V
BU
S
I2C DATA BUS
-100 V -101 V
FARADAYCUP
IONIZER
TEMPERATURESENSOR
GROUND DEFLECTOR PLATE
HOT DEFLECTOR PLATE
BA
FF
LE (IO
N-D
EF
LEC
TO
R)
DIGITAL DATA ANALOG DATA
DE
TE
CT
OR
AN
OD
ES
15V BUS
Incoming Neutrals
20III - DANDE Science Instruments 20
Wind and Temperature Spectrometer
1.Neutral particle (blue) enters the collimator. (Ions rejected)2.Neutral particle is ionized inside of a field free electron bombardment region3.Neutral particle enters the energy selector and undergoes acceleration towards the
exit 4.Outside the selector, the particle is accelerated abruptly by a -3kV potential towards
the Micro-Channel Plate (MCP)5.The impact on the MCP causes a cascade of electrons to travel towards one of the
anodes which measures the impact. Which anode is triggered depends on the angle at which the neutral particle entered the collimator.
21III - DANDE Science Instruments 21
Wind and Temperature Spectrometer
Total number densities across all spectra as the satellite spins
-180
-155
-130
-105-80
-55
-30-520457095120
145
170
050
010
0015
0020
0025
00
WACC-4
ACC-6
ACC-3 ACC-
2
ACC-
5
ACC-1
ω
Angular position about the satellite spin axis, degrees
# of
par
ticle
s im
pact
ing
dete
ctor
Peak count of vertical distribution
~2000 counts
R
T
22III - DANDE Science Instruments 22
WTS Science Data Product Analysis
wind angle
N2 wind mag.
O wind mag.
O temp. N2 temp.
23III - DANDE Science Instruments 23
Wind and Temperature Spectrometer
• Will meet science requirements and goals
•The error depends on the number of particles registered.•Determined for a true wind velocity magnitude W of 10 m/s:
Parameter % error*
Noise(Peak cts)
W T N(O) N(N2)
3%(1000)
13% 0.40% 0.55% 0.38%
1%(10,000)
5% 0.13% 0.18% 0.13%
*from Herrero et. al. unpublished work
DANDE
24III - DANDE Science Instruments
Wind and Density Requirement Relationship
Design
25III - DANDE Science Instruments
Density Error – Drag and Wind Data
26III - DANDE Science Instruments
Complex Geometry Effects
A behavior different from that of smooth spheres is observed for the faceted spheres. What is the physical drag coefficient of a faceted surface?
[Bowman & Moe 2005]
Starshine I
Physical CDP, 100% diffuse
Physical CDP, partly quasi-specular
Fitted CD
Expected fit
27III - DANDE Science Instruments
Results: Impacts on Starshine SurfacePercentage of Total Impacts
“longitude”
“la
titu
de”
2∘ x 2∘ bins
0.06 %
0.01 %
28III - DANDE Science Instruments
Drag Coefficient of DANDE
Bias induced by CD uncertainty using method of [Moe and Moe, 1996] at solar max
(2.216 - 2.118)/2.216 = 4.5%
2929
Spacecraft Engineering
30IV - Spacecraft Engineering
DANDE Overview
ESPA Ring DANDE Sphere
Lightband Adapter Bracket (LAB)
Baseline Configuration
18”
31IV - Spacecraft Engineering 31
Mission Timeline• Phase 1: LV Separation and
commissioning1. Launch Mode - time delay –
Safe Mode2. Full charge and checkout
[18 – 30 hours]3. Lightband jettison
• Phase 2: Attitude Acquisition1. Spin Up [24 h]2. Spin-Axis Alignment [120h]3. Reserve time [24h]
LV SEPARATION AND COMMISSIONING PHASE
Day 2Day 1
Wind
Composition
Acceleration
Tracking
Tracking
SCIENCE PHASE
DATA ACQUISITION1 orbit SCIENCE1 orbit STANDBY
DOWNLINK/UPLINK~2x in 24 hours
ATTITUDE ADJUST~1 orbit per day
RE-ENTRY DYNAMICS~LAST WEEK OF ORBIT
200 km – 100 km
Day 9 Day 100
• Phase 3: Science [~90 days]1. Science Mode2. Standby Mode3. Comm. Pass4. Attitude Adjust5. Repeat
32IV - Spacecraft Engineering
Spacecraft Layout
33IV - Spacecraft Engineering 33
–Spin stabilization about orbit normal• 40°/sec (10 rpm)• Only two maneuvers:
spin-up and axis alignment
–Sensors• Magnetometer for spin-up• Horizon Crossing Indicators for
spin axis alignment
–Actuators• 2x Torque rods: one along spin axis
and one transverse• Passive nutation damper
DANDE Attitude
3434
Program Status
35V - Program Status
Completed Formal Testing
TESTING
36V - Program Status
State of the DANDE Program: Hardware
HARDWARE & MANUFACTURING
Engineering Design UnitLessonsLearned Competition Review Hardware
37V - Program Status
Integration & Testing Schedule
Today Competition Review
38
Questions
dande.colorado.edu