Post on 11-Jan-2016
description
Lunar CRater Observation and Sensing Satellite Project
Impact Site Selection Workshop
October 16, 2006 NASA Ames Research Center
Anthony Colapreteand the LCROSS Team
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LCROSS Mission Selection
• LCROSS mission was selected on 4/10/06, via an ESMD two-step AO– Step 1: Proposal generation
• (Pre-Phase A formulation phase)
– Step 2: Down-select of field of (19) proposals to (4)
• (Phase A formulation phase)
– Step 3: Selection of LCROSS proposal
• (Phase B entrance)
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The LCROSS Mission is a Lunar Kinetic Impactor employed to reveal the presence & nature of water ice on the Moon
– LCROSS Shepherding S/C (S-S/C) directs the 2000[kg] (4410[lb]) Centaur into a permanently-shadowed crater at 2.5[km/s] (1.56 [miles/s])
– ~200 metric tons (220 tons) minimum of regolith will be excavated, leaving a crater the size of ~1/3 of a football field, ~15 feet deep.
– The S-S/C decelerates, observing the Centaur ejecta cloud, and then enters the cloud using several instruments looking for water
– The S-S/C itself then becomes a 700[kg] (1,543[lb]) 'impactor' as well
– Lunar-orbital and Earth-based assets will also be able to study both clouds, (which may include LRO, Chandrayaan-1, HST, etc)
LCROSS Mission Overview
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A fast, capable team:– ARC provides the overall project management, systems engineering,
risk management, and SMA for the mission
– Northrop-Grumman provides the S/C and S/C integration for this mission as well as launch systems integration support
– ARC provides the Science, Payloads, and Mission Ops for this mission
– ARC, JPL, and GSFC provides the Navigation and Mission Design role
– JPL is providing DSN services
– KSC/LM is providing Launch Vehicle services
– JHU-APL is providing avionics environmental testing
LCROSS Project Team
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LCROSS Science Team
Tony Colaprete (ARC)Geoff Briggs (ARC)Kim Ennico (ARC)Diane Wooden (ARC)Jennifer Heldmann (SETI)Tony Ricco (Stanford)Luke Sollitt (NGST)Andy Christensen (NGST)Erik Asphaug (UCSC)Don Korycansky (UCSC)Peter Schultz (Brown)
Principal InvestigatorDeputy Principal InvestigatorPayload ScientistObservations/Analysis Observation CoordinatorNIR SpectrometersImaging systemsScience RequirementsImpact ProcessesImpact ProcessesImpact Processes
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The LCROSS mission science goals:• Confirm the presence or absence of water ice in a
permanently shadowed region on the Moon
• Identify the form/state of hydrogen observed by at the lunar poles
• Quantify, if present, the amount of water in the lunar regolith, with respect to hydrogen concentrations
• Characterize the lunar regolith within a permanently shadowed crater on the Moon
The LCROSS mission rational:• The nature of lunar polar hydrogen is one of the most important
drivers to the long term Exploration architecture
• Need to understand Quantity, Form, and Distribution of the hydrogen
• The lunar water resource can be estimated from a minimal number of “ground-truths”
• Early and decisive information will aid future ESMD and LPRP missions
Mission Measurement ObjectivesClementine Mosaic - South Pole
Neutron Map - South Pole (Elphic et al.)
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Pre-Launch Launch Transfer
VIF Ops
Pad Ops
LV Ascent
Park Orbit Coast
LRO Inject/Sep
Centaur Venting &Re-Target
Centaur Handover
To LCROSS Checkout TCM-1 TCM-2
TCM-3 Swing by Calibration
[TCM-4]
Day -1 Day 0 Day 2Day 1 Day 3 Day 4 Day 5 Day 6 Day 7
Cruise
Final Targeting
Day 15 Day 36 Day 57 Day 69
Impact and Data Collection
FinalTargeting
Burn
EDUSSeparation
BrakingBurn
DataCollection
EDUSImpact
S-S/CImpact
Day 86
Day 85
Day 64
[TCM-6] [TCM-7] TCM-9[TCM-5] TCM-8
Day 76
TCM-11
Timp– 8hrs Timp– 7hrs Timp– 6.5hrs Timp– 2hrs T = 0 Timp+ 10min
TCM-10
Mission Timeline
8( Click green button to start QuickTime movie )
LCROSS Mission Animation
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The Atlas Centaur Impact:• Mass: ~2000 kg• Velocity: 2.5 km/sec• Angle: ~75 degrees
Minimize false positives by
controlling EDUS contamination• Total H/O bearing materials (e.g.
LOX, H2, H2O in batteries) kept below
reported and kept below 100 kg
Minimize false negatives by
combining multiple detection
methods
Crater Diameter, Depth and Excavated Water(Assumes a 10 cm desiccated Layer with uniform water mixing below)
…using 6.5 Billion Joules
Prospecting for Water
0
5
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25
0 20 40 60 80
Impact Angle (degrees)
Cra
ter
Dia
met
er, D
crat
er (
m)
Cra
ter
Dep
th, H
crat
er (
m)
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Eje
cta
Wat
er M
ass
(kg
)
DcraterHcraterMass H2O (0.1%)Mass H2O (1%)Mass H2O (5%)
For a 2.5 km/sec, 2000 kg Impact, den = 300 kg/m3
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CBEIM Crater Size
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15
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Met
ers
Crater Depth Crater Diameter Crater RimDiameter
Low
High
CBE
The Current Best Estimate Impact Model (CBEIM)
• The CBIEM summarizes the results of numerous impact models / assessments.
• Used as the base to drive mission design and instrument selection.
• Efforts continue to refine the model with an update due December, 2006.
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Montecarlo study of ejecta mass: Simulation varied the crater radius (Rcrat), velocity function exponent ()total mas (Me), and ejecta flight angle (See LCROSS technical note “LCROSS ejecta dynamics–Monte Carlo model (09/16/06)“ for details)
Montecarlo Study of Ejecta MassAverageMedian
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Average Ejecta Curtain Characteristics – 1% water content
CBEIM and Sensitivity Studies
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0 100 200 300 400 500 600
Time (sec)
Eje
cta
Cu
rtain
Wate
r Ic
e M
ass A
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ve
an
Alt
itu
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kg
)
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Wate
r V
ap
or
Mass A
bo
ve a
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ltit
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kg
)
Ice Ice Ice Ice Ice Ice
Vapor Vapor Vapor Vapor Vapor Vapor
2 km 5 km 10 km 15 km 25 km 35 km
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Stages of the Impact Process
Ejecta Curtain
Simulation using the Ames Vertical Gun Range
Peter Schultz
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Impact Flash and Vapor CloudVisible Component:
• Compaction / Intergrain Strain• ~0.1 sec• F~0.001-1 W m-2 (r=1000 km)
NIR Component:• Blackbody Emission of Vapor Cloud• ~1 sec• F~0.01-10 mW m-2 (r=1000 km)
Total energy sensitive to target properties such as material strength, density and water content.
Shape of the curve reflects the penetration depth, changes in material competence
A variety of visible and NIR spectral emissions relate to composition of target material and the fraction of the impactor which vaporizes
Lunar FlashAVGR Flash
Flash Brightness vs Time
Stages of the Impact Process
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Ejecta Curtain EvolutionAfter the flash, target material is ejected outward on ballistic trajectories.
Visible Component:• Curtain illuminated by sunlight• Spectral brightness dependant on particle density, size,
composition, shape• Excitation / Florescence from species such as OH- and
H2O+
NIR Component:• Curtain illuminated by sunlight• Spectral brightness dependant on particle density,
composition, size, shape
Mid-IR Component• Curtain thermal emission• Evolution sensitive to initial ejecta temperature (~100
K), particle size, volatile composition (water) and solar exposure
• Grains with radii <100 m will warm within ~1-100 seconds to ~250 K after solar exposure.
• Spectral brightness dependant on particle density, composition, size, shape
Stages of the Impact Process
WaterVapor
WaterIce
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Curtain Clearing / Crater ExposureAfter ~5 minutes the bulk of the ejecta “settles” exposing the fresh crater
Mid-IR Component• Remnant thermal emission from the crater (=6-15 m)• At 5 minutes post impact the crater temperature will be
~200 K, against a ~100 K background• Crater temperature sensitive to water content• Determination of crater size
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200
250
300
350
400
450
0 2 4 6 8 10 12 14
Time After EDUS Impact (min)
Cra
terF
loo
r T
emp
erat
ure
(K
)
Temperature of Crater Floor After Impact
Stages of the Impact Process
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LCROSS Measurement Plan
Flash Photometry• Total brightness in visible and NIR wavelengths
Visible Spectroscopy• Visible emission (e.g., OH-, H2O+)• Surface and ejecta curtain reflectance/absorption
NIR Spectroscopy• Surface and ejecta curtain reflectance/absorption
NIR Imaging• Surface and ejecta curtain reflectance• Band-depth maps (=1.4 m)
Middle IR Imaging • Surface and ejecta curtain temperatures• Band-depth maps (=12 m)
Visible Imaging• Surface and ejecta curtain reflectance
WaterVapor
WaterIce
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Measurement / Technique Trace
Direct / Strong = Very direct measure with little modeling / assumption; highly sensitiveIndirect / Strong = Indirect measure with the goal removed by several steps; highly sensitiveIndirect / Weak = Indirect measure with the goal removed by several steps; moderately sensitive
Measurement Requirement Flash Photometry
Visible Spectroscopy
NIR Spectroscopy
NIR Imaging Mid-IR Imaging
Visible Imaging
Total Water PRJ4.1.1-.4
Water Ice PRJ4.1.1-.3
Water Vapor PRJ4.1.1-.3
Organics PRJ4.1.3
Hydrated Minerals PRJ4.1.3
Target Properties PRJ4.1.5,4.1.7
Curtain Morphology PRJ4.1.8,4.1.4
Thermal Evolution PRJ4.1.8
Mineralogy PRJ4.1.5
Particle Size PRJ4.1.6
Direct / StrongIndirect / StrongIndirect / Weak
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MoonEarth
LCROSS Orbit & Impact Geometry
Ecliptic North
Moon’s Orbit
Nominal Impact Conditions:
• Target impact site: Shackleton Crater (-89.5 lat; 0 lon)
• Incident impact angle: ~75 deg
• Impact velocity: 2.5 km/sec
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Basic S/C Concept
• Hybrid propulsive control authority:– 5[lbf] thrusters for large delta-V– 1[lbf] thrusters for high precision
control authority for attitude control• No deployments or mechanisms except
separation bands
• Straight load path LRO accommodation with high structural margins
• ESPA ring used as the primary spacecraft structure, similar to the AFRL DSX mission.
• TDRSS tank supported on a simple cone on the upper ESPA ring interface
• Propulsion booms and equipment panels attach to Secondary Payload Interfaces
D1666VS PAF &Spacer
B1194VS PAF &Spacer
Centaur
ESPARing
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Space Vehicle Overview
Star tracker
PL Optical Bench
Omni antenna (2)- 4 pi steradian coverage
Adjustable MGA (2)+/- 20 deg FOV+/- 45 deg adjustability pre-launch
Solar array
Propellant tank- Mounting skirt
PL support structure
Thruster mounting brackets (4)- Two 22N and eight 5N total
ESPA ring- Six attachment ports
LRO derivative spacecraft avionics distributed on 5 equipment panels-C&DH, PSE, PDE, STA, IRU, Transponder, RF components
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9 Instruments:1 Visible Context Camera:
4 color, 6 degree FOV, <0.5 km resolution at T-10 min to S-S/C impact
2 NIR Cameras1.4 m water ice band depth maps1 km resolution at T-10 min
2 mid-IR Cameras7 and 12.3 m< 0.5 km resolution
1 Visible Spectrometer0.25 to 0.8 m, ~0.002 m resolution
2 NIR Spectrometers1.35 to 2.45 m, 0.012 m resolution
1 Total Visible Luminance PhotometerBroadband from 0.6 – 1.2 m, sample rate >1000 Hz, < nW NEP @ 1000 Hz
Payload OverviewDHU
Spec sensor
Spec sensor
Spec sensor
Observation deck
sensors
Baffle
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Instrument sensitivity calculated using CBEIM, scattering calculations, and instrument performance models
LCROSS S-S/C Utilizes backscattered solar light to make water absorption measurements (Differential Absorption Spectroscopy)
Ejecta Curtain Scattering Assumptions (for NIR):Dominant Particle Radius = 45 mmParticle Density = 2000 kg/m3
Single Scatter Albedo = 0.8Asymmetry Factor = 0.8q = 30°
Earth-Sun-Moon Geometry30 °>q>160°
Instrument Sensitivity Studies
q
Backscatter Geometry from an Solar Illuminated Curtain
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Instrument Sensitivity Studies
Time after impact, t = 60 sec
N = 1 scan N = 10 scans
0.00955
0.0096
0.00965
0.0097
0.00975
0.0098
0.00985
1.25 1.5 1.75 2 2.25 2.5
Wavelength (microns)
I/F
0.00958
0.0096
0.00962
0.00964
0.00966
0.00968
0.0097
0.00972
0.00974
0.00976
0.00978
1.25 1.5 1.75 2 2.25 2.5
Wavelength (microns)
I/F
a) b)
NIR Spectrometer Sensitivity to 1% Regolith Water Concentration
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0.001
0.01
0.1
1
0 100 200 300 400 500 600Time after EDUS Impact (sec)
Cam
era
Res
olu
tio
n (
km/p
ixel
)
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Time After EDUS Impact (sec)
Cam
era
FO
V (
km)
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1400
Alt
itu
de
(km
)
Vis Cam FP
MIR Cam FP
Altitude (km)
Instrument Sensitivity Studies
Instrument Sensitivity Example – Visible and MIR Cameras
Camera Resolutions
Each point represents a IR camera image
Altitude for a 2.5 km descent velocity
Camera FOVs
Maximum Expected EDUS Crater Rim Diameter
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Potential Supporting Platforms• LRO• International lunar missions• Earth-orbiting• Ground based
These platforms can provide unique vantage points and capabilities to monitor the impact event for water.
LCROSS provides support to these missions in the form of science rationale, impact expectations, observation recommendations, and technical data for observation (e.g., timing, direction for telescope pointing).
• Working directly with Facility/Instrument leads to plan observations (e.g., HST, SWAS, LRO, Keck).
• LCROSS Co-I has participated in the observation of SMART-1 to gain experience in observing the moon using large earth based telescope.
• Information will be provided through a web portal, modeled after the very successful Deep Impact mission.
Impact Observations Support
LROHST
Keck
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Impact Observations Support
The opportunity for ground based assets to observe the impact depends on the date and time of impact:
• Phase of the moon: >30° from new or full moon
• Moon position in the night sky: <2 air masses (>45 ° from horizon) with >2 hours of observing time
FullMoon
NewMoon
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Impact Observations Support
Platform / Instrument to Measurement Trace
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LCROSS Payload Data Plan
Receive Level-1 data (uncalibrated) from MOS• MOS station to Science station
All calibration and analysis performed by Science Team• Analysis / Retrieval routines developed prior to impact• Will adopt the LRO coordinate system
Impact + 3 months:• The LCROSS payload data will be calibrated and reduced to physical
units• A report on the LCROSS payload results will be delivered to LPRP and
ESMD
Impact + 6 months:• The LCROSS Payload data will be appropriately formatted and delivered
to the PDS
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S-S/CPerformance
InstrumentPerformance
RadiancePredictions
ChemistryPredictions
Impact SiteSelection
ProjectConstraints
Trades
Inputs / Requirements
MissionGoals
ImpactPredictions
The impact model predictions formed the bases for mission design and instrument selection.
Mission Design and the Impact
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The uncertainty to which we know where a place and altitude is on the Moon is a function of both latitude and longitude.
Current uncertainties in lunar geodetic maps are:
• ±3-4 km in the horizontal and ~±0.5 km in the vertical.
• Newest USGS map (due in January 2007), these errors may be as small as ~±1 km in the horizontal.
This error will be reduced by the time of impact:
• Using LRO data can reduce current uncertainty by a factor of ~2.
Impact Site Selection – The Geodetic Map
Maximum (uncorrelated) targeting error, assuming unimproved geodetic map, is ±4 - 5 km (3).
• Current S-S/C targeting performance estimated to be better than ±1 km (3).
Clementine Mosaic of South Pole
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The mission baseline is to impact Shackleton Crater
Shackleton meets the primary criteria for targeting:• Shadowed• Large (D>10 km)• Apparent association with increased [H]• High latitude (Impact Angle >70°)• Near side with portion of interior visible to Earth
Impact Site - Baseline
ShackletonLP Neutron Counts (Maurice et al.)
Blue indicates [H]Radar Topography (Margot et al.)
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Shackleton may not be the best target given secondary considerations, including:
• Visibility to Earth assets (lat and lon) and Lunar phase (position of terminator)
• Site surface properties, including regolith depth (age) and surface roughness (effects the total ejecta dynamics and volume)
A Target Selection Committee will consider all candidates and weigh their merit against:
• Project constraints (e.g. targeting accuracy)
• Project impact (due to departure from baseline)
• Primary and secondary considerations.
Impact Site Selection - Adjustments
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Impact Site Selection - Process
Targeting Committee
WorkshopInput
Project Impact
ESMD/ LPRP
Other Input
Project(Baseline)
“Top Five”
Project(Final)
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Backup Slides
Backup Sides
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Time After EDUS Impact (Sec)
Cu
rtai
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ass
Ab
ove
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m (
kg)
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rtai
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Curtain Mass Above 2 km (kg)
Curtain Radius (km)
CBEIM Ejecta Curtain Geometry
EDUS Separation Selection• To maximize S-S/C instrument
response, instrument FOV should be filled at peak sunlit ejecta opacity
• Sunlit ejecta opacity:
• Maximum sunlit ejecta mass (assuming a 2 km sun-mask) occurs at ~1 min after impact
• At 1 min after EDUS impact the ejecta curtain radius, R, is R~5 km, and at 2 min, R~15 km
To maximize the total integrated signal-to-background ratio over the maximum extent of time, the S-S/C should follow the impact by 8-10 minutes.
The CBEIM and Centaur Separation Time
curtain
ejecta
A
M~
0.0001
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Time After EDUS Impact (Sec)
Op
tica
l Dep
th
Ejecta
Water Ice