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Polar Topographic KnowledgePrior to LCROSS Impact
David E. Smith1, Maria T. Zuber2
1NASA/Goddard Space Flight Center
2Massachusetts Institute of Technology
LCROSS Site Selection Workshop
NASA/Ames Research Center
October, 2006
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Question:
What topographic data can LOLA provide before and after the impact of LCROSS?
What can LOLA data be used for:– Improved location of planned impact site?– “Imaging” of permanently shadowed impact region
to characterize pre-impact regolith, including surface roughness, surface reflectance, slopes, topography, etc
– Identification of existing craters?
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Rx Telescope
Beam Expander
Earth RangingPort
Lunar Ranging PortLunar Ranging Port
LaserRadiator
Lunar Ranging Port
S/C VelocityPattern Clock Angle = 26°
D~ 56 mds
~65 m
25 m
5 m
Measurement Pattern
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Measurement Accuracy/Precision
Range to surface: <10 cm, each 5 meter spot
Surface Roughness: 30 cm, each 5 meter spot
Albedo (1064 nm): ± 0.02, each 5 meter spot
Slopes, 2 directions: ± 0.3o, 25 meter baseline
Orbital altitude: < 1 meterAlong track position ~ 25 meters
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10 cm range precision
28 Hz, 532 nm
10 cm range accuracy
28 Hz, 1064 nm
LRO Precision Tracking
In conjunction with the altimeter and S-band tracking we estimate positional accuracies of 50 m along track and <1 meter radially (CoM) after improvement of the lunar gravity field.
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Orbital Variations
Altitude Inclination
60 km
40 km
90.8
89.2
90.0
Eccentricity
0.0080.002
Because of the eccentricity of the orbit the nadir panel will be offset from the sub-satellite position by ±0.3 to ±2.5 degrees along track each orbit. (~ 2 km from 50 km)
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TLI Impulsive 2008 OCT 28 10:23:53.2864 - 10:23:53.2864 LOI-1 Finite 2008 NOV 02 09:54:22.9236 - 10:32:06.8603 LOI-2 Finite 2008 NOV 03 11:04:35.5207 - 11:16:35.5212 LOI-c Finite 2008 NOV 04 06:41:29.4881 - 06:48:56.0716 LOI-p Finite 2008 NOV 04 07:34:50.0094 - 07:37:02.7396 MOI-1 Impulse 2008 DEC 13 16:10:34.6627 - 16:12:22.4381 MOI-2 Impulse 2008 DEC 13 17:37:52.3966 - 17:38:04.3777 MOI-3 Impulse 2008 DEC 13 18:36:52.2089 - 18:37:00.1690 SK-1 Impulse 2009 JAN 09 23:47:47.9146 -
00:43:26.8193 SK-2 Impulse 2009 FEB 06 07:37:37.0569 -
08:31:29.3491 SK-3 Impulse 2009 MAR 05 13:34:55.2297 - 14:30:01.6998 SK-4 Impulse 2009 APR 01 21:21:52.7953 - 22:17:10.2313 SK-5 Impulse 2009 APR 29 05:09:38.6602 - 06:04:44.1272 SK-6 Impulse 2009 MAY 26 12:57:36.7456 - 13:52:31.8429 SK-7 Impulse 2009 JUN 22 18:52:29.0597 - 19:47:24.8620 SK-8 Impulse 2009 JUL 20 02:39:15.7389 - 03:34:15.6089 SK-9 Impulse 2009 AUG 16 10:26:54.1674 - 11:21:39.7218 SK-10 Impulse 2009 SEP 12 18:14:26.0226 - 19:09:24.4532 SK-11 Impulse 2009 OCT 10 02:01:21.2589 - 02:55:58.7047 SK-12 Impulse 2009 NOV 06 09:48:36.7283 - 10:43:30.6627 SK-13 Impulse 2009 DEC 03 17:35:12.8728 - 18:29:53.9120
Date Start StopLRO Maneuvers
The LRO orbit is circularized every month to 50 km in order to avoid impacting the surface
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South Pole Coverage, 87S->Pole
• All altitudes at the South Pole each month (35-65 km).
• Not all months the same.
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LOLA COVERAGE
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Coverage of Southern Partof Shackleton Crater
Nov 2 - Dec 13 Nov 2 - Jan 9
Nov 2 - Feb 6
The coverage varies significantly from month to month
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After 1 year:
Approx one 5-meter spot every 10 x 10 meter block
Coverage at the End of Mappingof Shackleton Crater
Coverage in the polar regions at the end of the LRO mission is not likely to be a problem…
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Nov 2 - Dec 13 Dec 13 - Jan 9
Jan 9 - Feb 6
Monthly Coverage 88S to PoleIncluding Shackleton and de Gerlache Craters
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Open: LOLA SP Crater slide show
1. SP_nadir2. SP_89p7_nadir3. SP_89p7_buildup
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Close-Up of Region of “Permanent Light”
Actual ground tracks of Lunar Prospector near Shackleton and de Gerlache craters.
Poorest regional coverage is with a few km around the pole.
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Close-Up of Region “Permanent Light”
LRO Commissioning Orbit - 6 weeks
~ 1.0 km
~ 1.2 km Typical landing site area ~ 1.2 sq km
Coverage:Nov 2 - Dec 13
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Close-Up of Region “Permanent Light”
LRO Mapping Orbit - 1st Month
4 weeks -Dec 13 - Jan 9
~ 1.0 km
~ 1.2 km
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Close-Up of Region “Permanent Light”
LRO Commissioning + 2 Months Mapping Orbit
13 weeks (91d) -
Nov 2 - Feb 6
~ 1.0 km
~ 1.2 km
Average of one 5-meter spot every 20 x 20 meter block
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Open: LOLA SP Crater slide show
1. Shackleton_nadir_buildup
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Regularizing the Coverage of a Landing Site Region
• A small off-nadir roll of LRO could change location of ground track.
• A roll of 2 mrad produces a 100 m movement of the ground track from 50 km altitude.
• Adjustments of less than 100 m unnecessary due to LOLA’s swath width of ~65 m.
• Accuracy of LOLA unaffected by small of-nadir pointing
• NOTE: Along track position of LRO will be non-nadir by 1 to 2 km due to eccentricity of the orbit!
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QuickTime™ and aTIFF (Uncompressed) decompressor
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QuickTime™ and aTIFF (Uncompressed) decompressor
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Nominal Attitude - NadirGround Track Off-Nadir
Displacement 100 m from 50 km
Effect of Pointing Off-Nadir 2 millrads
~ 1.2 km
~ 1.0 km
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QuickTime™ and aTIFF (Uncompressed) decompressor
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QuickTime™ and aTIFF (Uncompressed) decompressor
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Nominal Attitude - NadirGround Track Off-Nadir
Displacement 200 m from 50 km
Effect of Pointing Off-Nadir 4 millrads
~ 1.2 km
~ 1.0 km
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Summary & Conclusions
Prior to LCROSS impact: Characterize impact site
• LOLA will provide accurate elevations (~10 cm) with average coverage of 1 observation in a 20 x 20 meter block inside Shackleton. (Slightly better further from the pole).
• The elevation data will be complemented by roughness estimates, surface slopes and reflectance at 1064 nm.
Post LCROSS impact: Characterize the impact site again for evidence of the impact
• Elevation coverage in Shackleton 3 or 4 time better. Reflectance at the few % in sunlit and permanent shadow regions.
• Global coordinate system providing locations of features.