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Polar Topographic Knowledge Prior to LCROSS Impact

Polar Topographic Knowledge Prior to LCROSS Impact. David E. Smith 1 , Maria T. Zuber 2 1 NASA/Goddard Space Flight Center 2 Massachusetts Institute of Technology LCROSS Site Selection Workshop NASA/Ames Research Center October, 2006. Question:.

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Polar Topographic Knowledge Prior to LCROSS Impact

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  1. 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

  2. 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?

  3. Measurement Pattern Pattern Clock Angle = 26° S/C Velocity 5 m 25 m Beam Expander D~ 56 m Rx Telescope Laser Radiator ds Lunar Ranging Port Earth Ranging Port Lunar Ranging Port Lunar Ranging Port ~65 m

  4. 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 meter Along track position ~ 25 meters

  5. 10 cm range accuracy 28 Hz, 1064 nm 10 cm range precision 28 Hz, 532 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.

  6. Orbital Variations 90.8 Inclination Altitude 60 km 90.0 40 km 89.2 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) 0.008 0.002 Eccentricity

  7. LRO Maneuvers Date Start Stop • 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 The LRO orbit is circularized every month to 50 km in order to avoid impacting the surface

  8. South Pole Coverage, 87S->Pole • All altitudes at the South Pole each month (35-65 km). • Not all months the same.

  9. LOLA COVERAGE

  10. Coverage of Southern Part of Shackleton Crater The coverage varies significantly from month to month Nov 2 - Dec 13 Nov 2 - Jan 9 Nov 2 - Feb 6

  11. Coverage at the End of Mapping of Shackleton Crater Coverage in the polar regions at the end of the LRO mission is not likely to be a problem… After 1 year: Approx one 5-meter spot every 10 x 10 meter block

  12. Monthly Coverage 88S to Pole Including Shackleton and de Gerlache Craters Nov 2 - Dec 13 Dec 13 - Jan 9 Jan 9 - Feb 6

  13. Open: LOLA SP Crater slide show 1. SP_nadir 2. SP_89p7_nadir 3. SP_89p7_buildup

  14. 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.

  15. Close-Up of Region “Permanent Light” LRO Commissioning Orbit - 6 weeks ~ 1.2 km Typical landing site area ~ 1.2 sq km Coverage: Nov 2 - Dec 13 ~ 1.0 km

  16. Close-Up of Region “Permanent Light” LRO Mapping Orbit - 1st Month ~ 1.2 km 4 weeks - Dec 13 - Jan 9 ~ 1.0 km

  17. Close-Up of Region “Permanent Light” LRO Commissioning + 2 Months Mapping Orbit 13 weeks (91d) - Nov 2 - Feb 6 ~ 1.2 km Average of one 5-meter spot every 20 x 20 meter block ~ 1.0 km

  18. Open: LOLA SP Crater slide show 1. Shackleton_nadir_buildup

  19. 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!

  20. Effect of Pointing Off-Nadir 2 millrads Ground Track Off-Nadir Displacement 100 m from 50 km Nominal Attitude - Nadir ~ 1.2 km ~ 1.0 km

  21. Effect of Pointing Off-Nadir 4 millrads Ground Track Off-Nadir Displacement 200 m from 50 km Nominal Attitude - Nadir ~ 1.2 km ~ 1.0 km

  22. 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.

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