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: 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?

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

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:± 0.3 o, 25 meter baseline Orbital altitude:< 1 meter Along track position~ 25 meters

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.

Orbital Variations Altitude Inclination 60 km 40 km Eccentricity 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)

TLI Impulsive2008 OCT 28 10:23: :23: LOI-1 Finite 2008 NOV 02 09:54: :32: LOI-2 Finite 2008 NOV 03 11:04: :16: LOI-c Finite 2008 NOV 04 06:41: :48: LOI-p Finite 2008 NOV 04 07:34: :37: MOI-1 Impulse2008 DEC 13 16:10: :12: MOI-2 Impulse2008 DEC 13 17:37: :38: MOI-3 Impulse2008 DEC 13 18:36: :37: SK-1 Impulse2009 JAN 09 23:47: :43: SK-2 Impulse2009 FEB 06 07:37: :31: SK-3 Impulse2009 MAR 05 13:34: :30: SK-4 Impulse2009 APR 01 21:21: :17: SK-5 Impulse2009 APR 29 05:09: :04: SK-6 Impulse2009 MAY 26 12:57: :52: SK-7 Impulse2009 JUN 22 18:52: :47: SK-8 Impulse2009 JUL 20 02:39: :34: SK-9 Impulse2009 AUG 16 10:26: :21: SK-10 Impulse2009 SEP 12 18:14: :09: SK-11 Impulse2009 OCT 10 02:01: :55: SK-12 Impulse2009 NOV 06 09:48: :43: SK-13 Impulse2009 DEC 03 17:35: :29: Date Start Stop LRO Maneuvers The LRO orbit is circularized every month to 50 km in order to avoid impacting the surface

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

LOLA COVERAGE

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

After 1 year: Approx one 5-meter spot every 10 x 10 meter block 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…

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

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

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.

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

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

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

Open: LOLA SP Crater slide show 1. Shackleton_nadir_buildup

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!

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

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

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.