1. Lunar CRater Observation and Sensing Satellite Project LCROSS Site Selection Workshop Oct. 16-17, 2006 NASA/ARC, Mountain View, California LCROSS Orbital Dynamics and Targeting Constraints Ken Galal/ARC

2. LCROSS Orbital Dynamics and Targeting Constraints 2 Orbit Description Launch Date: ~3 day windows every 2 weeks (total of 18 launch dates identified Oct-Dec 2008) ~5-day translunar trajectory to moon (same as LRO) Swing-By of moon following TLI –Instrument calibration during swingby (2000-4000 km altitude) –Swingby of moon is passive (no thrusting) 81 days in post-swingby cruise orbit –Current baseline is 3-month trajectory with south pole impact –Two revolutions in high ecliptic inclination (~50 deg), 40-day period Earth orbit –~7 hours prior to impact, LCROSS will separate from Centaur upper stage and perform a ~10-minute delay maneuver (~30 m/s) to enable LCROSS to fly through Centaur impact plume

3. LCROSS Orbital Dynamics and Targeting Constraints 3 LCROSS Orbit – From Ecliptic NorthLCROSS Orbit – Side View Orbit Description Moon Earth

4. LCROSS Orbital Dynamics and Targeting Constraints 4 LCROSS Earth Range

5. LCROSS Orbital Dynamics and Targeting Constraints 5 Ecliptic North Moon’s Orbit Nominal Impact Conditions: Nominal impact site: Shackleton Crater TBR (-89.5 lat; 0 lon) Incident impact angle: ~75 deg Impact velocity: 2.5 km/sec Orbit Description

6. LCROSS Orbital Dynamics and Targeting Constraints 6 Target Latitude vs Impact Angle (south pole approach) Project Requiremt

7. LCROSS Orbital Dynamics and Targeting Constraints 7 Observatory Viewing Constraints Assumptions: 1)Observatory needs to be 2hrs from dawn/dusk at impact 2)Elevation angle of moon at impact relative to observatory must be greater than 45 deg 3)Impact must occur when moon is more than 30 deg away from new moon or full moon for ground viewing (Note: The combination of constraints 1 & 2 necessitate being more than ~76 deg from new moon) 4)Maximum impact time adjustment of +/-12 hrs allowed (due to DV limitations) 5)HST cannot point within 51 deg of sun, which translates to a constraint of approximately +/-51 deg of new moon; HST has no full moon viewing constraint

8. LCROSS Orbital Dynamics and Targeting Constraints 8 Targeting Examples Impact Viewing Conditions for October 29, 2008 LRO Launch Date

9. LCROSS Orbital Dynamics and Targeting Constraints 9 Sun-Earth-Moon Geometry at Impact on 1/23/09 (Assuming Oct. 29, 2008 LRO Launch) Nominal Sun-Earth-Moon Angle: 32 deg

10. LCROSS Orbital Dynamics and Targeting Constraints 10 Oct. 29 Launch -- Impact Viewing Geometry Example

11. LCROSS Orbital Dynamics and Targeting Constraints 11 October 08 LRO Launch Dates Oct. 28-30 LRO Launch Window Inclination of lunar equator to ecliptic: 1.5 deg Inclination of lunar equator to lunar orbit plane: 6.7 deg Inclination of orbit to ecliptic: 5.1 deg

12. LCROSS Orbital Dynamics and Targeting Constraints 12 Targeting Examples Impact Viewing Conditions for November 12, 2008 LRO Launch Date

13. LCROSS Orbital Dynamics and Targeting Constraints 13 Sun-Earth-Moon Geometry at Impact on 2/07/09 (Assuming Nov. 12, 2008 LRO Launch) Nominal Sun-Earth-Moon Angle: 152 deg

14. LCROSS Orbital Dynamics and Targeting Constraints 14 Nov. 12 Launch -- Impact Viewing Geometry Example Minimum DV Trajectory --- no impact time adjustment

15. LCROSS Orbital Dynamics and Targeting Constraints 15 Nov. 12 Launch -- Impact Viewing Geometry Example 5hr impact time adjustment to permit viewing over Hawaii

16. LCROSS Orbital Dynamics and Targeting Constraints 16 November 08 LRO Launch Dates Nov 12-14 LRO Launch Window Nov 24-27 LRO Launch Window

17. LCROSS Orbital Dynamics and Targeting Constraints 17 LCROSS Impact Targeting Summary For each LRO launch date, there is an associated minimum DV LCROSS trajectory with corresponding impact time and lunar observation geometry Certain LRO launch windows provide better impact viewing conditions than others: – Impact could occur near new or full moon – Lunar pole may be tilted toward or away from sun or Earth Can adjust arrival time to improve geometry –Increase lunar phase angle by 27 deg with extra month in orbit (added operational cost) –Adjust arrival time by up to +/-12 hrs to place observatory in view of moon (added DV cost) North pole impact trajectory implications –Additional DV cost due to nominal LRO insertion over South Pole –Added mission design costs to maintain dual south/north pole options