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

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LCROSS Orbital Dynamics and Targeting Constraints

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

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LCROSS Orbital Dynamics and Targeting Constraints

LCROSS Orbit – From Ecliptic North LCROSS Orbit – Side View

Orbit Description

Moon

MoonEarth

Earth

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LCROSS Orbital Dynamics and Targeting Constraints

LCROSS Earth Range

LCROSS Range from Earth

0

100000

200000

300000

400000

500000

600000

700000

0 10 20 30 40 50 60 70 80 90

Time from Injection (days)

Range from Earth (km)

Oct. 29 Launch

Nov. 12 Launch

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LCROSS Orbital Dynamics and Targeting Constraints

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

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LCROSS Orbital Dynamics and Targeting Constraints

Target Latitude vs Impact Angle (south pole approach)

Pro

ject

Re

quire

mt

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LCROSS Orbital Dynamics and Targeting Constraints

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

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LCROSS Orbital Dynamics and Targeting Constraints

Targeting Examples

Impact Viewing Conditions

for October 29, 2008 LRO Launch Date

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LCROSS Orbital Dynamics and Targeting ConstraintsSun-Earth-Moon Geometry at Impact on 1/23/09

(Assuming Oct. 29, 2008 LRO Launch)

Nominal Sun-Earth-Moon Angle: 32 deg

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LCROSS Orbital Dynamics and Targeting Constraints

Oct. 29 Launch -- Impact Viewing Geometry Example

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LCROSS Orbital Dynamics and Targeting ConstraintsOctober 08 LRO Launch Dates

Oct

. 28-

30 L

RO

Lau

nch

Win

dow

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

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LCROSS Orbital Dynamics and Targeting Constraints

Targeting Examples

Impact Viewing Conditions

for November 12, 2008 LRO Launch Date

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LCROSS Orbital Dynamics and Targeting ConstraintsSun-Earth-Moon Geometry at Impact on 2/07/09

(Assuming Nov. 12, 2008 LRO Launch)

Nominal Sun-Earth-Moon Angle: 152 deg

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LCROSS Orbital Dynamics and Targeting Constraints

Nov. 12 Launch -- Impact Viewing Geometry Example

Minimum DV Trajectory --- no impact time adjustment

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LCROSS Orbital Dynamics and Targeting Constraints

Nov. 12 Launch -- Impact Viewing Geometry Example

5hr impact time adjustment to permit viewing over Hawaii

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LCROSS Orbital Dynamics and Targeting ConstraintsNovember 08 LRO Launch Dates

Nov

12-

14 L

RO

Lau

nch

Win

dow

Nov

24-

27 L

RO

Lau

nch

Win

dow

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LCROSS Orbital Dynamics and Targeting Constraints

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