LCROSS

1
Mission Design Observation Campaign Constraints
Ken Galal/ARC
2
LRO/LCROSS Launch Dates

• Launch Requirements
• LCROSS launch dates set by LRO
• Driven by LRO sun beta angle constraint at lunar
  solstices
• Launch blocks consist of daily launch
  opportunities over 3-4 consecutive days
• 2 weeks between each launch block
• /-30 minute maximum launch window with launch
  possible on 10 minute centers
• Currently 18 possible launch dates identified
  from Oct. 28 to Dec. 25 (additional dates in
  December under consideration)

3
Nominal LCROSS Launch Blocks
Current Range of Launch/Impact Opportunities a
subset may be chosen that best satisfies LCROSS
propellant and observation constraints
Preliminary
LRO Launch Blackout Time
4
Driving Mission Requirements

• Impact Conditions
• V gt 2.5 km/s
• Impact angle gt 60 deg relative to horizontal
• Impact targeting accuracy of 10 km, with a goal
  of under 1.75 km
• Impact Observation
• Crater sun Earth tilt angle lt90 deg (angle from
  normal to crater floor to sun/Earth)
• DSN 70m station coverage required for LCROSS
  science data collection
• Ground observatory elevation angle gt45 deg
• Lunar phase gt30 deg from new or full moon
• Impact time occurs when observatory is minimum of
  2 hrs from dawn/dusk (with a goal of gt3hrs)

5
Ground Observatory Impact Geometry
Observatory Lunar Phase 2 hr Dawn/Dusk Lighting
Constraint
Observatory Viewing Elevation Constraint
? 45

? 30
Resulting impact lunar phase exclusion zones
?
6
Sample Impact Geometry
Sample Impact Viewing Geometry for Nov. 24 (3.5M,
0-P30 launch window) or Dec. 9 (3M) Launch Dates
7
Crater Impact Geometry

• Sun tilt angle (in blue)
• Key for ejecta cloud lighting
• Yearly variation due to 1.5 inclination of lunar
  equator relative to ecliptic plane
• Additional monthly variation function of crater
  latitude (larger amplitudes away from pole)
• Earth tilt angle (in green)
• Key for observatory viewing
• 6.7 Monthly variation of due to inclination of
  lunar equator wrt lunar orbit plane
• For a given impact date, lighting and viewing
  geometry varies greatly from crater to crater

8
Target Impact Conditions

• Baseline Candidate Craters
• Faustini, Shoemaker, Cabaeus Shackleton
• Crater Incident impact angle gt60 deg
• Impact velocity 2.5 km/sec

9
Driving Mission Constraints

• Mission Lifetime
• lt120 days (limited by LV separation system
  qualification and budget!)
• DV Capacity
• A maximum of 50 m/s allocated to re-targeting of
  LCROSS by launch vehicle post-LRO separation
• A maximum of 135 m/s available to establish
  LCROSS orbit and to adjust impact time by up to
  /-12 hours
• Navigation
• Impact targeting precludes performing large orbit
  maneuvers (e.g., to alter impact time or target a
  different crater) too close to impact
• DSN Scheduling
• DSN 70m station at Canberra is scheduled to be
  unavailable for support for 6 months starting
  10/08 (scheduled maintenance)
• DSN 70m station at Madrid is scheduled to be
  unavailable for support for 6 months starting 4/09

10
Mission Design Process
Candidate LRO launch dates
Baseline trajectory Impact Date/Time
Science/Obs Requirements
Yes
Mission Constraints
Satisfy Req Constraints?
Calculate Impact Geometry DV
Requirements
Navigation Considerations
No
Candidate impact targets observatories
Refine Inputs
Candidate trajectories
11
Family of LCROSS Trajectories

• 3 Month Cruise
• (32 resonance)
• Baseline Trajectory
• 3 Lunar orbits about Earth (27 day period)
• 2 LCROSS orbits about Earth (40 day period),
  86-day total mission
• Southern swingby, Southern impact

• 3.5 Month Cruise
• (3.52.5 ratio)
• 3.5 Lunar orbits about Earth (27 day period)
• 2.5 LCROSS orbits about Earth (38 day period)
  100-day total mission
• Northern swingby,
• 180 deg change in lunar phase from 3M

• 4 Month Cruise
• (43 resonance)
• 4 Lunar orbits about Earth (27 day period)
• 3 LCROSS orbits about Earth (36 day period)
  114-day total mission
• Southern swingby
• 27 deg change in lunar phase from 3M

12
Launch Impact Date/Time General Guidelines

• Each impact date will have a fixed nominal impact
  time and target crater
• Trajectories within a 3-4 day launch block will
  use the same trajectory type (i.e., 3M, 3.5M or
  4M) and have impact dates within a few days of
  each other
• Trajectories within a /-30 minute launch window
  on a given launch day may have different impact
  dates (by no more than 1 day)
• Trajectories associated with different launch
  blocks can have the same impact date/times
• Once launched, nominal impact time will be
  targeted, but offsets of a few minutes may be
  allowed (i.e., a cutoff in impact time
  adjustments will occur several weeks before
  impact)
• Late December launch dates may drive us to using
  a 2.5M trajectory due to poor geometry

13
Common LCROSS Impact Dates
LRO Launch Blackout Time