Lunar CRater Observation and Sensing Satellite Project LCROSS Astronomer Workshop Feb. 29, 2008 NASA/ARC, Mountain View, California Mission Design & Observation Campaign Constraints Ken Galal/ARC
LCROSS Mission Design & Observation Campaign Constraints 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)
LCROSS Mission Design & Observation Campaign Constraints 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
LCROSS Mission Design & Observation Campaign Constraints 4 Driving Mission Requirements Impact Conditions: |V| > 2.5 km/s Impact angle > 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 <90 deg (angle from normal to crater floor to sun/Earth) DSN 70m station coverage required for LCROSS science data collection Ground observatory elevation angle >45 deg Lunar phase >30 deg from new or full moon Impact time occurs when observatory is minimum of 2 hrs from dawn/dusk (with a goal of >3hrs)
LCROSS Mission Design & Observation Campaign Constraints 5 Ground Observatory Impact Geometry Observatory Lunar Phase & 2 hr Dawn/Dusk Lighting Constraint Observatory Viewing Elevation Constraint + ≥ 30° ≥ 45° Incoming Sunlight Resulting impact lunar phase exclusion zones
LCROSS Mission Design & Observation Campaign Constraints 6 Sample Impact Geometry Sample Impact Viewing Geometry for Nov. 24 (3.5M, 0-P30 launch window) or Dec. 9 (3M) Launch Dates
LCROSS Mission Design & Observation Campaign Constraints 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
LCROSS Mission Design & Observation Campaign Constraints 8 Target Impact Conditions Baseline Candidate Craters: Faustini, Shoemaker, Cabaeus & Shackleton Crater Incident impact angle: >60 deg Impact velocity: 2.5 km/sec
LCROSS Mission Design & Observation Campaign Constraints 9 Driving Mission Constraints Mission Lifetime: <120 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
LCROSS Mission Design & Observation Campaign Constraints 10 Mission Design Process Candidate impact targets & observatories Satisfy Req & Constraints? No Yes Science/Obs Requirements Candidate LRO launch dates Candidate trajectories Calculate Impact Geometry & DV Requirements Baseline trajectory & Impact Date/Time Refine Inputs Mission Constraints Navigation Considerations
LCROSS Mission Design & Observation Campaign Constraints 11 Family of LCROSS Trajectories 3 Month Cruise (3:2 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 (3.5:2.5 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 (4:3 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 3-Month Trajectory 3.5-Month Trajectory4-Month Trajectory
LCROSS Mission Design & Observation Campaign Constraints 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
LCROSS Mission Design & Observation Campaign Constraints 13 Common LCROSS Impact Dates LRO Launch Blackout Time