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Mission Design & Observation Campaign Constraints

Mission Design & Observation Campaign Constraints. Ken Galal/ARC. 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

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Mission Design & Observation Campaign Constraints

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  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| > 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)

  5. Incoming Sunlight 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: >60 deg • Impact velocity: 2.5 km/sec

  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

  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. 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-Month Trajectory 3.5-Month Trajectory 4-Month Trajectory Family of LCROSS Trajectories 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

  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

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