# Presentation: 252031

## 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
- ~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)

## 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

## 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)

## Ground Observatory Impact Geometry

**Observatory Lunar Phase & 2 hr Dawn/Dusk Lighting Constraint**

**Observatory Viewing Elevation Constraint**

**+**

****

****** ****≥**** ****30****°**

****** ****≥**** ****45****°**

- Resulting impact lunar phase exclusion zones

## Sample Impact Geometry

- Sample Impact Viewing Geometry for Nov. 24 (3.5M, 0-P30 launch window) or Dec. 9 (3M) Launch Dates

## 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

## Target Impact Conditions

-   Baseline Candidate Craters:
- Faustini, Shoemaker, Cabaeus & Shackleton
-   Crater Incident impact angle: >60 deg
-   Impact velocity: 2.5 km/sec

## 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

## 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

## 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

## 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

## Common LCROSS Impact Dates

- LRO Launch Blackout Time