Principle Investigator Payload Manager

Lunar CRater Observation and Sensing Satellite Project

Target Selection

February 29, 2008 NASA Ames Research Center

Principle Investigator Payload Manager

Anthony Colaprete

2Target Selection Criteria

D=3.5 kmD=3.5 km

D=3.5 km

A

B

C

D

The four primary criteria for selection:

• Terrestrial Observations (to insure minimum success requirements).

• Illumination of ejecta by sunlight

• Target properties (e.g., surface roughness, slopes, and regolith depth)

• Observed concentration of increased hydrogen

3Terrestrial Viewing Constraints

Observatory Viewing Constraints:

• Observatory needs to be 2hrs from dawn/dusk at impact

• Impact must occur when moon is more than 30 deg away from new moon or full moon

• Elevation angle of moon at impact relative to observatory must be greater than 45 deg

• Maximum impact time adjustment of 12hrs allowed (due to DV limitations)

4Ejecta Illumination

0

0.2

0.4

0.6

0.8

1

1.2

1.4

86.5 87 87.5 88 88.5 89 89.5 90 90.5

Sun Tilt Angle (degrees)

Est

imat

ed %

Wat

er S

ensi

tivi

ty

3 km 2.5 km 2 km

Predicted NIR Spec Water Ice Sensitivity

Cabaeus

To Earth

Shackleton

Shoemaker

Ejecta Illumination dominates sensitivity analysis.

Altitude Mask

5Optimum Target vs Launch Date

The optimum site varies with launch date due to changes in solar illumination angle and impact angle (from ARC-04.01.SciImpSite.01.v-3.0):

The LCROSS Science Team recommends a target be selected for each possible LRO launch date and if possible all targets be limited to the South Pole.

Furthermore, the LCROSS Science Team recommends new data be used to refine targeting up until 30 days prior to Centaur separation.

6Target Selection Process

Selection Process:

TerrestrialObservations

Hydrogen

Surface Properties

Ejecta Illumination

SC Water Sensitivity, RFA PL-CDA-02

Crater Selection

Craters A, B, C, or D

Craters A, B or D

Craters A or B Crater B

Project Requirements(e.g., dV)

New Data

7Target Selection Process

8

Cabaeus

A

Selected Targets

Target Selection Products• Impact Site Selection Workshop, October 2006

• Impact Site Report from the Site Selection Committee: Impact Site Selection Committee Report (ISSCR) (November, 2006)

• LCROSS Science Team Impact site Position Report (STIPR) (January, 2007)

• Baseline Target Review (July, 2007) Campbell et al., 2007

9

ShFa

Selected Targets

10Baseline 2008 Impact Sites

# Launch Date Orbit Type Impact Crater Observatory Meets:

1. 10/28/2008 3.5M Faustini Hawaii A, B, C

2. 10/29/2008 3.5M Faustini Hawaii A, B, C

3. 10/30/2008 3.5M Shoemaker Hawaii A, B, C

4. 11/11/2008 3M Faustini Hawaii A, B, C

5. 11/12/2008 3M Faustini Hawaii A, B, C

6. 11/13/2008 3M Shoemaker Hawaii A, B, C

7. 11/13/2008 3M Shoemaker Hawaii A, B, C

8. 11/24/2008 3.5M Faustini* Hawaii A, B




A: Visibility to Earth

B: Good sensitivity margin

C: Knowledge of target properties

* Faustini as selected when sensitivity margins in Shoemaker were low, and was selected over Shackleton due to its high sensitivity margins and knowledge of target properties.† Cabeaus was selected when all other target sensitivity margins where marginal or poor relative to the requirement or Cabeaus.

11

# Launch Date Orbit Type Impact Crater Observatory Meets:

12. 12/9/2008 3M Faustini* Hawaii A, B




*16. 12/22/2008 4M Cabeaus† Chile B

17. 12/23/2008 4M Cabeaus† Chile A, B



A: Visibility to Earth

B: Good sensitivity margin

C: Knowledge of target properties

* Faustini as selected when sensitivity margins in Shoemaker were low, and was selected over Shackleton due to its high sensitivity margins and knowledge of target properties.† Cabeaus was selected when all other target sensitivity margins where marginal or poor relative to the requirement or Cabeaus.

Baseline 2008 Impact Sites

12Target Refinement

LCROSS retains the ability to change our target with the southern polar region (with about ~100 km of our original target):

Target refinement within current targeted craters based on on-going analysis of existing data and analysis of new data (table below)

Target refinement can occur as late as 30 days prior to impact date (e.g., for a 3 month cruise, approximately 60 days after launch).

Table 4. Applicable Data Sets for LCROSS Target Selection Instrument / Platform Application to LCROSS Target Selection

Visible Imaging / SMART-1 Imaging of PSRs using crater rim scatter Radar / Goldstone; Arecibo Topography and roughness Altimetry / SELENE Topography and slopes Radar / Chandaryaan-1 Topography, roughness, water ice Altimetry / MOLA-LRO Topography and slopes Temperatures / Diviner-LRO Identification of cold traps UV Imaging / LAMP - LRO Imaging of PSRs Radar / MiniRF-LRO Topography, roughness, water ice Epithermal Neutron Maps / LEND-LRO Hydrogen distribution Visible Imaging / LROC - LRO Imaging of PSRs using crater rim scatter

13Target Selection

Backup Slides

14WEH, ISRU and the Sensitivity Requirement

Figure 3. The distribution of hydrogen as derived from the Lunar Prospector neutron spectrometer data: (A) hydrogen map without an deconvolution of the neutron spectrometer footprint and permanent shadowed regions (Maurice et al., 2003), (B) water equivalent hydrogen map derived from a deconvolution of the LP data and the distribution of permanently shadowed regions (from Elphic et al., 2007).

H2 Extraction

Equator (100 ppm H) Pole (1 % water ice)

Specific Energy, kWh/kg

2250 50.8

Production Cost Ratio

1 50-100

Water content > 1-2% wt would constitute a more cost efficient than mining “dry” equatorial regolith

The most recent water equivalent hydrogen (WEH) retrievals deconvolve the low resolution data set with models of the permanently shadowed regions (Elphic et al., 2007).

• The only estimates of WEH for individual craters

• Depends on the DEM to create shadowed regions

Pervious estimates broadly (unconvolved) place WEH ~1%

Several theoretical treatments place WEH ~1-2 %

Radar returns associated with water ice requires volumetric scattering that places WEH limits > 20%

For In-Situ Resource Utilization (ISRU), water concentrations of >1% make polar mining more efficient than equatorial mining.

• This sets the required sensitivity of detection threshold of 0.5% (RFA PL-CDA-02).

15Percent Water Sensitivity

The sensitivity of the LCROSS SC nadir viewing NIR spectrometer was used as a verification of the Projects ability to sense regolith water.

• The Project must be sensitive to water concentrations of 0.5% wt (RFA PL-CDA-02).• The NADIR NIR Spectrometer is the most sensitive instrument to ejecta cloud water ice, the expected

dominant form of water initially within the ejecta cloud.

The performance of the instrument was estimated using a discrete ordinate scattering algorithm (DISORT) and linear mixing of optical constants for water ice and dust.

Water ice and dust opacities were estimated using impact model predictions.

Instrument sensitivity was calculated using expected throughput and noise equivalent power (recent system level calibrations confirm this performance).

For each impact date, several factors, which dominate measurement sensitivities to water ice, are taken into account in the model:

• Impact Angle• Solar Illumination Angle• Crater Wall Height

Synthetic spectra for the first 30 seconds following impact are used to determine sensitivity for various concentrations of water ice in the regolith (see backup slides). While a complete error analysis has not been done, it is believed that these estimates are uncertain to approximately ±0.1 %

16Lunar Polar Hydrogen

Crider & Vondrak, 2003

Feldman et al., 2001

0

1

2

3

4

5

Dep

th (

m)

10-6 10-5 10-4 10-3 10-2

[H] (wt. parts)

GardenedLayer (1Byr)

DesiccatedLayer

• Space weathering homogenizes [H] at a rate of ~1.5 m per Gyr (Crider & Vondrak, 2003).

• Below ~2 m compaction greatly reduces pore space and reduces diffusive [H] capacity, however, burial is still possible.

• Impacts which excavate to ~1.5 m deep and have diameters of ~10 m occur on timescales of ~15 Myrs/km2, or about sixty 10 m craters km-2 on a surface 1 Gyrs old.

• This crater density results in a mean distance between 10 meter diameter craters of ~150 meters (or 450 meters for 100 Myo surface).

• Thus, H2O likely to be horizontally heterogeneous on scales of ~100 m to depths of ~1.5 m.

0.5

1.0

1.5

2.0Dep

th (

m)

D~5 m (~1 Myrs km-2)

D~10 m (~15 Myrs km-2)

Horizontal Distance

Crater

Crater burial of “dry” material

17

• If heterogeneity is controlled by 10 meter craters (crater excavation controlled), which are out of equilibrium with diffusive and space weathering processes, then the aerial fraction that is in equilibrium, i.e., “wet” is ~1.-102/1002 = 99%.

• LP sensed the top meter (~70 cm) Derived LP values representative of this excavation controlled regolith “horizon”: high concentration pockets (WEH greater than few %) in the top meter not likely.

• Diffusive and space weathering processes likely to enforce their own horizontal modulation due to environmental effects (e.g., temperature and porosity)

Lunar Polar Hydrogen

D (m) N5 40

10 520 140 0.180. 0.01

1 km

1 k

m D~10 meter

For a 100 Myr Old Surface:

18

East Crater ~30 meters

Apollo 11 Craters

West Crater ~200 meters

1.2 km

1.0

km

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