Lunar CRater Observation and Sensing Satellite Project

LCROSS

NASA Ames May 4, 2007

Principle Investigator Payload Manager

Anthony Colaprete

presented byGwen Bart

2LCROSS Science Background

Lunar Prospector detected an increase in hydrogen concentration over the lunar poles.

The debate over the form, concentration and distribution has continued ever since.

If the hydrogen in an accessible and usable form, it could be a potential resource

Form, distribution and concentration of [H] relevant to inner solar system asteroid/comet fluxes, lunar volatiles and planetary evolution.

Several key questions:• Is the hydrogen in the form of water? • Is the hydrogen diffuse and uniform, or

concentrated and distributed in pockets?• Is the lunar regolith in a permanently shadowed

crater the same as that characterized at the Apollo landing sites?

Feldman et al., 1998

SP Hydrogen Abundance

LCROSS will provide the most unambiguous data set to address these questions.

3

The LCROSS mission rational:• The nature of lunar polar hydrogen is one of the most important drivers to the long

term lunar exploration architecture

• Need to understand Quantity, Form, and Distribution of the hydrogen

• The lunar water resource can be estimated from a minimal number of “ground-truths”

• Early and decisive information will aid future ESMD missions

The LCROSS mission science goals:• Confirm the presence or absence of water ice in a permanently shadowed region

on the Moon

• Identify the form/state of hydrogen observed by at the lunar poles

• Quantify, if present, the amount of water in the lunar regolith, with respect to hydrogen concentrations

• Characterize the lunar regolith within a permanently shadowed crater on the Moon

LCROSS ESMD Mission Objectives

44LCROSS Science

Nature and form of the hydrogen?• Water, hydrated minerals, hydrocarbons?• Grain size?• Distribution within regolith?

Nature of PSR regolith?• Strength? Depth?• Grain size?• Composition?• Is it similar to Apollo sites?

The Lunar Atmosphere / Volatile Processes?• How does the Lunar atmosphere respond?• What are the times scales for recovery?• How do volatiles/dust migrate?

5

Launch stacked with LRO in Spring (April?) 2009

After Lunar swing-by, enter a 3-4 month cruise around Earth

Target the Centaur Upper Stage and Position S-S/C to fly four minutes behind

S-S/C observes impact, ejecta cloud and resulting crater, making measurements until impacting itself

1. 2.

3. 4.

The LCROSS Mission

MoonEarth

LCROSS Orbit – Side View

MoonEarth

LCROSS Orbit – Side View

6

0

50

100

150

200

250

300

350

400

0 20 40 60 80

Impact Angle (degrees)

Ejec

ta M

ass

(Met

ric T

ones

)

LCROSSSMART-1LPLCROSS S-S/C

SMART-1 (grazing impact) LP

Estimates of the total ejecta mass as a function of impact angle for four impactors: LCROSS, LCROSS S-S/C, Lunar Prospector (LP), and SMART-1

LCROSS

LCROSS S-S/C

SMART-1 (hill side impact)

The Mission – How LCROSS is Different

7Impact Target 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

• Illumination of ejecta by sunlight

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

• Observed concentration of increased hydrogen

Selection process ongoing until 30 days prior to impact

To Earth

F

North Pole Targets:A: 84.5 N 55 EB: 88.0 N 318 EC: 87.1 N 24 ED: 85.5 N 45.2 EE: 89.2 N 128 E

Candidate North Pole Craters

1 = Shackleton [89.5 S, 0 E]2 = Shoemaker [88.1 S, 44.9 E] 3 = Cabeus [84.9 S, 324.5 E]4 = Faustini [87.3 S, 77 E]

1

2

3

4

Candidate South Pole Craters

10

Deconvolved Hydrogen Maps (Elphic et al., 2007)

Lunar Polar Hydrogen

Original Lunar Prospector Hydrogen Map (Maurice et la., 2003)

Water is heterogeneous from one crater to anotherAccumulation/retention processes differ at carter scales of ~50-100 km?Possibly different at smaller scales.

11The Spacecraft and Payload

Spacecraft entering Northrop Grumman Thermal Vacuum Chamber

12Payload Hardware

NIR SpectrometerUV/Visible Spectrometer

Visible Color

Camera

MIR Cameras

NIR Cameras Flash Radiometer

Solar NIR Spec

1313The Anatomy of the Impact: Flash, Curtain, Crater

Impact flashImpact flash

Ejecta Curtain Into

sunlight

Ejecta Curtain Into

sunlight

“Sunrise”

Reverse ejecta

Crater rimIncandescent particles

Tim

e

Tim

e

Step 1

Step 2

Step 3

Step 4

Step 5

Step 6

Step 7

Step 8

ARC Vertical Gun Experiments

Nadir View of Impact and Ejecta Curtain

Scales to ~2 sec after Centaur impact Pete Schultz

14

For Mass above 2 km

0.0001

0.001

0.01

0.1

1

1 10 100 1000Time After EDUS Impact (Sec)

Opt

ical

Dep

th1

10

100

1000

% F

ill fo

r 1

deg

FOV

Ejecta

Water Ice

100

1000

10000

0 30 60 90 120 150 180 210 240 270 300

Time After EDUS Impact (Sec)

Cur

tain

Mas

s A

bove

2 k

m (k

g)

0

10

20

30

40

50

60

70

80

90

100

Curt

ain

Radi

us (k

m)

Curtain Mass Above 2 km (kg)

Curtain Radius (km)

Impact Expectations: Curtain Properties

Curtain Mass and Radius Curtain Dust and Water IceOptical Depth

For Mass above 2 km

The most observable portion of the ejecta curtain will be between 10 and 60 seconds after impact, corresponding to a curtain radius of between 1 and 10 km.

15

The radiance for the ejecta cloud only (derived be subtracting off the spectra from the lunar surface) for several times after Centaur impact.

0

0.5

1

1.5

2

2.5

3

3.5

4

0 0.5 1 1.5 2 2.5 3 3.5

Wavelength (microns)

Rad

ianc

e (W

m-2

mic

ron-1

str-1

)

t=10t=20t=30t=40t=60

t=70t=80t=90t=100

Expectations: Curtain Brightness

16Expectations: LCROSS Water Detection

-0.01

0.04

0.09

0.14

0.19

0.24

0

1

2

3

4

5

6

7

8

9

10

1.35 1.55 1.75 1.95 2.15 2.35

% A

bsor

ptio

n

Rad

ianc

e (W

m-2μ

m-1

str-1

)

Wavelength (microns)

IrradianceAbsorption11 bin average

Calculated ejecta cloud radiance (left axis) and synthetic NIR spectrometer data for 1% water content

17Conclusions

We’ll know next year!

•Earliest likely impact date May 10, 2009

•Should be quite visible (Mag 9-10 per half arcsec) from Earth in the Pacific (including west coast) (See Jennifer Heldmann’s poster).

• Impact target selection an on-going process (See Gwen Bart’s poster)

•LCROSS SC and Instrument development demonstrated a novel approach (See Kim Ennico’s poster)

18

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

1 10 100 1000Time After Centaur Impact (sec)

Ejec

ta C

loud

Opt

ical

Dep

th

Tau Cloud, Area AverageTau Cloud, EdgesTau Cloud, Middle r = 40 μm

0.00001

0.0001

0.001

0.01

0.1

1

1 10 100 1000Time After Centaur Impact (sec)

Ejec

ta C

loud

Opt

ical

Dep

th

Tau Cloud, Area AverageTau Cloud, EdgesTau Cloud, Middle

tn=tn+1+Δt

t2t3

Edge Area

t1

Middle Area

For the Edge/Middle Model the ejecta mass fills a volume described by two conic sections. The projected area is estimated along the edges and in the middle portion of the cloud. The edge area is estimated using an average projected edge length (calculated from curtain radius and ejecta angle). The middle area is estimated from the difference between conic sections, separated by the curtain wall thickness (assumed here to be 100 meters).

Edge projected length

Edge Middle

Impact Expectations: Side View

19

The Incident Flux at Earth from the ejecta cloud was estimated using the Area Average and Edge/Middle models presented on the previous slides (r=40 μm).

(a) The Incidence at Earth using the radiance estimates and ejecta cloud projected area from the Area Average model.

(b) The Incidence at Earth using the radiance estimates and ejecta cloud projected area from the Edge/Middle Average model. Incidence is only shown for the cloud edge.

Impact Expectations: Earth Incidence

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

0 20 40 60 80 100

Time After Centaur Impact (sec)

Inci

denc

e at

Ear

th (W

m-2

)

Incidence (W m -̂2) @ 500 nmIncidence (W m -̂2) @ 2000 nm

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

0 20 40 60 80 100Time After Centaur Impact (sec)

Inci

dent

Irra

dian

ce a

t Ear

th (W

m-2 μ

m-1)

Incidence (W m -̂2 micron -̂1) @ 500 nmIncidence (W m -̂2 micron -̂1) @ 2000 nm

Ejecta Cloud Edge Estimate

Ejecta Cloud Area Average Estimate

(a)

(b)

20Impact Expectations: Earth Brightness

Apparent Magnitude of curtain edge on for a 0.5 arc sec FOV

21The LCROSS Experiment: Smooth or Chunky?

Crider & Vondrak, 2003Feldman 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 (1Gyr)Desiccated

Layer

• Lunar Prospector was sensitive to hydrogen in the top ~1 m of regolith, the extent which is expected to be gardened in ~1Gyr

• Impacts which excavate to ~1 m deep and have diameters of ~10 m occur on timescales of τ~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 m diameter craters of ~150 m on a 1 Gyo surface.

0.51.01.52.0D

epth

(m)

D~5 m (τ~1 Myrs km-2)

D~10 m (τ~15 Myrs km-2)

Horizontal Distance

Crater

Crater burial of “dry” material

22

• If the 1-meter-deep heterogeneity is controlled by 10 m which are out of equilibrium with diffusive and space weathering processes, then the aerial fraction that is in equilibrium, i.e., “wet” is:

~1 – Crater Diameter2/Crater Spacing2 = 1.-102/1002 = 99%

⇒Top meter sensed by LP is near the derived value: 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 – Chances of a “Slash”

D (m) N5 40

10 520 140 0.180. 0.01

1 km

1 km

D~10 meter

For a 100 Myr Old Surface: