**Introduction**

The primary objective of the LCROSS (Lunar Crater Observation and
Sensing Satellite) mission is to help advance the U.S. Space Exploration
Policy by investigating the presence of water on the Moon. The LCROSS
mission, which is a comanifested payload launching with the Lunar
Reconnaissance Orbiter, will use the Atlas V Centaur Earth departure
upper stage (EDUS) of the launch vehicle as a 2000 kg kinetic impactor.
The impact creates an ejecta plume whose properties, including water ice
and vapor content, will be observed a shepherding spacecraft (S-S/C)
plus Earth- and space-based telescopes. Following a similar trajectory
of the EDUS, the S-S/C will fly through the EDUS impact plume and then
the 700 kg S-S/C will also impact the Moon. The S-S/C impact will likely
also be observable to ground-based and space-based telescopes.

Interest in the possible presence of water ice on the Moon has both
scientific and exploration foundations. It is thought that water has
been delivered to the Moon over its history from multiple impacts of
comets, meteorites and other objects. The water molecules migrate in the
Moon's exospheric type atmosphere though ballistic trajectories and can
be caught in permanently shadowed polar cold traps that are cold enough
to hold the water for billions of years. Verification of its actual
existence would help science constrain models of the impact history of
the lunar surface and the effects of meteorite gardening,
photo-dissociation, and solar wind sputtering. Measurements of the ice
distribution and concentrations would provide a quantitative basis for
studies of the Moon's history.

Deposits of ice on the Moon could have practical implications for future
human activities on the Moon. A source of water could enable long
duration human activities and serve as a source of oxygen, another vital
material that otherwise must be extracted by melting and electrolyzing
the lunar regolith. Hydrogen derived from lunar ice could be used as a
rocket fuel. These attractive considerations influence the architecture
and plans for human activities on the Moon. Thus, the determination of
the *non-*existence of water ice at the poles may cause a re-alignment
of the architecture and plans. Operations from a lower latitude near
side base would lead to substantially simpler communications approach,
would focus exploitation on regolith processing instead of ice
processing and would negate the challenge of developing robotic
technologies capable of working in cryo-craters and nearly perpetual
darkness.

**The LCROSS Mission**

The primary objective of the Lunar Crater Observation and Sensing
Satellite (LCROSS) is to confirm the presence or absence of water ice in
the Moon's polar region. This mission uses a 2000 kg kinetic impactor
with more than 200 times the energy of the Lunar Prospector (LP) impact
to excavate more than 250 metric tons of lunar regolith. The resulting
ejecta cloud will be observed from a number of lunar-orbital and
Earth-based assets. The impact is achieved by steering the launch
vehicle's spent Earth Departure Upper Stage (EDUS) into a permanently
shadowed polar region. The EDUS is guided to its target by a Shepherding
Spacecraft (S-S/C), which after release of the EDUS, flies toward the
impact plume, sending real-time data and characterizing the morphology,
evolution and composition of the plume with a suite of cameras and
spectrometers. The S-S/C then becomes a 700 kg impactor itself, to
provide a second opportunity to study the nature of the Lunar Regolith.
LCROSS provides a critical ground-truth for Lunar Prospector and Lunar
Reconnaissance Orbiter neutron and radar maps, making it possible to
assess the total lunar water inventory, as well as provide significant
insight into the processes that delivered the hydrogen to the lunar
poles in the first place.

**Mission Relevance and Impact to State of Knowledge**

LCROSS will address elements of all five of the science questions
contained in NASA Strategic Sub-goal 3C. This mission is also relevant
to Strategic Goal 6 (Establish a lunar return program having the maximum
possible utility for later missions to Mars and other destinations).

In the NRC Decadal Survey's "Twelve Key Scientific Questions that
Underpin the Overall Exploration Strategy", LCROSS specifically
addresses "What is the history of volatile compounds, especially water,
across the solar system" and "What global mechanisms affect the
evolution of volatiles on planetary bodies".

## LCROSS Science Goals

The LCROSS mission science goals, in order of priority, are:

1.  Confirm the presence or absence of water ice in a permanently
    shadowed region on the Moon

2.  Identify the form/state of hydrogen observed by Lunar Prospector at
    the lunar poles

3.  Quantify, if present, the amount of water in the lunar regolith,
    with respect to hydrogen concentrations observed by Lunar Prospector

4.  Characterize the lunar regolith within a permanently shadowed crater
    on the Moon

## LCROSS Shepherding Spacecraft (S-S/C) Measurement Goals

Multiple measurement techniques will be acquired by the LCROSS S-S/C
that include some measurement goal overlap. By addressing each
measurement goal with overlapping techniques a level of robustness
against misinterpretation can be achieved and the mission susceptibility
to false positive / negative results minimized. Each measurement
technique is summarized below.

[Flash Photometry]{.underline} -- At the moment of impact, compaction
and/or crushing of the impactor and intergrain interactions results in
the conversion of kinetic energy into highly energized plasma and vapor,
which upon relaxations, emits visible light. This visible "flash",
depending on the maximum temperature achieved, will contain emissions
associated with vaporized portions of the impactor and target material.
Also, the total brightness and temporal profile of the flash is
sensitive to the strength (competence) of the target material and its
distribution with depth. Therefore, the flash is a good indicator of the
depth of impactor penetration.

[Visible Spectroscopy]{.underline} -- Here visible spectroscopy refers
to the measurement of spectra between 0.25 microns and 0.8 microns with
a resolving power of l/dl \>100. The LCROSS S-S/C will observe the pre-
and post-EDUS-impacted lunar regolith in and outside the targeted region
at a spatial resolution and viewing angle unobtainable from Earth. The
visible spectrometer shall record the sunlit plume evolution, and track
the evolution of OH^-^ radicals from sunlight-dissociated water vapor
molecules. The visible spectrometer will measure the OH^-^ (308 nm) and
H2O+ (619 nm) transitions simultaneous which shall assess the water
vapor production.

NIR (Near Infrared) Spectroscopy -- Here NIR spectroscopy refers to the
measurement of spectra between 1.0 micron and 4.0 microns with a
resolving power of l/dl \>100. The LCROSS S-S/C will monitor spectral
bands associated with water vapor, ice, and hydrated minerals covering
the first overtones of the symmetric and asymmetric stretches of water;
this band, relatively free from interferences, is more brightly
illuminated by sunlight than the fundamentals near 3 microns, more than
compensating the weaker absorption of the overtones. The regions near
1.4 and 1.9 microns, normally obscured by terrestrial atmospheric
background in spectra from icy surfaces, will provide a sensitive
indication of water vapor from ice or hydrates. The remainder of the
spectral band will reveal the nature of ice crystals and mineral
hydrates.

[NIR Imaging]{.underline} -- Imaging provides spatial resolution of the
observed target. Two NIR imaging schemes are possible for LCROSS. The
baseline includes two imagers, both with bandpass filters, one inside a
water absorption line (e.g. at 1.6 microns) and one outside the line
(e.g. at 1.4 microns), allowing the creation of water absorption band
depth maps. The second scheme utilizes only a single broad band NIR
imager to provide scene context for the NIR spectroscopy.

[MIR (Mid Infrared) Imaging]{.underline} -- For LCROSS, MIR imaging
refers to imaging at thermal wavelengths between 6 and 15 microns. The
same two NIR imaging schemes apply to MIR imaging. Pre- and post- impact
thermal images of the impact terrain will be obtained from MIR cameras
on the S-S/C to characterize the surface material (rock vs. regolith),
obtain the thermal evolution of the plume (which is dependent on the
water content), and observe the ejecta blanket and freshly exposed
regolith.

[Visible Imaging]{.underline} -- Visible imaging for LCROSS refers to
imaging at wavelengths between 0.4 and 0.8 mm with broad bandpass
filtering for color.

**LCROSS Shepherding Spacecraft Payload**

The LCROSS payload consists of nine science instruments, their
supporting electrical, mechanical and optical harnesses and a central
data handling unit assembled onto one of six radiator panels on the
LCROSS space vehicle.

The nine science instruments are a visible wavelength context imager
provided by Ecliptic Enterprises Corporation, two near-infrared (1.0-1.4
micron/ 1.0-1.7 micron) cameras from Goodrich Sensors Unlimited, one
mid-infrared (6-9 micron) thermal imager from Thermoteknix Systems,
Ltd., one mid-infrared (6-17 micron) camera from FLIR Systems/Indigo
Operations, a custom-built highly sensitive total luminance photometer,
a UV-visible spectrometer (260-650 nm) provided by Ocean Optics, and two
compact low-power near infrared spectrometers (1.2-2.4 micron) built by
Polychromix. The three spectrometers are connected via fiber optics to
specially designed fore-optics provided by Aurora Design & Technology.
These nine instruments are powered and controlled by a Data Handling
Unit (DHU) provided by Ecliptic Enterprises. The DHU is interfaced with
the space-vehicle command and data handling and power systems. Thermal
control of the science payload is provided using heaters and
thermostats.

**Impact Characterization**

The LCROSS mission uses the impact of the EDUS to excavate and eject
lunar surface material from a permanently shadowed region into sunlight
where the ejecta can be imaged and spectroscopically studied at visible
through mid-IR wavelengths by the LCROSS S-S/C and from the UV through
radio. Modeling the impact facilitates effective planning and execution
of the observational campaign.

Models for the LCROSS impact are based on numerical hydrodyanamic codes,
impact experiments with the NASA Ames Research Center vertical gun, and
analytical models using semi-empirical scaling relations derived from
laboratory experiments. All approaches contribute information to the
task of guiding the design of the LCROSS mission and observational
campaign. Such a variety of approaches and the corresponding ranges of
results will very likely prove more useful in bracketing the expected
outcomes.

To aid in the formulation of the LCROSS mission and measurement design,
a compilation of model results has been built which summarizes the
current best estimate for the impact event. This summary, called the
Current Best Estimate Impact Model (CBEIM), includes both high and low
values for a variety of relevant physical quantities including crater
dimensions and ejecta velocities. In most cases the "current best
estimate" was used for design purposes, however, on a case-by-case bases
additional "margin" was allowed for by using the model results between
the best estimate and the modeled low estimate (e.g., often the values
closer to the low-end expectation for the total ejected mass above 2 km
were used in order to build in margin). To date, models for the impact
indicate that the impact flash will evolve in tens of milliseconds and
the impact ejecta will rise into sunlight and fall back to the lunar
surface in less than about 2 minutes, thereby motivating the use of
rapid measurement techniques for ground- and space-based telescopes.
Only the temporal evolution of the OH^-^ exosphere is expected to
persist for more than tens of minutes.

## Impact Contamination Control and Mitigation

After launch the Centaur stage of the Atlas V rocket contains some water
or hydrogen and oxygen bearing compounds that may constitute
contamination to the actual hydrogen signal trying to be measured. This
contamination on the Centaur stage is in the form of liquid hydrogen and
oxygen, hydrazine, and water, in batteries and as part of adhesives,
potting materials, etc. (It must be noted that the presence of hydrogen
does not necessarily translate to a contaminant. The measurement
techniques to be employed by the LCROSS S-S/C are not sensitive to
hydrogen by itself, but rather compounds that contain hydrogen.) To
minimize the effect of water contamination that may be present in the
impacting Centaur several measures will be taken:

1.  Liquid hydrogen and oxygen fuel remaining after the lunar transit
    burn will be vented.

2.  Remaining hydrazine fuel will be vented.

3.  The launch vehicle provider will make an estimate of all water or
    water/hydrogen bearing materials.

4.  The total combined hydrogen and oxygen mass be kept to below 100 kg
    (corresponding the maximum amount allowed to keep the contamination
    level to 0.1%, assuming a total ejected mass of 200,000 kg).

**Observational Support**

Ground-based and orbital observatories can observe the dust and water
vapor plume caused by the two impacts into the lunar surface. Compared
to the Deep Impact (DI) Mission encounter with comet 9P/Tempel, LCROSS's
EDUS impact plume will have 100 times less mass at 360 times closer
range, so the surface brightness will be higher. However, the
dust-to-ice ratio for the impact location regolith is expected to be
orders of magnitude greater, perhaps \~100 in comparison to \~0.5 for
Deep Impact. Therefore, ground-based telescopes can observe the thermal
evolution of and the properties of the dust in the ejecta plume, and
8-10 m class telescopes will be required to search for water vapor using
the non-resonant fluorescent lines at \~3 μm. The longer time scale
evolution of the OH^-^ exosphere can be followed by telescopes around
the world. The timing of the two impacts should allow for simultaneous
observations from Hawaii, the Continental US, and/or from South America
(e.g. Chile).

### Lunar Polar Hydrogen -- What We Know and Don't Know {#lunar-polar-hydrogen-what-we-know-and-dont-know .unnumbered}

Scientists have long considered the possibility that water ice deposits
may exist in permanently shaded craters near both lunar poles \[Watson
et al., 1961; Arnold*,* 1979\].  We know that the floors of such craters
should be extremely cold (\<100K) \[Vasavada et al*.,* 1999\], and that
a significant number of water molecules delivered by meteoric infall can
survive loss processes, find their way to these craters and be
cold-trapped for billions of years \[Butler 1997\].  Implanted solar
wind hydrogen could yield impact-liberated water molecules, leading to
concentrations as high as 4 wt% in polar shadow \[Crider and Vondrak*,*
2003\].  Yet the existence of cold-trapped water ice (and other
volatiles) in permanently shadowed craters near the lunar poles
continues to be very controversial.  Evidence in favor includes the
Lunar Prospector neutron spectrometer (LPNS) data indicating the
presence of polar hydrogen enhancements \[Feldman et al.*,* 1998; 2000;
2001; Lawrence et al*.,* 2006; Elphic et al*.,* 2007\], and anomalous
bistatic radar returns from the Clementine lunar orbital mission have
been interpreted in terms of icy materials \[Nozette et al*.,* 1996;
2001\].  But Earth-based radar imaging of the Moon has not revealed
large, bright, depolarized features like those seen at Mercury \[Stacy
et al*.,* 1997; Campbell et al*.,* 2003\].  The Earth-based radar
returns from the lunar poles are similar to those seen for crater ejecta
and blocky terrain at lower latitudes, where ice could not possibly
exist \[Campbell et al., 2006\]. But cold-trapped ice residing in the
spaces between regolith grains at several tens of percent by volume
would not produce anomalous radar backscatter \[Stacy et al*.,* 1997;
Campbell et al*.,* 2003; 2006\].  Indeed, Lunar Prospector neutron data
allow upwards of \~20 wt% H2O ice concentrations in limited (10%) areas
of permanently shadowed crater floors \[Elphic et al*.,* 2007\].  If
cold-trapped volatiles are truly only concentrated in limited areas,
then orbital techniques will not be sufficient to localize them.  Only
by exploring the surface can we determine unambiguously the presence,
abundance, composition and spatial distribution of cold-trapped
volatiles.

### The History of Lunar Volatiles: Sources and Sinks {#the-history-of-lunar-volatiles-sources-and-sinks .unnumbered}

Whether deposited in large quantities in discrete events (comets) or
accumulating slowly and steadily for eons (migrating water vapor),
volatiles that are delivered to the permanently shadowed regions at the
lunar poles have the advantage of low temperature to help preserve them
against sublimation. However, there are other processes at work in the
permanently shadowed regions that can remove the volatiles. Although
sunlight never reaches these places, Earthshine, UV starlight, and
scattered UV of zodiacal light may photolyze exposed volatiles. In
addition, solar wind and magnetospheric plasma do have access to the
permanently shadowed regions (PSRs) and may sputter volatiles away. Both
photons and ions affect volatiles only at the extreme surface. However,
the lunar surface is constantly evolving as a result of meteoroid
impacts on all scale sizes. Nearby impacts bury exposed volatiles and
may protect them from future loss. Closer to the impact site, localized
portions of volatile deposits are vaporized, but may recondense in the
same cold trap. It is currently unknown which processes dominate the
source and sink of volatiles in lunar PSRs, nor whether they are the
same at the Moon as Mercury. It is clear that one must understand the
sinks in order to relate the present day volatile contents to the
sources.

**Additional** **Sample Text: Experimental Design, Description of
Experiment**

This section provides draft text that can be edited for relevance
specific to an individual investigation. This example provides
information for using spectroscopy to detect aqueous minerals as a
source of hydrogen.

[Experimental Design]{.underline}

(Example: spectroscopy to detect aqueous minerals as a source of
hydrogen). We propose to detect or set strong constraints on **[what
property]{.underline}** *\[the presence of aqueous minerals\]* in the
regolith of a permanently shadowed lunar crater by observing **[the
scattered light continuum at what wavelength]{.underline}** *\[near
\~0.8 µm or \~3 µm\]* with **[telescope+instrument]{.underline}**
*\[insert your observing platform here\]*. If the ejected regolith
contains 1E6 kg of particulates at 40--60\~s, then
**[instrument]{.underline}** can detect **[what
bands/lines]{.underline}** *\[3 µm bands from phyllosilicates\]* in the
LCROSS ejecta curtain. At the distance of the Moon, a column density of
2.5E9 30µm-radii particles km^--2^ filling a 2km x 2km beam (1 arcsec by
1 arcsec) yields an extended source flux density of F~λ~≈2.32E-15 W
m^-2^ µm^-1^ per arcsec-sq at λ=3µm (updated since Wooden 2008). This
flux density per arcsec-sq translates to a **[SNR\~XX in 1 minute of
on-source integration time]{.underline}** with **[instrument; at 3µm,
the sky needs to measured every 30 s -- 1 minute by nodding the slit off
source]{.underline}**. Hydrated mineral features can have a 3 µm band
depth of \~20--30% for \~7 wt% H~2~O, and \~5--10% for 1--2% H~2~O
(Rivkin et al. 2003). A SNR≈20 is required to assess the presence of
hydrated mineral features (e.g., Fig. 5 of Rivkin et al. 2002, or Rivkin
et al. 2003). A challenge of detecting the 3µm hydrated mineral features
is the need to span \~2.4 to \~3.4 µm to assess the 'continuum' on
either side of the broad feature (Rivkin et al. 2002, 2003). If the
ejecta curtain is as bright as this conservative estimate, then
**[telescope+instrument]{.underline}** will be able to discern the
hydrated mineral features with adequate SNR. The unique aspect of the
LCROSS experiment means that observations with
**[telescope+instrument]{.underline}** are worthy of the attempt. **[(If
necessary for the case, what other instruments could do this experiment
and why is this one instrument important)]{.underline}** We request
**[telescope+instrument]{.underline}**; **[special configuration
required(?)]{.underline}**. The **[high sensitivity, spectral resolving
power, spatial resolution, capability provided (uniquely) by
telescope+instrument]{.underline}** are critical for this experiment.

[Description of Experiment (Again, example given for
spectroscopy)]{.underline}

Our idea is to position the slit parallel to the rim of the shadowed
crater so that the radial evolution of the ejecta curtain is recorded
along the slit. The ejecta curtain evolves rapidly in radius but
sustains approximately constant height (\~2\--3 km = 1\--1.5 arcsec)
above the crater rim due to lunar gravity. Within \~3 minutes the
curtain spreads radially: the ejected mass peaks at 30\--50 seconds at a
radius 3 arcsec, and by 240 seconds the mass above the rim is one-tenth
and the radius is 30 arcsec. From Earth, instruments will observe the
ejecta curtain edge-on, so the growing surface area of the ejecta
curtain (a side-ways expanding lamp shade) means that for 30\--150
seconds the surface brightness declines only by a factor of a few
(Wooden 2008). Water ice sublimes from \~30 µm soil particles within 10
s, but it takes hours for the water vapor to become dissociated into
OH^--^ by sunlight. Models for the LCROSS impact yield a maximum ejecta
curtain mass of \~6000 kg at 2\--5 km above the crater floor (0\--3 km
above the crater rim). If the mass is in 100 µm-radius (1E-4 m-radius)
grains, then the mass surface density at 40 s yields a particle number
density of \~3\--6 E+3 particles m^--2^, and an optical depth of less
than unity. The particulates that produce scattered light and thermal
emission at longer wavelengths (\> 3-5µm) fall back down to the lunar
surface while the water vapor creates an exosphere that persists.

The bright Moon will create a gradient in the sky brightness. We plan to
use **[what technique]{.underline}** to measure the sky; measuring the
scattered light before the night of impact will insure a more robust sky
subtraction.

To view and record the spatial evolution of the scattered light, we
propose to use **[slit-viewing/guide camera with field of view of XX
arcsec by YY arcsec at a pixel scale of zz arcsec/pxl. The camera is
sensitive enough to detect the ejecta curtain (mag/sq
aresec).]{.underline}**

We request **XX hours**

\-- in 2008B for proof of concept observations with
**[telescope+instrument]{.underline}** to confirm instrument
configurations, pointing, tracking, and assess the problem of scattered
light from the bright Moon (phase angle 90˚\--130˚).

\-- in 2009A to prepare for the experiment and for the night of impact.

## References

Arnold, J.R. "Ice in the lunar polar regions", *J. Geophys. Res*.
**84**, 1979.

Butler, B.J. "The migration of volatiles on the surfaces of Mercury and
the Moon", *J. Geophys. Res.* **102**, 1997.

Campbell, D.B., Campbell, B.A., Carter, L.M., Margot, J.L., and N.J.S.
Stacy. "No evidence for thick deposits of ice at the lunar south pole",
*Nature* **443**, 2006.

Campbell, D.B. et al. "Radar imaging of the lunar poles", *Nature*
**426**, 2003.

Crider, D.H. and R.R. Vondrak. "Space weathering effects on lunar cold
trap deposits", *J. Geophys. Res* **108**, 3845-3862, 2003.

Elphic, R.C., Eke, V.R., Teodoro, L.F.A., Lawrence, D.J., and D.B.J.
Bussey. "Models of the distribution and abundance of hydrogen at the
lunar south pole", *Geophys. Res. Lttrs* **34**, 2007.

Feldman, W.C. et al. "Fluxes of fast and epithermal neutrons from Lunar
Prospector: Evidence for water ice at the lunar poles", *Science*
**281**, 1998.

Feldman, W.C., Lawrence, D.J., Elphic, R.C., Vaniman, D.T., Thomsen,
D.R., Barraclough, B.L., Maurice, S., and A.B. Binder. "Chemical
information content of lunar thermal and epithermal neutrons", *J.
Geophys. Res.* **105**, 2000.

Feldman, W.C, Maurice, S., Lawrence, D.J., Little, R.C., Lawson, S.L.,
Gasnault, O., Wiens, R.C., Barraclough, B.L., Elphic, R.C., Prettyman,
T.H., Steinberg, J.T., and A.B. Binder. "Evidence for water ice near the
lunar poles", *J. Geophys. Res.* **106**, 2001.

Lawrence, D.J., Feldman, W.C., Elphic, R.C., Hagerty, J.J., Maurice, S.,
McKinney, G.W., and T.H. Prettyman. "Improved modeling of Lunar
Prospector neutron spectrometer data: Implications for hydrogen deposits
at the lunar poles", *J. Geophys. Res.* **111**, 2006.

Nozette, S. et al. "The Clementine Bistatic Radar Experiment", *Science*
**274**, 1996.

Nozette, S., Spudis, P.D., et al. "Integration of lunar polar
remote-sensing data sets: Evidence for ice at the lunar south pole", *J.
Geophys. Res* **106**, 2001.

Rivkin, A. S., Howell, E. S., Vilas, F., Lebofsky, L. A. "Hydrated
Minearals on Asteroids: The Astronomical Record", in *Asteroids III*, U.
Arizona Press: Tucson, pp. 235-253, 2002.

Rivkin, A. S., Davies, J. K., Johnson, J. R., Ellison, S. L., Trilling,
D. E., Brown, R. H., Lebofsky, L. A. "Hydrogen concentrations on C-class
asteroids derived from remote sensing", *Meteoritics and Planetary
Science* **38**, 1383-1398, 2003.

Stacy, N., Campbell, D.B., and P.G. Ford . "Arecibo radar mapping of the
lunar poles", *Science* **276**, 1997.

Vasavada, A.R., Paige, D.A., and S.E. Wood. "Near-surface temperatures
on Mercury and the Moon and the stability of polar ice deposits",
*Icarus* **141**, 1999.

Watson, K., Murray, B., and H. Brown. "On the possible presence of ice
on the Moon", *J. Geophys. Res*. **66**, 1961.

Wooden, D. H. 2008, LCROSS Astronomer's Workshop presentation