MISSION_DESCRIPTION |
LCROSS launched as a secondary payload with Lunar Reconnaissance
Orbiter (LRO) on June 18, 2009 5:32 Eastern Time. After
trans-lunar injection, LRO separated and performed its mission.
The LCROSS Shepherding Spacecraft (SSC) remained attached to the
spent Atlas upper stage, called the Centaur. Over 112 days, the
Shepherding Spacecraft adjusted the Centaur's course to bring it
to an impact within the Cabeus Crater near the South Pole of the
moon.
LCROSS used the Centaur as a 2300 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 was observed from a number of
Lunar-orbital and Earth-based assets, and the LCROSS spacecraft.
After releasing the Centaur, the SSC flew toward the impact
plume, sending real-time data to characterize the morphology,
evolution and composition of the plume with a suite of cameras
and spectrometers. The SSC then became a 700kg impactor itself,
providing a second opportunity to study the nature of the Lunar
Regolith.
Mission Phases
==============
LCROSS and LRO launched on June 18, 2009 at 21:32 UTC aboard an
Atlas V launch vehicle in the 401 configuration (4-meter
fairing, no solid rocket boosters, single-engine Centaur).
After achieving low-Earth orbit, the Centaur performed a 23
minute coast, and then re-ignited to perform the trans-lunar
injection (TLI) burn for both LCROSS and LRO.
Three minutes after TLI, the Centaur separated from LRO and then
maneuvered to increase separation to avoid contaminating LRO.
To minimize the residual propellant species aboard the Centaur
at lunar impact (potential contaminants of water measurements),
the Centaur next performed a sequence of propellant depletion
maneuvers with both cryogenic and hydrazine-based reaction
control systems. During these depetion maneuvers, the Centaur
powered the SSC up and pointed its solar array at the sun.
After the maneuvers were finished, the Centaur ceded attitude
control to the SSC and shut down.
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Transfer Phase [6/18/2009 - 6/23/2009]
The transfer phase covered the period from TLI to lunar
swingby.
This phase contained the QUICKLOOK and STARFIELD data collection
periods. Both periods were used to confirm instrument function
and pointing prior to the lunar swingby.
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Lunar Swingby [6/23/2009]
The lunar swingby was a gravity assist maneuver that placed
LCROSS in a steeply-inclined, nearly circular orbit around Earth
at approximately lunar distance. Called a Lunar Gravity Assist
Lunar Return Orbit (LGALRO), this trajectory returned LCROSS to
the moon again after three orbits.
Just after closest approach to the moon, the instruments were
pointed at the surface and turned on to gather calibration data.
The instruments were swept across the surface, pausing three
times at targets on the surface with distinctive spectral
characteristics. Finally, the instruments were swept back and
forth across the limb. This limb-crossing data was used to
confirm instrument pointing to within 0.1 degree.
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Cruise Phase
Cruise phase activities included trajectory correction
maneuvers and additional periods of payload data collection
observing the Earth and Moon.
Several 'Cold Side Bake' activities were also performed to
reduce ice in the Centaur insulation that remained since launch.
During these maneuvers, the SSC and Centaur were turned to place
cold side of the spacecraft, which was normally in darkness, in
sunlight. Sublimating ice embedded in the insulation generated
enough thrust to be detectible in doppler measurements. If left
in place, this ice could potentially have contaminated
observations of the Centaur's impact.
On the second half of the second Earth orbit, LCROSS experienced
a major propellant loss stemming from a short-lived Inertial
Reference Unit (IRU) glitch. This was discovered immediately
before the third Cold Side Bake event. With the mission in
jeopardy, LCROSS declared an emergency and transitioned to
maximum DSN coverage to enable full-time monitoring. Over the
following two weeks, the flight team developed strategies to
prevent another glitch and to minimize propellant usage during
planned maneuvers. With operational and software protections in
place, the LCROSS project returned to a nominal operational
posture on Day 78, albeit with a significantly smaller
propellant margin.
The deadline for final selection of the Centaur target crater
was 30 days prior to impact. This late date allowed the Team to
use early data from LRO to improve the targeting decision.
During the final two weeks of cruise, the Science Team twice
refined the target location within the crater.
------
Separation
Centaur separation was performed successfully 9 hours 40 minutes
prior to Centaur impact and, with the substantial change of mass
properties, was accompanied by a transition to a completely new
set of attitude control modes tuned for post-separation
conditions. One minute following separation, the SSC flipped
180 degrees to point the payload at the receding Centaur. These
observations are contained in the SEPARATION data collection
period. Forty minutes after separation, the SSC performed the
Braking Burn, a delta-v maneuver used to produce a 600 km
separation between the Centaur and the SSC at the moment of
Centaur impact.
------
Impact
Approximately one hour prior to centaur impact, the spacecraft
was turned to point the instruments at the predicted impact
location. Fifty minutes of calibration data are contained in the
PREIMPACT data collection. Five minutes of data are contained in
the IMPACT data collection, starting one minute prior to Centaur
impact.
The Centaur impacted the moon at 11:31:19.51 UTC on 10/9/2009 at
-84.68 deg latitude, -48.69 deg longitude, Mean Earth frame.
The SSC impacted the surface at 11:35:34 UTC.
Earth-based Observations
========================
The LCROSS project provided funding for four investigators to record
Earth-based observations of the LCROSS impact using various observatory
facilities, and to archive their data in the PDS. Many other Earth-based
facilities also observed the impact. The four LCROSS-sponsored observers
were:
(1) Dr. Marc Buie, Southwest Research Institute in Boulder, CO, using the
PHOTDOC and PHOTGJON cameras on the Magdalena Ridge Observatory 2.4-m
telescope, Socorro, NM
(2) Dr. Nancy Chanover, New Mexico State University, using the Agile
camera on the Astrophysical Research Consortium 3.5-meter telescope at
the Apache Point Observatory, Sunspot, NM
(3) Dr. Faith Vilas, University of Arizona, using the CCD47 and CLIO
cameras at the MMT Observatory, Tucson, AZ
(4) Dr. Eliot Young, Southwest Research Institute in Boulder, CO, using
three facilities: the Gemini North telescope at the Mauna Kea Observatory
on the island of Hawaii; the SPEX spectrograph and imager on the
3.0-meter Infrared Telescope Facility (IRTF) at the Mauna Kea Observatory;
and the Near Infrared Spectrograph (NIRSPEC) on the 10-meter Keck II
telescope, Keck Observatory, Kamuela, Hawaii.
References
==========
Ennico, K., et al., 'LCROSS Science Payload Ground Development, Test
and Calibration Results', 39th Lunar and Planetary Science
Conference, Lunar and Planetary Science Institute, No. 1391, League
City, TX, 2008, p 1474.
Strong, J., et al., 'Transport and Use of a Centaur Second Stage in
Space', AIAA Space Ops 2010 Conference, Delivering on the Dream,
AIAA, Washington, DC, 2010, Paper 2010-2197 (submitted for
publication).
Tompkins, P., et al., 'Flight Team Development in Support of LCROSS:
A Class D Mission', AIAA Space Ops 2010 Conference, Delivering on
the Dream, AIAA, Washington, DC, 2010, Paper 2010-2223 (submitted
for publication).
Tompkins, P., et al., 'Flight Operations for the LCROSS Lunar
Impactor Mission', AIAA Space Ops 2010 Conference, Delivering on the
Dream, AIAA, Washington, DC, 2010, Paper 2010-1986 (submitted for
publication).
Andrews, D., 'LCROSS Lunar Impactor: Pioneering Risk-Tolerant
Exploration in a Search for Water on the Moon', Proceedings of the
7th International Planetary Probe Workshop, Barcelona, Spain, June
2010 (submitted for publication).
Colaprete, A., et al., 'An Overview of The Lunar
Crater Observation and Sensing Satellite (LCROSS) Mission - An ESMD
Mission to Investigate Lunar Polar Hydrogen,' Bulletin of the
American Astronomical Society, September, 2006, Vol. 38, p. 591.
|
REFERENCE_DESCRIPTION |
Andrews, D., LCROSS Lunar Impactor: Pioneering Risk-Tolerant Exploration in a
Search for Water on the Moon, Proceedings of the 7th International Planetary
Probe Workshop, Barcelona, Spain, (submitted for publication) June 2010.
Colaprete, A., et al., An Overview of The Lunar Crater Observation and Sensing
Satellite (LCROSS) Mission - An ESMD Mission to Investigate Lunar Polar
Hydrogen, Bulletin of the American Astronomical Society, September, Vol. 38, p.
591, 2006
Ennico, K., et al., LCROSS Science Payload Ground Development, Test and
Calibration Results, 39th Lunar and Planetary Science Conference, Lunar and
Planetary Science Institute, No. 1391, League City, TX, p 1474, 2008.
Strong, J., et al., Transport and Use of a Centaur Second Stage in Space, AIAA
Space Ops 2010 Conference, Delivering on the Dream, AIAA, Washington, DC, Paper
2010-2197 (submitted for publication), 2010.
Tompkins, P., et al., Flight Team Development in Support of LCROSS: A Class D
Mission, AIAA Space Ops 2010 Conference, Delivering on the Dream, AIAA,
Washington, DC, Paper 2010-2223 (submitted for publication), 2010.
Tompkins, P., et al., Flight Operations for the LCROSS Lunar Impactor Mission,
AIAA Space Ops 2010 Conference, Delivering on the Dream, AIAA, Washington, DC,
Paper 2010-1986 (submitted for publication), 2010.
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