Lunar Crater Observation and Sensing Satellite (LCROSS)

Description

The Lunar Crater Observation and Sensing Satellite (LCROSS) is designed to search for water ice on the Moon's surface by directing a 2000 kg Centaur upper stage into an impact with the Moon while observing the collision from behind. The objective is to observe the resulting ejecta plume and look for evidence of exhumed water or hydrated materials that would indicate water ice is present at or near the surface at the lunar poles.

Mission Profile

LCROSS launched along with the Lunar Reconnaissance Orbiter (LRO) spacecraft, on an Atlas 5 401 at 21:32 UT (5:32 p.m. EDT) on 18 June 2009. LCROSS separated from LRO at 22:16:43 UT. LCROSS passed the Moon on 23 June at 10:30:33 UT at a distance of 3200 km, receiving a gravity assist and going into Earth orbit. The mission consists of a Shepherding Spacecraft (S-S/C) attached to the Centaur upper stage. The S-S/C will guide the Centaur after orbital insertion through two highly eccentric 40-day Earth orbits. The S-S/C then guided the Centaur into a trajectory which caused it to impact in Cabeus, a 98 km diameter crater centered at 84.9 S, 324.5 E near the lunar south pole, chosen for its likelihood of containing water ice. Centaur impact took place on 9 October 2009 at 11:31:19.5 UT at 84.678 S lon., 311.275 E lat.at approximately -3825 meters lunar altitude The Centaur impacted the lunar surface at a velocity of approximately 2.5 km/sec and an angle of roughly 75 degrees, throwing up debris, possibly including water, hydrocarbons, and/or hydrated material. The S-S/C separated from the Centaur at 01:50 UT on 9 October and performed a delay burn of 50 m/s to follow a few minutes behind. The S-S/C took images and collected other data on the impact and cloud of ejecta for approximately four minutes as it flew through it before also striking the Moon, at 11:35:36.1 UT at 84.72 S lat., 310.38 E lon. at a lunar altitude of approximately -3809 meters.

Spacecraft and Subsystems

The S-S/C is built on an EELV Secondary Payload Adaptor (ESPA) 158 cm diameter ring with a dry mass of 534 kg and 300 kg of hydrazine propellant. Peak power for the system of 372 W is supplied by a 600 W solar array charging a 40A-h Li-Ion battery. Propulsion is through two 8-thruster pods supplied by a mono-propellant fuel tank mounted inside the ring. Communications will be via an S-band transponder and two omnidirectional and two medium-gain horn antennas. Attitude control is achieved through a system of star trackers, 10 sun sensors, and an inertial measurement unit controlling an N2H4 reaction control system. Outer radiator panels, heat pipes, and multilayer insulation are used for thermal control. The S-S/C is equipped with two visible cameras, three infrared cameras, three spectrometers, and a photometer for observations.