An artist's conception of the LCROSS mission. Left: The upper stage impactor separates from the payload adapter/satellite. Right: The upper stage impacting the lunar pole. Courtesy NASA.
April 10, 2006, NEW YORK -- NASA announced today a new robotic mission to the moon that will launch in late 2008 with the already-scheduled Lunar Reconnaissance Orbiter (LRO). The new mission, called the LCROSS, or Lunar Crater Observation and Sensing Satellite, takes advantage of the extra payload capacity of NASA's new Evolved Expendable Launch Vehicle (EELV). The new mission has two components: An impactor will slam into the moon’s South Pole, sending up a massive plume of lunar dust almost 40 miles high. Meanwhile, an orbiting satellite will fly through the plume, sampling the ejected debris for water vapor, a sign of ice. Then the satellite will itself impact the lunar surface in a separate area, sending up another plume for analysis by the LRO and Earth based observatories. “This mission will generate a huge amount of data,” said Scott Horowitz, assistant administrator for NASA’s Exploration Directorate. “It’ll generate quite a few PhDs."
The new mission is designed to fit an extraordinarily tight $80 million budget, and to weigh fewer than 2,025 lbs. The satellite portion of the spacecraft is built around the EELV’s payload adapter – the device that links the LRO to the EELV’s upper stage, and the impactor is the upper stage itself. “This spacecraft is really high-heritage,” said Dan Andrews, a project manager at NASA Ames. “The sensing portion is basically a big hunk of aluminum that we’ve fitted with the rest of the components of a spacecraft.”
The impactor will orbit the Earth twice after the LRO separates, and reach the moon’s south pole in roughly 90 days, and impacting the surface at an angle of about 75 degrees and a velocity of 6600 mph. The impact crater will be about 16 feet deep. “It’s pretty high energy,” says Andrews. “The spent upper stage has the mass of a large SUV.”
The material in the impact plume will be large enough to fill more than 10 Space Shuttle payloads, and although the bulk of the debris will fall back to the lunar surface within hours, an exosphere will remain for days. If there is water vapor in the plume, it will remain in that exosphere, making it easier to detect. According to Andrews, the plume will be large enough to be detected by amateur astronomers on Earth. “It’s a pretty large swath we’re kicking up,” he says. It might also create a visible flash.
In order to take advantage of the extra 2,025 lbs of EELV payload capacity unused by the relatively light LRO, NASA solicited over 19 proposals, which were quickly narrowed down to four. The LCROSS mission won in part because of its simplicity and because of the crucial role water ice will play in NASA’s plans for manned interplanetary missions. If ice does exist, it might be possible to mine it and then separate it into hydrogen and oxygen for rocket fuel. Scientists believe if there is ice is most likely to exist in the shadows of the lunar poles. According to NASA officials, the impactor will most likely target the Shackelton crater.
The satellite portion of the spacecraft will take visual photographs of the impact at about one per every other second. Out of the $600 million price tag for the two missions, LCROSS costs only $73 million.