A spacecraft bites the lunar dust.
- By Mohi Kumar
- Air & Space magazine, March 2009
This summer, backyard astronomers may be able to peer through their telescopes and see what happens when a spacecraft smashes into the moon. The impact will be no accident: With an eye to sending humans back to the moon as early as 2020, NASA is on a collision course with Earth’s nearest neighbor to learn about potential landing sites for astronauts who may touch down there again—only much more gently.
Like a bullet hitting sand, the Lunar CRater Observation and Sensing Satellite, or LCROSS, is expected to plow into a deep, dark crater on the moon’s north pole. The impact should kick up at least 220 tons of lunar material—enough to fill 10 school buses—composed of dust, soil, and possibly water in the form of ice or hydrated minerals. The visible portion of the debris plume is expected to rise about six miles above the surface.
Finding lunar water is critical to U.S. space exploration goals. “If you wish to live off the land, a source of water on the moon could possibly sustain humans over extended durations,” explains project manager Daniel Andrews, whose team at NASA’s Ames Research Center in California proposed the mission. From drinking water to water turned into oxygen to breathe or use as an oxidizer for fuel, H2O has the potential to transform the prospect of space colonization into reality. And its worth far exceeds its weight in gold: Shipping a bottle containing two cups of water from Earth to the moon costs as much as $10,000.
NASA first became intrigued by the possibility of water on the moon after two spacecraft, Clementine in 1994 and Lunar Prospector in 1998, found elevated hydrogen levels while exploring the permanently shadowed craters in the lunar poles. “That hydrogen could be trapped protons from the sun or it could be some kind of hydrated mineral,” says Anthony Colaprete, LCROSS principal investigator and a planetary scientist at Ames. “Or, these dark craters could hold water ice that is literally three to four billion years old, pristine cometary water” brought in by comets that hit the moon during its early formation.
Built in three years for $79 million by Ames and Northrop Grumman, LCROSS is a secondary payload on an Atlas V rocket that will carry the Lunar Reconnaissance Orbiter, a NASA spacecraft designed to survey the moon’s topography and identify possible landing sites for humans. The rocket is scheduled to launch from Florida’s Cape Canaveral Air Force Station in late April. Unlike the lunar orbiter, which should arrive at the moon in just a few days, LCROSS will fly by the moon about five days after launch and use lunar gravity to slingshot into an orbit inclined somewhat more than 60 degrees relative to the moon’s equator. After a series of orbits around the Earth and the moon both to pick up speed and to align its course for the target crater, the spacecraft will be on its final approach to the moon about 80 days after launch.
LCROSS will be sacrificed for science. About 10 hours before impact, the spacecraft will separate into two parts: the Centaur upper stage, which will keep flying toward the moon, and the Shepherding Spacecraft, which will perform a maneuver to distance itself from the Centaur. Scientists are aiming at one of two craters, one more than a mile deep, the other a little more than half a mile. The 4,400-pound Centaur, about the size of a large SUV, will slam into one of the craters at a sharp angle at 5,616 mph. The impact is expected to gouge out an area half the size of an Olympic swimming pool to a depth of 16 feet. Four minutes later, the Shepherding Spacecraft will fly through the debris plume, taking pictures and measuring the composition of the material, and transmit that data to Earth in real time. Then the 1,500-pound spacecraft will crash on the lunar surface.
“Our pay dirt is going to be the ice, not the dirt,” says LCROSS co-investigator Peter Schultz, a geologist at Brown University and an expert on impact craters. Scientists say that, depending on the volume of water-ice excavated, they should be able to determine within one hour of the impacts if the moon really holds vast reserves of water.
Both impacts will be monitored by the Lunar Reconnaissance Orbiter and perhaps by other orbiting spacecraft such as Japan’s Kaguya, India’s Chandrayaan-1, as well as the Hubble Space Telescope and Earth-based telescopes. “We’re specifically timing the impact to optimize viewing conditions from the large observatories of Hawaii,” says LCROSS co-investigator Jennifer Heldmann of Ames. The timing is tricky. “We don’t want to impact at new moon, and we don’t want to impact at full moon because the moon will be too bright,” she says. “We want to have the moon high in the sky and a good distance from dawn or dusk to optimize viewing conditions.”