LCROSS Set For June 18 Launch
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By Michael Mecham
As it nears launch, the Lunar Crater Observation and Sensing Satellite (LCROSS) mission has drawn a full array of ground- and space-based observatories that want to take its picture when it slams into the bottom of a shallow crater on the moon's south pole in October.
The LCROSS mission, which will be carried piggyback with NASA's Lunar Reconnaissance Orbiter (LRO) in a liftoff now set for the afternoon of June 18, is to look for evidence of water ice and hydrogen on the lunar surface.
To find it, NASA will separate LCROSS, built by Northrop Grumman Aerospace Systems, from the mission's 4,400-pound Centaur upper stage nine hours before impact. Then both the Centaur and LCROSS will successively slam into the floor of a crater. The idea is to kick up regolith and dust that can be imaged by optical and infrared observatories for the few minutes - perhaps hours - that it remains suspended in the thin lunar atmosphere.
Due to range availability and other issues, LRO/LCROSS is 20 months behind its original schedule. But for LCROSS, the timing couldn't be better. It's giving Principal Investigator Anthony Colaprete of NASA Ames Research Center an embarrassment of riches because he's got to pick a single crater to hit from a big field of candidates.
To do so, he's been relying on maps from many previous missions, including the most recent images from Japan's Kaguya orbiter. The Japan Aerospace Exploration Agency deliberately plunged it into the lunar surface June 11 at the conclusion of its survey mission (Aerospace DAILY, June 13). It hit in a grazing trajectory and didn't kick up much dust when it impacted near the Gill crater, at 65 degrees south latitude.
Colaprete wants a crater that's between 78-85 degrees south of the lunar equator. Since his mission is optimized for impact at an 85-degree angle, he expects far more frozen regolith to fly free.
"This is one of the best launch blocks we've seen in terms of impacts and illumination," he says. His science team needs perfect backlighting to highlight the flying regolith. But it also must avoid striking a crater when the surface is too brightly lit, such as during a full moon, which would wash out camera images.
"We're headed back to the south pole for an October impact," he says. "That resulted in this very nice impact angle, a very steep angle. The sun will be overhead to the south. Great."
Colaprete wants to hit the crater's floor, not its sides, to get the best spread of debris. Most spacecraft that hit the moon, such as Kaguya, do so at a grazing angle so they don't dislodge much regolith. LCROSS's descent at 85 degrees is designed to maximize the mess.
The launch's mid-June timing dictates that LCROSS will pursue a south pole target. As on Earth, the moon's poles are colder than its mid-latitude regions, so they have the best chance of preserving frozen water ice or hydrogen in the shadows of craters. Colaprete's target craters are in the Cabeus area on the west side of the south pole as viewed from Earth.
Observatories in Hawaii, Arizona, California and New Mexico will take part, along with an array of spacecraft. The Hubble Space Telescope will study the impact on five orbits using its Widefield Planetary Camera 3 and Space Telescope Imaging Spectrograph. Additionally, Sweden's Oden orbiting observatory is signed up and India's Chandrayaan mapper is expected as well.
Artist's concept of LCROSS: NASA
