NASA's two new lunar probes -- Lunar Reconnaissance Orbiter (LRO), Lunar CRater Observation and Sensing Satellite (LCROSS), lifted off Thursday on a landmark mission to scout water sources and landing sites in anticipation of leading astronauts back to the moon in 2020.
LCROSS will search for water ice on the moon by sending the spent upper-stage Centaur rocket to impact part of a polar crater in permanent shadows. It will fly into the plume of dust left by the impact and measure the properties before also colliding with the lunar surface.
After being launched by an Atlas V rocket, LRO will separate from LCROSS and continue on to the moon. The LCROSS (shepherding) spacecraft will retain the Atlas V's Centaur upper stage rocket and use it as the primary impactor for the mission, something that has never been done with a Centaur. After sufficient distance from LRO is achieved, the shepherding spacecraft and the Centaur will perform a "blowdown" maneuver to vent any remaining fuel inside the Centaur to help prevent contamination of the impact site.
Five days later, the shepherding spacecraft and the Centaur will execute a flyby of the moon and enter into an elongated Earthorbit to position LCROSS for impact on a lunar pole. This elongated orbit portion of the mission is expected to be four months. The exact length of time is dependent on the exact time of launch and is calculated to satisfy a number of competing mission constraints, including hitting a specific target crater, timing the impact to achieve proper illumination of the debris plume at the time of impact, and staying within spacecraft propellant limits.
On final approach, LCROSS and the Centaur will separate. The Centaur will act as the first impactor to create a debris plume with some of the heavier material reaching a height of up to 6.2 miles (10 km) above the lunar surface. Following four minutes behind, the LCROSS will fly through the debris plume, collecting and relaying data back to Earth before impacting the lunar surface and creating a second debris plume.
Lunar orbiting satellites and Earth-based telescopes on the ground and in orbit will observe the impacts and resulting debris plumes. The impacts are expected to be visible from Earth using telescopes 10-to-12 inches and larger. Data from these multiple sources will be used in preparation for the eventual return of humans to the moon.
The LCROSS science payload consists of two near-infrared spectrometers, a visible light spectrometer, two mid-infrared cameras, two near-infrared cameras, a visible camera, and a visible radiometer. The LCROSS instrument payload was designed to provide mission scientists with multiple complementary views of the debris plume created by the Centaur impact.
As the debris plume rises above the target crater's rim, it is exposed to sunlight and any water ice, hydrocarbons, or organics will vaporize and break down into their basic components. These components primarily will be monitored by the visible and infrared spectrometers. The near-infrared and mid-infrared cameras will determine the total amount and distribution of water in the debrisplume. The spacecraft's visible camera will track the impact location and the behavior of the debris plume while the visible photometer will measure the flash created by the Centaur impact.
Source:Xinhua
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