Another lunar mission is drawing to a close, if not with a bang, then a thump. On Thursday, NASA held a press conference to discuss the final weeks of the Lunar Atmosphere and Dust Environment Explorer (LADEE) mission before the spacecraft makes a controlled impact on the far side of the Moon on or before April 21.
Since its launch last year, LADEE has been sending back data with the aim of providing scientists with a better understanding of the dust and tenuous atmosphere around the Moon, as well as a demonstration on the use of lasers for deep-space communications. Now reaching the end of its extended science mission, ground controllers at NASA's Ames Research Center in Moffett Field, California, are preparing to move the spacecraft gradually into a very low lunar orbit only about 1 to 2 mi (2 to 3 km) above the lunar surface.
According to NASA, natural orbital decay will soon bring LADEE down. Unfortunately, the nature of the Moon’s gravity means that it isn't possible to target LADEE to hit on a specific spot. This is why the impact is planned for the far side, so the spacecraft won’t pose a threat of contaminating historic landing sites on the near side.
"The Moon's gravity field is so lumpy, and the terrain is so highly variable with crater ridges and valleys that frequent maneuvers are required or the LADEE spacecraft will impact the Moon’s surface," says Butler Hine, LADEE project manager at Ames. "Even if we perform all maneuvers perfectly, there's still a chance LADEE could impact the Moon sometime before April 21, which is when we expect LADEE's orbit to naturally decay after using all the fuel onboard."
In the coming weeks, LADEE will execute a series of course correction burns to keep it on target with the final burn on April 11 designed to use up the last of the fuel to minimize surface contamination. NASA says that LADEE will continue to send back scientific data until contact is finally lost before impact,.
The main threat that LADEE faces between now and impact is a lunar eclipse on April 15. This will throw the Moon into darkness for four hours and there is the danger that the spacecraft may lose power and freeze, making it inoperative. The best mission control can manage is to carry out all the maneuvers beforehand and monitor the craft as it comes back into sunlight.
"We're very eager to see how LADEE handles the prolonged exposure to the intense cold of this eclipse, and we've used flight data to predict that most of the spacecraft should be fine," says Hine. "However, the eclipse will really put the spacecraft design through an extreme test, especially the propulsion system."
NASA says that it will not be able to see the impact directly, but will know when it occurs when the spacecraft fails to reappear from behind the Moon. Because NASA cannot predict the impact point, the space agency is running a contest that challenges the public to guess where the probe will hit the Moon. The "Take the Plunge: LADEE Impact Challenge" will accept submissions until 3 PM PDT Friday, April 11.