In space, no one can hear you hit the Moon at near-hypersonic speed. Today, NASA's Ames Research Center announced that the Lunar Atmosphere and Dust Environment Explorer (LADEE) made a controlled impact on the far side of the Moon some time between 9:30 and 10:30 pm PDT on Thursday, bringing to an end its mission to study the lunar atmosphere.
Launched in September 2013 from NASA's Wallops Flight Facility, Virginia, LADEE entered Lunar orbit on October 6 and proceeded to carry out an extensive study designed to provide 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. Because the flight plan required LADEE to maintain a very low-altitude lunar orbit, its extended science mission was put on course for a dramatic end on April 11, when NASA used the last of the unmanned probe's fuel to put it into a very low lunar orbit only about 1 to 2 mi (2 to 3 km) above the lunar surface.
The purpose of this new orbit was to send LADEE on course for a controlled impact on the far side of the Moon, as its orbit naturally decayed due to the uneven lunar gravitational field. The far side was chosen in order to avoid contaminating any of the historic landing sites from previous missions. Though NASA was unable to predict precisely when or where the probe would crash, the impact was confirmed when its radio signal failed to reappear after it passed behind the Moon yesterday.
Despite the fact that there was no one to see it, NASA says that the impact would have been spectacular, with the washing-machine sized spacecraft hitting at orbital speeds, causing it to heat to hundreds of degrees or even vaporize as it struck the lunar surface.
"At the time of impact, LADEE was traveling at a speed of 3,600 miles per hour (5,800 km/h) – about three times the speed of a high-powered rifle bullet," says Rick Elphic, LADEE project scientist at Ames. "There’s nothing gentle about impact at these speeds – it’s just a question of whether LADEE made a localized craterlet on a hillside or scattered debris across a flat area. It will be interesting to see what kind of feature LADEE has created."
According to NASA, one plus for LADEE’s last days was that its solar power systems and batteries survived this week’s total lunar eclipse. NASA engineers feared that the extended period of darkness might cause the electrical system to fail, resulting in the craft to freezing to death.
Despite the demise of LADEE, the mission still has a few tasks left to tidy up. NASA's Lunar Reconnaissance Orbiter (LRO) will hunt for the impact site of the probe, which will not only provide scientific data, but will determine the winner of NASA’s “Take the Plunge” contest, where the public were invited to guess the date and time of LADEE’s impact.
"LADEE was a mission of firsts, achieving yet another first by successfully flying more than 100 orbits at extremely low altitudes," says Joan Salute, LADEE program executive, at NASA Headquarters in Washington. "Although a risky decision, we're already seeing evidence that the risk was worth taking.”