LADEE ends mission with planned impact on the moon
BY STEPHEN CLARK
Posted: April 19, 2014
Closing out a trailblazing six-month mission at the moon, NASA's LADEE spacecraft impacted the lunar surface early Friday as designed after surveying the moon's tenuous atmosphere, measuring dust particles and demonstrating a breakthrough laser communications system.
A final burn by the main engine on the Lunar Atmosphere and Dust Environment Explorer on April 11 put the probe on a trajectory to strike the far side of the moon, away from any of the historic Apollo landing sites and out of view of Earth.
A NASA press release stated the spacecraft hit the moon some time between 12:30 a.m. and 1:22 a.m. EDT (0430-0522 GMT). That is when LADEE was traveling over the the far side of the moon, and mission controllers at NASA's Ames Research Center in California did not receive a radio signal when the probe was expected to emerge over the lunar horizon and establish contact with Earth.
"At the time of impact, LADEE was traveling at a speed of 3,600 miles per hour -- about three times the speed of a high-powered rifle bullet," said Rick Elphic, LADEE project scientist at Ames, in a press release. "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."
Further analysis of LADEE's orbit should yield an estimate of where the spacecraft went down, and scientists plan to order a high-resolution camera on NASA's Lunar Reconnaissance Orbiter to look for LADEE's final resting place.
In early April, controllers commanded LADEE to lower its orbit within a mile of the lunar surface to begin a brief campaign to collect unprecedented measurements of the moon's ultra-thin atmosphere.
"LADEE was a mission of firsts, achieving yet another first by successfully flying more than 100 orbits at extremely low altitudes," said 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."
The lunar gravity field is not uniform, so the moon's pull made the spacecraft's orbit unstable, ensuring LADEE would impact the moon within weeks. The moon's lumpy gravity also made it difficult to predict exactly when LADEE's mission would end.
"It's bittersweet knowing we have received the final transmission from the LADEE spacecraft after spending years building it in-house at Ames, and then being in constant contact as it circled the moon for the last several months," said Butler Hine, LADEE project manager at Ames.
In its final days, LADEE weathered a lunar eclipse that threatened to freeze parts of the spacecraft's propulsion system or drain its batteries. Officials say LADEE's survival of the eclipse, in which the spacecraft spent several hours in shadow, demonstrated the probe's robust design.
The mission was designed for a short lifetime, and its primary data-gathering phase lasted just 100 days and ended in March.
LADEE's three science instruments scooped up dust particles, identified the chemical make-up of the moon's atmosphere, and looked for signs of hydrated compounds, such as water and hydroxyl (OH), migrating from the moon's middle latitudes toward polar cold traps in permanent shadow, where scientists say ice can sit undisturbed for billions of years.
The moon's atmosphere is nothing like our own. Its atoms never collide, technically making the lunar atmosphere an exosphere.
But the moon's atmosphere is an analog to most atmospheres in the solar system, so scientists have used LADEE's observations as a proxy to understand the atmospheres of Mercury, the moons of other planets and even large asteroids.
Scientists expected LADEE's final weeks skimming just above the moon's mountain ranges would reveal new insights into the dust environment, in which particles of lunar dust are levitated miles into space by impacts of tiny micrometeoroids, creating a dust halo around the moon.
The unique LADEE spacecraft also hosted a laser communications terminal, which successfully accomplished the first laser linkup between the moon and Earth, demonstrating a new optical relay paradigm that could drastically boost data return from future deep space missions.
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