April 5, 2014
NASA’s LADEE Satellite Prepares For Planned Lunar Impact
April Flowers for redOrbit.com - Your Universe Online
NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) launched in September 2013 on a mission to gather detailed information about the atmosphere of the Moon. LADEE, pronounced "laddie," was also supposed to report back on conditions near the surface, as well as environmental influences on lunar dust. LADEE's science mission is nearly over, with an impact on the lunar surface planned for April 21 of this year. But LADEE isn't done yet, according to a recent NASA report.Ground controllers at NASA's Ames Research Center are gradually lowering the spacecraft's orbital altitude to fly approximately one to two miles above the surface of the Moon. This will allow LADEE to gather science measurements at the lowest altitude possible before it runs out of fuel, forcing an orbital decay.
The ground control team is planning a final maneuver to ensure that LADEE's trajectory will cause the impact to occur on the far side of the Moon, which is not in view of Earth or near any previous lunar mission landings. The margin for error, however, is small. With the navigation system aboard LADEE, and the low orbital altitudes, even a small error could make the difference between an impact and the spacecraft remaining in orbit. For this reason, the team is not attempting to target a specific impact location.
"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," said 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."
Until mid-April, LADEE's altitude control thrusters will be fired once a week to keep the spacecraft in its target orbit. The final orbital maneuver will be performed on April 11, just ahead of the total lunar eclipse on April 15. During the four-hour eclipse, when Earth's shadow passes over the Moon causing it to turn blood-red, LADEE will be exposed to conditions at the limits of what it was designed to withstand.
The eclipse will be easily observable with the naked eye over most of North America, CBS San Francisco reports. The color of the moon is a result of the sun's light filtered through Earth's atmosphere and projected onto the moon.
"If LADEE survives the eclipse, we will have nearly a week of additional science at low altitudes before impact," said Rick Elphic, LADEE project scientist at Ames. "For a short mission like LADEE, even a few days count for a lot – this is a very exciting time in the mission."
The ground control team will assess LADEE's functionality after the eclipse to see if it is healthy enough to continue acquiring and transmitting data. If the spacecraft is able, this will continue as long as its altitude and contact with ground controllers allow.
"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," said Hine. "However, the eclipse will really put the spacecraft design through an extreme test, especially the propulsion system."
LADEE launched from NASA's Wallops Island Flight Facility and reached lunar orbit on October 6, 2013. On November 10, the vending-machine sized spacecraft began gathering science data. LADEE began its primary 100-day science phase orbit on November 20 and has been in extended mission operations since February 28, 2014.
"Because the LADEE team has flawlessly performed every maintenance maneuver, they've been able to keep the spacecraft flying in its proper orbit and have enabled this amazing mission extension and science to continue up until the very end," said Joan Salute, LADEE program executive at NASA Headquarters in Washington.
Aboard LADEE, three science payload instruments have taken more than 700,000 measurements in an effort to unravel the mysteries of the moon's atmosphere. Previously, LADEE's closest approach to the surface of the moon was between 12.5 and 31 miles, while the farthest was between 47 and 93 miles. This positioning allowed LADEE to pass from lunar day to lunar night every two hours, providing a unique vantage point on the full range of changes and processes occurring within the moon's tenuous atmosphere.
The essential question driving LADEE's data acquisition was to discover if lunar dust, electrically charged by sunlight, is responsible for the pre-sunrise glow detected during several Apollo missions above the lunar horizon. The science instruments are also gathering data about the structure and composition of the thin lunar atmosphere. Understanding these characteristics more thoroughly will help scientists understand other bodies in the solar system, such as large asteroids, Mercury, and the moons of outer planets.
Want to get involved? On Friday, NASA announced that it wants to hear your best guess on when LADEE will actually impact the lunar surface through the “Take the Plunge: LADEE Impact Challenge.” Winners will be announced after impact and will be e-mailed a commemorative, personalized certificate from the LADEE program. The submission deadline is 3 p.m. PDT Friday, April 11.