Dec 13, 2012

Dwayne Brown Headquarters, Washington 202-358-1726 dwayne c brown@nasa gov

D C Agle Jet Propulsion Laboratory, Pasadena, Calif 818-393-9011 agle@jpl nasa gov

Sarah McDonnell Massachusetts Institute of Technology, Cambridge, Mass 617-253-8923 s_mcd@mit edu

RELEASE: 12-434

TWIN NASA PROBES PREPARE FOR DEC 17 MISSION-ENDING MOON IMPACT

PASADENA, Calif -- Twin lunar-orbiting NASA spacecraft that have allowed scientists to learn more about the internal structure and composition of the moon are being prepared for their controlled descent and impact on a mountain near the moon's north pole at about 2:28 p m PST (5:28 p m EST) Monday, Dec 17

Ebb and Flow, the Gravity Recovery and Interior Laboratory (GRAIL) mission probes, are being sent purposely into the lunar surface because their low orbit and low fuel levels preclude further scientific operations The duo's successful prime and extended science missions generated the highest resolution gravity field map of any celestial body The map will provide a better understanding of how Earth and other rocky planets in the solar system formed and evolved

"It is going to be difficult to say goodbye," said GRAIL principal investigator Maria Zuber of the Massachusetts Institute of Technology in Cambridge "Our little robotic twins have been exemplary members of the GRAIL family, and planetary science has advanced in a major way because of their contributions "

The mountain where the two spacecraft will make contact is located near a crater named Goldschmidt Both spacecraft have been flying in formation around the moon since Jan 1, 2012 They were named by elementary school students in Bozeman, Mont , who won a contest The first probe to reach the moon, Ebb, also will be the first to go down, at 2:28:40 p m Flow will follow Ebb about 20 seconds later

Both spacecraft will hit the surface at 3,760 mph (1 7 kilometers per second) No imagery of the impact is expected because the region will be in shadow at the time

Ebb and Flow will conduct one final experiment before their mission ends They will fire their main engines until their propellant tanks are empty to determine precisely the amount of fuel remaining in their tanks This will help NASA engineers validate fuel consumption computer models to improve predictions of fuel needs for future missions

"Our lunar twins may be in the twilight of their operational lives, but one thing is for sure, they are going down swinging," said GRAIL project manager David Lehman of NASA's Jet Propulsion Laboratory in Pasadena, Calif "Even during the last half of their last orbit, we are going to do an engineering experiment that could help future missions operate more efficiently "

Because the exact amount of fuel remaining aboard each spacecraft is unknown, mission navigators and engineers designed the depletion burn to allow the probes to descend gradually for several hours and skim the surface of the moon until the elevated terrain of the target mountain gets in their way

The burn that will change the spacecrafts' orbit and ensure the impact is scheduled to take place Friday morning

"Such a unique end-of-mission scenario requires extensive and detailed mission planning and navigation," said Lehman "We've had our share of challenges during this mission and always come through in flying colors, but nobody I know around here has ever flown into a moon mountain before It'll be a first for us, that's for sure "

During their prime mission, from March through May, Ebb and Flow collected data while orbiting at an average altitude of 34 miles (55 kilometers) Their altitude was lowered to 14 miles (23 kilometers) for their extended mission, which began Aug 30 and sometimes placed them within a few miles of the moon's tallest surface features

JPL manages the GRAIL mission for NASA's Science Mission Directorate in Washington The mission is part of the Discovery Program managed at NASA's Marshall Space Flight Center in Huntsville, Ala Lockheed Martin Space Systems in Denver built the spacecraft

For more information about GRAIL, visit:

http://www nasa gov/grail

-end-

To subscribe to the list, send a message to: hqnews-subscribe@mediaservices nasa gov To remove your address from the list, send a message to: hqnews-unsubscribe@mediaservices nasa gov

The following information is a reminder of your current mailing list subscription:

You are subscribed to the following list: [list_name]

using the following email: example@example.com

You may automatically unsubscribe from this list at any time by visiting the following URL:

https://aus-city com/cgi-bin/dada/mail cgi/u/NASA_REPORTS/example/example com/

If the above URL is inoperable, make sure that you have copied the entire address Some mail readers will wrap a long URL and thus break this automatic unsubscribe mechanism

You may also change your subscription by visiting this list's main screen:

<[program_url]/list/[list]>

If you're still having trouble, please contact the list owner at:

<mailto:[list_owner_email]>

The following physical address is associated with this mailing list:

[physical_address]