GRAIL Team Celebrates the End of Ebb and Flow


The energy built in the room as a voice from the Jet Propulsion Laboratory (JPL) came over NASA TV.

“It’s coming over the ridge and is on target for impact.”

Light clapping started, and then the signal from the first of two lunar orbiters died. When the second signal vanished, a room full of Lockheed Martin GRAIL (Gravity Recovery And Interior Laboratory) team members erupted in applause and whistles. The same could be heard over the communications line from JPL.

“All right!” said Stu Spath, Lockheed Martin’s GRAIL program manager. “Congratulations, everyone.”

Spath circled the room shaking hands with the team. They had successfully piloted the two washing-machine sized orbiters named Ebb and Flow around the moon for the past 15 months as part of NASA’s GRAIL mission. Because of the performance of the orbiters and the skill of the GRAIL team, NASA has successfully completed a primary and secondary science mission of mapping the gravity of the moon. 

Launched Sept. 10, 2011, the two GRAIL probes were captured into orbit that New Year’s Eve and New Year’s Day. The GRAIL primary mission, which ended on May 29, yielded the highest-resolution gravity field map of any celestial body—about 1000 times more accurate than previous maps. Future gravity field models developed from data collected during the extended mission will be of even higher resolution. The map will provide a better understanding of how the moon, Earth and other terrestrial planets in the solar system formed and evolved.

Based on the initial success, NASA awarded GRAIL a six-month mission extension from May 30 through Dec. 15. During the extended mission, the spacecraft flew at harrowingly low altitudes providing increased science visibility into the moon’s impact craters and other crustal features.

Over the entire mission, the course of their flight was carefully controlled by the Lockheed Martin team working from the Waterton campus near Denver. The team’s job was to fly the two orbiters traveling up to 100 miles apart with such precision that their exact locations could be measured within a hair’s breadth of accuracy. JPL provided their world-class navigation, in addition to mission management.

On Dec. 17, the team celebrated the end of the mission and the successful planned collision of the orbiters into a lunar mountain. The impact site was named after Sally Ride, NASA’s first female astronaut, who oversaw the mission’s MoonKam education outreach program through her company, Sally Ride Science, in San Diego. Space enthusiasts followed the orbiters’ end via a live NASA television broadcast and on Twitter, where followership of the GRAIL hashtag increased by 800 percent in the final hour of the mission.

Erin Roethlisberger, a Lockheed Martin systems engineer in real-time operations, worked with GRAIL-B—also known as “Flow”—from the lunar orbit insertion to the impact.

“This was a very fast-paced mission, which is different from other missions I’ve worked,” she said. “It’s nice to see one through from start to finish.”

Spath credits the entire GRAIL team with the success. “We were lucky from the beginning to assemble an all-star team, and they’ve been exceptional all the way through.”

NASA's Jet Propulsion Laboratory, Pasadena, Calif., managed the GRAIL mission. The Massachusetts Institute of Technology, Cambridge, is home to the mission's principal investigator, Dr. Maria Zuber. The GRAIL mission is part of the Discovery Program managed at NASA's Marshall Space Flight Center in Huntsville, Ala.