Artist concept of GRAIL mission.
Artist concept of GRAIL mission. Grail will fly twin spacecraft in tandemorbits around the moon to measure its gravity field in unprecedenteddetail. Image credit: NASA/JPL
› Larger image
PASADENA, Calif. -- NASA will host a two-day launch Tweetup for 150 of its Twitter followers on
Sept. 7-8 at the agency's Kennedy Space Center in Florida. The Tweetup is expected to culminate in
the launch of the twin lunar-bound GRAIL spacecraft aboard a Delta II rocket from Cape Canaveral
Air Force Station in Florida.

The launch window opens at 5:37 a.m. PDT (8:37 a.m. EDT) on Sept. 8. The two GRAIL spacecraft
will fly in tandem orbits around the moon for several months to measure its gravity field, from its
crust to core, in unprecedented detail. The mission also will answer longstanding questions about the
moon and provide scientists with a better understanding of how Earth and other rocky planets in the
solar system formed.

The Tweetup will provide NASA's Twitter followers with the opportunity to tour the Kennedy Space
Center Visitor Complex; speak with scientists and engineers from GRAIL and other upcoming
missions; and, if all goes as scheduled, view the spacecraft launch. The event also will provide
participants the opportunity to meet fellow tweeps and members of NASA's social media team.

2011 is one of the busiest ever in planetary exploration; GRAIL's liftoff is the third of four space
missions launching this year under the management of NASA's Jet Propulsion Laboratory in
Pasadena, Calif. Aquarius launched June 10 to study ocean salinity; Juno will launch Aug. 5 to study
the origins and interior of Jupiter; and the Mars Science Laboratory/Curiosity rover heads to the Red
Planet no earlier than Nov. 25.

Tweetup registration opens at 6 a.m. PDT (9 a.m. EDT) on Tuesday, July 26, and closes at 9 a.m.
PDT (noon EDT) on Thursday, July 28. NASA will randomly select 150 participants from online

For more information and rules about the Tweetup and registration, visit:

To follow NASA on Twitter, visit:

For information about more ways to connect and collaborate with NASA, visit:

GRAIL's principal investigator is Maria Zuber of the Massachusetts Institute of Technology,
Cambridge. JPL, a division of the California Institute of Technology in Pasadena, manages the
mission for NASA.

For more information about GRAIL, visit: and

News Media Contact

Veronica McGregor 818-354-9452
Jet Propulsion Laboratory, Pasadena, Calif.

Stephanie L. Schierholz 202-358-4997
Headquarters, Washington