NASA's Moon Twins Going Their Own Way

NASA's Gravity Recovery And Interior Laboratory (GRAIL)-B spacecraft successfully executed its first flight path correction maneuver Wednesday, Oct. 5. The rocket burn helped refine the spacecraft's trajectory as it travels from Earth to the moon and provides separation between itself and its mirror twin, GRAIL-A. The first burn for GRAIL-A occurred on Sept. 30.

"Both spacecraft are alive and with these burns, prove that they're kicking too, as expected," said David Lehman, GRAIL project manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "There is a lot of time and space between now and lunar orbit insertion, but everything is looking good."

GRAIL-B's rocket burn took place on Oct. 5 at 11 a.m. PDT (2 p.m. EDT). The spacecraft's main engine burned for 234 seconds and imparted a velocity change of 56.1 mph (25.1 meters per second) while expending 8.2 pounds (3.7 kilograms) of propellant. GRAIL-A's burn on Sept. 30 also took place at 11 a.m. PDT. It lasted 127 seconds and imparted a 31.3 mph (14 meters per second) velocity change on the spacecraft while expending 4 pounds (1.87 kilograms) of propellant.

Moon Mission Ready to Fly

At the prelaunch news conference Tuesday, the twin moon-bound GRAIL spacecraft and the United Launch Alliance Delta II rocket that will send them on their mission were reported ready to fly, with the late-summer Florida weather presenting the only question for launch day.

Launch Weather Officer Joel Tumbiolo reported that a stationary front that will be parked over the state and plume of tropical moisture will produce anvil clouds and local showers that give the launch team a 40 percent chance of acceptable weather at liftoff time on Thursday. The same conditions will continue on Friday, with an improving weather picture going into the weekend.

Earlier in the day, the final Launch Readiness Review was conducted and the rocket and spacecraft were given a "go" for launch from Cape Canaveral Air Force Station's Space Launch Complex 17B in Florida. There are two instantaneous launch windows at 8:37:06 a.m. and 9:16:12 a.m. EDT.

NASA's GRAIL Moon Twins are Joined to Their Booster

NASA's lunar-bound GRAIL twins were mated to their Delta II launch vehicle at the Cape Canaveral Air Force Station's Launch Complex 17 at 8:45 a.m. EDT (5:45 a.m. PDT) today. The 15-mile (25-kilometer) trip from Astrotech Space Operations in Titusville, Fla., is the last move for GRAIL before it begins its journey to the moon. NASA's dynamic duo will orbit the moon to determine the structure of the lunar interior from crust to core and to advance understanding of the thermal evolution of the moon.

"We are about to finish one chapter in the GRAIL story and open another," said Maria Zuber, GRAIL's principal investigator, based at the Massachusetts Institute of Technology in Cambridge. "Let me assure you this one is a real page-turner. GRAIL will rewrite the book on the formation of the moon and the beginning of us."

Now that the GRAIL spacecraft are atop their rocket, a final flurry of checks and tests can begin to confirm that all is go for launch. The final series of checks begins tomorrow, Aug. 19, with an on-pad functional test. The test is designed to confirm that the spacecraft is healthy after the fueling and transport operations. Next week, among all the upcoming final tests, reviews and closeout operations leading up to liftoff, the GRAIL team will install the launch vehicle fairing around the spacecraft.