NASA launches GRAIL lunar orbiters

Cape Canaveral, Florida: A United Launch Alliance (ULA) Delta II rocket carrying two Gravity Recovery and Interior Laboratory (GRAIL) spacecraft for NASA was launched on Saturday. The launch marked the ninth flight for ULA in 2011 and the 49th Delta II mission for NASA. It also marked the final launch from the Space Launch Complex 17-B here.

NASA's two GRAIL spacecraft designed and built by Lockheed Martin, will map the gravitational field of the moon in unprecedented detail. This data will be used to determine the structure of the lunar interior from crust to core and advance our understanding of the thermal evolution of the moon.

The first of the two robotic spacecraft separated from the Delta II upper stage 1 hour and 21 minutes after launch at 10:28 a.m. ET and the second spacecraft separated eight minutes later.

Even though the spacecraft duo was launched on the same day, they will arrive at the moon one day apart. The first orbiter, GRAIL-A arrives on 31 Dec 2011 and GRAIL-B arrives 25 hours later on 1 Jan 2012.

At the start of the science phase, the spacecraft will be in a polar, nearly-circular orbit 34 miles (55 km) above the surface. The science phase of collecting gravity data will last 82-days.

As for the final launch from SLC-17-B, Michael Gass, ULA president and CEO said: "With the final launch from SLC-17, we reflect on the tremendous historical significance of this complex and the impact of the military and scientific payloads that began their missions from this site."

"From the Global Positioning System satellites launched for the US Air Force, to NASA's Mars rovers Spirit and Opportunity, in total this complex has been the origin for 259 critical Delta missions to protect our country and explore our universe."