NASA Twin Spacecraft On Final Approach For Moon Orbit

Artist's impression of the GRAIL Spacecraft
(Image Credit NASA)

NASA's twin spacecraft to study the moon from crust to core will make New Year's Eve and New Year's Day main-engine burns to place the duo in lunar orbit. The Gravity Recovery And Interior Laboratory (GRAIL) spacecraft are scheduled to be placed in orbit beginning at 1:21 p.m. PST (4:21 p.m. EST) for GRAIL-A on Dec. 31, and 2:05 p.m. PST (5:05 p.m. EST) on Jan. 1 for GRAIL-B.

The Earth is approximately 250,000 miles (402,336 kilometers) from the Moon and NASA's Apollo crews took about three days but the GRAIL craft are taking about 30 times that long, covering more than 2.5 million miles (4 million kilometers) using a low-energy, long-duration trajectory. This has allowed the spacecraft's Ultra Stable Oscillator to be continuously powered for several months to reach a stable operating temperature long before it begins making science measurements in lunar orbit.

The spacecraft will transmit radio signals precisely defining the distance between them as they orbit the moon. As they fly over areas of greater and lesser gravity, caused both by visible features such as mountains and craters and by masses hidden beneath the lunar surface. they will move slightly toward and away from each other. An instrument aboard each spacecraft will measure the changes in their relative velocity very precisely and scientists will translate this information into a high-resolution map of the Moon's gravitational field.

The data will allow mission scientists to understand what goes on below the surface. This information will increase our knowledge of how Earth and its rocky neighbors in the inner solar system developed into the diverse worlds we see today. Maria Zuber, GRAIL principal investigator from the Massachusetts Institute of Technology (MIT) said "This mission will rewrite the textbooks on the evolution of the moon."

Moon Mission In Final Preparations For September 8th Launch

Image credit: NASA

NASA's Gravity Recovery And Interior Laboratory (GRAIL), mission to study the moon is in final launch preparations for a scheduled September 8th launch onboard a Delta II rocket from Cape Canaveral Air Force Station in Florida.

GRAIL's twin spacecraft are tasked for a nine-month mission to explore the Moon in unprecedented detail. They will determine the structure of the lunar interior from crust to core and advance our understanding of the thermal evolution of the moon.

David Lehman, GRAIL project manager for NASA's Jet Propulsion Laboratory in Pasadena, said "Yesterday's final encapsulation of the spacecraft is an important mission milestone. Our two spacecraft are now sitting comfortably inside the payload fairing which will protect them during ascent. Next time the GRAIL twins will see the light of day they will be about 95 miles up and accelerating."

The spacecraft twins, GRAIL A and B, will fly a circuitous route to lunar orbit taking 3.5 months and covering approximately 2.6 million miles (4.2 million kilometers) for GRAIL-A, and 2.7 million miles (4.3 million kilometers) for GRAIL-B.

In lunar orbit, the spacecraft will transmit radio signals precisely defining the distance between them. Regional gravitational differences on the moon are expected to expand and contract that distance. GRAIL scientists will use these accurate measurements to define the moon's gravity field. The data will allow mission scientists to understand what goes on below the surface of our natural satellite.