Using a precision formation-flying technique, the twin GRAIL spacecraft will map the moon’s gravity field, as depicted in this artist’s rendering. Radio signals traveling between the two spacecraft provide scientists the exact measurements required as well as flow of information not interrupted when the spacecraft are at the lunar farside, not seen from Earth. The result should be the most accurate gravity map of the moon ever made. The mission also will answer longstanding questions about Earth’s moon, including the size of a possible inner core, and it should provide scientists with a better understanding of how Earth and other rocky planets in the solar system formed. GRAIL is a part of NASA’s Discovery Program. Image credit: NASA/JPL-Caltech
The first of two NASA spacecraft to study the moon in unprecedented detail has entered lunar orbit.
NASA’s Gravity Recovery And Interior Laboratory (GRAIL)-A spacecraft successfully completed its planned main engine burn at 2 p.m. PST (5 p.m. EST) today. As of 3 p.m. PST (6 p.m. EST), GRAIL-A is in a 56-mile (90-kilometer) by 5,197-mile (8,363-kilometer) orbit around the moon that takes approximately 11.5 hours to complete.
“My resolution for the new year is to unlock lunar mysteries and understand how the moon, Earth and other rocky planets evolved,” said Maria Zuber, GRAIL principal investigator at the Massachusetts Institute of Technology in Cambridge. “Now, with GRAIL-A successfully placed in orbit around the moon, we are one step closer to achieving that goal.”
The next mission milestone occurs tomorrow when GRAIL-A’s mirror twin, GRAIL-B, performs its own main engine burn to place it in lunar orbit. At 3 p.m. PST (6 p.m. EST) today, GRAIL-B was 30,018 miles (48,309 kilometers) from the moon and closing at a rate of 896 mph (1,442 kph). GRAIL-B’s insertion burn is scheduled to begin tomorrow at 2:05 p.m. PST (5:05 p.m. EST) and will last about 39 minutes.
“With GRAIL-A in lunar orbit we are halfway home,” said David Lehman, GRAIL project manager at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. “Tomorrow may be New Year’s everywhere else, but it’s another work day around the moon and here at JPL for the GRAIL team.”
Once both spacecraft are confirmed in orbit and operating, science work will begin in March. The spacecraft will transmit radio signals precisely defining the distance between them as they orbit the moon in formation. As they fly over areas of greater and lesser gravity caused by both visible features, such as mountains and craters, and masses hidden beneath the lunar surface, the distance between the two spacecraft will change slightly.
Scientists will translate this information into a high-resolution map of the moon’s gravitational field. The data will allow scientists to understand what goes on below the lunar surface. This information will increase knowledge of how Earth and its rocky neighbors in the inner solar system developed into the diverse worlds we see today.
JPL manages the GRAIL mission for NASA’s Science Mission Directorate at the agency’s headquarters in Washington. The GRAIL mission is part of the Discovery Program managed at NASA’s Marshall Space Flight Center in Huntsville, Ala. Lockheed Martin Space Systems in Denver built the spacecraft.
For more information about GRAIL, visit
