by Dr. Ken Kremer
NASA’s GRAIL-B spacecraft ignited her main braking rockets precisely as planned on New Year’s Day to go into orbit around the Moon, chasing behind GRAIL-A, which arrived on New Year’s Eve.
“Now we have them both in orbit. What a great feeling!!!!” NASA manager Jim Green told me just minutes after the thruster firing was over. Green is NASA’s Director of Planetary Science and witnessed the events inside Mission Control at the Jet Propulsion Laboratory (JPL) in Pasadena, Ca. “It’s the best New Year’s ever!!”
The lunar arrivals of GRAIL-A and GRAIL-B capped a perfect year for NASA’s planetary science research. “2011 began the Year of the Solar System, which is a Mars year (~670 Earth days long)… and includes Grail B insertion, Dawn leaving Vesta this summer … And the landing of MSL!” Green said.
After years of hard work, GRAIL principal investigator Maria Zuber of MIT told me that she was very relieved soon after hearing the good news at JPL Mission Control. “Since GRAIL was originally selected, I’ve believed this day would come,” Zuber said. “But it’s difficult to convey just how relieved I am right now. Time for the Science Team to start their engines!”
The hydrazine-fueled main thrusters placed the spacecraft duo into near-polar, highly elliptical orbits. Over the next two months, engineers will trim the orbits of both spacecraft to a near-polar, near-circular, formation-flying orientation. Their altitudes will be lowered to about 34 miles, and the orbital periods trimmed from their initial 11.5-hour duration to about two hours. The science phase begins in March 2012. For 82 days, the mirror-image GRAIL-A and GRAIL-B probes will be flying in tandem with an average separation of about 200 kilometers as the moon rotates beneath.
“GRAIL is a journey to the center of the moon,” Zuber explains. “It will use exceedingly precise measurements of gravity to reveal what the inside of the moon is like.” As one satellite follows the other in the same orbit, they will perform range-rate measurements to measure the changing distance between each other to within 1 micron, the width of a red blood cell, using a Ka-band instrument. When the first satellite goes over a higher mass concentration or higher gravity, it will speed up slightly, which will increase the distance. Then as the second satellite goes over, that distance will close again. The data returned will be translated into gravitational field maps of the moon that will help unravel information about the makeup of the moons mysterious core. GRAIL will map the gravity field 100 to 1000 times better than ever before.The GRAIL twins blasted off from Florida atop a Delta II booster on September 10, 2011. “Ebb” & “Flow” – are the dynamic duo’s new official names. A classroom of America’s youth from a Bozeman, Montana elementary school submitted the stellar winning entry in NASA’s nationwide student essay contest to rename the twin probes.
Ebb & Flow achieved Lunar orbit on New Year’s Weekend 2012. NASA’s twin GRAIL-A & GRAIL-B spacecraft are orbiting the Moon in this astrophoto taken on Jan. 2, 2012.
Check Ken’s GRAIL features online at Universe Today:
2011: Top Stories from the Best Year Ever for NASA Planetary Science!
Two new Moons join the Moon – GRAIL Twins Achieve New Year’s Orbits
America’s Youth Christen NASA’s Twin New Lunar Craft – Ebb & Flow
Astronomy Outreach by Ken Kremer
Rockland Astronomy Club RAC, Rockland Community College, Suffern, NY, Mar 16, 8 PM, “NASA’s Year of the Solar System: Mars, Moon, Mercury, Vesta, Jupiter, Comets and Beyond (plus 3-D”). Website: http://www.rocklandastronomy.com/
New Jersey Astronomical Association NJAA- Vorhees State Park: High Bridge, NJ, March 24, Sat., 8 PM “Atlantis, the End of America’s Shuttle Program and What’s Beyond for NASA”. Website: http://www.njaa.org/
Ken Kremer: Spaceflight magazine & Universe Today
Ken has a selection of his Shuttle photos and Mars mosaics for sale as postcards and frameable prints.