NASA's GRAIL-A spacecraft 24 hours away from Moon

December 31, 2011
Artist concept of GRAIL mission. Grail will fly twin spacecraft in tandem orbits around the moon to measure its gravity field in unprecedented detail. Image credit: NASA/JPL

(PhysOrg.com) -- NASA's Gravity Recovery And Interior Laboratory (GRAIL)-A spacecraft is within 24 hours of its insertion burn that will place it into lunar orbit. At the time the spacecraft crossed the milestone at 1:21 p.m. PST today (4:21 p.m. EST), the spacecraft was 30,758 miles (49,500 kilometers) from the moon.

Launched aboard the same rocket on Sept. 10, 2011, GRAIL-A's mirror twin, GRAIL-B, is also closing the gap between itself and the moon. GRAIL-B is scheduled to perform its lunar orbit insertion burn on New Year's Day (Jan. 1) at 2:05 p.m. PST (5:05 p.m. EST).

As they close in on the moon, both orbiters move toward the moon from the south, flying nearly directly over the lunar south pole. The lunar orbit insertion burn for GRAIL-A will take approximately 40 minutes to complete and change the spacecraft's velocity by about 427 mph (687 kph). GRAIL-B's insertion burn - occurring 25 hours later -- will last about 39 minutes and is expected to change its velocity by 430 mph (692 kph).

The insertion maneuvers will place each orbiter into a near-polar, with an of 11.5 hours. Over the following weeks, the GRAIL team will execute a series of burns with each spacecraft to reduce their period down to just under two hours. At the start of the science phase in March 2012, the two GRAILs will be in a near-polar, near-circular orbit with an altitude of about 34 miles (55 kilometers).

During the science phase, the moon will rotate three times underneath the GRAIL orbit. The collection of gravity data over one complete rotation (27.3 days) is referred to as a Mapping Cycle. When science collection begins, the spacecraft will transmit precisely defining the distance between them as they orbit the moon in formation. Regional gravitational differences on the moon are expected to expand and contract that distance. GRAIL scientists will use these to define the moon's . The data will allow mission scientists to understand what goes on below the surface of our natural satellite. This information will help us learn more about how the moon, Earth and other terrestrial planets formed.

Explore further: NASA twin spacecraft GRAIL on final approach for moon orbit

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6 comments

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Raygunner
5 / 5 (3) Dec 31, 2011
I hope they find TMA-1 (Tycho Magnetic Anomaly-1) this trip... missed it last time.
Cave_Man
1 / 5 (5) Dec 31, 2011
Doesn't it seem a little misconceived that our whole concept of gravity is based on our geocentric view of accelerating weight?

If Einstein had done his famous experiments on jupiter or on pluto would we be living in a different type of civilization today?

I hope they interpret the data correctly, where they see errors I would assume there might be new science.
aroc91
5 / 5 (3) Dec 31, 2011
Doesn't it seem a little misconceived that our whole concept of gravity is based on our geocentric view of accelerating weight?


What's geocentric about it? Gravity depends on mass; mass is everywhere, so what would be different about discovering gravity on any other planet? Acceleration of mass isn't exclusive to Earth.
Cave_Man
1 / 5 (4) Dec 31, 2011
Yes but there is no way of knowing (unless you do it) how mass accelerates at different gravity. Which is why I proposed that the outcome may have been different if the experiments were done in a high gravity or low gravity environment.

I understand that we have a gravitational constant which is derived from matter falling in a vacuum. Well is that vacuum at 1 earth gravity or 100X earth gravity and would that make a difference? Even the tiniest difference could change the computer models of the large scale universe.
Richardmcsquared
5 / 5 (3) Dec 31, 2011
Relativity theory explains how mass affects gravity and time .I don't see a problem in the amounts of either
antialias_physorg
5 / 5 (2) Dec 31, 2011
I hope they find TMA-1 (Tycho Magnetic Anomaly-1) this trip... missed it last time.

It's a gravity mission. The GRAIL probes don't carry any instruments for detecting magnetic fields.

If Einstein had done his famous experiments on jupiter or on pluto would we be living in a different type of civilization today?

No. the outcome would have been the same.
(Or: Yes. Since if he had dome it on Jupiter we would likely be very different beings - i.e. beings that could survive on Jupiter)

Apart from that: Einstein didn't do any experiments concerning gravity (famous or otherwise). He was a theoretical physicist.
Others did the experiments.

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