NASA twin spacecraft GRAIL on final approach for moon orbit

December 28, 2011
The twin GRAIL spacecraft are prepared for launch. Image credit: NASA/JPL-Caltech/LMSS

( -- NASA's twin spacecraft to study the moon from crust to core are nearing their New Year's Eve and New Year's Day main-engine burns to place the duo in lunar orbit.

Named Gravity Recovery And Interior Laboratory (GRAIL), the 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.

"Our team may not get to partake in a traditional New Year's celebration, but I expect seeing our two spacecraft safely in should give us all the excitement and feeling of euphoria anyone in this line of work would ever need," said David Lehman, project manager for GRAIL at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif.

Moon. Image credit: NASA

The distance from Earth to the is approximately 250,000 miles (402,336 kilometers). NASA's Apollo crews took about three days to travel to the moon. Launched from Sept. 10, 2011, the GRAIL spacecraft are taking about 30 times that long and covering more than 2.5 million miles (4 million kilometers) to get there.

This low-energy, long-duration trajectory has given mission planners and controllers more time to assess the spacecraft's health. The path also allowed a vital component of the spacecraft's single , the Ultra Stable Oscillator, to be continuously powered for several months. This will allow it to reach a stable operating temperature long before it begins making science measurements in lunar orbit.

"This mission will rewrite the textbooks on the evolution of the moon," said Maria Zuber, GRAIL principal investigator from the Massachusetts Institute of Technology (MIT) in Cambridge. "Our two spacecraft are operating so well during their journey that we have performed a full test of our science instrument and confirmed the performance required to meet our science objectives."

As of Dec. 28, GRAIL-A is 65,860 miles (106,000 kilometers) from the moon and closing at a speed of 745 mph (1,200 kph). GRAIL-B is 79,540 miles (128,000 kilometers) from the moon and closing at a speed of 763 mph (1,228 kph).

Artist's concept of lunar interior and exterior. Image credit: NASA

During their final approaches to the moon, both orbiters move toward it from the south, flying nearly over the lunar south pole. The lunar orbit insertion burn for GRAIL-A will take approximately 40 minutes and change the spacecraft's velocity by about 427 mph (688 kph). GRAIL-B's insertion burn 25 hours later will last about 39 minutes and is expected to change the probe's velocity by 430 mph (691 kph).

The insertion maneuvers will place each orbiter into a near-polar, elliptical orbit with a period of 11.5 hours. Over the following weeks, the GRAIL team will execute a series of burns with each spacecraft to reduce their orbital period from 11.5 hours 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).

When science collection begins, 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 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.

Explore further: NASA's moon twins going their own way

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4.7 / 5 (13) Dec 28, 2011
Oliver Manuel, regardless of the veracity of your explanation of solar processes, why must you always hijack sun-related article comments with your research? If all researchers saw article comments as an opportunity to advertise their work, wouldn't we have a mess? Is this really the best way to gain acceptance of a theory?
1.1 / 5 (14) Dec 28, 2011
Oliver Manuel, regardless of the veracity of your explanation of solar processes, . . . Is this really the best way to gain acceptance of a theory?

Thanks for your comment. You are right.

Although impatient, I also know that the SSM model of the Sun was too entrenched in the scientific community to be dislodged by observations until selected as the cornerstone of the AGW model of Earth's climate.

So the universe seems to be unfolding exactly as it should and today all is well.

Again, thanks for your comment.

Best wishes for the New Year!
not rated yet Dec 28, 2011
Electric Sun Oliver. Why do you not address the flaws in your theory? Let's start with 1987A. Electric theory adds up. Your theory falls short. How would the "pearls" exist if you were right?
5 / 5 (2) Dec 29, 2011
I think this technology can not be applied to the sun. These probes need to fly just 55km from the surface to have enough precision, and they also benefit from the small moon radius. Gravity decay with they square of the distance, similar probes could not fly close enough to the sun as required for a gravity map with decent resolution, not to mention the added noise produced by solar wind and coronal mass movements. The sun is a very dynamic system, too much for this technology
1 / 5 (9) Dec 29, 2011
1. I think this technology can not be applied to the Sun . . . .

2. The Sun is a very dynamic system, too much for this technology

1. No measurement is more important to the thousands of people who are discouraged, unemployed, surviving on food stamps and/or homeless because industries were closed down to save Earth's climate from the "danger" of CO2 in the atmosphere - the insulating layer of gases that actually protect us from sudden changes in Earth's heat source - the Sun [A,B].

A. Journal of Fusion Energy 21, 193-198 (2002)

B. Energy and Environment 20, 131-144 (2009)

2. I agree, the Sun is dynamic! In fact the Sun itself is evolving and it has kept Earth's climate and life on Earth in a state of perpetual evolution.

C. J Modern Physics 2, 587-594 (2011)

May 2012 Bring World Peace!
Oliver K. Manuel

5 / 5 (1) Dec 30, 2011
I thought you addressed all serious inquiries...
1.6 / 5 (65) Dec 30, 2011
MODERATORS: Why is omatumr exempt from the following?
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1.3 / 5 (13) Jan 03, 2012
FH funny you talk about Guidelines, yet you have how many sockpuppets manipulating rankings? Must be your progressive bullying streak showing.

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