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December 23rd: GRAIL Spacecraft Twins: New Year's Arrival at the Moon


Date: December 23, 2011

Title: GRAIL Spacecraft Twins: New Year’s Arrival at the Moon

Podcaster: Jane Platt

Organization: JPL

Links: http://www.jpl.nasa.gov

Description: The two spacecraft of NASA’s Gravity Recovery And Interior Laboratory (GRAIL) mission will arrive in orbit around the moon just in time for the New Year. The mission will create the most accurate gravitational map of the moon to date, improving our knowledge of the near-side gravity by 100 times and of far-side gravity by 1,000 times. The high-resolution gravitational field, especially when combined with a comparable-resolution topographical field, will enable scientists to deduce the moon’s interior structure and composition. This will help them piece together the history of how the moon, Earth and terrestrial planets formed.

Bio: David Lehman of JPL is the GRAIL Project Manager.

Jane Platt is News Chief of the Media Relations Office at NASA’s Jet Propulsion Laboratory in Pasadena, California. During her prior career in broadcast journalism, she was the West Coast correspondent for ABC Radio Network, and worked as a reporter for other networks and stations. She covered a variety of stories, including earthquakes, fires, high-profile trials, Space Shuttle landings, the Voyager Neptune flyby and the Academy Awards. Jane draws on this broadcast news background in her current job, where she is part of a team that uses traditional and social media to
communicate information about JPL missions and science discoveries.

Sponsors: This episode of “365 Days of Astronomy” is brought to you by Cosmic Vibrations. Bringing you experimental ambient music featuring sounds from the cosmos. Visit www.reverbnation.com/kiddscosmicvibrations.

This episode of “365 Days of Astronomy” has also been brought to you by Matthew Goeringer.


Open with music….

Narrator: The moon is expecting twins—for the New Year.

I’m Jane Platt with NASA’s Jet Propulsion Laboratory in Pasadena, California.

The New Year will bring the arrival of twins—twin spacecraft, that is—at the moon.

The two GRAIL spacecraft, launched September 5th from Cape Canaveral, Florida, are scheduled to begin orbiting the moon—one on New Year’s Eve, the other New Year’s Day. David Lehman of JPL is the GRAIL Project Manager.

Lehman: OK, On New Years’ Eve, the GRAIL-A spacecraft is going to be sent into orbit around the moon. Alright, we’re going to go through the south pole of the moon and do about a 38-minute burn, a 38-minute maneuver to slow the spacecraft down enough so it’s going to go into orbit around the moon. And the orbit’s about a period of 11-1/2 hours. It takes 11-1/2 hours to go around the moon.

Narrator: It’s a tricky task, but Lehman says the team is up for the challenge….thanks to some very careful preparations.

Lehman: To capture the spacecraft into orbit takes a lot of planning and a lot of practice and a lot of maneuvers before that happens. Like just recently, the GRAIL-A spacecraft, we did a maneuver to change the speed by .05 miles per hour. That’s how small we had to make this change in order to affect going into orbit precisely around the moon. So it does take a lot of planning, a lot of testing and then a lot of small maneuvers in order to get ready to set up to get into this big maneuver when we go into orbit around the moon.

Narrator: So GRAIL-A enters moon orbit on New Years’ Eve, and then the next day, the team does it again—with GRAIL-B.

Lehman: The purpose of the GRAIL mission is to obtain gravity data on the moon. And with that data, the scientists are able to determine the structure of the lunar interior, from crust to core.

Narrator: This info will help scientists figure out how the planets in our solar system were formed.

Lehman: Five billion years ago, the Earth was formed, and all the other terrestrial planets were formed, and the moon was formed. But since that time, the Earth evolved, there’s earthquakes, there’s erosion, there’s lots of rain. And so when we study the earth now, we really don’t have good feeling for what happened because it changed so much.

Narrator: So they hope to fill in pieces of the puzzle by studying how the moon was formed, using not one, but two spacecraft.

Lehman: The reason we need two spacecraft is we use the spacecraft to measure the distance between each other. And with that information, we’re able to determine the gravity. Because we’re gathering this information on the distance between the two and how they change over time very precisely. And with that information we can understand the gravity. For example, as the spacecraft flies over a big moon mountain, GRAIL-A will accelerate towards that mountain. And then a few minutes later, GRAIL-A passes that mountain, GRAIL-B will get close to that mountain, and it will accelerate towards that mountain. So that’s how the distance between the two is changing, and with that information, you can infer the gravity.

Narrator: And then in February, the team will start putting the two spacecraft into formation, which is a technique currently being used by the Grace mission to measure Earth’s gravity. With GRAIL—it’s the moon.

Lehman: So we have to start formation flying. And we have to align the spacecraft very precisely together. That to me is the challenging part is setting up the maneuvers so that the spacecrafts are very precisely aligned from the orbit’s standpoint.

Narrator: More information on the GRAIL mission is online at www.nasa.gov/grail . Thanks for joining us for this podcast from NASA’s Jet Propulsion Laboratory.

Music close

End of podcast:

365 Days of Astronomy
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