Twin NASA spacecraft deliberately crash into moon

Dec 17, 2012 by Alicia Chang
An artist’s depiction of the twin spacecraft (Ebb and Flow) that comprise NASA’s Gravity Recovery And Interior Laboratory (GRAIL) mission. Credit: NASA/JPL-Caltech/MIT

A pair of NASA spacecraft tumbled out of orbit around the moon and crashed back-to-back into the surface on Monday, ending a mission that peered into the lunar interior.

Engineers commanded the twin spacecraft, Ebb and Flow, to fire their engines and burn their remaining fuel. Ebb plunged first, slamming into a mountain near the moon's north pole. Its twin, Flow, followed about a half minute later and aimed for the same target.

By design, the final resting place was far away from the Apollo landing sites and other historical spots on the moon.

After the double impacts, mission chief scientist Maria Zuber of the Massachusetts Institute of Technology said the spot has been named after team member Sally Ride, the first American woman in space, who died earlier this year.

"It's really cool to know that when you look up now at the moon there's this little corner of the moon that's named after Sally," said Ride's sister, Rev. Bear Ride, adding that she hoped schoolchildren will be inspired.

Since the crash site was in darkness, the final act was not visible from Earth. The Lunar Reconnaissance Orbiter circling the moon will pass over the mountain and attempt to photograph the skid marks left by the washing machine sized-spacecraft as they hit the surface at 3,800 mph.

After rocketing off the launch pad in September 2011, Ebb and Flow took a roundabout journey to the moon, arriving over the New Year's holiday on a gravity-mapping mission.

More than 100 missions have been flung to Earth's nearest neighbor since the dawn of the Space Age including NASA's six Apollo moon landings that put 12 astronauts on the surface.

The demise of Ebb and Flow comes on the same month as the 40th launch anniversary of Apollo 17, the last manned mission to the moon.

Ebb and Flow focused exclusively on measuring the moon's lumpy gravity field in a bid to learn more about its interior and early history. After flying in formation for months, they produced the most detailed gravity maps of any body in the solar system.

This graphic provide by NASA shows the projected paths into the moon by spacecraft Ebb and Flow. The twin craft on Monday, Dec. 17, 2012, is expected to slam into a lunar mountain near the north pole after nearly a year in orbit. (AP Photo/NASA)

Secrets long held by the moon are spilling out. Ebb and Flow discovered that the lunar crust is much thinner than scientists had imagined. And it was severely battered by asteroids and comets in the early years of the solar system—more than previously realized.

Data so far also appeared to quash the theory that Earth once had two moons that collided and melded into the one we see today.

Besides a scientific return, the mission allowed students to take their own pictures of craters and other lunar features as part of collaboration with a science education company founded by Ride, who died in July of pancreatic cancer at age 61.

Scientists expect to sift through data from the $487 million mission for years.

Obtaining precise gravity calculations required the twins to circle low over the moon, which consumes a lot of fuel. During the primary mission, they flew about 35 miles above the lunar surface. After getting bonus data-collecting time, they lowered their altitude to 14 miles (22 kilometers) above the surface.

With their fuel tanks almost on empty, NASA devised a controlled crash to avoid contacting any of the treasured sites on the moon. Mission control at the NASA Jet Propulsion Laboratory applauded when controllers lost signal from the spacecraft.

The last time the space agency intentionally fired manmade objects at the moon was in 2009, but it was for the sake of science. The crash was a public relations dud—spectators barely saw a faint flash—but the experiment proved that the moon contained water.

Explore further: SDO captures images of two mid-level flares

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Eugene
5 / 5 (2) Dec 17, 2012
I think the crash was not visible because it was on the lunar farside, not because it was on the dark side. Remember the moon orbits with the same face toward the earth because it is tidally locked. Both near and far sides experience approx. 28 day night/day cycles. A crash on the farside would not be visible in day or night.
FMM
3 / 5 (2) Dec 18, 2012
Good for Eugene. The press has gotten in the bad habit about talking about the "dark" side of the moon. They need to put something in their style manuals to the effect that the far side is what we can't see on Earth while the dark side is the side that happens to not be illuminated by the sun at any particular time.
GSwift7
1 / 5 (2) Dec 18, 2012
They only said that the mountain was currently dark. Nobody mentioned anything about either the dark side or the far side. They did not say this mountain is permanently dark either. I assume that since they stated that the LRO will be taking pictures of the crash site, it will be sunlit at that time. LRO can't take pictures in the dark. This location could also have just been in the shadow of another mountain at the time of the crash. Things at the poles cast very long shadows.
Eugene
not rated yet Dec 24, 2012
I would think (I have not calculated the energy release) that the energy released by the impact of two 132kg satellites moving at orbital speeds would create a bright flash that would be detectable by instruments on the earth if the impact sight was on the near-side. The LRO could easily have detected this impact with the LROC (camera)or DLRE (radiometer). Waiting for the orbits of the various spacecraft to sychronize so the LRO could be overhead when the impact happened probably would have exhausted the fuel on the GRAIL spacecraft and they would not have been able to control where the impact occured. That is assuming that the orbital inclination is close enough.

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