2 space probes set to crash on moon's dark side
Ebb and Flow, two space probes the size of washing machines that have been orbiting the moon, will perform an orchestrated death plunge Monday, crashing into the body's dark side.
The New York Times
NASA's latest moon mission will end Monday — not with a whimper, but a splat.
Two splats, actually.
Ebb and Flow, two space probes the size of washing machines that have been orbiting the moon and measuring its gravity field, will perform an orchestrated death plunge Monday, crashing into the body's dark side.
The exercise will not be for the advance of science, but rather something of a garbage-disposal operation, to make sure the probes — which are running out of fuel — do not come to rest in a historically significant place, like Neil Armstrong's footprints.
The moon has been affronted this way many times, especially during the space race of the 1960s, but NASA is trying to dispose of its litter more carefully.
This time, the first impact will come 40 seconds past 2:38 p.m. when Ebb slams into a mountain near the moon's north pole at 3,760 mph. The second, from Ebb's twin, Flow, will come 20 seconds later.
Unfortunately, since the action will happen on the dark side of the moon, there will be nothing for earthlings to see.
"We're not expecting a flash that is visible from Earth," Maria Zuber, the mission's primary investigator, said Thursday during a telephone news conference.
That is by design as NASA wraps up its Gravity Recovery and Interior Laboratory mission, or Grail, for short.
To map the gravity, the two spacecraft are in an orbit passing over the moon's north and south poles. They pass over all parts of the lunar surface as the moon revolves below.
If the probes' fuel ran out and their orbits decayed, they could crash anywhere on the moon, and there would be a slim chance — 8 in 1 million — that one could obliterate those famous footprints or another historic site.
With the spacecraft guided into a mountain, the chances are zero.
Even in their demise, however, Ebb and Flow may be able to aid the cause of science. Another of NASA's spacecraft, the Lunar Reconnaissance Orbiter, will pass over the crash sites, and scientists hope they will be able to tell something about the mountain — which is a remnant of a crater rim — from the gouges created by Ebb and Flow.
Asked what the crash might look like to someone standing there, David Lehman, the project manager for Grail, said, "It'll be like a washing machine landing on top of you, and it'll be a very bad day for you."
Launched in September 2011, the two spacecraft slipped into lunar orbit at the beginning of this year.
Because of Ebb and Flow, scientists now have more precise measurements of the moon's gravity than of the Earth or any other planet.
Data from the mission has shown that the moon's crust is thinner than thought and that it was pulverized by impacts during the early history of the solar system.
Information in this article, originally published Dec. 13, 2012, was corrected Dec. 14, 2012. previous version of this story misstated part of the name of a NASA mission. It is the Gravity Recovery and Interior Laboratory, not the Grail Recovery and Interior Laboratory.