WASHINGTON – A pair of lunar probes that are running out of fuel will be crashed into the northern part of the moon on Tuesday (Dec. 18), NASA said this week.
The Gravity Recovery and Interior Laboratory (GRAIL) lunar probes have been flying in formation since August mapping the moon’s gravity fields. Mission planners said the moon’s uneven gravity fields, thought to be caused by mass concentrations, or “masscons” in the lunar crust, quickly depleted GRAIL’s fuel supply.
Skimming over the lunar surface at altitudes as low as 14 miles (23 km), the twin probes created the highest resolution gravity field map of any celestial body, the space agency claimed.
The washing machine-sized probes, which are flying in a polar orbit, are expected to hit northern lunar surface at 3,760 mph (1.7 km/sec.). The crash landing will occur in the lunar dark, so no imagery will be available, NASA said.
Mission managers said they selected a northern mountainous site near the lip of an old crater buried by ejecta from the formation of other craters. The trajectory is intended to avoid historic Apollo and Russian landing site near the moon’s equator. “Nobody I know around here has ever flown into a moon mountain before,” said David Lehman, GRAIL project manager at NASA's Jet Propulsion Laboratory.
NASA said it’s unclear how much fuel remains aboard the probes. Hence, a “depletion burn” on Friday (Dec. 14) will gradually lower their orbits to skim the lunar surface until the spacecraft collide with the northern mountain.