Twin Lunar Orbiters Will Move to Lower Altitudes

Ebb and Flow, the two spacecraft making up the NASA Gravity Recovery and Interior Laboratory (GRAIL) mission, have begun their extended science phase in lunar orbit. This milestone was reached on August 30, and now the vehicles are getting ready to lower their altitude.

Lasting until December 3, the extended mission will enable researchers to gain a deeper understanding of the lunar interior. The two probes analyze the distribution of mass under the surface by analyzing how the distance between them varies.

Since more mass equals more gravity, passing a denser region causes a more intense tug on the leading spacecraft, which therefore moves ever so slightly faster than the trailing one. This distance constantly changes, and experts use it to create a 3D map of how mass is distributed within the satellite.

By flying lower, the GRAIL spacecraft will be able to create even more detailed maps of the lunar underground, Space reports.