The Gravity Recovery and Interior Laboratory (GRAIL) was an American lunar science mission in NASA's Discovery Program which used high-quality gravitational field mapping of the Moon to determine its interior structure. The two small spacecraft, GRAIL A (Ebb) and GRAIL B (Flow), were launched on 10 September 2011 aboard a single launch vehicle: the most-powerful configuration of a Delta II, the 7920H-10. GRAIL A separated from the rocket about nine minutes after launch, GRAIL B followed about eight minutes later. They arrived at their orbits around the Moon 25 hours apart. The first probe entered orbit on 31 December 2011 and the second followed on 1 January 2012. The two spacecraft impacted the lunar surface on December 17, 2012.
Key Facts
| Subject | GRAIL |
| Category | NASA orbiter mission to the Moon (2011–2012) |
| Reading time | 1 min · Advanced |
| Key date | 2011 |
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