GRAIL (Ebb and Flow)
GRAIL — twin NASA spacecraft, Ebb and Flow, that flew one behind the other in low polar orbits around the Moon in 2012, measuring the distance between them so precisely that they mapped the Moon's gravity in detail. Their map showed how the mass concentrations under the lunar basins were made by large ancient impacts. On 17 December 2012 both were flown into the Moon near its north pole. (Shown at Ebb's position.)
Key facts
Mission & specifications
Mission
- Operator
- NASA / JPL / MIT
- Launched
- September 10, 2011
- Status
- Completed
Trajectory
- Speed rel. the Moon
- 1.68 km/s
- Computed from the cached state vector, relative to the Moon
- Distance from the Sun
- 1 AU
- Computed from the cached position
- Distance from Earth
- 0.334 AU
- Computed from cached positions
- Distance from Venus
- 0.366 AU
- Computed from cached positions
Mission
GRAIL, the Gravity Recovery and Interior Laboratory, was a pair of identical NASA spacecraft launched together on a Delta II on 10 September 2011. They took three and a half months to reach the Moon on a slow, low-energy path by way of the Sun–Earth L1 point, and entered lunar orbit about a day apart: GRAIL-A on 31 December 2011 and GRAIL-B on 1 January 2012. They were later renamed Ebb and Flow. In near-circular polar orbits about 50 km up, one following the other by 175 to 225 km, they measured the distance between them with a precise radio link. Every lump and hollow in the Moon's gravity pulled the leader and the follower slightly differently, and from those changes the mission mapped the Moon's gravity in detail. The map confirmed that the mascons — mass concentrations beneath the great lunar basins — were made when large asteroids or comets struck the young Moon. At the end of the mission both were flown into the Moon near its north pole on 17 December 2012. (Its position here is JPL Horizons' for Ebb.)
- 2011GRAIL launches toward the Moon on a Delta II rocketLaunch
Both spacecraft on one rocket, taking a slow route by way of the Sun–Earth L1 point.
- 2011GRAIL-A in lunar orbitArrival
After a 60-minute engine burn.
- 2012GRAIL-B in lunar orbitArrival
About 25 hours after its twin.
- 2012Into the Moon near the north poleMission end
Both spacecraft, at the end of the mission.
Images
Images from open archives · credit shown per image