GRAIL Spacecraft

GRAIL (Gravity Recovery And Interior Laboratory) will fly twin spacecraft in tandem around the Moon to precisely measure and map variations in the Moon's gravitational field. GRAIL is a part of NASA's Discovery Program. It was launched on September 10, 2011.

NEWS UPDATE:   NASA's GRAIL Spacecraft Have Been Re-named.

More than 11,000 students took part in the contest to rename the twin craft which aim to map the Moon's surface, determine its gravity field and reveal the contents of its inner core.

The winner was a fourth grade class of nine and 10-year-olds at Emily Dickinson School in Bozeman, Montana.

Other such contests have been held in the past to name NASA spacecraft, such as the Mars rover Curiosity, coined in 2009 by a 12-year-old essay winner in Kansas named Clara Ma.

Mission Overview

GRAIL’s primary science objectives will be to determine the structure of the lunar interior, from crust to core and to advance understanding of the thermal evolution of the Moon. As a secondary objective, GRAIL will extend knowledge gained from the Moon to the other terrestrial planets.

Science investigations will include:

  •  Map the structure of the crust and lithosphere
  •  Understand the Moon’s asymmetric thermal evolution
  •  Determine the subsurface structure of impact basins and the origin of mascons
  •  Ascertain the temporal evolution of crustal brecciation and magmatism
  •  Constrain deep interior structure from tides
  •  Place limits on the size of a possible solid inner core

GRAIL's short mission duration (270-days) includes a 90-day gravity mapping Science Phase (March 2012 - May 2012).

Spacecraft

GRAIL (Gravity Recovery And Interior Laboratory) mission is using two identical spacecraft orbiting the moon in a low, polar orbit. The spacecraft are based on the flight-proven XSS-11 technology demonstration satellite developed for the Air Force Research Laboratory. A single-string architecture meets this short mission's reliability requirements.

Each spacecraft bus is a rectangular composite structure. The science payload ranging antennas are in thermal enclosures and are mounted so that they are nominally on the line between the two spacecraft’s centre of masses. The other components of the payload instrument are on a single interior bus panel for easy integration and test.

There are 2 non-articulated solar arrays of XSS-11 heritage that are deployed just after separation from the Launch Vehicle. Warm gas systems identical to XSS-11 provide V for manoeuvres and unloading of the 3 reaction wheels. Additional attitude sensing components include an IMU, sun sensor and star tracker.

The C&DH, power management and lithium ion battery are also XSS-11 heritage. The S-band telecommunications system for communication with the DSN uses heritage components (Themis and Genesis).

The spacecraft was built, the science payload integrated and the systems tested at Lockheed Martin's Denver facility. Lockheed Martin will use two system-level spacecraft test labs (STL) and one software simulator (SoftSim) testbed with unlimited copies that enable integration and verification of all hardware and software throughout the Assembly Test and Launch Operations (ATLO) cycle.

Specs:

Mass:             132.6 kg (292 lb)
Power:         (Solar array / Li-ion battery)
Cost:              $496 million USA dollars
Mission Life: 3 months

Mission Design

The GRAIL spacecraft was launched side-by-side on a single Delta II vehicle during a 26-day launch period that opened on September 8, 2011. The mission was designed to avoid the December 10th, 2011 and June 4th 2012 lunar eclipses which interfere with the mission. The Goldstone complex will implement initial acquisition including solar array deployment.

The trans-lunar cruise phase consists of a 3.5-month low-energy transfer via the Sun-Earth Lagrange point 1 (EL1). Compared to a direct trajectory, this low-energy transfer was chosen to reduce the spacecraft fuel requirements (by ~130 m/s), to allow more time for spacecraft check-out and out-gassing and to increase the number of days available in the launch period each month.

Both spacecraft approach the Moon under the South Pole where they execute a 60-minute Lunar Orbit Insertion (LOI) manoeuvre to put them in an elliptical orbit with a period of just over 8 hours. The LOI for each of the spacecraft are separated by one day. Each LOI is simultaneously visible from the Goldstone and Canberra DSN complexes.

A series of four manoeuvres are then performed to reduce the orbits to near circular with a mean 50-km altitude and 113-minute period. Further manoeuvres position the spacecraft to the desired initial separation distance, which then drifts between 175 km to 225 km.

The 90-day Science Phase is divided into three 27.3-day nadir-pointed mapping cycles. Two daily 8-hour DSN tracking passes acquire the science and "E/PO MoonKam" data. Following the Science Phase (or extended mission phase), a 5-day decommissioning period is planned, after which the spacecraft will impact the lunar surface in approximately 40 days.

History: Mission to Moon

NASA's GRAIL spacecraft launched to the moon aboard a United Launch Alliance Delta II rocket on September 10, 2011 from Space Launch Complex 17B Cape Canaveral Air Force Station, Florida, USA. GRAIL mission was competitively selected through the Discovery Program.

Just over a day after the first of two NASA spacecraft went into orbit around the Moon, its twin successfully entered lunar orbit. The Gravity Recovery And Interior Laboratory (GRAIL) B spacecraft inserted itself into an elliptical lunar orbit at 5:43 pm EST (2143 GMT) Sunday after a 37-minute engine burn. GRAIL-B entered orbit just over 24 hours after GRAIL-A entered orbit around the Moon.

GRAIL-A spacecraft successfully fired its main engine orbited the moon on 31st December 2011.
GRAIL-B spacecraft entered orbit just over 24 hours after GRAIL-A on Sunday 1st January 2012.

NASA's Gravity Recovery And Interior Laboratory (GRAIL) twin spacecraft will study the moon from crust to core.

A student contest that began in October 2011 also will choose new names for the spacecraft. The new names are scheduled to be announced in January 2012. Ride and Maria Zuber, the mission's principal investigator at the Massachusetts Institute of Technology in Cambridge, chaired the final round of judging.

Did you know:  NASA GRAIL Satellites were launched 112 days ago. (as of 31 December 2011).

Key Mission Partners

Caltech’s Jet Propulsion Laboratory (JPL) will manage GRAIL’s mission operations from its Pasadena facility and provide navigation and mission support using heritage operations systems (Multi-mission Ground System Services and the Deep Space Network). GRAIL’s industrial partner, Lockheed Martin Space Systems will conduct spacecraft flight operations from the Denver facility that also supports Mars Odyssey, the Mars Reconnaissance Orbiter, and the Phoenix mission.

Maria Zuber of the Massachusetts Institute of Technology, Cambridge, Massachusetts is GRAIL's principal investigator. NASA's Jet Propulsion Laboratory, Pasadena, California manages the project.

The mission's team of expert scientists and engineers also includes former NASA astronaut Sally Ride, who leads the mission's public outreach efforts.

Did you know?

* Unlike the Apollo program which required 3 days to reach the moon, GRAIL makes use of a 3 to 4 month low energy trans-lunar cruise via the Sun-Earth Lagrange point 1 to reduce fuel requirements, protect instruments and reduce the velocity of the spacecraft at lunar arrival time to help achieve the extremely low orbits with separation between the spacecraft.

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 GRAIL Spacecraft (Mission to Moon) Links:

• NASA - GRAIL:

• GRAIL | Gravity Recovery and Interior Laboratory: By Mit.edu

• GRAIL MoonKAM: MoonKAM(Moon Knowledge Acquired by Middle school students) is GRAIL's signature education and public outreach program.