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Gravity Recovery And Interior Laboratory-B (GRAIL)



The Gravity Recovery And Interior Laboratory (GRAIL) mission is a dual spacecraft effort designed to determine the structure of the lunar interior and to advance understanding of the thermal evolution of the Moon. The primary science objectives are to: 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; and place limits on the size of the possible inner core. The GRAIL mission was selected through the NASA Discovery Program.

Spacecraft and Subsystems

GRAIL comprises twin spacecraft built on the Lockheed Martin Experimental Small Satellite (XSS-11) bus with a science payload derived from the GRACE terrestrial gravity mission. The bus is a rectangular prism with a composite structure and a dry mass of 132.6 kg, fully fueled mass is 202.4 kg. Two solar panels extend from the upper platform which also holds a 22 N thruster for propulsion. Fine control is provided by a warm gas system and 3 reaction wheels. A sun tracker, star tracker, and IMU are used for guidance and attitude knowledge. Power from the solar panels is stored in a lithium-ion battery. Communication with Earth is via S-band. A Ka-band payload, the Lunar Gravity Ranging System (LGRS) will be used to allow high precision range-rate measurements between the two spacecraft. The Ka antenna is mounted in a thermal enclosure and in line with the two-spacecraft center-of-mass. The spacecraft will also each be equipped with up to 5 MoonKam cameras which will be used for education and public outreach.

Mission Profile

Both GRAIL spacecraft (GRAIL-A and GRAIL-B) were launched from Cape Canaveral Air Force Station on a single Delta II 2920-10 on 10 September 2011 at 13:08:52 UT. They were launched into 3.5 month low energy trans-lunar cruises via the Sun-Earth Lagrange point 1 for checkout and outgassing. The spacecraft flew under the south pole of the Moon and executed separate 60-minute lunar orbit insertion maneuvers roughly 25 hours apart, GRAIL-A on 31 December 2011 and GRAIL-B on 01 January 2012. They went into eight-hour elliptical polar orbits, followed by four manuevers to lower them into tandem 50 km, 113 minute near-circular lunar polar orbits separated by 175-225 km. From these orbits GRAIL entered a 90 day Science Phase to perform gravity mapping of the Moon. This phase was divided into three 27.3 day cycles. Data downlink occurred in two DSN tracking passes. The mission ended in a decommissioning phase and lunar surface impacts on 17 December 2012. GRAIL-A impacted at 75.6088 N, 26.5940 W and GRAIL-B at 75.6508 N, 26.8341 W. The estimated cost of the mission is $375 million.

Alternate Names

  • 37802
  • Flow
  • urn:nasa:pds:context:instrument_host:spacecraft.grail-b

Facts in Brief

Launch Date: 2011-09-10
Launch Vehicle: Delta II
Launch Site: Cape Canaveral, United States
Mass: 132.6 kg

Funding Agency

  • National Aeronautics and Space Administration (United States)


  • Planetary Science

Additional Information

Questions and comments about this spacecraft can be directed to: Dr. David R. Williams



NameRoleOriginal AffiliationE-mail
Mr. David H. LehmanProject ManagerNASA Jet Propulsion
Dr. Michael M. WatkinsProgram ScientistNASA Jet Propulsion
Dr. David E. SmithDeputy Mission Principal InvestigatorNASA Goddard Space Flight
Dr. Maria T. ZuberMission Principal InvestigatorMassachusetts Institute of

Selected References

  • Fahnestock, E. G., et al., Spacecraft Thermal And Optical Modeling Impacts on Estimation Of The GRAIL Lunar Gravity Field, 2012 AIAA/AAS Astrodynamics Specialist Conference, AIAA 2012-4428, doi:10.2514/6.2012-4428, Aug. 2012.
  • Hoffman, T. L, GRAIL: Gravity Mapping the Moon, 2009 IEEE Aerospace Conference, pp. 1-8, doi:10.1109/AERO.2009.4839327, Mar. 2009.
  • Lehman, D. H., et al., The Gravity Recovery and Interior Laboratory mission, 2013 IEEE Aerospace Conference, pp. 1-11, doi:10.1109/AERO.2013.6496866, Mar. 2013.
  • Zuber, M. T., et al., Gravity Recovery and Interior Laboratory (GRAIL): Mapping the Lunar Interior from Crust to Core, Space Sci. Rev., 178, No. 1, 3-24, doi:10.1007/s11214-012-9952-7, Sept. 2013.
GRAIL Diagram

Diagram of the GRAIL spacecraft

Press Releases

New NASA Mission to Reveal Moon's Internal Structure and Evolution (11 December 2007)
NASA Announces Discovery program selections (30 October 2006)

Related Information/Data at NSSDCA

Lunar Exploration Timeline
Moon Home Page
Moon Fact Sheet

Other Sources of GRAIL Information/Data

GRAIL Home Page (Massachusetts Institute of Technology)

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