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GRAIL Mission to Earth's Moon

Mission Type: Orbiter
NASA Center: Goddard Institute for Space Studies, Jet Propulsion Laboratory
Spacecraft Mass: Dry Mass 132.6 kg
Project Manager: Dave Lehman, NASA's Jet Propulsion Laboratory (JPL)
Principal Scientists: Dave Smith, Deputy Principal Investigator (Goddard Space Flight Center (GSFC)
Principal Investigator: Dr. Maria Zuber, Principal Investigator, Massachusetts Institute of Technology (MIT)
Total Cost: $375 million
NASA's GRAIL Homepage:

MIT's GRAIL Homepage,

The Gravity Recovery And Interior Laboratory, or GRAIL, is flying twin spacecraft in tandem around the Moon to precisely measure and map variations in the Moon's gravitational field. This detailed information will reveal differences in density of the Moon's crust and mantle and will help answer fundamental questions about the Moon's internal structure, thermal evolution, and history of collisions with asteroids.

The new knowledge about lunar gravity will significantly assist the planning of any future manned or unmanned missions to land on the Moon. The data can be used to help target desirable landing sites and to program the descent to the surface to avoid a crash landing.

Knowledge acquired about the Moon from GRAIL will be extended to understand the broader evolutionary histories of the rocky planets in the inner solar system: Earth, Venus, Mars, and Mercury. The Moon is key to understanding how the terrestrial planets evolved because it is the most accessible planetary body that preserves a surface record spanning most of solar system history.

Mission Objectives

GRAIL has two primary science objectives:

  1. Determine the structure of the lunar interior, from crust to core.
  2. Advance understanding of the thermal evolution of the Moon.

Additional mission objectives include:

  1. Extend knowledge gained on the internal structure and thermal evolution of the Moon to other terrestrial planets.
  2. Reduce risk to future lunar robotic or human science and exploration missions by providing a high resolution, global gravity field that will eliminate gravity uncertainties for precision lunar navigation and landings.

GRAIL is the lunar counterpart of the very successful Gravity Recovery and Climate Experiment (GRACE), twin satellites that launched in 2002 to make detailed measurements of Earth's gravity field. Major breakthroughs from GRACE include establishing the rapid melting of ice mass in recent years in Greenland and Antarctica and major changes in water storage in China's Yangtze River and other water sources-sometimes as a result of human use.

The knowledge from GRACE should lead to a better understanding of the forces that drive El Niño and La Niña, more accurate seasonal forecasts of Earth's weather patterns, an ability to track the changing distribution of water resources in critically important land aquifers, and improved forecasting of natural hazards.

GRAIL: Studying the Moon from Crust to Core
Key Dates
10 Sep 2011:  Launch
31 Dec 2011:  GRAIL A Orbit Insertion
1 Jan 2012:  GRAIL B Orbit Insertion
17 Dec 2012:  GRAIL-A Lunar Impact (22:28:41 UTC)
17 Dec 2012:  GRAIL-B Lunar Impact (22:29:01 UTC)
Status: Science Analysis Phase
Fast Facts
GRAIL Facts GRAIL is the lunar counterpart of the successful GRACE mission (right), twin satellites launched in 2002 to make detailed measurements of Earth's gravity field.

GRAIL is part of NASA's Discovery Program of lower-cost, highly focused planetary science investigations.

Studying the Moon is key to understanding how terrestrial planets evolved because it is the most accessible body that preserves a surface record spanning most of our solar system's history.

The GRAIL orbiters -- Ebb and Flow -- were named by Nina DiMauro's fourth graders at Emily Dickinson Elementary School in Bozeman, Mont.
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Last Updated: 30 Dec 2014