Earth Orbiting Satellites Maneuvered to Now Study the Moon

In another case of NASA reusing and recycling spacecraft, two of the five THEMIS spacecraft — which were studying the cause of geomagnetic substorms here on Earth — have a new mission. They made some very unique and complex maneuvers to reach two different LaGrange Points, and will turn their focus on the Moon. Particularly, they will try to determine how the solar wind electrifies, alters and erodes the lunar surface. This is timely since the discovery last year of water across the surface of the Moon which may be created by the solar wind interacting with the lunar surface.

The original THEMIS mission (Time History of Events and Macroscale Interactions during Substorms) featured five satellites that have now successfully completed their 2 year mission. Because they are continuing to work perfectly, NASA is re-directing the outermost two spacecraft to special orbits at and around the Moon. This new mission, which is called ARTEMIS: Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with the Sun.

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It took more than a year and nearly all remaining fuel aboard the satellites to get them to the L1 and L2 Lagrangian points, where one is located on the far side of the Moon, and the other on the Earth-facing side. ARTEMIS-P1 is the first spacecraft to navigate to and perform stationkeeping operations around the Earth-Moon L1 and L2 Lagrangian points.

On August 25, 2010, ARTEMIS-P1 reached the L2 Lagrange point on the far side of the Moon. Following close behind, ARTEMIS-P2 entered the opposite L1 Lagrange point on Oct. 22nd.

Recently, one of the spacecraft was hit by a meteoroid but still seems to be operating.

As the Moon orbits the Earth, it passes in and out of the Earth’s magnetic field and the million-mile per hour stream of solar wind particles. While in these regions, the two ARTEMIS spacecraft will seek evidence for turbulence, particle acceleration, and magnetic reconnection, three fundamental phenomena that control the nature of the solar wind’s interaction with the Earth’s magnetosphere.

By using their instruments and unique two-point vantage points, the spacecraft will study the vacuum the Moon carves out in the solar wind, and the processes that eventually fill this lunar wake. Nearer the Moon, they will observe the effects of surface electric fields, ions sputtered off the lunar surface, and determine the internal structure of the Moon from transient variations in its magnetic field induced by external changes.