NASA recycles two small satellites for lunar mission

Having finished their primary mission investigating the formation of auroral light displays at Earth's poles, two diminutive NASA satellites have been dispatched to the moon for bonus science.

Artist's concept of an ARTEMIS spacecraft near the moon. Credit: NASA

Packed with magnetometers and electrical instruments specially designed to probe shocking solar storms, the two are now positioned to study the mysterious interaction between the solar wind and the moon.

Scientists call the new mission ARTEMIS, or Acceleration, Reconnection, Turbulence and Electrodynamics of Moon's Interaction with the Sun.

"Using two repurposed satellites for the ARTEMIS mission highlights NASA's efficient use of the nation's space assets," said Dick Fisher, director of the heliophysics division in NASA's science directorate.

The two satellites were part of a fleet of five platforms launched in February 2007 to fly through Earth's magnetosphere, a nearly invisible bubble that protects the planet from radiation and charged particles originating from the sun and the cosmos.

Called the THEMIS mission, the five satellites discovered the natural mechanism that triggers geomagnetic storms, which manifest themselves as spectacular light shows known as aurora, or the Northern and Southern Lights.

With the primary mission completed, NASA moved two of the satellites from their unique, high-altitude orbit around Earth to never-before-explored regions at gravitationally stable points less than 40,000 miles from the moon.

Three remaining THEMIS satellites are still circling Earth in an extended mission observing the Northern Lights.

Using a series of novel thruster firings and taking advantage of lunar gravity, engineers guided the two highest THEMIS satellites to Lagrange points averaging about 37,000 miles from the near and far sides of the moon. The Lagrange points are sites where the gravity of two celestial bodies, the Earth and moon in this case, balance to create a stable home for scientific spacecraft.

One of the box-shaped spacecraft reached its Lagrange point Aug. 25, and the other arrived Oct. 22, according to NASA.

The newly-christened ARTEMIS probes are in stable orbits around each Lagrange point. The satellites are already collecting data, according to NASA.

More complex maneuvers are planned to place the satellites in elliptical orbits around the moon by May 2011. The probes will fluctuate between about 60 miles and 12,000 miles above the lunar surface.

NASA has approved ARTEMIS for a two-year mission. The mission is also named for Artemis, the Greek goddess of hunting and the wilderness often linked to lunar mythology.

A drawing depicting three THEMIS satellites in Earth orbit and two ARTEMIS probes near the moon. Credit: NASA

"ARTEMIS will provide a unique two-point view of the moon's under-explored space environment," said Vassilis Angelopoulos, THEMIS principal investigator at the University of California, Los Angeles. "These two spacecraft are headed for an incredible new adventure."

Five instruments on each satellite will measure the electric and magnetic fields, ions and electrons around the spacecraft, uncovering unprecedented details on the space environment close to the moon.

The moon does have a robust magnetosphere like Earth, leaving the lunar surface exposed to erosion from the solar wind, a stream of ionized particles flowing from the sun into the solar system.

ARTEMIS observations began this week to measure how the solar wind charges, alters and erodes the lunar surface, according to a NASA press release.

Scientists say ARTEMIS will be the most extensive study of the space environment around a planetary body without a magnetosphere.

Results from ARTEMIS will be crucial for characterizing the lunar radiation environment before possible long-term human voyages or robotic exploration.