The second phase of a project to acquire a 3-D view of the magnetic fields on and around the moon launches this weekend.

On Sunday, July 17, the second of two space probes will join its twin as it drops into a permanent orbit around the moon.

While the two probes will have similar orbits, each will move in an opposite direction.

The two spacecraft, built by the University of California, Berkeley, comprise what NASA calls its ARTEMUS mission.

ARTEMUS stands for Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with the Sun.

As soon as the second ARTEMUS space probe assumes its orbit, both will immediately begin the first-ever twin satellite observations of the lunar surface, its magnetic field and the surrounding magnetic environment.

Both ARTEMUS spacecraft were originally launched into Earth’s orbit with three other probes in February 2007, as part of NASA’s THEMIS (Time History of Events and Macroscale Interactions during Substorms)mission.

THEMIS explored how the sun’s magnetic field and the million-mile-per-hour solar wind interacted with Earth’s magnetic field on the side of our planet opposite the sun.

After completing their roles with the THEMIS mission, the ARTIMIS pair was put into a long meandering orbit which set them on a path to the moon.

“These are the most fully equipped spacecraft that have ever gone to the moon,” says David Sibeck, THEMIS and ARTEMIS project scientist at the Goddard Space Flight Center (GSFC) in Maryland. “For the first time we’re getting a unique, two-point perspective of the moon from two spacecraft, and that will be a major component of our overall lunar research program.”

The ARTEMIS probes will join NASA’s Lunar Reconnaissance Orbiter, which has been in orbit around the moon since 2009, taking high-resolution photographs and looking for signs of water ice.

This September, NASA is scheduled to launch two GRAIL (Gravity Recovery and Interior Laboratory) spacecraft to map the moon’s gravitational field.

And, in 2013, the agency plans to launch LADEE (Lunar Atmosphere and Dust Environment Explorer) to characterize the lunar atmosphere and dust environment.

Vassilis Angelopoulos, principal investigator for the THEMIS and ARTEMIS missions and a professor of space physics at UCLA, says the exploration is cost-effective, too.

“ARTEMIS will be doing totally new science, as well as reusing existing spacecraft to save a lot of taxpayer money.”