NASA's twin GRAILs reunite in lunar orbit

Formation-flying probes reach the Moon

NASA's GRAIL spacecraft duo are back together again and circling the Moon in preparation for their lunar study mission.

The second Gravity Recovery And Interior Laboratory flyer, GRAIL-B, got into lunar orbit at 10.43pm GMT on New Year's Day, after completing its planned main engine burn.

GRAIL-A was already circling the Moon in a near-polar, elliptical orbit, having reached the rocky satellite at 10pm on New Year's Eve.

In the next few weeks, the twin ships will be manoeuvring into formation-flying position to reduce their orbital period to just under two hours, flying together 34 miles (55km) above the surface of the Moon in order to map the body's gravitational field.

That information should allow space boffins to figure out what's going on underneath the surface of the Moon.

The two craft "will vastly expand our knowledge of our moon and the evolution of our own planet", NASA administrator Charles Bolden said in a canned statement.

While the GRAILs gather data for the boffins, they'll also be taking snaps of the celestial body for the kids back home, courtesy of their onboard MoonKAMs (Moon Knowledge Acquired by Middle school students).

"We begin this year reminding people around the world that NASA does big, bold things in order to reach for new heights and reveal the unknown," Bolden boasted.

As well as being big and bold, the US space agency also likes to be on the cutting edge, which is no doubt why it decided to give the GRAIL mission its very own iPhone app.

Unfortunately, unlike the Cassini mission app, which reviewers rate as "excellent" and "very cool", the GRAIL app is not scoring well, with one downloader complaining that the news on the mission isn't updated enough and another saying "don't bother".

However, since the science part of the mission isn't starting until March this year, the critics might be a teensy bit premature with their assessments. ®