Artist concept of GRAIL-B performing its lunar orbit insertion burn to join GRAIL-A in lunar orbit (Image: NASA/JPL-Caltech)
Nasa’s twin GRAIL (Gravity Recovery And Interior Laboratory) spacecraft are now in orbit around the Moon. Having achieved lunar orbit at 2 pm PST on New Year’s Eve, GRAIL-A was joined by GRAIL-B at 2:43 pm PST on New Year’s Day. The twin spacecraft are now in a near-polar, elliptical orbit with an orbital period of approximately 11.5 hours. In readiness for the science phase of the mission which is due to start in March 2012, both spacecraft will undergo a series of burns to place them in a near-polar, near-circular orbit with an altitude of about 34 miles (55 km) and orbital period of just under two hours.