2007 in spaceflight Moon. Japan's Kaguya orbiter, along with the smaller Okina and Ouna relay spacecraft, was launched on 14 September. The spacecraft entered Selenocentric orbit on 3 October. China launched its first Lunar probe, Chang'e 1, on 24 October, with the spacecraft entering Selenocentric orbit on 5 November. In 2009, two satellites launched into highly elliptical Earth orbits in 2007 as part of the THEMIS mission were also sent to the Moon. They are expected to arrive in October 2010. In August, the NASA Phoenix spacecraft was launched towards Mars, followed by the Dawn mission to the Asteroid belt in September. Cassini
Lunar orbit to become the nominal circular when the LM made its return rendezvous with the CSM. But the effect was overestimated by a factor of two; at rendezvous the orbit was calculated to be by . Study of the mascons' effect on lunar spacecraft led to the discovery in 2001 of "frozen orbits" occurring at four orbital inclinations: 27°, 50°, 76°, and 86°, in which a spacecraft can stay in a low orbit indefinitely. The Apollo 15 subsatellite PFS-1 and the Apollo 16 subsatellite PFS-2, both small satellites released from the Apollo Service Module, contributed to this discovery. PFS-1 ended up