China's Chang'E 2 succeeds in thrilling asteroid flyby
By Brian Dodson
December 17, 2012
China has now joined the very select group of countries to have succeeded in carrying out an interplanetary probe mission. According to reports from China's official news agency Xinhua, the Chang'E 2 probe passed a mere 3.2 km (2 miles) from the near-Earth asteroid Toutatis at 8:30:09 GMT on December 13, making it the closest asteroid flyby to date ... and resulting in some remarkable photographs.
Toutatis has a long axis of 4.5 km (2.8 miles) and a mass in the neighborhood of 50 gigatons. Although it is not an Earth-crossing asteroid (one whose orbit actually crosses that of the Earth), it can approach to within half a million miles. Toutatis' orbit is chaotic, but even so the probability of colliding with Earth is essentially zero in the next 600 years. It does cross Mars' orbit and makes frequent close passes by Jupiter, so it is more likely to be eventually ejected from the inner solar system than it is to hit Earth.
Initially launched as a lunar orbiter in 2010, the primary mapping camera on Chang'E 2 is a pushbroom species. These cameras provide high resolution with a minimum of weight, but are difficult to reposition quickly and reports originating with Chinese National Space Administration researchers state that the Toutatis photos were actually taken by the solar panel monitoring camera, which was powered up shortly prior to the flyby.
The method used to send Chang'E 2 to its rendezvous with Toutatis (it was sent from lunar orbit to the Earth's L2 Lagrangian point and then into an extremely low delta-V orbit) is also a first.