The NASA spacecraft Messenger has finally arrived in orbit around Mercury – a first for the US space agency. A 14 minute burn of it’s 600 Newton thrust engine at 00:45 GMT today (Friday 18 march 2011) placed the probe into a highly elliptical 12 hour orbit, with a low point at around 200 km altitude. The spacecraft will have to operate in an extreme thermal environment, given that Mercury is so close to the Sun. The thermal power from the Sun is around 9 kW per square metre, and the surface temperature of Mercury (around 600 oC at the equator) means that the infrared emission from the planet is also significant in heating up Messenger. Its principal means of surviving this extreme environment is to remain sheltered from direct solar input by a large thin ceramic Sun shield – see accompanying picture. It will take a while to commission the payload instruments, but Messenger should be up and running in early April. The surface imagery should be spectacular!
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