Comet hopping

In July 2002, a spacecraft will set off to visit three comets that cross the
Earth’s orbit, assuming all goes to plan. Last week, NASA gave the go-ahead for
the Comet Nucleus Tour or “Contour” mission. The spacecraft will visit Comet
Encke, a comet that has been orbiting near the Sun for thousands of years. It
would then rendezvous with Comet Schwassmann-Wachmann-3, which split into three
pieces in 1995. The final port of call is Comet d’Arrest in 2008, but the
spacecraft might make a detour to check out a newly discovered comet, should one
appear in time.