Relief crew and Europe's Leonardo en route for the ISS

Discovery is carrying the first scheduled relief crew for the ISS. Once the shuttle docks with the station - the rendezvous should take place at about 5.30 am UT on Saturday, 10 March - Commander Yury Usachev and astronauts James Voss and Susan Helms will take over from Bill Shepherd, Yuri Gidzenko and Sergei Krikaler, who have completed their four-month tour of duty as the station's first inhabitants.

Just as important for ISS development, the shuttle's cargo hold contains the Italian-built multi-purpose logistics module Leonardo. Often described as a "moving van in space", Leonardo is the first of four MPLMs that will carry bulky and often delicate equipment to and from the ISS. Constructed by Alenia Spazio in Turin as part of an agreement between NASA and the Italian space agency ASI, the Leonardo module will dock with the station to allow cargo transfer.

This trip, Leonardo is carrying assorted equipment racks, including the station's first scientific payload - a Human Research Facility that will be used to conduct life science experiments. While the module is attached to the station, astronauts will be able to work aboard it in shirt-sleeve comfort: its ECLSS life-support system is an ESA contribution.

The station's crew, newcomers and old hands alike, will have a busy time before the shuttle departs on 17 March. Once Leonardo has been unpacked, the module will be loaded with used equipment and station trash, all of which will be returned to Earth.

Such exchanges will soon be an ISS routine. The next MPLM - Raffaello - is scheduled for a shuttle launch on 19 April. The April flight will mark another ISS milestone, on board will be Umberto Guidoni, the first European Space Agency astronaut to reach the station.