The shuttle blasted off at 6:11 a.m. (1011 GMT), taking a crew of seven astronauts, including Russian cosmonaut Yuri Usachev, on a long-delayed 10-day mission to perform maintenance work on the station.

The launch, originally scheduled for April 13, was postponed for the first time to April 24 when Commander James Halsell, who leads the crew, injured his ankle. Bad weather caused three more launch holdups, the latest on Tuesday.

The Atlantis crew are to prepare the two modules of the ISS already in orbit for the arrival of the Russian service module Zvezda scheduled for July. Equipment will be loaded on to the station for use by crews arriving later in the year.

Assembled in December 1998, the space station is currently comprised of two modules -- the US-built Unity and the Russian module Zarya.

After the lift-off, Atlantis is to take two days to reach the ISS and dock there for six days at an altitude of 300 kilometers (185 miles).

The astronauts will change three batteries and install fans to prevent the accumulation of polluted air in the Zarya module. Then they will transfer from the shuttle to the ISS one ton of US and Russian equipment, including computers, exercise equipment and clothing for use by the space station crew later in the year.

The mission is to feature a six-hour space walk in which astronauts Jeffrey Williams and James Voss will secure a mechanical arm that was attached to the exterior of the Unity module during a mission June of last year and which has had persistent problems.

They will also install security rails to the exterior of the ISS, to help future maintenance missions, and repair an antenna.

The shuttle will move Zarya and Unity some 32 kilometers (19 miles) further from the earth, as they are losing 2.7 kilometers (1.7 miles) in altitude each week. This orbit maintenance operation will be completed by the Russian service module, Zvezda, scheduled for launch in July.

The astronauts are also carrying with them an Olympic torch and flag that will be used to launch the summer Olympic Games in Sydney, Australia, in September.

When the shuttle return to Earth, the torch will be taken to Greece where it will be lit before being carried to Australia for the opening ceremony of the games.

Although this will be Atlantis' 21st mission, the space shuttle has not flown since 1997. A number of upgrades have been made to it, including a reworking of the control panel to make it more effective in crises.

The shuttle is scheduled to return here on May 29.