About 1600 kilograms (3600 pounds) of equipment will be loaded into the ISS during the 11-day mission, due to launch on 20 May.

But Nasa said on Tuesday that maintenance would also be required. The early communication system has not switched on despite attempts on 23 and 29 April.

Spares are already on board and will be used once the problems have been localised.

Other maintenance includes:

• changing the electrical systems' batteries,
• surveying and possibly replacing an antenna that has not worked properly,
• photographing discoloured patches on handrails and other parts of the ISS.

On the last task, Nasa Flight Director, Wayne Hale, said getting the thermal characteristics of these areas was important: "You'd hate to have a handrail that was too hot to hold on to."

Astronauts switch on the ISS lights during the last mission

Launch Package Manager, Sharon Castle, compared her job in organising the logistics as like packing for a holiday. However, she has 123 suitcases and 270kg (600lbs) of water to contend with.

The equipment which will be transferred from the shuttle to the ISS includes laptop computers, cameras, a printer, maintenance tools, spare parts, clothing and even rubbish bags. Over half is of Russian origin, with most of the rest from the US.

Astronauts will enter the ISS on day five of the mission and spend three days inside. Before this, on day four, two astronauts will perform a 6.5 hour spacewalk to attach a US crane to the outside of the ISS. The will also attach the first parts of a Russian crane.

Both will be used by later missions for further ISS construction.

No holding on

The Space Shuttle Discovery will dock with the ISS without using its robotic arm to grab the station as it did in the previous mission. Nasa engineers say the ISS is now heavy enough for this not to be necessary.

The shuttle will also have new titanium bolts on its drag chute door. This is used on landing to slow the shuttle but, on the last mission, the door shook off whilst on the launch pad.

Nasa say the new bolts are stronger, but not too strong to stop the drag chute being relseased when it is deployed using an explosive charge.

Following Discovery's flight, the Space Shuttle Atlantis is scheduled to visit the International Space Station in October. By that time the unpiloted Service Module should have docked automatically with the new outpost.