Astronauts from the space shuttle Discovery have entered the International Space Station (ISS) and started on repairs.

Their main task over the next three days is to prepare the station for its first inhabitants next year.

But they are also repairing batteries and communications systems and adding soundproofing. Nasa say it is not a surprise that a small number of problems have arisen this early, given the complexity of the ISS's structure.

The station is currently orbiting 230 miles above Earth and travelling at a speed of 16,000 miles per hour.

Members of the seven-strong team of astronauts had to pass through six hatches to get into the station, with American Tamara Jernigan and Russian Valery Tokarev entering first, followed by Canadian Julie Payette.

Astronaut Jernigan opens the hatch into the ISS

Mission Control in Houston told them as they entered the 14ºC capsule: "Make yourself at home ... you might want to bring a sweater."

Jernigan replied: "We are absolutely delighted to be aboard."

During the next three days, the astronauts will stock the space station with 1,632 kilogrammes (3,600 pounds) of equipment. The supplies include computers, clothes, rubbish bags, water and even signs pointing to the emergency exit.

Repairs under way

The first repairs were done inside the Russian-built Zarya control module. Tokarev and Payette pulled up the floor and replaced 18 electrical meters.

Repairs began immediately

These indicate whether the ISS's batteries have been fully charged by solar energy but had been giving false readings.

In the American-built Unity module, astronauts Rick Husband and Daniel Barry replaced two electronics boxes for a communication system that future ISS residents will use.

This system has been receiving signals from Earth but, since mid-April, has not been replying. The new boxes produced an immediate recovery in the system.

"In high-tech like this, you're going to have problems," explained Nasa's Milt Heflin explained.

He said the ISS designers were trying to save money by using "off-the-shelf" hardware whenever possible, so it was no surprise that the six-month-old station already needed repairs.

Six hatches were opened including this one between Unity and Zarya

"When you use off-the-shelf hardware, from time to time you're going to run into some of these problems," he said. "But there's a considerable amount of hardware on ISS and an awful lot of that is working just great."

The crew will also install insulation around some fans inside Zarya to reduce the noise level. Currently the noise is over 72 decibels, like a loud television. ISS officials hoped the mufflers would reduce the noise level to about 60 decibels.

Space walk

The work inside the ISS followed a marathon spacewalk outside. It was the second longest ever made from the space shuttle and the astronauts rigged cranes and tools to the exterior.

Daniel Barry spent his wedding annversary building the new space station

Tamara Jernigan and Daniel Barry spent seven hours 55 minutes working outside the shuttle. But at the end they seemed reluctant to go back inside.

"You can't be telling me we're almost done? Wow. It feels like we just walked outside," said Mr Barry.

The $60bn ISS construction programme is the first truly international space mission. It brings the US, Russia, Japan, Canada and Brazil together with the 11 members of the European Space Agency.

The current mission, STS-96, is the first construction activity on the ISS since the first two pieces - the Russian-built Zarya and the American-built Unity module - were launched late last year. It is due to be completed by 2005 after an estimated 158 more spacewalks.

On Saturday, Discovery made history by becoming the first space vehicle to dock with the orbiting space station. Discovery is due to remain docked with the station until 3 June, before returning to Earth on 6 June.