Nasa's space shuttle Atlantis is due to blast off from Kennedy Space Centre this evening on a mission to deliver Europe's long-delayed science lab to the International Space Station.

Officials at the space agency gave the all-clear for a 4.31pm (21.31 GMT) liftoff from Cape Canaveral following emergency repairs to patch up gouges in the insulating foam that shrouds the shuttle's 15-storey main fuel tank.

The launch of the €1bn (£700m) Columbus laboratory will end an agonising wait for scientists and engineers, some of whom have dedicated more than 20 years to the project. For several of those, the lab has languished in a warehouse in Germany, grounded by a string of funding cuts and accidents which severely set back its construction. When the lab was conceived in the early 1980s, scientists expected it would be aloft and running by 1992.

The shuttle is expected to reach the space station on Saturday for a 17,500mph rendezvous 213 miles above the Earth. On arrival, Commander Steve Frick will ease the shuttle into a gentle backflip, allowing cameras aboard the 200-tonne station to scan heat-resistant tiles on the craft's underbelly and wing edges for damage. The safety checks were introduced after falling insulation struck the wing of another shuttle, Columbia, causing damage that led to the loss of the ship and her seven crew on re-entry in 2003.

On Sunday, astronauts will spacewalk to the shuttle's cargo hold to power up the science lab before it is swung into place by the station's robotic arm.

"Excitement is very high. A lot of engineers are looking forward to seeing their baby finally flying and operating," said Dr Martin Zell, head of research operations at the European Space Agency.

Columbus is Europe's cornerstone contribution to the $100bn (£48bn) space station project and will double its capacity for scientific research. Once it is in place, European Space Agency astronauts will be entitled to more seats on future flights to the space station, a change that is expected to shift the culture of a construction project that has so far been dominated by the US and Russia.

"The way it is managed will take on a European flavour because they will have more influence now," said Tim Stevenson, chief engineer at the space research centre at Leicester University. "When it's the Russians and the Americans, the level of negotiation is almost zero - they're constantly at each other's throats."

The seven-metre-long cylindrical laboratory carries five major science facilities, three within the lab and two attached to the outside. In one, the BioLab, experiments will investigate conundrums such as how germinating plant seeds know which way is up, and whether gravity makes their roots curl.

Physiological tests will examine how the space environment affects the human body, information which will be crucial if astronauts are ever to attempt more ambitious forays into the solar system. Those aboard will give blood samples before and after the flight to assess whether space radiation damages immune cells in their veins. They will also be monitored for early signs of osteoporosis, a condition accelerated by spaceflight.

Further experiments will expose fungal spores and lichens to the icy vacuum of space to find out whether probes flung from Earth to other planets risk contaminating them with homegrown microbes.

Professor Steve Gabriel, head of astronautics at Southampton University, is one of a handful of British scientists with experiments aboard the new lab. His research will expose materials to space radiation to see how they degrade over time, the results of which will influence how future spacecraft are built.

"It is my first piece of hardware to actually fly in space and that it will be launched on the space shuttle is particularly gratifying," he said. "I'm really looking forward to when it's switched on for the first time and we start to get some data back. I just hope it works."

After the mission - the 121st shuttle flight - Nasa will face an intense schedule to complete the assembly of the orbiting station before the shuttle fleet is retired in 2010. Early next year, Kibo, a huge Japanese science lab, is due to be delivered to the space station, further expanding its capability for space-based research.

Dr Keith Cowing, a former Nasa engineer who worked on the space station before starting the Nasawatch website, said the addition of the European and Japanese labs would change the face of the space station and make it more than a mere destination for the space shuttle to fly to.

"It's going to go from a lot of people floating around saying hi to each other to something far more serious," he said.

Though drastically scaled down by a string of budget cuts, the space station was a crucial nursery slope for future space missions, such as the Bush administration's much-publicised hopes for a moon base and a crewed voyage to Mars, said Cowing.

"You've got to practise things first. To say the purpose of the space station is to be fixed is to some extent true. There's a difference between sitting down here and thinking 'will this work in space?' versus being there and testing it out in real conditions.

"If you're going to Mars, you're going to need a big spaceship, it'll be complex and it will need a lot of taking care of," he said. If we lacked experience of what could go wrong in Earth orbit, the consequences could be disastrous if something broke on the way to Mars, he added.

The mission is projected to last at least 11 days, and will be the first trip to space for Nasa astronaut Leland Melvin, a snowboarder and former wide-receiver for the Detroit Lions American football team.