The shuttle is facing increasingly serious technical and political problems. On Tuesday, the Discovery shuttle was to have launched a satellite to look at the state of the ozone layer. It was pulled back from the brink with just 11 seconds of countdown to go. Less than two weeks ago, the Columbia shuttle launch was abandoned, with only three seconds to lift-off, when one of its three liquid-fuel engines failed.
Nasa officials will have been hopeful last night that Discovery's relaunch, early this morning, went smoothly.
But dissenting voices in Britain, Europe and within the US space programme call for an end to 'flag-waving' manned space missions, whose main purpose is to massage national pride. British space officials are privately crowing that for the past five years they have rejected the value of sending people into space.
They have stuck to this line - arguing that the real future is in earth observation satellites, fulfilling environmental and commercial roles - to the disgust of most of the rest of Europe. But gradually, soundings within the European Space Agency hint that animosity to the British stance is on the wane.
The pressure is also increasing on American space scientists to justify their commitment to manned missions. Continued delays on shuttle launches are adding to concern that it may not be up to one of its key tasks for the future - ferrying parts into space to construct Nasa's ambitious Freedom space station. The space station has an uncertain future, with the election of a US administration that questions the huge investment in space at a time of economic hardship on Earth.
Nasa's controllers know their livelihoods are in jeopardy with each shuttle launch. 'When you realise you are betting the future of the US space programme every time you launch the thing, you have to be cautious,' one senior US space scientist said.
But it is not just caution that is dogging shuttle launches. Its technology is creaking; most of it was designed 20 years ago. Of the 53 shuttle launches, most have had technical problems. Launch dates have been pushed back time and again; 14 launches have got as far as countdown, then been abandoned.
The shuttle is arguably the most complicated machine ever built, held together by more than 3 million lines of software code and 300 miles of wiring. 'It should come as no surprise that the shuttle goes wrong so often,' according to John Pike, director of space policy at the Federation of American Scientists.
Professor Pike is despondent and pessimistic about the shuttle's future. 'All these technical problems point to the fact that there is a very high probability that we will have a repeat of the Challenger disaster by the end of the decade,' he said.
However, he drew short of calling for an end to manned space flights. To do so in the US, he said, would be dangerous and destabilising. 'You British have the monarchy and Westminster Abbey. We have the space programme and the Air and Space museum. The space programme, like the monarchy, is a national symbol - although a less than perfect one.' The professor believes the shuttle is now so unreliable it should be scrapped, and predicts it could be cancelled this year.
He would 're-invent the Apollo capsule and put it on top of a Titan rocket', to keep the crew away from the fuel and cargo. 'It would not necessarily be more reliable, but there would be a higher chance of saving the crew if something went wrong. We would then have a major accident on our hands instead of a national catastrophe.'
Nasa has become increasingly defensive since the loss of seven lives with the Challenger disaster in 1986. Yesterday, a spokesman at its Kennedy space centre in Florida said: 'If people are using delays as an excuse not to fund the space programme then that's a pretty low blow. Cuts would be very unfair. You cannot use the fact that the safety systems work as a reason for not funding . . . that should be a reason for more funding.'
The agency is under attack from all sides in the US. Its budget is being cut relentlessly, and President Clinton has instructed the agency to re-work the design of its prize project - the Freedom space station.
On Tuesday, President Clinton's science advisor, John Gibbons, announced that the US would seek Russian help with this emergency re-design. The goal is a space station costing half its original dollars 31bn ( pounds 20.5bn) price tag.
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