With ‘Endeavour’ overhead, Nasa now plans the final flights in the shuttle programme

THE SPACE SHUTTLE Endeavouris currently orbiting overhead and could be seen above Ireland from early this morning. If you were up early, 5.33am in Dublin, you might have been lucky – but don't delay because space shuttle flights are coming to an end.

The National Aeronautics and Space Administration's (Nasa) current plans just four more shuttle launches after Endeavour, the last involving the Discoveryvessel, which is due to fly on September 16th.

That launch will bring to a close 29 years of space-shuttle flights. These have brought highs such as the repair of the HubbleSpace Telescope and the building of the International Space Station, and terrible lows with the loss of two shuttles and their entire crews on the Challengerand Columbia.

As is typical with the US space programme, the shuttle was born as much from politics as from the notion of a great space adventure. President John F Kennedy will forever be remembered as the catalyst for taking humans to the moon on board the Apollomissions, culminating in the first man on the moon in July, 1969.

But even then Nasa was casting about for a successor to the Apolloprogramme, says Brian Harvey, author of a number of books on the Russian, Chinese and European space programmes and an authority on human space flight generally.

President Nixon did not want a continuation of what was known to be a Kennedy initiative.

“There was also a concern that if they continued to fly to the moon someone would eventually be left behind,” Harvey says. “The shuttle was very much a Nixon decision.”

Planners began working on shuttle designs even as the Apolloskept flying. There was to have been up to an Apollo 20, but the last, Apollo 17, launched in December, 1972.

From early on, the shuttle was in a sense a victim of its own propaganda. “The shuttle was conceived around 1969 or 1970, but was envisioned as a way to transport crew and supplies to an orbiting space station,” says Harvey. “There was an illusion that you could build enough safety into it to make it as safe as an aircraft.”

This led to three major flaws in thinking of aircraft-like safety, frequent flights, with monthly lift-offs and low cost because the shuttle could be re-used. None of these proved to be the case, says Harvey, and enormous pressures was placed on Nasa to achieve these near impossible goals.

“The seeds of its failure were sown early,” says veteran Irish space commentator Leo Enright. “It meant they had to commit themselves to an impossible architecture, mainly the solid rocket boosters.”

Strapped to the shuttle's huge external liquid fuel tank, effectively these were little more than enormous bombs, explosives packed into long tubes, says Enright. The failure of one of these boosters triggered the loss of the shuttle Challenger, which exploded 73 seconds after lift-off on January 28th, 1986. All seven crew were lost.

This stalled the shuttle programme and forced a complete rethink on safety. “After that they had the wit to build the shuttle around the original idea. The shuttle stopped being a cargo carrier and was rebuilt around its true original vocation, to fly to the space station,” says Harvey.

Yet this did not save the Columbiain 2003. It lost some of the tiles, essential to protect it from the heat of re-entry. It broke up over Texas and crashed seven years ago this month, with the loss of all seven crew members.

After that, the shuttle programme’s days were clearly numbered. This rate of loss was equivalent to losing two aircraft a day on the Dublin to London route, says Harvey.

For all that, the shuttle helped space scientists achieve remarkable advances. It carried aloft the International Space Station piece by piece ( Endeavourcarries two large modules on this flight). It also carried the HubbleSpace Telescope into orbit in April 1990, a launch delayed due to the Challengerdisaster.

Perhaps more spectacularly, the shuttle made a number of visits to repair Hubble after flaws were discovered in its optics. And only last May the shuttle conducted what is likely to have been its last Hubble while on a servicing mission to install new experiments including a new camera and spectrograph.

All remaining flights will involve visits to the space station, with the last shuttle flight is scheduled for September 16th. It will bring to a close almost 30 years of shuttle-based manned space flight with great uncertainty hanging over what comes next.

In a speech earlier this month, US president Barak Obama called a halt to Nasa's next generation of crewed spacecraft built around the Constellation programme. So after September, the Russian Soyuswill be used to ferry crew to and from the space station.

Leo Enright will be happy to see the last shuttle safely back to earth. “I am nostalgic, but so glad the political system has found a way to do this. The women and men are willing to take these risks [on the shuttle] but we shouldn’t ask them to,” he says.

Those wishing to see Endeavouras it orbits overhead must make an early start this morning. From Dublin, it is visible in the south-eastern sky, tracking east to south-east, at 5.33am and 7.05am, according to Nasa data. It will also be visible tomorrow at 5.55am, on Saturday at 5.07am and on Sunday, St Valentine's Day, at 5.07am and 6.39am. For times elsewhere, visit http:// spaceflight.nasa.gov/realdata/ sightings/