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Last Updated: Saturday, 17 January, 2004, 15:17 GMT
Why Hubble is being dropped
By Dr David Whitehouse
BBC News Online science editor

Without doubt the Hubble Space Telescope is one of the most important telescopes ever built. Its clear view of the cosmos, above the turbulent and distorting atmosphere, has changed our understanding of the Universe in which we live.

Hubble has been a spectacular success
Its science is remarkable, its images iconic and it had much more to give. So why is it being abandoned?

Few were expecting such an announcement about the demise of Hubble.

Just a few weeks ago Steven Beckwith, the director of Hubble's home institution, the Space Telescope Science Institute in Maryland, told BBC News Online that he was looking forward to the next servicing mission and the upgrade Hubble would receive.

Mr Beckwith said that Hubble was working more efficiently than when it was new and could get even better.

With Hubble's replacement - the James Webb Telescope - not due in orbit until 2012 at the earliest, he hoped that Hubble could survive until the handover.

So what happened? Why is the US space agency (Nasa) abandoning one of the most productive scientific instruments of all time?

Safety first

The main reason is safety. It is said that the decision was made solely by Nasa's chief, Sean O'Keefe, and that it was not related to President George Bush's new space plan for a return to the Moon and missions to Mars. Money was not an issue.

Whatever happens Hubble's end will be tricky and expensive - doing nothing is not an option

Following the loss of the space shuttle Columbia in February last year, all shuttle fights will now be to the International Space Station (ISS).

This is so that the shuttle crew have a lifeboat in space if there are any problems.

But Hubble is not in an orbit from which it is possible to get to the ISS. New safety and inspection procedures would have had to be developed just for this one mission and it was deemed unfeasible.

Hubble's next servicing mission was due in 2005. During the flight, two major instruments - the Wide Field Camera 3 and the Cosmic Origins Spectrometer - would have been installed.

They would have been magnificent additions to Hubble, significantly boosting its performance.

Now they are not going the scientists concerned will be devastated and will want to explore other ways to get the instruments into space. Even if they are successful in flying them, it will be on a smaller mission and they will not benefit from Hubble's extraordinary ability to intercept light from the cosmos.

Although abandoning Hubble solves one problem it raises another - a big one.

Debris danger

Left alone, Hubble will fall back to Earth sometime in 2012 and it is big enough not to burn up completely.

"Its main mirror, and its titanium support ring, will survive and reach the ground," Steven Beckwith told BBC News Online.

One estimate says there is a one in 700 chance of human casualties resulting from an uncontrolled Hubble re-entry. That is, everyone agrees, unacceptable.

The plan was that on a follow-on shuttle visit a propulsion module would be attached to Hubble to bring it down in a predictable way, on to an uninhabited region of the Earth. Clearly that plan cannot now happen.

The de-orbit module will still have to be fitted, only by an automatic docking, and currently Nasa does not have the technology to do this. Russia does. So perhaps it may be asked to help out.

But whatever happens Hubble's end will be tricky and expensive. Doing nothing is not an option.

Although some of Hubble's scientists are reported to be preparing job applications at other institutes, there is still a lot of science Hubble can do. But with the announcement that it will not be re-serviced, most of its science is now behind it and it could cease working altogether at any time.

Hubble has six gyroscopes which control its pointing. Only four are working. In normal circumstances it requires three for normal operations (though some science can be done with two). If any more fail, as they are bound to do eventually, that could spell the end its life.

If all goes well, Hubble will continue exploring and will still have a few surprises for us. Abandoned it may have been, but it has not finished yet.

Death knell for space telescope
17 Jan 04 |  Science/Nature
In pictures: Hubble's successes
17 Jan 04 |  Photo Gallery
Hubble obtains deepest space view
16 Jan 04 |  Science/Nature
Hubble's stunning new vision
30 Apr 02 |  Science/Nature


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