Final days for Hubble telescope?

The Hubble space telescope celebrates 15 years in orbit at the weekend, but its days may be numbered, writes Dick Ahlstrom

Astronomers across the world will this Sunday celebrate a remarkable 15 years of astronomical discovery provided by the Hubble Space Telescope (HST). They will be celebrations tinged with sadness however because the outstanding Hubble mission will end sooner than it should due to budgetary cutbacks.

Launched into orbit on April 24, 1990, Hubble has revolutionised both astronomy and cosmology. It has delivered observations that have brought us back billions of years, close to the creation of the first galaxies and stars. Hubble has also turned its gaze to closer objects, the great planets and Mars, to give us beautiful pictures that have inspired both astronomers and an interested public.

"The Hubble has become an old friend, it will be sad to see it go," says Robert Hill who heads education and outreach activities at Armagh Observatory. Armagh is the official conduit into Ireland of Hubble related images and information, but this flow is to end sooner than expected. The US National Aeronautics and Space Administration, a partner in the development and launch of Hubble with the European Space Agency, last January ruled out any further servicing missions for the HST, now orbiting 600km overhead.

NASA's space shuttle has always been a crucial part of the HST programme. An early and unexpected trip to the Hubble in December 1993 had astronauts space walking to install a pair of "spectacles" to correct flaws in its main telescope preventing the HST from seeing clearly.

There have been four servicing missions since but the next will not now take place at all. Originally scheduled for 2004 and delayed to 2006 because of the tragic loss of the Columbia space shuttle over Texas on February 1, 2003, the servicing flight has been abandoned. NASA decided instead to put its reduced budget, trimmed last year by the US Congress, into two other activities.

One is the International Space Station. It depends on the space shuttle to deliver modules that add to the scale of the station. The other is the next generation orbiting observatory, the James Webb Space Telescope. This is another joint effort involving NASA, ESA and the Canadian Space Agency with a launch date of August 2011.

There has been a hue and cry from astronomers since NASA's decision to end HST servicing missions. The influential American Astronomical Society released a statement on the issue last month in which AAS president Robert Krishner described the "considerable disappointment" expressed by Society members and the wider astronomical community.

Given that the next servicing mission was already budgeted and that two scientific instruments, already built, were ready to be installed giving the HST even more scientific impact "makes this decision particularly unfortunate and difficult to accept", Krishner says.

The HST has "revolutionised our understanding of the universe in which we live and it has inspired a new generation of students and the public at large with its discoveries", he believes.

These were points echoed by Hill who has seen first hand how students and people of all ages respond to the remarkable images captured by the HST. "I have no doubt it has inspired many new amateurs and brought kids into astronomy over the years. The HST has changed astronomy and cosmology. It is a sad day for astronomers."

The next HST servicing mission might have extended the instrument's lifetime by 10 or perhaps 15 years, Hill says. There had been talk of sending up a robotic mission both to boost the HST into a higher orbit but also possibly to install the new instruments, but this has now been abandoned as too costly.

This seals HST's fate. In five or perhaps six years it will drift down into the upper atmosphere, slow and eventually crash back to Earth.

On the positive side Hubble will continue to make a significant contribution with the few years it has left. There is nothing preventing the instrument from continuing its string of outstanding discoveries.

Its success to date has prompted ESA to celebrate the HST with a book, a DVD and a CD of original music composed as part of the festivities. ESA has also reserved two stunning images taken by the HST for release on its "birthday" this Sunday.

Armagh Planetarium will present these at the Ulster Museum, Belfast at a free event for all ages on Sunday, April 24 starting at 2pm. There will be several live presentations and visitors will also be able to make their own space observations using the Faulkes Robotic Telescope based in Hawaii.

Information about the celebrations, the book, DVD and CD is available from the website, www.spacetelescope.org