The largest space telescope ever constructed in Britain is to be taken out of storage at the University of Leicester's Space Research Centre to go on display at the Science Museum in London.

The JET-X (Joint European X-Ray Telescope) instrument is a 3.5 m focal length X-ray telescope built by a consortium of groups from Italy and Russia and scientific groups from the UK; from the University of Leicester, the University of Birmingham, the Mullard Space Science Laboratory and the Rutherford Appleton Laboratory.

Leicester led the consortium and was responsible overall design of the instrument, assembly and test of the telescope and for development of the X-ray detectors.

The telescope was assembled and tested by the Leicester team from sub-systems and components developed and supplied by the partners using the specially built large clean room in the Department of Physics and Astronomy. JET-X is 5 meters long and 1 meter in diameter, and weighs 450 kg when fully assembled.

Two test models of the telescope were built to test the mechanical, electrical and electronics design of the telescope and these models were delivered to Moscow to be assembled on the test model of the Russian Spectrum X-Gamma satellite. These tests were successfully completed in Moscow between 1990 and 1992.

Meanwhile, the flight telescope was assembled and tested back in Leicester but was could not be delivered to Moscow because the flight spacecraft had not been completed.

JET-X was one of a six instruments provided by the international scientific community for Russian SPECTRUM-RONTGEN-GAMMA (Spectrum X-Gamma) high energy astrophysics mission.

Launch was originally planned for 1992-93, but severe delays to the program occurred in the wake of the collapse of the Soviet Union and the severe economic crisis in Russia that followed. Eventually, the mission was indefinitely postponed once it became clear that other international space missions had overtaken Spectrum X-Gamma's earlier scientific lead. Spectrum X-Gamma never flew and the JET-X telescope was placed in storage at Leicester.

Although this was a sad outcome for all those involved in the project, there have been compensations and rewards for all the work done in building JET-X.

The design of the x-ray detectors for JET-X led to a new technology that has since been used, with great success on the European Space Agency's XMM mission, which was launched in 1999, with the X-ray detectors on that mission still working well after almost a decade in orbit.

In 1997, the Leicester group joined the NASA SWIFT Explorer project. A new X-ray telescope, based on JET-X designs, was built by a team from the University of Leicester, Pennsylvania State University and the Osservatoria di Brera in Italy. Mirrors from JET-X and a detector system deriving from JET-X and XMM experience were central to the SWIFT X-ray telescope.

SWIFT was launched in 2004 and is now in its 5th year of studying the enigmatic behavior of the mysterious gamma ray bursts. The SWIFT team was awarded the Rossi prize by the American Astronomical Society in 2007 in recognition of the scientific discoveries achieved by SWIFT.

Following many years of storage at Leicester the telescope is being moved to the Science Museum to illustrate the technical and scientific capability of the UK in building X-ray telescopes and space instruments as part of the new Cosmos and Culture exhibition which opens on 23 July.

Professor Alan Wells, former Director of the Space Research Centre and Program Director for the Spectrum X_Gamma project has commented: "The cancellation of the Spectrum X_Gamma project, when it came was a huge disappointment to all of us who had worked so hard and under such difficult conditions for such a long time. The great compensation, though, has been to see the technology that we so painstakingly developed for JET-X come to fruition in other projects, especially SWIFT. SWIFT is recognized as one of NASA's most productive space science missions and it is good to know that much of this success relates back to the hard work we put in on JET-X."

Professor (Dr in 1990s) Mark Sims, who worked on the development of JET-X added: "The JET-X project was a natural progression for me from an earlier X-ray telescope project ROSAT. Leicester led the assembly and test of the telescope which extended our capabilities in terms of designing, testing and handling large instruments. Many lessons from the project have been employed in projects since. It was an interesting experience to work with the Russians who had a very different way of working to what we were use to and whose space engineering capability was still considerable despite their funding problems at the time."

JET-X will be relocated from the University of Leicester on Monday 22 June.