A new gamma-ray observatory satellite to be launched in 2001 seems likely to become the first joint space mission between European, Russian and US space agencies. The satellite would cost an estimated £400 million (US$600 million) and would be between ten and 50 times more powerful than the two gamma-ray observatories now in orbit. As currently planned-and providing formal approval is obtained from each of the three space agencies-the project, known as INTEGRAL (for International Gamma-Ray Astrophysics Laboratory) would be run by the European Space Agency (ESA) as the second 'mediumsized' project in its science programme, Horizon 2000. One ofthe two main instruments, a germanium spectrometer, would be provided by the US National Aeronautics and Space Administration (NASA), which has also been asked to make available data-receiving facilities at two ground stations. The satellite would be launched by a Russian Proton rocket from the Baikonur Cosmodrome in Kazakhstan, in return for which scientists from the Russian Space Research Institute (IKI) would have access to the data. INTEGRAL was given top ranking over three rival projects last week at a meeting in Paris of ESA's space science advisory committee. The choice followed a two-day meeting at the headquarters of the United Nations Educational and Scientific Organization (UNESCO), in which details of the four projects were presented to 250 space scientists. In addition to the germanium spectrometer, INTEGRAL will carry a caesium iodide imager and two smaller instruments, an optical transient camera and an X-ray monitor. The overall goal is to improve both the angular and spectral resolution of gamma-ray observations. These will be made primarily in the plane of the galaxy, although observations will also be made of gamma-ray sources from outside the galaxy. INTEGRAL will follow up observations from the Russian GRANAT mission (which uses the French gamma-ray telescope SIGMA) launched in 1989 and now coming to the end of its mission, and the US Compton Gamma Ray Observatory, which was launched by the space shuttle in April 1991. The advisory committee's recommendation now goes to the ESA's science programme committee, representing the scientific communities of its 13 member states, which meets in early June. The committee must also take into account the project's
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