European Space Agency officials reported this week that problems with several instruments intended for the INTEGRAL spacecraft have put pressure on next year's planned launch of the gamma-ray observatory.

An artist's concept of INTEGRAL. Photo: ESA

At a science working group meeting earlier this month in the Netherlands, project officials agreed to a new timetable for the delivery of three instruments that will give the teams working on them more time to complete them while still preserving the planned April 2002 launch of the spacecraft.

The new schedule, however, offers little margin for error if additional problems develop. "We are fighting to stay on track," said system engineering manager Peter Jensen. "To meet the April 2002 launch objective we must recognize that this new schedule is still extremely tight and we cannot afford to have further delays."

One of the instruments, the Imager on Board the INTEGRAL Satellite (IBIS), is now scheduled for delivery to prime contractor Alenia Aerospazio in late March. The other two instruments, the Joint European X-Ray Monitor (JEM-X) and the Spectrometer on INTEGRAL (SPI), are scheduled for delivery in early May.

All three have been beset with technical problems during their development that project officials blame on difficulties inherent with the construction of new, sophisticated scientific instruments. The JEM-X team, for example, has been struggling to understand problems encountered during tests of a model of the detector. "We are investigating these difficulties and the two flight models are having to be assembled to incorporate the required changes," said principal investigator Neils Lund.

INTEGRAL spacecraft being integrated at Alenia Spazio in Turin. Photo: ESA

The three instruments, along with an optical camera that has already been completed, comprise the scientific payload of INTEGRAL. They will be mounted on a spacecraft body based on the design of ESA's XMM-Newton X-ray observatory. The 4.1-ton, 350 million euro (US$330 million) spacecraft will be launched on a Russian Proton rocket from Baikonur, Kazakhstan and placed in a high elliptical orbit that will keep the spacecraft away from the Earth's radiation belts for most of each three-day orbit.

INTEGRAL, a contraction of INTErnational Gamma Ray Astrophysical Laboratory, will be the most sophisticated gamma ray observatory ever launched. The IBIS instrument will provide the sharpest gamma ray images every produced, while the SPI instrument promises to measure gamma ray energies with a sensitivity 100 times greater than any previous instrument.

Astronomers are planning a wide range of studies with INTEGRAL. One focus will be searches for aluminum-26, a short-lived radioactive isotope generated by supernova explosions, in order to understand how much matter in the form of heavier elements has been made in the last million years of the galaxy's history. Other uses of the telescope will be to understand giant black holes and other massive, compact objects, as well as attempt to better understand the mysterious, powerful phenomenon known as gamma ray bursts.

INTEGRAL will also fill an existing gap in gamma ray astronomy created last year when NASA's Compton Gamma Ray Observatory was deorbited after one of its gyros failed. Because gamma rays are absorbed by the Earth's atmosphere, astronomers rely on orbiting spacecraft to conduct observations at those wavelengths, a capability they have been deprived of since the loss of Compton.