European gamma ray observatory launched

Posted: October 17, 2002

A new space-based observatory is in orbit today to give the clearest view of the most energetic explosions in the Universe.

Launch of the Russian Proton rocket with the European Space Agency's International Gamma Ray Astrophysics Laboratory in tow occurred as advertised at 0441 GMT (12:41 a.m. EDT) from the Baikonur Cosmodrome, Kazakhstan.

The Proton rocket lifts off with Integral. Photo: ESA/S.Corvaja
Integral is designed to help answer fundamental questions regarding the most powerful energy and radiation known in the Universe. This radiation in the gamma ray spectrum is invisible to the human eye and any conventional telescope mirror.

Three core stages of the massive Proton launcher and a single burn of the Block DM upper stage worked to successfully deliver Integral into its egg-shaped orbit around Earth. Satellite deployment was confirmed at 0614 GMT (2:14 a.m. EDT). The craft's power-generating solar arrays were verified extended and locked by 0635 GMT (2:35 a.m. EDT).

The initial orbit will be boosted over the coming weeks by Integral's on-board propulsion system, and the observatory will eventually settle into an operational orbit with an apogee, or high point of over 150,000 kilometers, and a perigee, or low point, of about 9,000 kilometers and inclination of 51.6 degrees.

Also upcoming is the deployment and checkout of the scientific payload. Science operations are slated to begin in mid-December.

Each lap around Earth will take about three days to complete, with the satellite traveling one-third of the way to Moon at the orbit's farthest point. Over the next five years, Integral will be allowed to slowly drift into a slightly higher orbit with an inclination change to about 85 degrees.

An artist's concept of Integral. Photo: ESA
This kind of orbit is ideal for Integral's armada of delicate instruments because such an altitude puts the craft high above the radiation belts that surround Earth. Radiation could cause disruption and interference in science observations. Plans call for science operations to be halted for a short time when Integral dips below about 40,000 kilometers high.

A gamma ray imager aboard Integral will gather the sharpest and most detailed images of gamma rays in the history of astronomy. To analyze the energy emitted by gamma ray sources, a spectrometer is also included in the complement of instruments. An X-ray imager and an optical camera are also carried along to help determine the origins of gamma rays.

Gamma rays are known to come from the vast supernovae of dying stars, black holes and gamma ray bursts, which are not completely understood. Supernovae are believed to have created new elements that built the Universe we know today. Some questions remain as to just how the energy and chemicals are released, and Integral will strive to help answer those questions.

One of the more unknown components of gamma ray energy are large bursts that occur about once a day. These short-lived explosions release vast amounts of energy sometimes in a matter of seconds, yet their sources are unknown. Integral will also study these bursts and perhaps determine where they come from and what they are caused by.

Officials with ESA hail Integral as the most advanced and sharpest gamma ray observatory ever launched. It builds upon science and data gathered by previous satellites, including NASA's Compton Gamma Ray Observatory.

The European Space Agency selected Italy's Alenia Aerospazio as the mission's prime contractor, but all of ESA's member states were involved in the project. Russia is providing the launch free for observation time using Integral. An American ground station at Goldstone, California, will be employed along with a tracking site in Belgium to send commands and receive data. Other contributions from the Czech Republic and Poland are also incorporated into the program.

Weighing close to 9,000 pounds with its fuel tanks full, Integral is a large and complex satellite in terms of spacecraft and payload systems. The craft's four scientific instruments account for about two tons of this weight, making this payload the heaviest ever for ESA.

The baseline mission for Integral lasts two years, but that lifetime could easily be extended to five years.

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