Granat

The International Astrophysical Observatory 'GRANAT' (usually known as Granat; Russian: Гранат), was a Soviet (later Russian) space observatory developed in collaboration with France, Denmark and Bulgaria. It was launched on 1 December 1989 aboard a Proton rocket and placed in a highly eccentric four-day orbit, of which three were devoted to observations. It operated for almost nine years. The International Astrophysical Observatory 'GRANAT' (usually known as Granat; Russian: Гранат), was a Soviet (later Russian) space observatory developed in collaboration with France, Denmark and Bulgaria. It was launched on 1 December 1989 aboard a Proton rocket and placed in a highly eccentric four-day orbit, of which three were devoted to observations. It operated for almost nine years. In September 1994, after nearly five years of directed observations, the gas supply for its attitude control was exhausted and the observatory was placed in a non-directed survey mode. Transmissions finally ceased on 27 November 1998. With seven different instruments on board, Granat was designed to observe the universe at energies ranging from X-ray to gamma ray. Its main instrument, SIGMA, was capable of imaging both hard X-ray and soft gamma-ray sources. The PHEBUS instrument was meant to study gamma-ray bursts and other transient X-Ray sources. Other experiments such as ART-P were intended to image X-Ray sources in the 35 to 100 keV range. One instrument, WATCH, was designed to monitor the sky continuously and alert the other instruments to new or interesting X-Ray sources. The ART-S spectrometer covered the X-ray energy range while the KONUS-B and TOURNESOL experiments covered both the X-ray and gamma ray spectrum. Granat was a three-axis-stabilized spacecraft and the last of the 4MV Bus produced by the Lavochkin Scientific Production Association. It was similar to the Astron observatory which was functional from 1983 to 1989; for this reason, the spacecraft was originally known as the Astron 2. It weighed 4.4 metric tons and carried almost 2.3 metric tons of international scientific instrumentation. Granat stood 6.5 m tall and had a total span of 8.5 m across its solar arrays. The power made available to the scientific instruments was approximately 400 W. The spacecraft was launched on 1 December 1989 aboard a Proton-K from the Baikonur Cosmodrome in Kazakh SSR. It was placed in a highly eccentric 98-hour orbit with an initial apogee/perigee of 202,480 km/1,760 km respectively and an inclination of 51.9 degrees. This meant that solar and lunar perturbations would significantly increase the orbits inclination while reducing its eccentricity, such that the orbit had become near-circular by the time Granat completed its directed observations in September 1994. (By 1991, the perigee had increased to 20,000 km; by September 1994, the apogee/perigee was 59,025 km / 144,550 km at an inclination of 86.7 degrees.) Three days out of the four-day orbit were devoted to observations. After over nine years in orbit, the observatory finally reentered the Earth's atmosphere on May 25, 1999. The hard X-ray and low-energy gamma-ray SIGMA telescope was a collaboration between CESR (Toulouse) and CEA (Saclay). It covered the energy range 35–1300 keV, with an effective area of 800 cm2 and a maximum sensitivity field of view of ~5°×5°. The maximum angular resolution was 15 arcmin. The energy resolution was 8% at 511 keV. Its imaging capabilities were derived from the association of a coded mask and a position sensitive detector based on the Anger camera principle. The ART-P X-ray telescope was the responsibility of the IKI in Moscow. The instrument covered the energy range 4 to 60 keV for imaging and 4 to 100 keV for spectroscopy and timing. There were four identical modules of the ART-P telescope, each consisting of a position sensitive multi-wire proportional counter (MWPC) together with a URA coded mask. Each module had an effective area of approximately 600 cm², producing a field of view of 1.8° by 1.8°. The angular resolution was 5 arcmin; temporal and energy resolutions were 3.9 ms and 22% at 6 keV, respectively. The instrument achieved a sensitivity of 0.001 of the Crab nebula source (= 1 'mCrab') in an eight-hour exposure. The maximum time resolution was 4 ms. The ART-S X-ray spectrometer, also built by the IKI, covered the energy range 3 to 100 keV. Its field of view was 2° by 2°. The instrument consisted of four detectors based on spectroscopic MWPCs, making an effective area of 2,400 cm² at 10 keV and 800 cm² at 100 keV. The time resolution was 200 microseconds.