Mission Overview

Originally called Astron 2, Granat was an X- and gamma-ray astronomical observatory studying high energy emissions from galactic and extra-galactic sources. It was launched from Tyuratam by a four-stage Proton (D-1-e) booster. The observatory was based on the main bus design of earlier Venera and VEGA missions. It was cylindrical, about 4 m long and 2.5 m in diameter. Two solar panels extended from either side of the main body. Mass was about 4 metric tons, with 2.3 metric tons of experiments. The major experiment was a French Sigma coded-mask gamma radiation telescope. It measured 3.5 m by 1.2 m diameter and had a 4.45 by 4.20 deg. field of view. The satellite also carried a spectroscope and an X-ray imaging telescope. The astrophysics payload was developed in cooperation with France, Bulgaria and Denmark. The mission was expected to last 18 months, however, lengthy ground delays may have reduced its on-orbit life to eight months.

Launch Information

Launch Date: 1989-12-01 at 20:20:00 UTC
Launch Vehicle: Proton
Launch Site: Tyuratam (Baikonur Cosmodrome), U.S.S.R
Decay Date: 1999-05-25

Trajectory Description
Type: Orbiter
Central Body: Earth
Epoch start: 1989-12-01 00:00:00 UTC

Orbital Parameters
Periapsis 2000.0 km
Apoapsis 200000.0 km
Period 5880.0 minutes
Inclination 51.599998474121094°
Eccentricity 0.9219340085983276

Instrumentation

X-Ray and Gamma-Ray Imaging Telescope

The SIGMA imaging telescope was one of the main devices aboard the Soviet astronomy satellite GRANAT. SIGMA had been designed to produce high-resolution images of the hard x-ray and soft gamma-ray sky, in the energy range from 35 keV to 1.3 MeV.

The SIGMA telescope was constructed by two French laboratories (Service d'Astrophysique de Saclay, and Centre d'Etude Spatiale des Rayonnements at Toulouse), both under contract to CNES (Centre National d'Etudes Spatiales, the French Space Agency). The instrument weighed about one ton, measured 3.50 m high and had a diameter at the base of 1.20 m.

The optical system was provided by a coded aperture mask placed 2.5 m in front of a position sensitive detector (PSD); it was an array of 49 x 53 square elements, whose basic pattern was a 29 x 31 Uniformly Redundant Array (URA). The opaque 1.5 cm thick tungsten mask elements were bonded to a honeycomb plate that supported and stiffened the mask assembly without hindering the transparency of the open mask elements. There were active and passive shielding devices present.

The full sensitivity field of view was 4.7 x 4.3 sq degrees. In a wider Partially Coded Field of View (PCFOV) the sensitivity decreased such that the half-maximum sensitivity boundary was a 11.5 x 10.9 sq degrees rectangle. The total detection area was determined by the 794 sq cm central rectangular zone of the PSD whose size matched the basic 29 x 31 mask pattern. The intrinsic angular resolution was 13 arc min. The point source location accuracy was less than 2 arc min. taking into account the PSD coding element size (1.175 x 1.175 mm). The SIGMA PSD was an Anger camera which measured energy and position of photons in the 0.035-103 MeV energy range. The detector measured scintillation flashes in a 57 cm diameter 1.25 cm thick NaI(Tl) crystal mounted within a carbon-fiber honeycomb-structure, an optically coupled to the crystal via a 1.25 cm thick pyrex disk. For onboard calibration an 241 Am radioactive (alpha+60keV photon) source was used. The anticoincidence shield was made of 31 independent CcI(T1) crystal blocks. A thin plastic scintillator was located on top of the active shield well to veto the incoming charged particles. A passive graded shield (0.1 mm lead, 0.1 mm tantalium and 0.4 mm tin) was wrapped around the tube holding the mask in order to minimize the low-energy induced background. A preliminary sensitivity curve had been published by Paul et al. (1991).

During a typical SIGMA observation, lasting approximately one day, the telescope recorded 3 series of “spectral” images (124x116 3.30 arcmin pixels) in 95 energy channels whcih covered the entire energy range varying with the energy resolution. In addition the total camera counts were stocked every 4 seconds. There were several operating modes possible based on the type of observation desired and the amount of memory required.

Energetic Particle Detectors from KS-18-M

This experiment is one of several provided by the Theoretical and Applied Space Physics Division of the Skobeltsyn Institute of Nuclear Physics of Moscow State University. The KS-18-M instrument was designed as a monitor of fluxes of charged particles of medium energy in interplanetary space. Solar x-rays may be also registered. There are two almost identical sensor blocks: one is sunward directed (S) and the other - anti-sunward (A). Each block contains the following sensors: two gas-discharge counters (C1, C2); two stand-alone SSD of Si (D1, D2) of 130 micron and 1000 micron of thickness respectively; a SSD system T1 of two Si-sensors of 70 and 1000 microns thickness plus an anti-coincident cup of SSDs; and a combined system T2 of solid state detectors (SSD) (50 micron Si) plus windowed gas-discharge counter SBT-9 plus anti-coincident cup of SSDs. View angle of each SSD sensor is as wide as +-25 degrees. Spacecraft memory is used for data storage; 20 minute time resolution is provided for all sensors; in addition, one channel from D1 and two channels from D2 may work with two minute time resolution if high intensity is observed. All sensors measure flux intensity continuously. All data are broken up to six groups according to their modes of timing.

Science
Summary