Information about Granat

International Astrophysical Observatory "GRANAT"
The Granat Spacecraft (credit: NASA)
General information
NSSDC ID:	1989-096A
Organization:	Soviet space program
Major contractors:	NPO Lavochkin
Launched:	1 December 1989
Launched from:	Baikonur Cosmodrome
Launch vehicle:	Proton rocket
Mission length:	9 years
Deorbited:	1999
Mass:	4 metric tons, with 2.3 metric tons of experiments
Orbit height:	Apogee 200000 km, perigee 2000 km
Orbit period:	4 days
Location:	Geocentric orbit
Type of orbit:	Highly Elliptical Orbit
Telescope style:	coded mask (SIGMA), coded mask (ART-P)
Wavelength:	X-ray to Gamma-Ray
Diameter:	1.2 m (SIGMA)
Collecting area:	800 cm2 (SIGMA)
Instruments
SIGMA:	Gamma-ray telescope
ART-P:	X-ray telescope
ART-S:	X-ray spectrometer
PHEBUS:	Gamma-burst detector
WATCH:	All-sky monitor
KONUS-B:	Gamma-ray burst experiment
TOURNESOL:	Gamma-ray burst experiment
Website:	[1] (Russian)

The International Astrophysical Observatory "GRANAT" os simply Granat 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 orbit with a period of four days of which three were devoted to observations. Granat operated for almost 9 years. After an initial period of pointed observations, the observatory was placed in survey mode in September 1994, when the attitude control gas was exhausted. Transmissions ceased on 27 November 1998. With seven different instruments onboard, Granat was designed to observe the Universe at energies ranging from X-ray to Gamma-Ray. Specific instruments were meant to study Gamma-Ray bursts and other transient X-Ray sources while others were intended to image X-Ray sources near the Galactic Center. One instrument (WATCH) was designed to monitor the sky continuously and alert the other instruments to new or interesting X-Ray sources.

Spacecraft

Granat was the last of the Venera-class spacecraft produced by the Lavochkin Scientific Production Association and was similar to the Astron observatory which was functional during 1983-1989, it was for this reason that it was originally called Astron 2 before having its name changed. The 4.4 metric ton Granat carried a multi-national scientific payload of almost 2.3 metric tons and stood 6.5 m tall with a total span across its solar arrays of 8.5 m. Power provided by the 3-axis-stabilized spacecraft to the payload was approximately 400 W.

Launch and Orbit

The spacecraft was launched on 1 December 1989 aboard a Proton rocket from the Baikonur Cosmodrome in Kazakhstan and placed in a highly eccentric 96 hour orbit with an initial apogee of 200,000 km and a perigee of 2000 km and inclination of 51.9 degrees. During Granat's nearly 5-year active life, its orbit was perturbed by solar-lunar perturbations, drastically increasing the inclination and reducing the eccentricity so that the orbit was circularized and by 1991 the perigee had increased to 20,000 km. By the end of operations in September, 1994, the orbital parameters were 59,025 km by 144,550 km and an inclination of 86.7 degrees. Three days out of the four day orbit were devoted to observations.

Instrumentation

SIGMA

The SIGMA telescope was a collaboration between CESR (Toulouse), CEA (Saclay), and IKI (Moscow). It covered the energy range 30-1300 keV with an effective area of 800 cm2 and a maximum sensitivity field of view of ~5° x5°. The maximum angular resolution was 10 arcmin. Its imaging capabilities were derived from the association of a coded mask and a position sensitive detector based on the Anger camera principle.

ART-P

The ART-P and ART-S instruments were both the responsibility of the IKI in Moscow. The ART-P instrument covered the energy range 4-60 keV for imaging and 4-100 keV for spectroscopy and timing. There were 4 identical modules of the ART-P telescope. Each consisted of a position sensitive Multi-Wire Proportional Counter (MWPC) together with a URA coded mask. Each module had an effective area of ~600 cm2. The field of view was 1.8° x 1.8°. The angular resolution was 5 arcmin. The instrument could achieve a 1mCrab sensitivity in an 8 hour exposure. The maximum time resolution was 4 ms.

ART-S

The ART-S instrument covered the energy range 3-100 keV. The field of view was 2° x 2°. The instrument consisted of 4 detectors based on spectroscopic MWPCs. The effective area was 2400 cm2 at 10 keV, 800 cm2 at 100 keV. The time resolution was 200 microseconds.

PHEBUS

The PHEBUS experiment was designed by CESR (Toulouse) to record high energy transient events in the range 100 keV - 100 MeV. It consisted of 2 independent detectors with their associated electronics. Each detector consisted of a BGO crystal 78 mm in diameter by 120 mm thick, surrounded by a plastic anti-coincidence jacket. The 2 detectors were arranged on the spacecraft so as to observe ~4-pi steradians. The burst mode was triggered when the count rate in the 0.1-1.5 MeV energy range exceeded the background level by 8 sigma in either 0.25 or 1.0 seconds. There were 116 energy channels.

WATCH

Four WATCH instruments, designed by the Danish Space Research Institute, were in operation on the Granat observatory starting in January 1990. The instruments could localize bright sources in the 6-180 keV range to within 0.5° using a Rotation Modulation Collimator. Taken together, the 3 fields of view of the instruments covered ~75% of the sky. The energy resolution was 30% FWHM at 60 keV. During quiet periods, count rates in 2 energy bands (6-15 keV, 15-180 keV) were accumulated for 4, 8, or 16 s, depending on memory filling. During a burst or transient event, count rates were accumulated with a time resolution of 1 second into 36 energy channels.

KONUS-B

The KONUS-B instrument, designed by the Ioffe Physico-Technical Institute in St. Petersburg]], consisted of 7 detectors distributed around the spacecraft. They responded to 10 keV - 8 MeV photons. They consisted of NaCl(Tl) scintillator crystals 200 mm in diameter x 50 mm thick, with a Be entrance window. The side surfaces were protected by a 5 mm thick lead layer. The burst detection threshold was 5 x 10-8 - 5 x 10-7 erg/cm2, depending on the burst spectrum and rise time. Spectra were taken in two 31 channel PHAs. The first 8 spectra were measured with 1/16 s time resolution. The remaining spectra had adaptive time resolutions depending on the count rate. The range of resolutions was 0.25 s - 8 s. The KONUS-B instrument operated from 11 December 1989 until 20 February 1990. Over that period, the "on" time for the experiment was 27 days. Some 60 solar flares and 19 cosmic gamma-ray bursts were detected.

TOURNESOL

The French TOURNESOL instrument consisted of 4 proportional counters and 2 optical detectors. The proportional counters detected 2 keV - 20 MeV photons in a 6° x 6° field of view. The visible detectors had a field of view of 5° x 5°. The instrument was designed to look for optical counterparts of high-energy burst sources, as well as performing spectral analysis of the high-energy events.

Science results

Over the initial 4 years of pointed observations, Granat observed many galactic and extra-galactic x-ray sources with emphasis on deep imaging and spectroscopy of the Galactic center region, broad-band observations of black hole candidates and X-ray Novae. After 1994 the spacefraft started operating in survey mode carrying out a sensitive all-sky survey in the 40-200 keV energy band. Some of the Highlights include:

• A very deep (more than 5 billion sec.) imaging of the galactic center region.
• Discovery of electron-positron annihilation lines from the Galactic "micro-quasar" 1E1740-294 and the X-ray Nova Muscae.
• Study of spectra and time variability of black hole candidates.
• Discovery of new black hole and neutron star candidates.

Impact of the dissolution of the USSR

After the fall of the USSR two problems arouse for the the project. First, the main spacecraft control center was located at Ukraine's Yevpatoria facility in the Crimea region where data collection and spacecraft operations were accomplished via a 70-m diameter dish antenna. The newly declared independence of Ukraine, coupled with the historical close ties of the Crimea to the Russian Federation, introduced new political obstacles. The most significant problem, however, was in financing the ongoing mission. The French space agency, with its substantial investment in Granat, directly subsidized continuing operations. The benefit was clear in the scientific discoveries of the spacecraft.

External links

• http://heasarc.gsfc.nasa.gov/docs/granat/granat_about.html
• http://nssdc.gsfc.nasa.gov/nmc/sc-query.html
• http://www.astronautix.com/thisday/decber01.htm
• http://imagine.gsfc.nasa.gov/docs/sats_n_data/missions/granat.html
• http://www.fas.org/spp/guide/russia/science/astronomy/granat.htm
• http://gtn.sonoma.edu/public/resources/history/granat.php
• http://space.skyrocket.de/doc_sdat/granat.htm
• http://hea.iki.rssi.ru/GRANAT/granat.html
• http://hea.iki.rssi.ru/GRANAT/index.html (Russian)