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Salyut 4



The Salyut 4 space station was launched on 26 December 1974. It was in an orbit with an apogee of 355 km and a perigee of 343 km. The orbital period was 01.3 minutes. It was at an inclination of 51.6 degrees. It reentered the Earth's atmosphere on 2 February 1977.


The Salyut 4 X-ray instrument, often called the Filin telescope, consisted of four gas flow proportional counters, three of which had a total detection surface of 450 sq cm in the energy range 2-10 keV, and one of which had an effective surface of 37 sq cm for the range 0.2-2 keV. The field of view was limited by a slit collimator to 3 deg x 10 deg FWHM. The instrumentation also included optical sensors which were mounted on the outside of the station together with the X-ray detectors, and power supply and measurement units which were inside the station. Ground based calibration of the detectors was considered along with in-flight operation in three modes: inertial orientation, orbital orientation, and sruvey. Data could be collected in 4 energy channels: 2-3.1 keV, 3.1-5.9 keV, 5.9-9.6 keV, and 2-9.6 keV in the larger detectors. The smaller detector had discriminator levels set at 0.2 keV, 0.55 keV, and 0.95 keV.


Among others, observations of Sco X-1, Cir X-1, Cyg X-1, and A0620-00 were published from the Filin data. A highly variable low energy (0.6-0.9 keV) flux was detected in Sco X-1. Cir X-1 was not detected at all during a 5 July 1975 observation, providing an upper limit on the emission of 3.5e-11 erg/sq-cm/s in the 0.2-2.0 keV range. Cyg X-1 was observed on several occasions. Highly variable flux, in both the time and energy domains, was observed.

Alternate Names

  • 7591
  • Salute 4
  • Salyut4

Facts in Brief

Launch Date: 1974-12-26
Launch Vehicle: Proton Booster Plus Upper Stage
Launch Site: Tyuratam (Baikonur Cosmodrome), U.S.S.R
Mass: 18500 kg

Funding Agency

  • Soviet Academy of Sciences (U.S.S.R)


  • Human Crew

Additional Information

Questions and comments about this spacecraft can be directed to: Coordinated Request and User Support Office

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