Salyut 4

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**Salyut 4 (DOS-4)**
Station statistics

Salyut 4 diagram

Call sign:	Salyut 4
Crew:	3
Launch:	December 26, 1974 04:15:00 UTC
Launch pad:	LC-81/24, Baikonur Cosmodrome, USSR
Reentry:	February 3, 1977
Mass:	18,500 kg
Length:	15.8 m
Width:	4.15 m
Living volume:	90 m³
Perigee:	136 mi (219 km)
Apogee:	168 mi (270 km)
Orbit inclination:	51.6 degrees
Orbital period:	89.1 minutes
Days in orbit:	770 days
Days occupied:	92 days
Number of orbits:	12,444
Distance travelled:	~313,651,190 mi (~504,772,660 km)
Statistics as of de-orbit and reentry
Configuration

Salyut 4 and Soyuz diagram

Salyut 4 (DOS 4) (Russian: Салют-4; English translation: Salute 4) was a Salyut space station launched on December 26, 1974 into an orbit with an apogee of 355 km, a perigee of 343 km and an orbital inclination of 51.6 degrees. It was essentially a copy of the DOS 3, and unlike its ill-fated sibling it was a complete success. Three crews attempted to make stays aboard Salyut 4 (Soyuz 17 and Soyuz 18 docked; Soyuz 18a suffered a launch abort). The second stay was for 63 days duration, and an unmanned Soyuz capsule remained docked to the station for three months, proving the system's long-term durability. Salyut 4 was deorbited February 2, 1977, and re-entered the Earth's atmosphere on February 3.

1 Instrumentation
2 Science
3 Specifications
4 Visiting spacecraft and crews
- 4.1 Salyut 4 Expeditions
5 See also
6 References

Instrumentation

Installed on the Salyut 4 were OST-1 (Orbiting Solar Telescope) 25 cm solar telescope, designed at the Crimean Astrophysical Observatory, and two X-ray telescopes. One of X-ray telescopes, often called the Filin telescope, consisted of four gas flow proportional counters, three of which had a total detection surface of 450 cm² in the energy range 2-10 keV, and one of which had an effective surface of 37 cm² for the range 0.2 to 2 keV (32 to 320 aJ). The field of view was limited by a slit collimator to 3 in × 10 in full width at half maximum. 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 survey. Data could be collected in 4 energy channels: 2 to 3.1 keV (320 to 497 aJ), 3.1 to 5.9 keV (497 to 945 aJ), 5.9 to 9.6 keV (945 to 1,538 aJ), and 2 to 9.6 keV (320 to 1,538 aJ) in the larger detectors. The smaller detector had discriminator levels set at 0.2 keV (32 aJ), 0.55 keV (88 aJ), and 0.95 keV (152 aJ).

Science

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 of 0.6 to 0.9 keV (96 to 144 aJ) flux was detected in Sco X-1. Cir X-1 was not detected at all during a July 5, 1975 observation, providing an upper limit on the emission of 3.5e-11 erg·cm^-2·s^-1 (35 fW/m²) in the 0.2 to 2.0 keV (32 to 320 aJ) range. Cyg X-1 was observed on several occasions. Highly variable flux, in both the time and energy domains, was observed.