Kosmos 690

Kosmos 690 or Bion 2(in Russian: Бион 2, Космос 690), was a Bion satellite launched by the Soviet Union in late 1974.

Launch
Kosmos 690 was launched on 22 October 1974, at 17:59:59 UTC from Plesetsk Cosmodrome with a Soyuz-U launch vehicle. It was placed in low Earth orbit, with perigee of 223 km, apogee of 389 km and orbital inclination of 62.80°, and orbital period of 98.40 minutes.

Spacecraft
The spacecraft was based on the Zenit spy satellite with emphasis on studying the problems of radiation effects on human beings.

It carried albino rats for biomedical research. Scientists from Czechoslovakia, Romania and Soviet Union subjected the rats to daily radiation doses from a gamma source by ground command. When they were recovered 21 days later, many rats had developed lung problems and their blood and bone marrow had changed more than those of control specimens. It had an on-orbit dry mass of 5500 kg.

An instrument module in the form of 2 connected truncated cones, weighing 2400 kg, 2.43 m in diameter and 2.25 m in length, carries in most of the auxiliary instrumentation in the hermetized part. Outwardly, ball valves with compressed nitrogen are attached to the gas nozzles of the stabilizer system. At the rear, the TDU-1 braking engine is located at a stroke of 15.83 kN and a maximum operating time of 45 seconds. Hypergolic KPL delivers a turbo pump to the combustion chamber. An auxiliary container containing chemical batteries and additional experiments, cylindrical with a diameter of 1.90 m and a height of 0.90 m is placed above the return module and dumped approximately a day before the landing.

Mission
After 21 days, Kosmos 690 returned to Earth and landing in Kazakhstan on 12 November 1974. The return module, weighing 3100 kg and 2.3 m in diameter, was covered with an ablative thermal shield 3 to 18 cm thick.