PS-1 (Prosteishiy Sputnik / Simplest Satellite)

The simplest satellite, the most advanced launch

PS-1 was the official code designation of Sputnik 1. When development of the one-ton scientific satellite Object D, approved by a Council of Ministers decree on 30 January 1956, fell behind schedule late that year, Sergei Korolev urged the government to switch to the simplest possible satellite rather than risk an American first launch during the International Geophysical Year. The Council approved the revised plan on 15 February 1957, and the "simplest satellite" went into production as a stripped-down design while Object D was postponed.

A spacecraft built to be a radio beacon

PS-1 was designed from November 1956: an aluminium sphere matching the R-7's payload capacity, carrying two alternating radio transmitters, temperature and pressure sensors, and a thermostatically controlled fan. Its mission was not scientific measurement but trajectory tracking of the carrier rocket. The transmitters broadcast on 20.005 and 40.002 MHz, a pair of frequencies chosen so that amateur radio operators worldwide could pick up the beeps without modifying their receivers.

The sphere on its orbit

PS-1 lifted off from the Tyura-Tam test range on 4 October 1957, carried by an R-7 launch vehicle. The satellite entered an elliptical orbit with a perigee of 288 km and an apogee of 947 km; its period was 96.2 minutes and its inclination about 65 degrees, which shifted the satellite 24 degrees in longitude each revolution as the Earth turned. Reception proved possible with ordinary amateur equipment at distances of 2,000 to 3,000 km, making the ionosphere observable from above for the first time. The satellite flew for 92 days, until 4 January 1958, completing 1,440 revolutions, and its radio transmitters worked for 21 days after launch before the batteries ran down.

What the flight demonstrated

PS-1's scientific contribution lay in radio and optical observations: measurement of ionospheric transmission at two frequencies, and of upper-atmosphere density from the decay of its orbit. Politically, the flight was the opening signal of the space age and of the Soviet-American space race, and it made the term Sputnik part of languages worldwide.