Sputnik 1 was spherical in shape. It was 0.579 metres in diameter and weighed 83.60 kilogrammes. Its hermetically sealed body was made of aluminium alloys, and its surface was polished and specially treated.

All its apparatus and power sources were located inside the body. Before being launched it was filled with a gaseous nitrogen.

On the outside surface, aerials were attached - four rods 2.39 metres to 2.90 metres) long. While the sputnik was being taken out to its orbit, these aerials were folded back against the body of the rocket, but after the first two steps had fallen away the aerials turned out on their hinges, assuming the position shown in the famous photo.

While travelling in its orbit, the sputnik is subjected from time to time to sharply changing heat influences - heating by the Sun's rays while on the "day" side of the Earth and cooling when flying in the Earth's shadow.

Then there is the effect of the atmosphere's heat and so on. A certain amount of heat is generated, too, when the apparatus on the sputnik is working.

As far as heat is concerned the sputnik is an independent heavenly body, exchanging radiant heat with the surrounding space. To ensure for a considerable period the normal temperature needed for the functioning of the apparatus on the satellite was, therefore, a fundamentally new and difficult problem.

The needed temperature on Sputnik I was ensured by regulating the heat resistance between the envelope and the equipment, through the forced circulation of the nitrogen in the satellite.

Two radio transmitters were installed in the sputnik, constantly emitting signals on frequencies of 20.007 and 40.002 megacycles (15 and 7.5 metre wavelengths respectively).