| Instruments |
| Upper Atmosphere : |
Composition of the upper atmosphere |
| Geiger counters : |
Charged particles |
| Micrometeoroid detectors : |
Micrometeoroids |
|} Sputnik 3 (Russian: Спутник-3, Satellite 3) was a Soviet satellite launched on May 15, 1958 from Baikonur cosmodrome by a modified R-7/SS-6 ICBM. It was a research satellite to explore the upper atmosphere and the near space.
In July 1956, the Soviet Union's OKB-1 drafted a project to design and build the first Earth satellite, designated ISZ (Artificial Earth Satellite). Sputnik 3 was planned to be the first satellite launched by the Soviet Union. The new R-7 intercontinental ballistic missile was ready to launch before Sputnik 3 was ready. The Sputnik 3 completion date kept slipping and Sergei Korolev substituted the relatively simple Sputnik 1 as the first satellite to be launched, instead. The Sputnik 2 was also ready earlier and launched earlier than Sputnik 3. Korolev was concerned that if he waited for Sputnik 3 to be ready, the United States would be the first to launch an artificial satellite.
Sputnik 3 was an automatic scientific laboratory spacecraft. It was conically shaped and was 3.57 m long and 1.73 m wide at its base. It weighed 1,327 kg. The scientific instrumentation (twelve instruments) provided data on pressure and composition of the upper atmosphere, concentration of charged particles, photons in cosmic rays, heavy nuclei in cosmic rays, magnetic and electrostatic fields, and meteoric particles. The outer radiation belts of the Earth were detected during the flight. Its tape recorder failed, so it could not map the Van Allen radiation belt. The spacecraft remained in orbit until April 6, 1960, when the orbit degraded from drag in upper atmosphere to the point causing the satellite to enter the atmosphere.
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