This article contains orbital elements but does not include an epoch, or date when those elements, which typically vary over time, were correct. Please help by adding the epoch for the current data, or changing the orbital elements to ones with a known epoch.
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). ISZ was known to its designers as "Object D." Design of Object D had begun in January 1956 with intent to launch it during the International Geophysical Year. Object D was planned to be the first satellite launched by the Soviet Union but ended up being the third following delays due to problems developing the extensive scientific experiments and their telemetry system. The new R-7intercontinental ballistic missile, also known by its GURVO designation 8K71, was ready to launch before Object D was finished. Worried at the prospect of America launching a satellite before he did, Sergei Korolev substituted the relatively simple "Prosteyshiy Sputnik-1" meaning "Simple Satellite 1", or PS-1, which was labeled Sputnik 1 by the Soviet Government, as the first satellite to be launched instead. The Sputnik 2 (PS-2) was also ready and launched earlier than Object D.
Sputnik 3 was launched by a modified R-7 Semyorka missile developed for satellite launches, the Sputnik 8K91. Following a launch failure on 27 April 1958, a development of Object D finally reached orbit, having been launched at 07:00:35 on 15 May 1958; the Soviet Government designated it Sputnik-3. Sputnik 3 was an automatic scientific laboratory spacecraft. It was conically shaped and was 3.57 m (11.7 ft) long and 1.73 m (5.68 ft) wide at its base. It weighed 1,327 kg (1.46 tons). 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. While The Earth's outer radiation belts were detected during the flight, its Tral-D tape recorder failed, so it was unable to map the Van Allen radiation belt. The Soviets, without full evidence, were "hog-tied". The spacecraft remained in orbit until 6 April 1960, when the orbit degraded from drag in the upper atmosphere to the point where the satellite reentered the atmosphere, disintegrating before impact.
Payloads are separated by bullets ( · ), launches by pipes ( | ). Manned flights are indicated in bold text. Uncatalogued launch failures are listed in italics. Payloads deployed from other spacecraft are denoted in brackets.