Sputnik 1 was the first artificial satellite to be launched into orbit, on October 4, 1957. The satellite had a mass of about 83 kg (184 pounds). It had two radio transmitters (20 and 40 MHz) and is believed to have orbited Earth at a height of about 250 km (150 miles). Analysis of the radio signals was used to gather information about the electron density of the ionosphere. Temperature and pressure was encoded in the duration of radio beeps, indicating the satellite was not punctured by a meteorite. Sputnik 1 was launched by an R-7 rocket. It incinerated upon re-entry on 3 January 1958.
Sputnik was the first of several satellites in the Soviet Union's Sputnik program, the majority of them successful. Sputnik 2 followed as the second satellite in orbit, also the first to carry an animal, the dog Laika. The first failure occurred with Sputnik 3.
The Sputnik 1 spacecraft was the first artificial satellite successfully placed in orbit around the Earth and was launched from Baikonur Cosmodrome at Tyuratam (370 km southwest of the small town of Baikonur) in Kazakhstan, then part of the Soviet Union. The Russian word "Sputnik" means "companion" ("satellite" in the astronomical sense). The full official name, however, translates as "Artificial Earth Satellite" (ISZ in Russian literature). In 1885 Konstantin Tsiolkovsky first described in his book Dreams of Earth and Sky (ISBN 1414701632) how such a satellite could be launched into a low altitude orbit. It was the first in a series of four satellites as part of the Sputnik program of the former Soviet Union and was planned as a contribution to the International Geophysical Year (1957-1958). Three of these satellites (Sputnik 1, 2, and 3) reached Earth orbit.
The actual sequence of decision-making as to the form of Sputnik 1 was convoluted. A tonne-and-a-half, cone-shaped artificial satellite capable of making many physics measurements in space was first planned by Academician Keldysh, but when the Soviets read that the American Project Vanguard had two satellite designs, a small one which was just to see if they could get something into orbit, the Soviets decided to have what translates as the "Simplest Satellite" too, one which was one centimeter larger in diameter, and much heavier, than Vanguard's "real" satellite. They had to see whether the conditions in low Earth orbit would permit the bigger satellite to remain there for a useful length of time. When, months after Sputnik 1, the Vanguard test satellite was orbited, Khrushchev ridiculed it as a "grapefruit." Once the Soviets found they could orbit a test satellite too, they planned to orbit Keldysh's space laboratory satellite as Sputnik 3, and did so after one launch failure.
The Sputnik 1 satellite was a 58.0 cm-diameter aluminum sphere that carried four whip-like antennas that were 2.4-2.9 m long. The antennas looked like long "whiskers" pointing to one side. The spacecraft obtained data pertaining to the density of the upper layers of the atmosphere and the propagation of radio signals in the ionosphere. The instruments and electric power sources were housed in a sealed capsule and included transmitters operated at 20.005 and 40.002 MHz (about 15 and 7.5 m in wavelength), the emissions taking place in alternating groups of 0.3 s in duration. The downlink telemetry included data on temperatures inside and on the surface of the sphere.
Since the sphere was filled with nitrogen under pressure, Sputnik 1 provided the first opportunity for meteoroid detection (no such events were reported), since losses in internal pressure due to meteoroid penetration of the outer surface would have been evident in the temperature data. The satellite transmitters operated for three weeks, until the on-board chemical batteries failed, and were monitored with intense interest around the world. The orbit of the then inactive satellite was later observed optically to decay 92 days after launch (January 4, 1958) after having completed about 1400 orbits of the Earth over a cumulative distance traveled of 70 million kilometers. The orbital apogee declined from 947 km after launch to 600 km by Dec. 9th.
The Sputnik 1 rocket booster also reached Earth orbit and was visible from the ground at night as a first magnitude object, while the small but highly polished sphere barely visible at sixth magnitude more difficult to follow optically. Several replicas of the Sputnik 1 satellite can be seen at museums in Russia and another is on display in the Smithsonian National Air and Space Museum in Washington, D.C.
The United States had also been working on satellites, primarily through teams working for the US Navy as Project Vanguard. Their first launch had originally been intended to launch before Sputnik, but was delayed several times before blowing up on the pad. A rush effort then started under the US Army's Jupiter project and succeeded launching Explorer I in January 1958. This is considered the start of the Space Race between the two superpowers, as an aspect of the Cold War. Both nations attempted to outdo each other in space exploration, eventually culminating in the launch of the Apollo 11 mission to the Moon.
In 2003 a back-up unit of Sputnik 1 called "model PS-1" was sold on eBay (minus the classified military radio parts that were removed in the 1960s). It had been on display in a science institute near Kiev. It is estimated that between four and twenty models were made for testing and other purposes.
A Sputnik 1 model was given as a present to the United Nations and now decorates the entry Hall of its New York City Headquarters.
- a recording of Sputnik's telemetry signal