Sputnik 1 was launched into low Earth orbit on 4 October
1957 by the Soviet Union. It was the first artificial satellite to be
launched into space.
The satellite was a metallic sphere 58 centimetres in diameter and had
a mass of 84 kilogram. Four antenna rods were attached to the sphere.
The final stage of the launcher, which had a mass
of around 4,000 kg, also made it into orbit. This rocket stage was about
30 metres long and could easily be seen from the ground in the evening
and morning twilight hours as it trailed across the sky.
Sputnik 1 contained a radio beacon transmitting on the frequency of 20.005
MHz. This could be received by a sensitive short wave receiver on the
ground, and many people heard the beep-beep-beep sound of this satellite
as it orbited around the Earth every 90 minutes or so. The beacon transmitted
for 21 days on internal batteries.
Sputnik 1 remained in orbit for about 3 months, finally burning up as it
re-entered the Earth's atmosphere.