Category:Satellites

1957: Sputnik 1, a simple radio transmitter with no reception or relay ability [image info]

1960: Echo 1: Essentially a giant orbiting inflated foil-covered balloon that one could bounce signals off [image info]

1962: The famous Telstar 1' communications satellite allowed the first live transatlantic TV broadcasts [image info]

The world's first purpose-built artificial satellite was the Soviet Union's Sputnik 1 (Satellite 1), launched in 1957.

The start of the Space Race

Known in the West as just "Sputnik" (because of a mistaken impression outside the USSR that this was a special name), "Sputnik 1" was simple metal sphere 23 inches across, with four trailing antennae, fitted with a simple radio transmitter, with enough battery life to transmit for 22 days. Launched on 4th October 1957, Sputnik 1's orbit was sufficiently titled away from the equator for its broadcasts to eventually reach almost every part of the globe, and the Sputnik's "bleeps" could be picked up by almost anyone owning "radio ham" equipment.

Suddenly, not only were satellites possible, but they were real, and you could hear them over you (with a receiver). Sputnik took the US government by surprise, galvanised the world into realising the the Space Age was suddenly here, and shocked the US into accelerating its own space programme.

Sputnik 1, in a low Earth orbit, was slowed by the drag of the Earth's upper atmosphere, and "re-entered" and burned up on 4th January 1958

Geostationary satellites

The time taken for a satellite to orbit the Earth depends on the orbital radius. For a very particular height, corresponding to an altitude above sea level of 35,786 km, the time taken to make a single orbit is 24 hours, equal to the time taken for the Earth to make a single rotation: A satellite above the equator orbiting at this height will appear to hover above a fixed location, which is perfect for radio relay stations and (latterly) communications satellites. One of the crudest initial communication relay devices as the American 1960 "Echo 1", which was literally a 100foot-diameter inflated balloon covered in a metallic film, which could be used at a transmission target so that signals could then be reflected back to Earth, to locations where there was no direct line-of-sight.

Later communications satellites used electronic transponders (powered by solar panels) to also boost the signal, allowing, for instance, tv signals to be relayed across the Atlantic, or all over Europe. The Astra 1 satellite, hovering over Africa, has a reach (a radcast "footprint") that allowed it to broadcast to the UK, and allowed the creation of Sky's multichannel satellite TV service starting in 1989.

Other types satellite

Other types of satellite (other than communications satellites) include weather satellites that image evolving weather systems, military spy satellites that take photos of foreign territory, structures and military formations, and GPS (Global Positioning System) satellites that were originally intended to allow military hardware to know its own location (but are now available for civilian use).The use of geostationary orbits becomes less important if one has a satellite constellation, that allows one to automatically switch to using whichever passing satellite in the group is currently closest.

External links

• Sputnik 1 (wikipedia.org)
  • Sputnik crisis (wikipedia.org)
• Geostationary Orbit (wikipedia.org)
• Telstar (wikipedia.org)