Extraterrestrial relays

Communications was another area in which satellite technology needed proving. A large satellite in orbit could act as a reflector for radio signals (tested by the Echo project, which began in May 1960). A satellite could also broadcast a pre-recorded signal across a wide area (as with SCORE, which transmitted a Christmas message from President Eisenhower to the world in 1958). A more direct precursor of today's communication satellites was the US Army's Courier 1B, launched in October 1960. The world's first active repeater satellite, it recorded signals sent from the ground and then retransmitted them.

Getting complex machines to work in space requires a number of innovations. One of the worst problems is the temperature difference between sunlight and shade, which can cause components to expand, contract, and eventually fracture. Silvered insulation can help by deflecting much of the Sun's radiation, while highly conductive heat pipes can carry heat from hot areas to cooler ones. Delicate electronics must be cushioned with internal filling against the stress of launch and must also be robust enough to cope with flying through a blizzard of radiation and charged particles. Most satellites and probes also need stabilization and steering systems.

SATELLITE DESIGN

arced 113,584km (70,549 miles) above the Earth before falling back to crash in the Pacific Ocean.

Further attempts at lofting a probe towards the Moon also met with failure. Pioneer 2 fell swiftly back to Earth when one of its rocket stages failed, and Pioneer 3, which used the Army's Juno II launch vehicle (a modified version of the finished Jupiter IRBM), suffered a similar fate. At least onboard radiation detectors on Pioneers 1 and 3 helped to define the extent of the Van Allen Belts.

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