Unmanned space missions

A robotic spacecraft is an uncrewed spacecraft, usually under telerobotic control. A robotic spacecraft designed to make scientific research measurements is often called a space probe. Many space missions are more suited to telerobotic rather than crewed operation, due to lower cost and lower risk factors. In addition, some planetary destinations such as Venus or the vicinity of Jupiter are too hostile for human survival, given current technology. Outer planets such as Saturn, Uranus, and Neptune are too distant to reach with current crewed spaceflight technology, so telerobotic probes are the only way to explore them.

Many artificial satellites are robotic spacecraft, as are many landers and rovers.

The first robotic spacecraft was launched by the Soviet Union (USSR) on 22 July 1951, a suborbital flight carrying two dogs Dezik and Tsygan. Four other such flights were made through the fall of 1951.

The first artificial satellite, Sputnik 1, was put into a 215-by-939-kilometer (116 by 507 nmi) Earth orbit by the USSR) on 4 October 1957. On 3 November 1957, the USSR orbited Sputnik 2. Weighing 113 kilograms (249 lb), Sputnik 2 carried the first living animal into orbit, the dog Laika. Since the satellite was not designed to detach from its launch vehicle's upper stage, the total mass in orbit was 508.3 kilograms (1,121 lb).

In a close race with the Soviets, the United States launched its first artificial satellite, Explorer 1, into a 193-by-1,373-nautical-mile (357 by 2,543 km) orbit on 31 January 1958. Explorer I was a 80.75-inch (205.1 cm) long by 6.00-inch (15.2 cm) diameter cyllynder weighing 30.8 pounds (14.0 kg), compared to Sputnik 1, a 58-centimeter (23 in) sphere which weighed 83.6 kilograms (184 lb). Explorer 1 carried sensors which confirmed the existence of the Van Allen belts, a major scientific discovery at the time, while Sputnik 1 carried no scientific sensors. On 17 March 1958, the US orbited its second satellite, Vanguard 1, which was about the size of a grapefruit, and remains in a 360-by-2,080-nautical-mile (670 by 3,850 km) orbit as of 2016^[update].

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