Being in orbit means falling around Earth fast enough to keep missing it
A satellite does not float above gravity. It is falling the whole time, just moving sideways so quickly that the ground curves away beneath it. Getting that speed still requires rockets, the only proven way to orbit, and the equation engineers use to plan them was published by Konstantin Tsiolkovsky in 1903.
The earliest rocket-travel proposal came from the Scottish astronomer William Leitch in an 1861 essay, but Tsiolkovsky's rocket equation, which links the change in speed a rocket can achieve to its exhaust velocity and how much of its mass is fuel, remains the core of mission design. Robert Goddard made the idea practical. His 1919 paper applied a flared de Laval nozzle to liquid-fuelled rockets, and on 16 March 1926 he launched the first one.
War accelerated everything. Nazi Germany's V-2 was the first guided rocket, and a June 1944 test climbed to 189 kilometres, the first human-made object in space. Afterwards Wernher von Braun and much of his team surrendered to the Americans, while the Soviets copied captured V-2 plants. Sergey Korolev's R-7 missile, built to carry nuclear warheads, lofted Sputnik 1 on 4 October 1957. After two humiliating Vanguard failures, the United States orbited Explorer 1 the following February, then trailed Yuri Gagarin's 1961 flight with Alan Shepard's short hop and John Glenn's orbit before committing to the Moon.
Reaching orbit usually takes stages. A first stage lifts the vehicle through the thick lower air and drops away, and an upper stage pushes the payload up to orbital speed. Space is most often said to begin at the Kármán line, 100 kilometres up, though the United States counts from 80. Launch times are fenced by windows, set mainly by Earth's rotation, and a loaded rocket can be enormous: Columbia weighed 2,030 tonnes on its first flight. Apollo crews first circled Earth in a parking orbit to check their ship before heading for the Moon; robotic probes usually skip that and go straight out.
Leftovers are a growing hazard. Spent upper stages and dead satellites often cannot bring themselves down, and when they collide or break apart they spray fragments that can trigger further crashes, a runaway feared as Kessler syndrome.
Source: Spaceflight
