To achieve orbit, the horizontal velocity is as important as the altitude. To stay in orbit at the Kármán line requires a speed of around 18 000 miles per hour. It takes 20 times more energy to gain enough speed for a low-earth orbit than to simply climb to that altitude. A German V2 rocket was the first to cross the Kármán line during a 1944 test flight, and in 1957 the Soviet satellite Sputnik 1 became the first man-made object to orbit the Earth. This was followed in 1961 by Vostok 1, in which Yuri Gagarin made the first human spaceflight.