Sub-orbital flight

The first US astronauts, Alan Shepard and Gus Grissom, flew sub-orbital Mercury test flights in 1961 aboard Redstone rockets, reaching over 160 km (99 miles) altitude. They were recognised as astronauts. When a Soviet Soyuz R7 booster failed in 1975,

causing the abort that led to Soyuz 18-1 making a sub-orbital flight to about 145 km (90 miles) altitude, the flight was credited as a “space flight” to the two cosmonauts.

The Redstone was the USA’s first intermediate-range ballistic missile and was pow­ered by one Rocketdyne A-7 engine, with a thrust of 35,380 kg (78,013 lb) burning liquid oxygen, ethyl alcohol and water. The Mercury-Redstone was 25.29 m (82.97 ft) high. Two such vehicles were used in the Mercury programme for manned flights, while a third was cancelled with the desire to press on to the first orbital manned flight using Atlas.