Orbital Launch
Orbital human spaceflight | |||||||
Name | Debut | Launches | |||||
---|---|---|---|---|---|---|---|
Vostok | 1961 | 6 | |||||
Mercury | 1962 | 4 | |||||
Voskhod | 1964 | 2 | |||||
Gemini | 1965 | 10 | |||||
Soyuz | 1967 | 110 | |||||
Apollo | 1968 | 15 | |||||
Shuttle | 1981 | 135 | |||||
Shenzhou | 2003 | 4 |
Orbital spaceflight from Earth has only been achieved by launch vehicles that use rocket engines for propulsion. To reach orbit, the rocket must impart to the payload a delta-v of about 9.3–10 km/s. This figure is mainly (~7.8 km/s) for horizontal acceleration needed to reach orbital speed, but allows for atmospheric drag (approximately 300 m/s with the ballistic coefficient of a 20 m long dense fuelled vehicle), gravity losses (depending on burn time and details of the trajectory and launch vehicle), and gaining altitude.
The main proven technique involves launching nearly vertically for a few kilometers while performing a gravity turn, and then progressively flattening the trajectory out at an altitude of 170+ km and accelerating on a horizontal trajectory (with the rocket angled upwards to fight gravity and maintain altitude) for a 5-8 minute burn until orbital velocity is achieved. Currently, 2-4 stages are needed to achieve the required delta-v. Most launches are by expendable launch systems.
The Pegasus rocket for small satellites instead launches from an aircraft at an altitude of 12 km.
Other techniques, such as use of a launch loop, have been proposed for non-rocket spacelaunch. These techniques are theoretical: no attempts have been made to orbit a vehicle using any of them.
Read more about this topic: Orbital Spaceflight
Famous quotes containing the word launch:
“Now launch the small ship, now as the body dies
and life departs, launch out, the fragile soul
in the fragile ship of courage, the ark of faith
with its store of food and little cooking pans
and change of clothes,”
—D.H. (David Herbert)