Friday, 25 May 2012

Wahana Antariksa Pengorbit

Sounding rockets are normally used for brief, inexpensive space and microgravity experiments. 

Current human-rated suborbital launch vehicles include SpaceShipOne and the upcoming SpaceShipTwo, among others (see space tourism). 

The delta-v needed for orbital launch using a rocket vehicle launching from the Earth's surface is at least 9,300 m/s (31,000 ft/s). 

This delta-v is determined by a combination of air-drag, which is determined by ballistic coefficient as well as gravity losses, altitude gain and the horizontal speed necessary to give a suitable perigee. 

The delta-v required for altitude gain varies, but is around 2 km/s (1.2 mi/s) for 200 km (120 mi) altitude.

Minimising air-drag entails having a reasonably high ballistic coefficient, which generally means having a launch vehicle that is at least 20 m (66 ft) long, or a ratio of length to diameter greater than ten. Leaving the atmosphere as early on in the flight as possible provides an air drag of around 300 m/s (980 ft/s). 

The horizontal speed necessary to achieve low earth orbit is around 7,800 m/s (26,000 ft/s). 

The calculation of the total delta-v for launch is complicated, and in nearly all cases numerical integration is used; adding multiple delta-v values provides a pessimistic result, since the rocket can thrust while at an angle in order to reach orbit, thereby saving fuel as it can gain altitude and horizontal speed simultaneously