Launch escape system
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A Launch Escape System (LES) is a top-mounted rocket connected to the crew module of a crewed spacecraft and used to quickly separate and launch the crew module away from the rest of the rocket in the case of an emergency. Since the escape rockets are above the crew module, an LES typically uses separate nozzles which are angled away from the crew module to prevent the LES exhaust from hitting it. The LES is used in situations where there is an imminent threat to the crew, such as an impending explosion.
Historically, LES's were used on American Mercury and Apollo spacecraft. They continue to be used on the Russian Soyuz spacecraft. The only emergency use of a LES occurred during the attempt to launch Soyuz T-10 on September 26, 1983. The rocket caught fire, just before launch, but the LES was able to carry the crew capsule clear, seconds before the rocket exploded. The crew were subjected to an acceleration of 14 to 17 G's for five seconds. Reportedly, the capsule reached an altitude of 2000m (6500 feet) and landed 4 km. (2.5 miles) from the launch pad.
The Russian Vostok and American Gemini spacecraft both made use of ejection seats. The European Space Agency's Hermes and the Russian Buran space shuttles would also have made use of them if they had ever flown with crews. As shown by Soyuz T-10a, an LES must be able to carry a crew compartment from the launch pad to a height sufficient for its parachutes to open. Consequently, they must make use of large, powerful (and heavy) solid rockets. If possible, spacecraft designers prefer to use ejection seats as they are lighter and would be available for use when the spacecraft is returning to Earth. However, ejection seats are not practical for spacecraft with large crews as a separate seat and exit hatch must be provided for each.
The Space Shuttle was initially fitted with ejection seats for the initial "shakedown" flights, but these were removed once the vehicle was deemed operational. Following the Challenger disaster, all surviving orbiters were fitted to allow for crew evacuation through the main hatch, though this can only be used when the shuttle is in a controlled glide. The new Orion spacecraft that is being developed to replace the Shuttle will revert to the Mercury and Apollo-style escape rocket system.
[edit] See also
[edit] External links
- 'Launch Escape Subsystem' - Detailed description of the Apollo launch escape system at http://www.apollosaturn.com/
- 'Soyuz T-10-1
