Launch escape system

A launch escape system (LES) or launch abort system (LAS) is a crew-safety system connected to a space capsule that can be used to quickly separate the capsule from its launch vehicle in case of an emergency requiring the abort of the launch, such as an impending explosion. The LES is typically controlled by a combination of automatic rocket failure detection, and a manual activation for the crew commander's use. The LES may be used while the launch vehicle is still on the launch pad, or during its ascent. Such systems are usually of two types:

*A solid-fueled rocket, mounted above the capsule on a tower, which delivers a relatively large thrust for a brief period of time to send the capsule a safe distance away from the launch vehicle, at which point the capsule's parachute recovery system can be used for a safe landing on ground or water. The tower and rocket are jettisoned from the space vehicle in a normal flight at the point where it is either no longer needed, or cannot be effectively used to abort the flight. These have been used on the Mercury, Apollo, Soyuz, and Shenzhou capsules.
*The crew are seated in seats that eject themselves (ejection seats) as used in military aircraft; each crew member returns to Earth with an individual parachute. Such systems are effective only in a limited range of altitudes and speeds. These have been used on the Vostok and Gemini capsules.

History

The idea of using a rocket to remove the capsule from a space vehicle was developed by Maxime Faget in 1958. The system, using the tower on the top of the space capsule to house rockets, was first used on a test of the Project Mercury capsule in March 1959.
Historically, LES were used on American Mercury and Apollo spacecraft. Both designs used a solid-fuel rocket motor. The Mercury LES was built by the Grand Central Rocket Company in Redlands, California (which later became the Lockheed Propulsion Company). Apollo used a design that had many similarities to the Mercury system. LES continue to be used on the Russian Soyuz and Chinese Shenzhou spacecraft. The SpaceX designed Dragon 2 uses a hypergolic liquid-fueled launch abort system integrated to the capsule and the Boeing Starliners. The European Space Agency's Hermes and the Soviet ''Buran''-class spaceplanes would also have made use of them if they had ever flown with crews. As shown by Soyuz T-10a, a 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. The Soyuz launch escape system is called ''CAC'' or ''SAS'', from the Russian/ transliterated Russian ''Система Аварийного Спасения'' or ''Sistema Avariynogo Spaseniya'', meaning emergency rescue system.

The Soviet Proton launcher has flown dozens of times with an escape tower, under the Zond program and the TKS program. All of its flights were uncrewed.

The Space Shuttle was fitted with ejection seats for the two pilots in the initial test flights, but these were removed once the vehicle was deemed operational and carried additional crew members, which could not be provided with escape hatches. Following the 1986 ''Challenger'' disaster, all surviving orbiters were fitted to allow for crew evacuation through the main ingress/egress hatch (using a specially developed parachute system that could be worn over a spacesuit), although only when the Shuttle was in a controlled glide.

The Orion spacecraft which was developed to follow the Space Shuttle program uses a Mercury and Apollo-style escape rocket system, while an alternative system, called the Max Launch Abort System (MLAS), was investigated and would have used existing solid-rocket motors integrated into the bullet-shaped protective launch shroud.

Under NASA's Commercial Crew Development (CCDev) program Blue Origin was awarded $3.7 million for development of an innovative 'pusher' LAS, it is used on the New Shepard Crew Capsule.

Also under NASA's CCDev program, SpaceX was awarded $75 million for the development of their own version of a "pusher" LAS. Their Dragon 2 spacecraft was to use its SuperDraco engines during a launch abort scenario. Although often referred to as a "pusher" arrangement since it lacks a tower, the Dragon 2 LAS removes both the capsule and its trunk together from the launch vehicle. The system is designed to abort with the Super Draco engines at the top of the abort stack as occurs with a more traditional tractor LAS. The concept was first tested in a Pad Abort test conducted at SLC-40, Cape Canaveral Air Force Station, on May 6, 2015. SpaceX tested the system on January 19, 2020 during ascent of the Falcon 9 rocket in Kennedy Space Center Launch Complex 39, from where it has later launched crews to the International Space Station.

The second crewed spacecraft selected by NASA for its CCDEV program was Boeing's CST-100 Starliner

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