Apollo LES pad abort test with boilerplate crew module.

Apollo spacecraft: Apollo Launch Escape System.

A Launch Escape System (LES) is a top-mounted rocket connected to the crew module of a crewed spacecraft and used to quickly separate the crew module from the rest of the rocket in case of emergency. Since the escape rockets are above the crew module, an LES typically uses separate nozzles which are angled away from the crew module. The LES is designed for use in situations where there is an imminent threat to the crew, such as an impending explosion.

Uses[link]

Historically, LESes 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. Launch Escape Systems continue to be used on the Russian Soyuz and Chinese Shenzhou programme spacecraft. The SpaceX-designed Dragon spacecraft uses a liquid fueled launch abort system integrated to the capsule to minimize spacecraft costs.

The LES may be used while the launch vehicle is still on the launch pad, or during its ascent.

Related systems[link]

The Russian Vostok and American Gemini spacecraft both made use of ejection seats. The European Space Agency's Hermes and the Russian Buran space planes 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.

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 crew would have had to reach the exit from their seats and jump out, to then return to earth via parachute).

The Multi-Purpose Crew Vehicle being developed to follow the shuttle program will use a Mercury and Apollo-style escape rocket system, while an alternative system, called the Max Launch Abort System (MLAS),^[1] has been floated to use existing solid-rocket motors integrated into the bullet-shaped protective launch shroud.

Under NASA's Commercial Crew Development (CCDev) program Blue Origin has been awarded $3.7 million for development an innovative 'pusher' LAS.^[2]

Also under NASA's CCDev program, Space X was awarded $75 million for the development of their own version of a "pusher" LAS.^[3]

Orbital Sciences Corporation intends to sell the LAS it was building for the Orion spacecraft to future commercial crew vehicle providers in the wake of cancellation of the Constellation project.^[4]

Usage[link]

The first fully operational test flight of an LES was Apollo mission A-004 on January 20, 1966. The mission used a Little Joe II booster, carrying an early version of the Apollo Command/Service Module.

The Soyuz T-10 spacecraft's crew narrowly escapes disaster.

Only one emergency use of an LES has occurred. This occurred during the attempt to launch Soyuz T-10-1 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 (140 to 170 m/s²) for five seconds. Reportedly, the capsule reached an altitude of 2,000 meters (6,500 ft) and landed 4 kilometers (2.5 mi) from the launch pad. On the Soyuz, the grid fins also deploy on the payload fairing to stabilize the craft.

The escape system unintentionally blasted off from the Mercury spacecraft on the failed Mercury-Redstone 1 mission

A previous launch accident occurred during the flight of Soyuz 18a on April 5, 1975. However in this case, the incident took place at high altitude, after the LES of the Soyuz had been discarded.^[5] The spacecraft automatically separated from the malfunctioning rocket and completed a successful re-entry.

See also[link]

• Apollo spacecraft
• Apollo abort modes
• Pad Abort Test-1 - Launch Escape System (LES) abort test from launch pad with Apollo Boilerplate BP-6.
• Pad Abort Test-2 - LES pad abort test of near Block-I CM with Apollo Boilerplate B-23A.

References[link]

 This article incorporates public domain material from websites or documents of the National Aeronautics and Space Administration.

External links[link]

Wikimedia Commons has media related to: Launch escape systems

• Launch Escape Subsystem - Detailed description of the Apollo launch escape system at Apollosaturn.com
• Soyuz T-10-1
• NASA Orion Pad Abort 1 Test Flight Photos
• NASA Pad Abort 1 Flight Test Video Highlights