A “tractor” escape system was used on the Apollo spacecraft.
Rockets in the launch escape tower pulled the crew capsule away from a malfunctioning rocket. NASA’s upcoming Orion capsule uses a similar tractor rocket.
A “pusher” escape system, such as the experimental Max Launch Abort System, puts the escape rockets at the bottom of the ship to push it up and away. SpaceX’s manned Dragon capsule will use a pusher system.
The first ejection seats for aircraft were developed in World War II. The only spacecraft to use ejection seats were the Soviet Vostok (which required the pilot to eject before landing), NASA’s two-man Gemini and the first four space shuttle launches, which also had only two crew members. As later shuttle missions carried up to 8 astronauts seated on two decks, the ejection seats were removed because not everyone could have been saved in an accident.
In 1958, NASA designer Maxime Faget equipped Mercury, America’s first manned spacecraft, with a tractor rocket to pull the entire capsule free in an emergency.
In 1983, an escape rocket pulled the three cosmonauts of Soyuz T-10-1 to safety when its booster exploded on the launch pad. As of 2015, this is the only case where an abort system saved a crew from a launchpad accident.
Apollo astronauts practiced firing their service module rocket engine to turn around and come home if mission-threatening failures occurred. In 1970, an explosion in Apollo 13’s service module made the big engine unreliable, so the smaller lunar module rocket engine was used instead.
A descending lunar module could abort its landing by casting off the descent stage and firing engines to return to the command module. Apollo 10 tested this abort procedure in 1969, during a dress rehearsal for Apollo 11’s landing attempt.
In the six seconds after the main engines ignited but before the solid-fueled boosters fired, computers could shut down the launch. This happened five times during the shuttle program. Once the solid-fueled boosters ignited, they could not be stopped.
The riskiest abort option, Return to Launch Site (RTLS), involved flipping the orbiter/external tank assembly around to send the craft back toward the East Coast of the United States. This abort mode was never tried, but astronauts were skeptical that it would work.
In 1985, STS-51-F (Challenger) became the only shuttle mission to experience an in-flight abort. One of the main engines shut down early. The shuttle failed to reach the correct speed and altitude, but it settled into a lower orbit.
Although it was never tested in real life, an ascending shuttle had the option to dump the booster rockets and external fuel tank to make an airport landing in one of several preselected trans-Atlantic sites.
Both fatal shuttle accidents happened at times when no abort options were available. After Challenger, NASA added a crew bailout option for a shuttle unable to make it safely to a landing site. The side hatch would be jettisoned, and an extending rod would be set up through the opening. Astronauts sliding out would be thrown clear of the orbiter’s wing before descending on parachutes.
Source SPACE.com: All about our solar system, outer space and exploration.
Source: http://www.space.com/29260-how-spacecraft-launch-aborts-work-infographic.html
