When NASA retires its space shuttles, the job of taking astronauts back and forth between Earth and the space station will fall solely on capsule-based spacecraft like the agency's new Orion spacecraft, currently pegged as an escape ship for the orbiting lab.

An important part of any spacecraft designed to carry humans is the Launch Abort System a set of rockets and motors that are engineered to deliver the crew safely back to the ground should an emergency such as an explosion or a fire occur during a launch.

NASA is planning to test Orion's Launch Abort System on May 6, 2010 at the U.S. Army's White Sands Missile Range near Las Cruces, N.M. This SPACE.com graphic shows how the escape system would work.

The Abort System motors will be contained within a tower-like structure at the topmost part of the Orion. The crew capsule will be attached to the base of the Abort System and, during a real launch, the rest of the exploration vehicle and the rocket boosters would be below the crew capsule.

During the test, the Abort System's three motors will rip a mockup of an Orion crew capsule from its mooring at speeds that should, ideally, be able to spare the crew capsule any damage during a launch emergency.

The primary motor will fire with 500,000 pounds of thrust to shoot the crew capsule away from the launch pad. The altitude control motor will steer and orient the capsule to maintain stability. Lastly, the jettison motor will pull the entire Abort System away from the capsule, so a parachute can be released and the capsule can land.

If an explosion or fire were to occur during a launch within or near the rocket boosters, which contain all the fuel needed to lift the vehicle into space, the crew capsule would have to be traveling at high speeds in order to move a safe distance from the boosters. With this Abort System, the capsule may reach a speed of 445 mph (716 kph) during its first three seconds of flight.

The overall forces an astronaut would feel while lying on his back inside the escaping capsule would be slightly less than a jet fighter pilot would feel after hitting the eject button while flying in a seated, upright position, said Roger McNamara, launch abort systems director for the Orion program at Lockheed Martin, which is building the spacecraft for NASA.

"What we'll probably pull here is about 15-1/2 Gs, but because the astronauts would be laying back in their launch position they can take more than a jet fighter pilot can take," McNamara said.

Fighter pilots typically take around 9 Gs (nine times the force of gravity ) during emergency ejections, but are sitting upright and feel the effects more, McNamara said.

Although these speeds and forces could possibly injure the astronauts, this system would be better than the alternative.

"They'll feel the effects. The bottom line is they'll be walking away," McNamara said.

To date, no Launch Abort System has been used during an American launch, though a similar system was used in 1983 to pull two Russian cosmonauts to safety when a fire broke out at the launch pad during the attempt launch of their Soyuz T spacecraft. NASA's space shuttles are not equipped with launch abort systems, though astronauts do wear pressure suits and have trained on ways to bail out during extreme emergencies.

Launch abort towers are also used on China's Shenzhou manned spacecraft, as well.

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