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, such as an impending explosion. The LES is typically controlled by a combination of automatic rocket failure detections, and a manual activation for the crew commander’s use. The LES could be used while the launch vehicle is still on the launch pad, or during its ascent.  

Space X Crew Dragon Module takes astronauts to the International Space Station on a rocket called a Falcon 9.s.

There are 3 ways to trigger the capsule’s abort system once it’s activated. The crew can pull a handle inside the spacecraft; mission control can send a remote command to the spacecraft; or the craft itself can automatically start the sequence if it detects a problem in the rocket. This will cause the eight small Super Draco rocket engines on the capsule to fire and lift the capsule away from the rocket. 

This is very abrupt and brutal for a spacecraft’s occupants. In a matter of seconds, the capsule goes from a standstill to rocketing skyward at about 350 mph. During the abort, the astronauts experience forces more than four times stronger than gravity, ascending about a mile and a half into the sky before the capsule descends and splashes down in the ocean under a parachute. It’s an extreme manoeuvre for extreme emergencies. 

If the astronauts need to be evacuated in less dire situations, they can grab a ride to the ground on a zipline attached to the tower. E.g., if the launch gets called off after the rocket is fuelled, the normal process is to keep the astronauts in the capsule until the fuel is drained. Then they can come down the tower the same way they went up. But if there’s a problem draining the propellant, it’s important to get the crew away from the live rocket ASAP so the problem can be fixed. It doesn’t make sense to put the astronauts at risk by doing an abort, so instead, they use the zipline to make their quick getaway. (Sounds quite fun).  

 The computers on Crew Dragon are watching for things like unexpected changes in acceleration or any deviation from the expected flight path. NASA divides the rocket’s ascent into seven “stages of abort.” Each phase of the launch has different parameters that would trigger an abort and protocols for how the capsule would be controlled. It’s a delicate balancing act and the abort system must work every time it’s needed however, it cannot be so sensitive that it triggers when everything is going fine. Setting the parameters correctly requires running thousands of computer simulations that throw random parameter changes at the capsule’s computers to see how they would respond. 

The accompanying picture is of SpaceX’s Dragon capsule progressing into orbit after its stage separation from the Falcon 9 Rocket, safely taking the astronauts to the International Space Station.  

Check out the below video to experience a real-life abort on the Space Shuttle (orbiter).  Even watching this short video gets your blood pumping. 

Watch this video: Last Second Shuttle Launch Abort