Fire in the hole: The abort motor for the new launch abort system was successfully tested in October 2008.
It will be possible for an abort command to be initiated by the crew, by ground-control personnel, or by the flight computer. Once the crew module and launch abort tower, which sits on top of the module, have been detached from the rocket, a second motor will steer the vehicle into a safe orientation. If activated on the launch pad, the crew module and abort tower will fly one mile into the air and three miles downrange relative to the rocket; during ascent, these distances would vary depending on flight conditions. Once the vehicle is oriented so that the heat shield is facing forward, a third motor fires to separate the launch abort tower from the crew module, parachutes deploy, and the capsule safely splashes down in the ocean for recovery.
The abort motor, the first motor to fire, has a unique design: its four nozzles turn the flow of the hot gases it produces away from the crew module. The second motor, which is located at the very top of the tower and used to control and steer the vehicle, is the most complex and consists of eight small thrusters that fire differentially to point the nose of the launch abort system in the direction that is determined the safest.
Apollo used a simple system that was passively controlled like a large dart, says NASA’s Rivers. “But because of the mass properties of the [new system], using a passive system was deemed to be aerodynamically unstable,” says David McGowan, lead engineer at Langley. “Without attitude control, the vehicle would just flip over.”
“The steering thrusters are pretty fantastic,” says Scott Uebelhart, a postdoctoral associate at MIT who studies human spaceflight. “And no one has tested a new rocket engine like this in almost 40 years. It’s a big leap forward.”
Last week, NASA tested an alternative launch abort system called the max launch abort system, which is based on some of the original concepts studied for the Constellation Program. The test demonstrated a stable trajectory, reorientation, and separation of the crew module from the abort system, and parachute recovery of the crew module simulator, but it was mostly designed for gathering data. It did not have to follow the same criteria as the newer system. “It was just a quick try and turn-around approach for research,” says Rivers.
The launch abort system for Orion will undergo its first flight test later this year and several more tests before it is ready for launch by 2015.
“We know we are building a system that is going to save lives,” says Fuhrmann. “It is something that we hope we never have to operate, but if it is called upon, it has to function flawlessly.”