NASA's New Crew Escape System
The next vehicle to carry humans to space will let astronauts safely abort in case of an emergency.
In building a successor to the space shuttle, NASA has made one component a necessity: a system to let the crew escape should a catastrophe occur on the launch pad or during the first few seconds of flight.
For this reason, a completely new launch escape system is being developed for the Orion crew exploration vehicle, which NASA plans to send into space aboard the Ares rockets in 2015. Both are part of NASA’s Constellation Program to send humans to the moon and, eventually, to Mars.
The new escape system would separate the crew module from the launch rocket in a fraction of a second with a small, controlled explosion. Almost simultaneously, a solid rocket motor would fire, providing a million pounds of thrust to accelerate the module from 0 to 600 miles per hour in 3.5 seconds, pulling the astronauts to a safe distance before the module’s parachutes deploy.
An escape system was judged an unnecessary addition to the space shuttle, which was originally designed to fly frequently, carrying huge payloads such as large satellites into orbit. “There were so many safety elements designed into the shuttle, people thought the safest thing was to just make sure the shuttle could always get back to the runway in case of engine shutdown,” says Jeffrey Hoffman, a former astronaut and currently a professor of aeronautics and astronautics at MIT. “In retrospect, people would agree we need an escape system.”
This point was proved tragically in 1986, when the Space Shuttle Challenger broke apart 73 seconds into flight due to a failure in one of its solid rocket boosters. “If the crew had a launch abort system, there may have been an opportunity for them to escape,” says Henri Fuhrmann, program manager of the new launch abort system at Orbital Sciences, an aerospace company that has partnered with NASA to design and develop the escape system. The space agency has also partnered with Lockheed Martin, Aerojet, and Alliant Techsystems (ATK) on the project.
The design of the new system is based on the launch escape system built for the Apollo capsule; it also has similarities to Russia’s abort system on the Soyuz spacecraft. The Russian system was used successfully in 1983 when a fuel spill caused a fire on the launch pad seconds before liftoff. But NASA’s new system will also feature novel technologies, including a motor for steering the crew module and nozzles to reverse the flow of hot gases. The system is the “first of its kind,” says Kevin Rivers, project manager at NASA’s Langley Research Center, in Hampton, VA. Unlike its predecessors, the system will function at an altitude of up to 91,440 meters during phases of the flight when the rocket is most susceptible to failures.
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.”