NASA CEV/launch abort system tested at AEDC

  • Published
  • By Philip Lorenz III
  • AEDC/PA
Arnold Air Force Base, Tenn. --  Dr. Richard Roberts, 716th Test Squadron project manager at Arnold Engineering Development Center (AEDC), believes what takes place behind the scenes to ensure space flight safety is an exciting story worth knowing. 

He wants the public to know what lengths NASA and other organizations, including AEDC, go to prevent accidents -- ones that could otherwise become source material for movies like Apollo 13 and other sensationalized dramatizations Hollywood has become famous for in the past. 

Dr. Roberts managed a team of engineers who recently conducted aerodynamics testing on NASA's Orion launch abort system during re-entry conditions in AEDC's Propulsion Wind Tunnel's (PWT) 16-foot transonic wind tunnel (16T). 

He said the purpose of the wind tunnel tests were to determine the jettison motor plume interaction effects on the crew module and boost protective cover/ launch abort system (LAS) separation aerodynamics following the abort fly-out to safety and just before the parachute deployment of an abort sequence from the Ares I launch vehicle. 

"[More simply put] the objective of this test was to study the separation of the crew module from the launch abort system," he said. "[It was] a fairly complicated test, and, as far as we know, the first test of its kind, [with the test article] actually flying backwards in the tunnel," he said. "[It involved] multiple balances with jet interaction. It's the first of a series of similar NASA wind tunnel tests, and will improve NASA's aero-database and computational simulation models which had been relied on previously." 

He said the test was exciting to do despite the challenges, including a complicated build-up. 

The wind tunnel test used a seven percent scale model of the Orion crew exploration vehicle, which included the crew module and launch abort system sections. The model was mounted with the heat shield forward while test controllers simulated plumes from the four jettison motor nozzles with high pressure air. 

Holding a plastic, 2 percent model of the crew module and LAS, Matthew Rhode, a NASA Langley Research Center engineer on the project, said, "Let me explain the abort situation and then you can kind of see where this test scenario falls in the whole scheme of things. In this stowed configuration, we have the crew module, the capsule that the crew will be in." 

Pointing to a slender portion of the model, he said, "We call this the launch abort system." 

Referring to the boost protective cover, he explained, "That is used to protect the crew module when it's flying through the air on the Ares I booster, but also it protects the crew module from the thrust and the plumes from the abort motors during fly-out, or jettison motor when it fires." 

Rhode said the abort sequence is fairly straight forward, but the aerodynamic effects on the components as they separate during a specific part of that chain of events is what the test will help to determine. 

"During an abort, if there's a problem with the booster rocket and the crew needs to escape, we'll fire the 400,000-pound thrust abort motor," he explained. "It's a solid-rocket motor with a common combustion chamber and four nozzles and that will burn for about three to five seconds. The abort motor is used to pull the crew up and away to safety. It's a pretty high-impulse motor." 

Rhode said while the abort motor pulls the crew module and abort system up and away from the Ares I launch vehicle, the attitude control motor (ACM), a controllable solid rocket motor with eight pintle-modulated valves/nozzles, will also be firing. 

"Each nozzle has what they call a pintle, which moves in and out of the throat controlling the amount of thrust," he continued. "The ACM nozzles can close off thrust, or lessen the amount of thrust in each nozzle for flight control." 

He said the attitude control motor helps to keep the vehicle stable and pointing forward 
during the emergency re-entry sequence. 

"About 20 seconds or so into the abort trajectory, we'll fire and move the attitude control motor thrust to a position that it'll kick the vehicle around so the it will be traveling heat shield forward," he continued. "So, it will be flying backwards in the air.
"The scarf nozzles, which are like a circle of four flush holes around the LAS just above the four nozzles of the abort motor, will fire. These are the four nozzles for the jettison motor, about a 40,000-pound rocket motor that fires for about one and a half to two seconds. 

"At the same time, pyrotechnic bolts will fire that hold the crew module and boost protective cover/ LAS together. What we're testing in the tunnel for this particular test is the jettison motor of the boost protective cover and separation between what was the launch abort system and the crew module." 

Rhode said it is important to understand what the test team is assessing. 

"We're looking at the influence of the proximity effects on the two bodies," he explained. "That's how the aerodynamic database is developed.
"You might have the given Mach number, angle-of-attack, side slip angle. You might have an actual force coefficient or normal force coefficient on the crew module/LAS component, and then you'll have a delta angle. 

"A delta would be added to that, which is determined by proximities. That can be based on, the X distance, the longitudinal distance and maybe a Z and a delta angle. In addition, we would also simulate the angle-of-attack." 

If all of this sounds like geek speak, David Mayfield, the Lockheed Martin staff engineer on the test, put the serious nature of the potential problems the team is trying to evaluate into perspective. 

"It would make a huge difference if the crew module and boost protective cover/LAS were to glide together," he explained. "The forward bay cover at the top part of the capsule is designed to eject after an abort event. 

"Once that ejects, then inside of the forward bay cover there are a variety of drogues and main parachutes. If the forward bay cover attaching hardware is damaged, it could cause an issue with the foreword bay cover deployment/jettison event. Or, in a more extreme case, it could actually rip a chute or one of the chute bags. If that happens, then it would be extremely difficult to execute a safe landing." 

So, how will the data the team collected from this testing be used? 

Rhode said one way the test information will be used is to augment a Computational Fluid Dynamic database. 

"In fact, we set the test up so that we could bring up real-time or almost real-time comparisons of the data coming out of the tunnel with what was already in the aerodynamic database at that point," he said. "Also, we will use the static testing information and the static part of the database to try and understand if there is a need to do an actual dynamics test." 

Rhode described previous, ongoing and future ground testing of the crew module and LAS. 

"We've already done dynamics tests on some of these launch abort system configurations," he continued. "We haven't done dynamic separation, but we've put this in a tunnel and applied the proper math properties to the computer model. One of the tests is to shake it back and forth and see how it responds dynamically to different frequencies, force oscillations." 

Rhode, referring to another dynamic test, said, "Both with the crew module and with the assembly, these components have been taken out to some of the ballistic ranges, like Eglin AFB, and the U.S. Army's Aberdeen Proving Ground, Md., and free flight types of tests have been conducted. 

"We flew a smaller model in the vertical spin tunnel at NASA's Langley Research Center, located in Hampton, Va. We put it out in the middle of the tunnel turned it upside down to see how it would respond in the launch abort system configuration, and let it go in free flight to see how stable it is. But for an event like this current test, unless we see something that is very out of the ordinary, there probably won't be a dynamics test." 

David Mayfield said a series of full-scale flight tests of the crew module and LAS are planned to begin in 2010.