This made me wonder, what is the policy for human-carrying commercial endeavors on altitude testing of critical systems? Whether propulsion, APU or anything else. Do they do ground testing in an altitude chamber, or just hope for the best?
Quote from: joema on 11/25/2014 10:55 pmI was watching a 2005 MIT video lecture on shuttle history and Aaron Cohen (former shuttle project manager) recalled that during shuttle development, they originally planned on not altitude testing the APUs. The engineers assured him it wasn't necessary -- they'd pull a vacuum on the exhaust to simulate space and this was sufficient. Plus altitude testing was expensive.Cohen was worried about this and found a little more money to test the APU in an altitude chamber -- it was at AEDC or Langley, I don't remember. However the APU repeatedly exploded during testing, despite having passed all ground-level tests. The problem was non-intutive -- the APU was surrounded by a heat shield with an approx 1/4 inch stand off. At sea level when the APU heated up air flowed up through the 1/4 inch space, keeping the APU cool. Only at altitude did the heat collect between the heat shield and the APU body, causing an overtemp and hydrazine explosion. Fortunately this was found during ground testing or STS-1 would have been a disaster.This made me wonder, what is the policy for human-carrying commercial endeavors on altitude testing of critical systems? Whether propulsion, APU or anything else. Do they do ground testing in an altitude chamber, or just hope for the best?Can cooling problem be actually found in altitude tests? I think not.
I was watching a 2005 MIT video lecture on shuttle history and Aaron Cohen (former shuttle project manager) recalled that during shuttle development, they originally planned on not altitude testing the APUs. The engineers assured him it wasn't necessary -- they'd pull a vacuum on the exhaust to simulate space and this was sufficient. Plus altitude testing was expensive.Cohen was worried about this and found a little more money to test the APU in an altitude chamber -- it was at AEDC or Langley, I don't remember. However the APU repeatedly exploded during testing, despite having passed all ground-level tests. The problem was non-intutive -- the APU was surrounded by a heat shield with an approx 1/4 inch stand off. At sea level when the APU heated up air flowed up through the 1/4 inch space, keeping the APU cool. Only at altitude did the heat collect between the heat shield and the APU body, causing an overtemp and hydrazine explosion. Fortunately this was found during ground testing or STS-1 would have been a disaster.This made me wonder, what is the policy for human-carrying commercial endeavors on altitude testing of critical systems? Whether propulsion, APU or anything else. Do they do ground testing in an altitude chamber, or just hope for the best?
You might want to brush up on the cause of the Apollo 6 engine failures... and how they found the problem.
From what I have read, pogo oscillation caused SIVB emergency of Apollo 6 mission.Did you mean that?POGO oscillation cannot be found in altitude tests either.
Do they do ground testing in an altitude chamber, or just hope for the best?
The problem in the igniter fuel lines was not detected during ground testing because a stainless steel mesh covering the fuel line became saturated with liquid air due to the extreme cold of the liquid hydrogen flowing through it. The liquid air damped a vibration mode that became evident when tests were conducted in a vacuum after the Apollo 6 flight. This was also a simple fix, involving replacing the flexible bellows section where the break occurred with a loop of stainless steel pipe. The S-IVB used the same J-2 engine design as the S-II and so it was decided that an igniter line problem had also stopped the third stage from reigniting in Earth orbit. Ground testing confirmed that the slight underperformance seen in the first S-IVB burn was consistent with damage to the igniter line.
For those not familiar with the Apollo 6 issues (which included me), this from wikipedia:QuoteThe problem in the igniter fuel lines was not detected during ground testing because a stainless steel mesh covering the fuel line became saturated with liquid air due to the extreme cold of the liquid hydrogen flowing through it. The liquid air damped a vibration mode that became evident when tests were conducted in a vacuum after the Apollo 6 flight. This was also a simple fix, involving replacing the flexible bellows section where the break occurred with a loop of stainless steel pipe. The S-IVB used the same J-2 engine design as the S-II and so it was decided that an igniter line problem had also stopped the third stage from reigniting in Earth orbit. Ground testing confirmed that the slight underperformance seen in the first S-IVB burn was consistent with damage to the igniter line.
....SpaceX tested its payload fairing (separation) in the vacuum chamber at Plum Brook, via a Space Act agreement. http://www.sanduskyregister.com/article/2357206....likely did/does some type of vacuum simulation testing of its engines and thrusters, possibly at McGregor...
Does McGregor have an altitude chamber for main engine testing?
