3 ms·

> The issue was with an oxygen relief valve on the rocket’s Centaur upper stage. > the valve was buzzing at a frequency of about 40 hertz, loud enough for team

> The issue was with an oxygen relief valve on the rocket’s Centaur upper stage. > the valve was buzzing at a frequency of about 40 hertz, loud enough for teams at the launch pad to hear it. > if the vibrations were full motions of the valve, the valve would be approaching its rated life of 200,000 cycles and would need to be replaced. That would require rolling the rocket back to its assembly building Are there any Rocket Scientists in the house, to tell us WTF a relief valve might be "thinking", to cycle at 40Hz? I'd suspect that is both symptomatic of a potential disaster, and of problems extending well beyond the valve itself.

bediger4000 3y ago
Atlas and Centaur are essentially stainless steel balloons, requiring internal pressure to keep from collapsing. Centaur uses cryogenic propellants, liquid oxygen and hydrogen. They boil at sea level temperatures. Both tanks on a Centaur have valves to allow oxygen or hydrogen gas to vent because of the boiling, but not too much, because of the need for internal pressurization. My guess is that's the valve in question. It has to open and shut repeatedly, pressure has to be maintained, so it has to tolerate lots of operations. But aerospace tends to have its own very specific jargon. I may be wrong
- bell-cot 3y ago
  Okay...but shouldn't there be a spec'ed range for that tank's pressure, and a non-trivial head space (vapor being quite compressible, liquid not) - so that the valve would operate in some sort of briefly_open / closed_for_a_while / briefly_open / closed... slow & steady pattern?
  - bediger4000 3y ago
    I'm sure that's desired. But staying inside a range is always difficult, and cryogenic temperatures probably make it harder, both for valve materials and things like water in air freezing on the valve or ice clogging vents. I'm told liquid hydrogen actually is somewhat compressible, and metals change properties when cold, so room temp and pressure physical intuition may mislead.

bediger4000 3y ago

Atlas and Centaur are essentially stainless steel balloons, requiring internal pressure to keep from collapsing. Centaur uses cryogenic propellants, liquid oxygen and hydrogen. They boil at sea level temperatures. Both tanks on a Centaur have valves to allow oxygen or hydrogen gas to vent because of the boiling, but not too much, because of the need for internal pressurization. My guess is that's the valve in question. It has to open and shut repeatedly, pressure has to be maintained, so it has to tolerate lots of operations. But aerospace tends to have its own very specific jargon. I may be wrong

bell-cot 3y ago
Okay...but shouldn't there be a spec'ed range for that tank's pressure, and a non-trivial head space (vapor being quite compressible, liquid not) - so that the valve would operate in some sort of briefly_open / closed_for_a_while / briefly_open / closed... slow & steady pattern?
- bediger4000 3y ago
  I'm sure that's desired. But staying inside a range is always difficult, and cryogenic temperatures probably make it harder, both for valve materials and things like water in air freezing on the valve or ice clogging vents. I'm told liquid hydrogen actually is somewhat compressible, and metals change properties when cold, so room temp and pressure physical intuition may mislead.