3 ms·

Isn't it pretty unlikely that this debris, flying against the exhaust, can reach the engines with significant energy?

by rmu09 3y ago

wkat4242 3y ago
Considering the energy they have comes from precisely that exhaust, I don't think so. I'm pretty sure some pieces would make it through.
malfist 3y ago
Rocket "engines" aren't like engines in your car. The bell and the plumbing for it is the engine. There's not too many moving parts besides a pump. Any sort of damage to the bell can cause a failure. The bells are cooled by pumping super cold fuel over them, a rock hitting those thin lines of fuel could rupture a line, or divert on causing a failure in the bell which eventually (seconds) ends in an engine rich fuel mixture.
beerandt 3y ago
That's my thinking, but ignition is a staggered 6 second duration, so there's at least a window for adverse directional flow. But looking at that pad and the damage to it- without deluge dampening, I bet the RC spalling might have been a bigger issue than just ground blowback. Put a blowtorch to some concrete a and watch how quickly trapped moisture starts causing miniature explosions and flying shrapnel. But that's just my first uninformed impression.
- cubefox 3y ago
  They have special concrete now which shouldn't explode from moisture. But apparently it didn't hold up at all. I don't think anyone expected this.
  - zaarn 3y ago
    The output power of a rocket is different than a blow torch. The sound pressure alone is near or above atmospheric pressure. That concrete is being exposed to vacuum and more than 1atm pressure fairly rapidly. The heat on top of that and if the concrete has any moisture, the water inside is going to rapidly sublimate and condense several times a second. That is on top of the concrete being slammed into by an entire atmosphere of pressure in the meanwhile. There is a reason that NASA dumps a few million liters of water under their rockets.
    - deleted 3y ago
      [deleted]
nordsieck 3y ago
My understanding is that one of the Starship prototypes were damaged by flying debris during a static fire. I think the available evidence points towards it being possible. https://www.youtube.com/watch?v=jM61ZkUoO4U https://www.youtube.com/watch?v=jM61ZkUoO4U > About 2 secs after starting engines, martyte covering concrete below shattered, sending blades of hardened rock into engine bay. One rock blade severed avionics cable, causing bad shutdown of Raptor. https://twitter.com/elonmusk/status/1328742122107904000 https://twitter.com/elonmusk/status/1328742122107904000
T-A 3y ago
Assuming that this photo https://twitter.com/LabPadre/status/1649062784167030785 https://twitter.com/LabPadre/status/1649062784167030785 is real, I guess not. What used to be in that crater couldn't just move sideways, it had to go up to get out of the hole. Engine exhaust hit the center of the crater, dislodged rocks, pushed them away radially and up the sides of the hole. Four of the six engines later seen to have gone dark were in the outer ring. Coincidence?

Isn't it pretty unlikely that this debris, flying against the exhaust, can reach the engines with significant energy?

by rmu09 3y ago

Isn't it pretty unlikely that this debris, flying against the exhaust, can reach the engines with significant energy?

Considering the energy they have comes from precisely that exhaust, I don't think so. I'm pretty sure some pieces would make it through.

malfist 3y ago

Rocket "engines" aren't like engines in your car. The bell and the plumbing for it is the engine. There's not too many moving parts besides a pump. Any sort of damage to the bell can cause a failure. The bells are cooled by pumping super cold fuel over them, a rock hitting those thin lines of fuel could rupture a line, or divert on causing a failure in the bell which eventually (seconds) ends in an engine rich fuel mixture.

beerandt 3y ago

That's my thinking, but ignition is a staggered 6 second duration, so there's at least a window for adverse directional flow. But looking at that pad and the damage to it- without deluge dampening, I bet the RC spalling might have been a bigger issue than just ground blowback. Put a blowtorch to some concrete a and watch how quickly trapped moisture starts causing miniature explosions and flying shrapnel. But that's just my first uninformed impression.

cubefox 3y ago
They have special concrete now which shouldn't explode from moisture. But apparently it didn't hold up at all. I don't think anyone expected this.
- zaarn 3y ago
  The output power of a rocket is different than a blow torch. The sound pressure alone is near or above atmospheric pressure. That concrete is being exposed to vacuum and more than 1atm pressure fairly rapidly. The heat on top of that and if the concrete has any moisture, the water inside is going to rapidly sublimate and condense several times a second. That is on top of the concrete being slammed into by an entire atmosphere of pressure in the meanwhile. There is a reason that NASA dumps a few million liters of water under their rockets.
  - deleted 3y ago
    [deleted]

nordsieck 3y ago

My understanding is that one of the Starship prototypes were damaged by flying debris during a static fire. I think the available evidence points towards it being possible. https://www.youtube.com/watch?v=jM61ZkUoO4U https://www.youtube.com/watch?v=jM61ZkUoO4U > About 2 secs after starting engines, martyte covering concrete below shattered, sending blades of hardened rock into engine bay. One rock blade severed avionics cable, causing bad shutdown of Raptor. https://twitter.com/elonmusk/status/1328742122107904000 https://twitter.com/elonmusk/status/1328742122107904000

T-A 3y ago

Assuming that this photo https://twitter.com/LabPadre/status/1649062784167030785 https://twitter.com/LabPadre/status/1649062784167030785 is real, I guess not. What used to be in that crater couldn't just move sideways, it had to go up to get out of the hole. Engine exhaust hit the center of the crater, dislodged rocks, pushed them away radially and up the sides of the hole. Four of the six engines later seen to have gone dark were in the outer ring. Coincidence?