Anything (mass, object) in the path of the engine exhaust will experience thermo-shock and mechanical stress. Both will cause the exhaust diverter or exhaust defuser to have significant wear and short life.

A flame trench suggests a solution. Keep any mass farther away from the engine exhaust. The logical extension of this would be to put the rocket elevated (high) over the ground to have minimal force from the exhaust. I suspect this would be too much distance to be practical.

An alternative could be to launch the rocket over a big pool of water. Please, not over a natural body of water with any living organisms in it. The environmental impact of the thermo-shock would be substantial.


Gene
-----------------------------------
Eugene Chang
+1-781-799-0233 (in Honolulu)





On Apr 24, 2023, at 9:16 AM, David Lang via Starlink <starlink@lists.bufferbloat.net> wrote:

On Mon, 24 Apr 2023, Dave Taht via Starlink wrote:

Everyone wants a water deluge system and flame diverter

and a flame trench...

about 3 months ago they started building water-cooled steel plates to go under the launch pad, but it wasn't ready yet and the testing they didn (static fire at 50% thrust and firing raptors into blocks of concrete at McGregor) made them think that the concrete would be badly eroded by a full power launch, but did not predict nearly the level of damage they saw

this is the probem you run into extrapolating from known data, you can't predict inflection points where the behavior changes significantly

a common answer I've been giving re: flame trench

Both Florida and Texas launch pads started with the ground just a few feet above sea level, so neither one can dig down (unless they want to create a permanent pool under the rocket, which would have all sorts of problems)

In Florida, NASA trucked in a huge amount of dirt and built up a hill, leaving a flame trench that they then lined with concrete and bricks, later adding a ramp to divert the exhaust (and had a lot of problem finding a material that would not wear away too fast). They also had problems with some shuttle launches tearing up the walls of the flame trench.

In Texas, SpaceX instead built stilts and put the rocket on top of that.

As I understand it, the distance from the nozzles to the ground is higher in Texas than in Florida

and the exhaust can get out in 6 direction, not just two.

So if they had put the Starship stack on NASAs mobile launch platform and launched it in Florida, it would have done significantly more damage there, probagly tearing up large chunks of ground around the pad as well (imaging the ground where the crawler goes disappearing)

The raptor engines have a significantly higher ISP than the F-1 that the Saturn 5 had, so it's exhaust is moving about 25% faster, and with double the thrust it's also moving about 60% more mass. These are conditions that have not existed anywhere on earth before this launch (I will note that the shuttle had even higher exhaust velocity from it's main engines, but less overall thrust)

David Lang
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