Re: [Starlink] some post Starship launch thoughts

[David Lang <david@lang.hm>]

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