[Starlink] some post Starship launch thoughts

[David Lang]

On Tue, 25 Apr 2023, Eugene Chang wrote:

> 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.

in Texas and Florida you can't go down, even a couple feet puts you below sea 
level (in Texas, high tide puts water right up to the fence less than 100 ft 
from the launch mount)

The launch mount is higher than the man-made mounds on either side of the Saturn 
5 flame trench

> 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.

long term, they do expect to have over-ocean launches.

If they dig a pool under the Starship Launch Mount, it will fill with water 
(they are already having to pump water out of the hole the rocket dug), if they 
line it with concrete, water will seep through, and the concrete will try to 
float on the water. Plus the water sitting in it will very quickly be considered 
'hazardous waste' and letting the rocket exhaust blast it around will be frowned 
on, and it will become a home for mosquitoes.

This is also sea turtle territory, any pool under the rocket would be a problem 
for them.

David Lang


>
> Gene
> -----------------------------------
> Eugene Chang
> eugene.chang at alum.mit.edu
> +1-781-799-0233 (in Honolulu)
>
>
>
>
>
>> On Apr 24, 2023, at 9:16 AM, David Lang via Starlink <starlink at 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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>