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boundary="Apple-Mail=_71EF7BAF-CB07-4D54-A33C-4692B1F06E2A"; protocol="application/pgp-signature"; micalg=pgp-sha256 MIME-Version: 1.0 X-OriginatorOrg: alum.mit.edu X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: CO6PR12MB5427.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: eb095657-3ee9-4cf8-31b6-08db452692e1 X-MS-Exchange-CrossTenant-originalarrivaltime: 25 Apr 2023 00:46:57.7880 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 3326b102-c043-408b-a990-b89e477d582f X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: E118k5P0sRQGyaupiREkJAYkTHQh+cyoxGOt50m7VjU8oz2CUxhvLurfDjkU02jfgcOeaWtBgamF5JIDteynwkufXLpcH/c/MymcdvkN7jU= X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS0PR12MB6559 Subject: Re: [Starlink] some post Starship launch thoughts X-BeenThere: starlink@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: "Starlink has bufferbloat. Bad." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 25 Apr 2023 00:47:01 -0000 --Apple-Mail=_71EF7BAF-CB07-4D54-A33C-4692B1F06E2A Content-Type: multipart/alternative; boundary="Apple-Mail=_2C4E8FAA-42F0-4FFE-9A72-228E2EED9ACA" --Apple-Mail=_2C4E8FAA-42F0-4FFE-9A72-228E2EED9ACA Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=us-ascii 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 eugene.chang@alum.mit.edu +1-781-799-0233 (in Honolulu) > On Apr 24, 2023, at 9:16 AM, David Lang via Starlink = wrote: >=20 > On Mon, 24 Apr 2023, Dave Taht via Starlink wrote: >=20 >> Everyone wants a water deluge system and flame diverter >=20 > and a flame trench... >=20 > 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 >=20 > this is the probem you run into extrapolating from known data, you = can't predict inflection points where the behavior changes significantly >=20 > a common answer I've been giving re: flame trench >=20 > 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) >=20 > 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. >=20 > In Texas, SpaceX instead built stilts and put the rocket on top of = that. >=20 > As I understand it, the distance from the nozzles to the ground is = higher in Texas than in Florida >=20 > and the exhaust can get out in 6 direction, not just two. >=20 > 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) >=20 > 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) >=20 > David Lang > _______________________________________________ > Starlink mailing list > Starlink@lists.bufferbloat.net > https://lists.bufferbloat.net/listinfo/starlink --Apple-Mail=_2C4E8FAA-42F0-4FFE-9A72-228E2EED9ACA Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=us-ascii 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
eugene.chang@alum.mit.edu
+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
_______________________________________________
Starlink mailing list
Starlink@lists.bufferbloat.net
https://lists.bufferbloat.net/listinfo/starlink

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