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[72.253.196.65]) by smtp.gmail.com with ESMTPSA id l6-20020a17090ad10600b00244938da9b9sm2194999pju.31.2023.04.25.16.55.12 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Tue, 25 Apr 2023 16:55:13 -0700 (PDT) From: Eugene Y Chang Message-Id: <8FDA8F57-622A-4ED5-A8FC-347890E3E09E@ieee.org> Content-Type: multipart/signed; boundary="Apple-Mail=_9F4EECC1-A05F-4CE5-AE9F-93A3657CFB16"; protocol="application/pgp-signature"; micalg=pgp-sha256 Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3696.120.41.1.3\)) Date: Tue, 25 Apr 2023 13:55:11 -1000 In-Reply-To: <41rrn842-n98o-on3s-s7oq-7720593s46rn@ynat.uz> Cc: Eugene Chang , Bruce Perens , Dave Taht via Starlink To: David Lang References: <74321D7F-D914-401B-8AE7-3185D9C2009C@alum.mit.edu> <8s710on2-s8r9-4n84-s0o0-386pn0psr08p@ynat.uz> <4108AD1D-235D-4243-8AAD-2155DAC6D68A@alum.mit.edu> <41rrn842-n98o-on3s-s7oq-7720593s46rn@ynat.uz> X-Mailer: Apple Mail (2.3696.120.41.1.3) 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 23:55:15 -0000 --Apple-Mail=_9F4EECC1-A05F-4CE5-AE9F-93A3657CFB16 Content-Type: multipart/alternative; boundary="Apple-Mail=_9B243E10-20A1-478C-AA67-81E05244DE05" --Apple-Mail=_9B243E10-20A1-478C-AA67-81E05244DE05 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=utf-8 Engine thrust is a combination of the mass of the gas and the = temperature (a measure of velocity). So coolling the gas (aka absorbing the heat) is part of absorbing the = momentum from the engine thrust. The more speed in the rocket exhaust, the more wear and tear of the = equipment in the exhaust=E2=80=99s path. I suggest it could be calculated how much speed of the rocket engine exhaust needs to be reduced for a = good life of the launch infrastructure and how much energy needs to be taken out of the rocket exhaust to = reduce the exhaust gas to the desired speed. how much water is needed to absorb the energy needed to reduce the = exhaust speed. Mass and energy are both conserved. They know how much energy is at the = rocket engine nozzle (point of max temperature and speed of the gas). = The mass and energy have to go somewhere. To say =E2=80=9Conly testing will tell us for sure=E2=80=9D is to = suggest cut-and-try engineering. Of course, testing is used to confirm the calculations. Gene ---------------------------------------------- Eugene Chang IEEE Communications Society & Signal Processing Society, Hawaii Chapter Chair IEEE Hawaii Section, Industry Engagement Coordinator IEEE Senior Life Member eugene.chang@ieee.org m 781-799-0233 (in Honolulu) > On Apr 25, 2023, at 1:22 PM, David Lang wrote: >=20 > On Tue, 25 Apr 2023, Eugene Chang wrote: >=20 >> I found this YouTube of a deluge system test. >> It doesn=E2=80=99t look like it uses enough water to succeed. >> My intuition is the mass of water needed is approximately equal to = the rocket=E2=80=99s mass. >=20 > nowhere close. The pad 39a where the Saturn 5 launched has a 300,000 = gal take, which is ~2.4M pounds, but the Saturn 5 launch weight was = around 6.5M pounds >=20 >> Maybe the system doesn=E2=80=99t have to fully absorb the momentum of = the engine exhaust. Still, 70% would be a much greater mass than what = the video shows. >=20 > it doesn't, it's not absorbing the momentum of the engine exhaust, = it's vaporizing to cool the area and disrupt the airflow so the exhaust = is less of a blowtorch when it hits a solid surface, and absorb enough = sound to prevent it from damaging the rocket. >=20 > distance helps with both of these, as do the materials that the = exhaust finally hits. Regular concrete has too much moisture in it and = the water flashes to steam and breaks the concrete (concrete is strong = in compression, weak in tension). >=20 > Elon mentioned a few weeks ago that even steel plates would wear down = quickly under the exhaust, and that water cooled plates were needed in = the long run (and they started building water cooled plates to put under = the launch mount) >=20 > will that be enough? only testing will tell us for sure. >=20 > not all rockets use a flame trench, and some have very little deluge >=20 > David Lang --Apple-Mail=_9B243E10-20A1-478C-AA67-81E05244DE05 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=utf-8
Engine thrust is a combination of the = mass of the gas and the temperature (a measure of velocity).

So coolling the gas (aka absorbing the = heat) is part of absorbing the momentum from the engine = thrust.

The more speed in the rocket exhaust, = the more wear and tear of the equipment in the exhaust=E2=80=99s = path.

I suggest it could be = calculated
  • how much = speed of the rocket engine exhaust needs to be reduced for a good life = of the launch infrastructure
  • and how much energy = needs to be taken out of the rocket exhaust to reduce the exhaust gas to = the desired speed.
  • how much water is needed to absorb = the energy needed to reduce the exhaust speed.

Mass and energy are both = conserved. They know how much energy is at the rocket engine nozzle = (point of max temperature and speed of the gas). The mass and energy = have to go somewhere.

To say =E2=80=9Con= ly testing will tell us for sure=E2=80=9D is to suggest cut-and-try = engineering.
Of course, testing is used to confirm = the calculations.


Gene
----------------------------------------------
Eugene Chang
IEEE Communications Society & = Signal Processing Society,    
    = Hawaii Chapter Chair
IEEE Hawaii Section, Industry = Engagement Coordinator
IEEE Senior Life Member
eugene.chang@ieee.org
m 781-799-0233 (in = Honolulu)



On Apr 25, 2023, at 1:22 PM, David Lang <david@lang.hm> = wrote:

On Tue, 25 Apr 2023, Eugene Chang wrote:

I found this YouTube of = a deluge system test.
It doesn=E2=80=99t look like it uses = enough water to succeed.
My intuition is the mass of water = needed is approximately equal to the rocket=E2=80=99s mass.

nowhere close. The pad 39a where = the Saturn 5 launched has a 300,000 gal take, which is ~2.4M pounds, but = the Saturn 5 launch weight was around 6.5M pounds

Maybe the system = doesn=E2=80=99t have to fully absorb the momentum of the engine exhaust. = Still, 70% would be a much greater mass than what the video shows.

it doesn't, it's not absorbing = the momentum of the engine exhaust, it's vaporizing to cool the area and = disrupt the airflow so the exhaust is less of a blowtorch when it hits a = solid surface, and absorb enough sound to prevent it from damaging the = rocket.

distance helps with both of these, = as do the materials that the exhaust finally hits. Regular concrete has = too much moisture in it and the water flashes to steam and breaks the = concrete (concrete is strong in compression, weak in tension).

Elon mentioned a few weeks ago that even steel = plates would wear down quickly under the exhaust, and that water cooled = plates were needed in the long run (and they started building water = cooled plates to put under the launch mount)

will that be enough? only testing will tell us for sure.

not all rockets use a flame trench, and some = have very little deluge

David = Lang

= --Apple-Mail=_9B243E10-20A1-478C-AA67-81E05244DE05-- --Apple-Mail=_9F4EECC1-A05F-4CE5-AE9F-93A3657CFB16 Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename=signature.asc Content-Type: application/pgp-signature; name=signature.asc Content-Description: Message signed with OpenPGP -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEERPTGiBqcibajhTSsv0/8FiYdKmAFAmRIaF8ACgkQv0/8FiYd KmC7FA/+LZYPrTlTeY4vqsyOXLvDYcUQvKRGGOuv0pfZKmWqJJ3IwHnYEkuc+yx4 NkeEcxUR+A72chIfs+h4Xx1iheFodJL9oPMkGEPAcWlCQu1kcz0425LEK8TAhnoC MAAIOgxpratZhZ7HsuOwh1Mk85p/5pd27fy2W00YK8yJyI59UXUqkr+j3g3JuRPg 1hsrUf+0hsIxQtJrzbeQhcK4ob1EKB0xjGnMrq1G2WA98gQxxaIP+25zWRMRPoyW RwVXSpDqwZvZHUXFndTMtmzcd3czTNzJ9o2wB7+rQ5IHQdxgi5mEgkrl77w5X3ri KO8ID/w1WIRnQ+g6ug0FPzNROndeQKJYj5+8Up5ZyXTLgHBlrI+Js8y3bIJGvulR NhSkUt/hPgYA0pL/uy1fCe6SsuRXtqs3YNueTT+TuONn46rfUDa+phF7c3AnbkAK ykPcWhQwURpl/3wU0fGfSys6Br0ggn/1PmyfuIkO8As76h6rLVkrB0U3kGEqZBYH XMPs7/yK3FvlgcX+/9Iww+U6KhKre4PjlCp9Nebpdk9ycDS+KOtCEeZ3RY9B0FiN pE2V+nFtausMPMLu491UH2Xa1xc8hweYjqhJKQulgwzvITr32NeBvHe/CIbXxNbp VKfnL4P/bmZBnTVgNeX68zY9XZD/b42SnRa6FkA0Oib8+mwU4t8= =l+CU -----END PGP SIGNATURE----- --Apple-Mail=_9F4EECC1-A05F-4CE5-AE9F-93A3657CFB16--