From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp101.iad3a.emailsrvr.com (smtp101.iad3a.emailsrvr.com [173.203.187.101]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id 9FECF3B2A4 for ; Tue, 25 Apr 2023 16:40:00 -0400 (EDT) Received: from app38.wa-webapps.iad3a (relay-webapps.rsapps.net [172.27.255.140]) by smtp21.relay.iad3a.emailsrvr.com (SMTP Server) with ESMTP id 269A924FBD for ; Tue, 25 Apr 2023 16:40:00 -0400 (EDT) Received: from deepplum.com (localhost.localdomain [127.0.0.1]) by app38.wa-webapps.iad3a (Postfix) with ESMTP id 0E9C7E1C18 for ; Tue, 25 Apr 2023 16:40:00 -0400 (EDT) Received: by apps.rackspace.com (Authenticated sender: dpreed@deepplum.com, from: dpreed@deepplum.com) with HTTP; Tue, 25 Apr 2023 16:40:00 -0400 (EDT) X-Auth-ID: dpreed@deepplum.com Date: Tue, 25 Apr 2023 16:40:00 -0400 (EDT) From: "David P. Reed" To: starlink@lists.bufferbloat.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_20230425164000000000_14494" Importance: Normal X-Priority: 3 (Normal) X-Type: html In-Reply-To: References: X-Client-IP: 209.6.168.128 Message-ID: <1682455200.058420642@apps.rackspace.com> X-Mailer: webmail/19.0.22-RC X-Classification-ID: bd8f0228-c311-4153-a6b1-cba4155ec282-1-1 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 20:40:00 -0000 ------=_20230425164000000000_14494 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable =0AIANARS. (and most people here probably aren't, either, so I don't feel b= ad potentially saying something naive)=0A =0AThe discussion here about Star= ship's launch disaster got me thinking. The result is below:=0A1. Clarifyin= g the hypotheses of problem and solution. (and a few jabs at Musk along the= way, though I'm impressed by the SpaceX folks while feeling sorry for them= having Musk as a boss).=0A2. A proposed better idea (at least my riffing o= n it) to launch that would be more environmentally sound, simpler, and appr= opriate for civilian (rather than military) rocketry.=0A =0AI have had a lo= t of experience with various sorts of fluid dynamics (the study of Navier S= tokes Differential Equation solutions under pragmatic boundary conditions p= retty much characterizes Fluid Dynamics), especially hydrodynamics and aero= dynamics near surfaces.=0A =0AI'm finding this discussion here unsatisfying= , because one thing that seems obvious to me is that people are extrapolati= ng their "gut instincts" about fluid flow at low reynolds number in laminar= flow to the situation at a rocket launch where the output is within a few = meters of the ground.=0A =0ANow I also briefly designed and tested small so= lid fuel amateur rocket engines (not Estes rockets - more the kind you see = in the movie October Sky - zinc and sulfur cast fuel in 150 cm steel tubes,= with machined steel nozzles. That was 55 years ago. This doesn't tell much= about modern rocketry design, but anyone who has done that kind of rocket = design (which is relatively simple) encounters very high reynolds number fl= ows around the nozzle, especially if launched with the nozzle near a "pad" = - which we avoided because of the instability of the thrust with tilt of th= e rocket relative to the ground causing non-vertical takeoff.=0A =0ANow the= issue here is that it is very, very hard to model or predict the transient= flows during initial acceleration off the pad. I'm not at all convinced th= at the naive reasoning on this list (including mine here) is particularly h= elpful.=0A =0AI am convinced that Elon Musk knows NOTHING about rocketry fl= uid dynamics - he's not a rocket engineer, though he pretends to be one, en= couraging all his fans and buddies to think naively, too. He's a narcissiti= c investor, and by all reports a *terrible* technical manager. So anything = he says is probably a completely distorted version of reality, and he tends= to no let the knowledgable people who work at his companies speak openly o= r honestly about engineering. (Certainly we see that at Tesla regarding "se= lf-driving" and Neuralink. A pretense of Musk being the scientific genius i= s required to work at those companies). I mention this because much of the = technological comment here is speculation driven by Musk's PR around SpaceX= and Starlink. [I'd love to hear Musk give a talk about turbulence and vort= icity and stability during the first few seconds of launch and have a rocke= try expert comment. I don't think he could give such a talk even with a tel= eprompter and ghostwritten script.]=0A =0AOK, so a question pops up for me = that has always bugged me. Other than old SF story covers always showing a = rocket sitting on its nozzle on a concrete pad, with all the complex fluid = dynamics involved as the fluid flow changes rapidly, why do we still try to= do it this way? =0A =0AIdeally, the initial acceleration of a rocket woul= d be better imparted by an external launcher (at least on the Earth - not i= nitially on Mars). For example, an electromagnetic linear accelerator that = contains the rocket while it accelerates. (We're not talking a sub-launched= missile or a carrier-launched airplane here, and even on carriers, electro= magnetic catapults have been developed that work better than steam ones - d= espite Trump's Musk-like idiotic statement that "steam is the best way" for= carriers).=0A =0AThe reusability of an electromagnetic launcher is clearly= far better than for the "reusable" launch stage that holds the equivalent = energy in fuel form. (snark: and Musk is a genius who "invented" a whole sy= stem for using tubes and magnets called Hyperloop).=0A =0AIt doesn't need t= o be a tube, it could be a "rail" (railguns work, and are cool in SF, too).= =0APowering it just needs a way to store and release electrical energy fast= - a battery, basically, which can be wired up as a collection of storage c= ells in parallel.=0A =0AAnd this wouldn't pollute the atmosphere anywhere n= ear as much, I'd guess.=0A =0AThe obvious drawback is that the weaponry app= lication of this approach is a problem. ICBM's and IRBM's and sub-launched = missiles really benefit from avoiding the need for external launch systems = attached to the ground. So, maube that's why NASA (which is 85% military in= its mission) didn't develop it. You don't want to have to put your ICBM's = where they can draw power from the grid to charge up their launcher.=0A =0A= Another drawback is that rocket scientists aren't electrical power engineer= s (they haven't been), so you need a more interdisciplinary team than usual= . They don't design linear accelerators, which are also not as simple as th= ey look, despite the fact that I can make a working railgun using the tools= and materials I have in my basement in maybe a hour that accelerates a cop= per ring to supersonic speeds. But they are pretty simple systems, it seems= to me, compared to managing N separate rocket exhaust streams with rapidly= varying and turbulent pressure fields of the sort that occur on the launch= pad of a sufficiently large multistage rocket.=0A =0AOf course, the struct= ure of a rocket intended to launch from an EM accelerator would have very d= ifferent stress loading initially, spread out more along the body of the ro= cket.=0A =0AIf I had Musk's capital assets, I'd even invest in such a desig= n. I don't, of course.=0A =0A =0A ------=_20230425164000000000_14494 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable

IANARS. (and most peop= le here probably aren't, either, so I don't feel bad potentially saying som= ething naive)

=0A

 

=0A

= The discussion here about Starship's launch disaster got me thinking. The r= esult is below:

=0A

1. Clarifying the hypotheses of = problem and solution. (and a few jabs at Musk along the way, though I'm imp= ressed by the SpaceX folks while feeling sorry for them having Musk as a bo= ss).

=0A

2. A proposed better idea (at least my riff= ing on it) to launch that would be more environmentally sound, simpler, and= appropriate for civilian (rather than military) rocketry.

=0A

 

=0A

I have had a lot of experien= ce with various sorts of fluid dynamics (the study of Navier Stokes Differe= ntial Equation solutions under pragmatic boundary conditions pretty much ch= aracterizes Fluid Dynamics), especially hydrodynamics and aerodynamics near= surfaces.

=0A

 

=0A

I'm= finding this discussion here unsatisfying, because one thing that seems ob= vious to me is that people are extrapolating their "gut instincts" about fl= uid flow at low reynolds number in laminar flow to the situation at a rocke= t launch where the output is within a few meters of the ground.

=0A

 

=0A

Now I also briefly design= ed and tested small solid fuel amateur rocket engines (not Estes rockets - = more the kind you see in the movie October Sky - zinc and sulfur cast fuel = in 150 cm steel tubes, with machined steel nozzles. That was 55 years ago. = This doesn't tell much about modern rocketry design, but anyone who has don= e that kind of rocket design (which is relatively simple) encounters very h= igh reynolds number flows around the nozzle, especially if launched with th= e nozzle near a "pad" - which we avoided because of the instability of the = thrust with tilt of the rocket relative to the ground causing non-vertical = takeoff.

=0A

 

=0A

Now t= he issue here is that it is very, very hard to model or predict the transie= nt flows during initial acceleration off the pad. I'm not at all convinced = that the naive reasoning on this list (including mine here) is particularly= helpful.

=0A

 

=0A

I am= convinced that Elon Musk knows NOTHING about rocketry fluid dynamics = - he's not a rocket engineer, though he pretends to be one, encouraging all= his fans and buddies to think naively, too. He's a narcissitic investor, a= nd by all reports a *terrible* technical manager. So anything he says is pr= obably a completely distorted version of reality, and he tends to no let th= e knowledgable people who work at his companies speak openly or honestly ab= out engineering. (Certainly we see that at Tesla regarding "self-driving" a= nd Neuralink. A pretense of Musk being the scientific genius is required to= work at those companies). I mention this because much of the technological= comment here is speculation driven by Musk's PR around SpaceX and Starlink= . [I'd love to hear Musk give a talk about turbulence and vorticity and sta= bility during the first few seconds of launch and have a rocketry expert co= mment. I don't think he could give such a talk even with a teleprompter and= ghostwritten script.]

=0A

 

=0A

OK, so a question pops up for me that has always bugged me. Other = than old SF story covers always showing a rocket sitting on its nozzle on a= concrete pad, with all the complex fluid dynamics involved as the fluid fl= ow changes rapidly, why do we still try to do it this way?  

= =0A

 

=0A

Ideally, the init= ial acceleration of a rocket would be better imparted by an external launch= er (at least on the Earth - not initially on Mars). For example, an el= ectromagnetic linear accelerator that contains the rocket while it accelera= tes. (We're not talking a sub-launched missile or a carrier-launched airpla= ne here, and even on carriers, electromagnetic catapults have been develope= d that work better than steam ones - despite Trump's Musk-like idiotic stat= ement that "steam is the best way" for carriers).

=0A

The reusability of an electromagnetic l= auncher is clearly far better than for the "reusable" launch stage that hol= ds the equivalent energy in fuel form. (snark: and Musk is a genius who "in= vented" a whole system for using tubes and magnets called Hyperloop).

= =0A

 

=0A

It doesn't need t= o be a tube, it could be a "rail" (railguns work, and are cool in SF, too).=

=0A

Powering it just needs a way to store and relea= se electrical energy fast - a battery, basically, which can be wired up as = a collection of storage cells in parallel.

=0A

 = ;

=0A

And this wouldn't pollute the atmosphere anywh= ere near as much, I'd guess.

=0A

 

=0A

The obvious drawback is that the weaponry application of thi= s approach is a problem. ICBM's and IRBM's and sub-launched missiles really= benefit from avoiding the need for external launch systems attached to the= ground. So, maube that's why NASA (which is 85% military in its mission) d= idn't develop it. You don't want to have to put your ICBM's where they can = draw power from the grid to charge up their launcher.

=0A

 

=0A

Another drawback is that rocket sci= entists aren't electrical power engineers (they haven't been), so you need = a more interdisciplinary team than usual. They don't design linear accelera= tors, which are also not as simple as they look, despite the fact that I ca= n make a working railgun using the tools and materials I have in my basemen= t in maybe a hour that accelerates a copper ring to supersonic speeds. But = they are pretty simple systems, it seems to me, compared to managing N sepa= rate rocket exhaust streams with rapidly varying and turbulent pressure fie= lds of the sort that occur on the launch pad of a sufficiently large multis= tage rocket.

=0A

 

=0A

O= f course, the structure of a rocket intended to launch from an EM accelerat= or would have very different stress loading initially, spread out more alon= g the body of the rocket.

=0A

 

=0A

If I had Musk's capital assets, I'd even invest in such a desi= gn. I don't, of course.

=0A

 

=0A

 

=0A

 

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