[Starlink] some post Starship launch thoughts

[David P. Reed]

IANARS. (and most people here probably aren't, either, so I don't feel bad potentially saying something naive)
 
The discussion here about Starship's launch disaster got me thinking. The result is below:
1. Clarifying 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).
2. A proposed better idea (at least my riffing on it) to launch that would be more environmentally sound, simpler, and appropriate for civilian (rather than military) rocketry.
 
I have had a lot of experience with various sorts of fluid dynamics (the study of Navier Stokes Differential Equation solutions under pragmatic boundary conditions pretty much characterizes Fluid Dynamics), especially hydrodynamics and aerodynamics near surfaces.
 
I'm finding this discussion here unsatisfying, because one thing that seems obvious to me is that people are extrapolating 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.
 
Now I also briefly designed 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 done that kind of rocket design (which is relatively simple) encounters very high reynolds number flows 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 the rocket relative to the ground causing non-vertical takeoff.
 
Now 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 that the naive reasoning on this list (including mine here) is particularly helpful.
 
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, 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 or honestly about engineering. (Certainly we see that at Tesla regarding "self-driving" and 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 stability during the first few seconds of launch and have a rocketry expert comment. I don't think he could give such a talk even with a teleprompter and ghostwritten script.]
 
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 flow changes rapidly, why do we still try to do it this way?  
 
Ideally, the initial acceleration of a rocket would be better imparted by an external launcher (at least on the Earth - not initially 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, electromagnetic catapults have been developed that work better than steam ones - despite Trump's Musk-like idiotic statement that "steam is the best way" for carriers).
 
The 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 system for using tubes and magnets called Hyperloop).
 
It doesn't need to be a tube, it could be a "rail" (railguns work, and are cool in SF, too).
Powering 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 cells in parallel.
 
And this wouldn't pollute the atmosphere anywhere near as much, I'd guess.
 
The obvious drawback is that the weaponry application 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.
 
Another drawback is that rocket scientists aren't electrical power engineers (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 they 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 copper 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.
 
Of course, the structure of a rocket intended to launch from an EM accelerator would have very different stress loading initially, spread out more along the body of the rocket.
 
If I had Musk's capital assets, I'd even invest in such a design. I don't, of course.
 
 
 
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