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Comment by Laremere | Hacker News Reader

"Busted" videos like this are low quality armchair analysis aimed at giving giving the viewer a sense of intellectual superiority. Saying "this solution breaks the laws of physics" can be valid if analysis is done correctly, saying "this problem is hard, and they haven't already solved every single piece of it so their whole business is stupid" is not valid.

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These types of videos have a very wide audience. Redditors love them.

I agree with you that the video could be more detailed on some of the technical analysis. However it raises enough technical arguments, to justify any approach to SpinLaunch to be done in private and with a very skeptical attitude.

Presumably NASA, who's paying for test launches, did a more thorough analysis than a YouTuber.

Only thing NASA seems to have contracted the company for is for a technology demonstrator, of throwing a small rocket at Mach 2.

The article describes it like they are throwing satellites into orbit. In reality even the far fetched plan, is to throw a small rocket into high altitude to save money on the first stage. Then the rocket is what will put the satellite in orbit.

I can't find a single reference to this agreement (yet) in any NASA official site. Not saying it's not real, just that I can't find an official NASA reference yet. It's not yet listed here under the current available ongoing agreements:

"Current Space Act Agreements"

https://www.nasa.gov/partnerships/about.html

Theranos had Walgreens, Nikola had GM...

This analysis also highlights the complexity risks. They will need to achieve Mach 10 and have a satellite capable to handle 20,000 G...

"Spinlaunch Feasibility Analysis":

https://colab.research.google.com/gist/jeff-hemingway/a3d322...

Edit: The HARP project is also mentioned in the analysis as a comparison.

https://en.wikipedia.org/wiki/Project_HARP

20,000g’s sounds much worse than it is. Some WWII era guns used ammunition with complex proximity fusses subjected to roughly 20,000g’s.

The real question is what kind of mass fraction is sacrificed to build something to survive being spun up.

And they did it without solid state electronics. Literally putting vacuum tubes in artillery shells.

Here's the thing: If you built something like Quicklaunch instead (https://en.wikipedia.org/wiki/Quicklaunch), your g forces would already be an order of magnitude lower. So the question is, why not do that instead?

They could have lowered the g forces by having a longer arm, they essentially picked the g forces as acceptable and then designed the system around that constraint.

As to why not use a gun, barrel damage is probably a deal killer for Quicklaunch and other such designs. Quickly spinning something in a vacuum and letting go should allow for launches roughly as fast as you can pull vacuum. Supporting something like a Starlink constellation seems possible with their design which could be incredibly profitable.

Starlinks are pizzabox-shaped. That's a terrible shape to launch unless you have a stack of them, and this won't be able to launch a stack of them.

As for barrel wear...it's possible that that would be higher than for a normal gun, but I'm pretty sure that the rather famous author of that design took that into consideration. (It doesn't seem like SpinLaunch's design is immune to firing wear either, considering the sudden rush of air into a space with hypersonic machinery in motion.)

You can have a door close behind the projectile to limit the amount of air that gets into the main chamber. I suspect spin launch to include that simply to reduce the amount of vacuum pumping needed. The idea showed up on one of the early space gun designs for similar reasons.

Starlink’s shape is optimized for it’s launch system, while I doubt spaceX is going to use a competitor anytime soon they would seriously consider sufficient cost savings.

You can reach somewhat higher accelerations by making the center of the rotor thicker than the periphery, but you start getting into ridiculous ratios pretty quickly.

I don't think Quicklaunch would have to suffer significant barrel damage, maybe some fouling that can be cleaned off. The pressures and temperatures required are pretty low, and the required chemistries are pretty tame; it's just the velocities that are high.

The g forces are from rotation not how fast you spin up. To take it to the extreme an arm that’s slightly longer than the radius of the earth for sometime moving at Mach 22ish hits ~1g, because that’s orbit. Hitting Mach 22 or even Mach 10 on an arm that’s 500m means vastly higher g-forces.

Yes obviously.

And how long is the arm supposed to be in the intended orbital system? Because if you want a 500m arm, you literally have a millions-of-cubic-meters-sized vacuum chamber -- and not only that, you have a vacuum chamber with a highly disadvantageous shape (a flat disc). That sounds like a mildly insane design to me.

50m sorry 500 was a typo.

“This test accelerator is 108 ft (33 m) in diameter, which makes it a one-third scale of the operational system that is being designed.”

Submerging the gun barrel in the ocean presents huge engineering and maintenance challenges. It's not impossible but building anything underwater is extremely expensive. And then you have to deal with currents, corrosion, storms, leaks. People who aren't experienced in marine engineering tend to drastically underestimate the costs.

One thing I was thinking about some time ago was that if you wanted such infrastructure while still being able to adjust azimuth and elevation, perhaps an artificial lake would work? At the very least you avoid salt water this way. Of course at that point you can't pick and choose your launch site after the fact, but that's not a regression compared to stationary launch pads anyway.

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