Also doubting the civilian use, but in the previous discussion somebody commented[0] that the main purpose might be military:
> For military applications on the other hand, it's close to perfect. You don't need orbital insertion, you can accelerate your payload silently without allowing for detection in the early phase of the attack, your projectile starts at essentially cruise speed and can only be detected by infrared emissions due to atmospheric heating for a few seconds until the launch ablative heatshields are ejected. It's a fantastic first strike weapon.
I don't know if this is a more likely application, but we should at least consider that we don't know the whole story, for better or worse. It might very well be a military startup that tries to give itself some SpaceX marketing-sheen.
Pure vapourware nonsense designed to extract money from investors with all the right buzzwords. Good luck getting a chemical rocket second-stage to survive 1000+ lateral g's and the immense thermal challenges of flying Mach 5+ at sea-level conditions.
Agreed. There is a bunch reasons we are still reliant on chemical rockets, and this silly thing does not solve for any of them. There are so many things that can go wrong here. The vacuum they need to pull in that HUGE chamber is not trivial. Even if they could... I want to see how they propose the exit. What are they planning to use that is strong enough to hold the vacuum, and yet can be punched through by the projectile? And even if they manage that... the aero forces around the exit will be insanely turbulent. Snake-oil. Again. A shit-load of money spent on not much more than a movie set.
re: the seal. It looks like it's just a big flat disk with a destructible seal over the exit tube for the projectile. I don't doubt that the bigness is a challenge, but the concept seems pretty simple.
There are about a dozen serious problems with this plan. What happens to the rest of your spin system when your payload releases? What about air resistance? If you’re spinning up in a vacuum what happens when your payload hits atmosphere at orbital velocity?
What are your neighbors going to think about living near complicated, delicate, high velocity things like this?
I also take issue with the notion that “scientists” are working on this. Engineers? Yes. Dreamers with a nifty idea? Yes.
Will it ever work? Maybe if what seem like insurmountable problems get solved. I’m not holding my breath though, and I don’t want to be within 10 miles or anywhere down range of the attempt.
> What happens to the rest of your spin system when your payload releases?
I mean, it's anchored to the ground, right? I'm sure it takes a shock but it shouldn't be out of the realm of stresses we already deal with regularly.
> What about air resistance? ... what happens when your payload hits atmosphere at orbital velocity?
This and the high Gs that must be involved are the biggest worry for me. Max Q is at full atmosphere right outside of the barrel of your gun? Protecting the payload and preventing the rocket from immediately disintegrating seems like the hardest part here. But it doesn't seem unsolvable if you can just glop on more and more shielding now that weight isn't as much of a concern.
"* > What happens to the rest of your spin system when your payload releases?*
"I mean, it's anchored to the ground, right? I'm sure it takes a shock but it shouldn't be out of the realm of stresses we already deal with regularly."
Consider having one arm on the rotational axis. While it is spinning up, the axle is under significant stress, with the mass of the arm plus the mass of the vehicle under significant centrifugal force (Scott Manley says 10,000G at peak loading), which is a hard problem in itself. When you release the vehicle, the vehicle mass portion of that force goes to zero effectively instantly. Not a mechanical engineer, but I would expect a certain amount of vibration. Or possibly rapid disassembly.
It's better if you have two arms with the vehicle on one and an equivalent mass on the other---when you launch the vehicle, you drop the other mass in the opposite direction. (Which is quite a synchronization problem.) (But where does that mass go?)
Spitballing here ... the mass is magnetic, and you shoot it down into a giant borehole that rapidly recaptures the momentum using magnetic regenerative breaking. Of course you need to use all the energy you recaptured (and more) to bring the mass back up to the surface for your next launch ...
Man, I have my opinions on Spinlaunch, too, but I find thunderf*t’s videos (especially the BUSTED ones) unenlightening & unhelpful to rationally discussing the pros and cons of some technology.
Scott Manley’s video (if video is the format you prefer) on Spinlaunch was much better. Scott Manley also has a much better understanding of rockets and space technology than thunderf*t.
https://youtu.be/JAczd3mt3X0
Thunderf00t can show great science at times, but most of his channel is just opinion pieces disguised as science. Most of his arguments are sound, which is not very difficult considering some of the things he attacks, but some are more debatable, or even just wrong. And he never back down, and he has a community of mindless followers which is more fitting to a cult leader than to a man of science.
The tumbling in this video is a good demonstration of the angular momentum problem. The projectile has a carp ton of angular momentum after release, and there's no system in place to fix that. Maybe you could cancel it using the atmo and aerodynamics except that would probably melt the fins.
And angular momentum is just one of the challenges that appear to be unsolvable. When you hit orbital height, your velocity is in the wrong direction. How do you add enough horizontal velocity? How do you construct a rocket engine that can survive the forces involved in initial launch? How do you prevent the bearings from melting? How do you construct a launch chamber which survives the explosive compression when the projectile penetrates the vacuum barrier into the atmo?
And all with a Theranos-level of founder knowledge.
> When you hit orbital height, your velocity is in the wrong direction.
Wait, why is your velocity in the wrong direction? You're right that you need to add a whole hell of a lot of horizontal velocity to reach orbit, but you do have ~400 meters per second of horizontal velocity borrowed from the surface rotation of the Earth. You're not going the wrong direction -- there's nothing you need to counter-act. You just need your 2nd stage (assuming we count the initial throw as a 1st stage) to provide all that velocity. The fuel you need to do that was launched up with you. What's the problem? It's a hell of a lot easier than the way we do it now.
> How do you ... survive forces involved
Yes, that is the real problem.
> The projectile has a carp ton of angular momentum after release
No, the centrifuge has a crap ton of angular momentum, some of which is converted to linear momentum in the projectile upon release.
Yep, the "wrong" velocity is what you suggest: the horizontal velocity is missing. Keep in mind the horizontal velocity is the critical detail that distinguishes "orbits" from "crash landings."
There is no conversion to linear momentum. The projectile is rotating once per turn of the centrifuge. Nothing they do eliminates that angular momentum. That's why in the linked video the projectile is, on close examination, rotating wildly. It's also why the projectile's nose exits the apparatus at a very different location than the tail.
I play Kerbal Space Program, so I know a thing or two about orbital mechanics! (I'm only 30% joking -- many of the answers on the Space Exploration Stack Exchange say "Go play Kerbal Space Program, then you'll understand). Yes, that horizontal velocity is hard to attain, but that's what 2nd stages have always been for. We're only talking about replacing the 1st stage, which is by far the most expensive. You're still way better off already being at orbital height, never having to accelerate directly against gravity and through all that air resistance. And the speed you need to reach orbit is less the higher up you are.
> The projectile is rotating once per turn of the centrifuge.
I keep trying to challenge this, but I think you must be right. I was thinking the angular velocity would be smaller than the arm, but it must be the same. Still, the angular momentum can be much smaller. And I'll paste my proposed (possibly infeasible) solution to that from another answer:
Attach the payload at two points in a narrow V, equidistant from the center of mass. In the instant before release, fire pistons that slightly extend the upper arm and retract the lower arm, applying the exact amount of force you pre-calculated was needed to counteract the differences in rotation between those two points. Release while this (hopefully uniform) force is still being applied.
Yeah, you're jolting the hell out of your payload, but that's peanuts compared to what it's about to experience anyway.
Random other idea: just put your entire payload inside a spherical fairing and launch the whole ball into space. Once past atmosphere, eject the fairing and stretch out. Like a dancer extending their arms, this itself will slow your rotation down. Then fire RCS thrusters anti-rotationally or use a reaction wheel (can we pre-load the reaction wheel with oppositional angular momentum before launch?) until you're steady.
Bonus: can you use the rotation of the ball to help guide you, curveball-style, into the direction of orbit?
>The tumbling in this video is a good demonstration of the angular momentum problem. The projectile has a carp ton of angular momentum after release
I'm not sure I follow; if the object is held rigidly to the launch arm until the point of release, it's going to have a lot of angular velocity, sure, but that doesn't imply rotation, does it?
The object is not a point mass at the end of the arm, it's a line. Different parts of the line are moving at different relative velocities & accelerations relative to the centre of rotation, and thus when released the rocket not going to go straight.
The longer the centrifuge arm relative to the length of the projectile, the less of an issue this is. We're already talking about an extremely long centrifuge arm.
Attach the payload at two points in a narrow V, equidistant from the center of mass. In the instant before release, fire pistons that slightly extend the upper arm and retract the lower arm, applying the exact amount of force you pre-calculated was needed to counteract the differences in rotation between those two points. Release while this (hopefully uniform) force is still being applied.
Yeah, you're jolting the hell out of your payload, but that's peanuts compared to what it's about to experience anyway.
GP has a point: consider the limiting case of an extremely long payload on an extremely short centrifuge arm. The payload is basically rotating around its own center of mass already, before release. Put your left index finger on the middle of your right arm, rotate the whole thing, and release -- you'll intuitively see that your right arm must keep rotating.
But see my other response above -- this does not seem like one of the bigger issues when the centrifuge arm is much longer than the payload. And we already know this launch system will only ever work for small, non-human, durable payloads.
>GP has a point: consider the limiting case of an extremely long payload on an extremely short centrifuge arm. The payload is basically rotating around its own center of mass already, before release.
But isn't the payload rotating around its own center of mass because the centripetal force acting on the "front" of the payload is not parallel with the centripetal force acting on the "rear" of the payload? As soon as you cease to apply the centripetal force (i.e. release the projectile) you're no longer going to generate any torque.
Imagine the payload being held by ropes on the back and on the front and then both ropes releasing exactly as its center of mass passes through horizontal.
A commenter on Ars who doesn't work at SpinLaunch but knows someone who does made some insightful comments last month after the release of the launch video:
This is super cool technology that will probably work given enough time, but I struggle to see the world in which it would be more economical than other terrestrial launch options. The tech could really shine in bulk material shipments outside of the atmosphere. Given the vacuum requirement it is already mostly designed to support that. The unfortunate part is that number of existing ventures it could be applied off-world is precisely zero at the moment.
Why outside of atmosphere? Launching from Earth poses some pretty hardcore requirements:
* Total system needs to achieve at least 7.2km/s.
* 7.2km/s initial velocity is not practical because of extreme atmospheric friction, heating, and vibration. You would need 9+km/s to escape atmosphere anyhow because of drag.
* You need a second stage which is heavy compared to payloads you want to launch, making the device capable to spinning a heavy second stage is challenging.
* Ideally you want your second stage to be as light as possible, which means less delta-V, which requires high `first-stage` spin speeds, which requires the launch device to be operated in the vacuum and second stage capable of withstanding lots of G forces.
Looking at off world applications, such as bulk launching materials from Moon, Mars, or asteroid belt, all of the above hard requirements are not there anymore. Escape velocity much lower, second stage is replaced with comparatively tiny terminal guidance stage or is significantly less massive, you have vacuum so no seals or atmospheric drag heating...
To summarize, I believe terrestrial economics will be quite iffy, but off world bulk material launches could workout (if the company survives till the point when the capability is needed).
There's some similarities with the supersonic trebuchet to these ideas, in terms of engineering.
Mach 33 is needed to escape orbit, so if you were going to launch a ball bearing into space, you'd need something at least 33 times more powerful than the rubber bands and 2x4 trebuchet.
It'd be interesting to run through those parameterizations with assumptions scaled to maximize a payload for reaching orbit using things like modern high strength steel and mechanical advantage and so on. It seems possible.
The amount of energy involved is terrifying - a space launch trebuchet would also be an anti-tank trebuchet.
Riffing off the $200 plywood and rubber band supersonic trebuchet was where I was going - e.g. if you used higher quality materials and a few thousand dollars, could you launch a 1kg steel ball into orbit? A 500g payload? Could you use ceramics for ablative shielding designed to break open in orbit, hatching a useful cubesat type device?
The idea of hobbyist level engineering achieving orbital escape velocities is the scary bit.
The design space equations used by the trebuchet guy could answer the questions, I think.
Roughly. But in theory it is easier/cheaper to harness that energy in a ground based system (like spinlaunch) than with a complex and traditionally unreusable rocket engine.
No, because you don't have to carry your fuel with you.
A rocket engine is subject to the Rocket Equation, where the amount of fuel you need is exponential in the amount of velocity you're trying to acquire. If you can impart all of that energy on the ground, you don't have to use 90% of the fuel to lift 10% of the mass halfway, and then 90% of that to get you the rest of the way, meaning your rocket outweighs your payload by almost 100x.
In this, the fuel all gets to remain on the ground. It's a bit like if you could take your capsule and put it on top of a giant exploding pile, getting all its speed all at once. You'd need a lot less fuel that way... except you wouldn't survive the explosion.
The energy savings of this are great. Everything else is completely bonkers.
