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I think their basic idea is sound, it'll probably eventually function. My concerns are if it'll be worth it, since there's a trade-off being made between fuel mass and heat shield mass, and at least based on Scott Manley's summary video this week, the rocket with the heat shield is close to the same mass as the Electron rocket. In which case I'm not sure the complexity of SpinLaunch is worth it.

Edit: the video in question: https://www.youtube.com/watch?v=8Phy3n_S3ng

and a more honest and detailed look at the company, again from Scott: https://www.youtube.com/watch?v=JAczd3mt3X0

⬐ gnramires

I haven't seen Scott Manley's video; but if the mass cost of a heatshield is so significant that's a problem.

However, there's a benefit in this case: heat shield probably scales with area (often something like mass^(2/3)), making it progressively less significant compared to fuel mass (which is roughly a constant fraction, i.e. it scales like mass^(1)). I think a high altitude launch site could make a significant difference as well (although that creates other logistic inconveniences). Atmospheric pressure approximately halves every 5km, and air resistance is roughly proportional to pressure.

⬐ kurthr

Building and SpinLaunching at above 10k feet (3km) seems like a no-brainer. It reduces heating and weight while increasing terminal altitude substantially... like 2x.

It would be more efficient, if they could use a whip effect to (match impedance) capture much more of the rotational energy they put into the spin, more like a trebuchet.

⬐ Schroedingersat

Is there any material strong enough to provide the whip? Or would you just make the spinning part slower?

⬐ sacrosancty

Is optimizing efficiency relevant at all? I'd think the electrical power cost must be negligible compared to the rest of the cost of a launch.

⬐ edrxty

It's not the electrical cost so much as system complexity. They could use less heat shield, more payload, spin the payload less hard, etc.

⬐ JumpCrisscross

NASA can probably trade the tech, if it even barely works, for budget from the Pentagon. This is a ballistic launch system without the tell of a rocket burn.

⬐ dotnet00

The Pentagon is already looking at them: https://spacenews.com/spinlaunch-joins-cadre-of-small-launch...

Scott Manley also put out a video on Spinlaunch:

https://www.youtube.com/watch?v=JAczd3mt3X0

He...encourages caution. It's one thing to call a technology "debunked", another to say it's very difficult or that it has a low probability of success.

⬐ MongooseMan

It's not impossible, but there's no reason to believe that the company is able to build it.

The founder has little demonstrable understanding of physics, and their demonstration video was misleading.

If SpinLaunch's idea was practical, it would've been in use for decades already. The company seems unaware of this... for now.

I look forward to watching SpinLaunch's progress.

A full tank is safer than an almost empty tank.. Also the tank is designed to keep the vapor part of the gasoline too saturated to explode, this is why there is a latch on the fill tube. I found this Quora post: https://www.quora.com/How-come-the-gasoline-in-gas-tanks-nev...

And even if it can explode in the situation where there's almost no fuel left, in that case it's not as bad as liberating the full energy of a full tank, which is what you'd do if you have a flywheel spinning with the same total energy as a full tank of gasoline. That would be madness.

Heh I came to think of the recent demo of the company that wants to spin up satellites on earth and THROW them into orbit. If something goes wrong in that spin-up, they would destroy the entire launch facility and whatever is in the way.

https://youtu.be/JAczd3mt3X0

I once had a CDROM open while the CD was spinning at like 40x or so, it ejected and went into the plaster wall. And that was just a CD..

Scott Manley on SpinLaunch: https://youtu.be/JAczd3mt3X0

⬐ FjgdymdjttdjG

I volunteer to be the first person to ride this ride.

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

⬐ NikolaeVarius

Thunderf00t is a contrarian with a cult audience.

⬐ GuB-42

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.

⬐ heyflyguy

His analysis of trajectory (the shadow of the missile against the terrain) was laughable.

I believe the parent is right, you couldn't hide it. Even if you succeed in building them completely stealthy, it's just a matter of time until the enemy finds out the locations using espionage or signals intelligence, and after that they will place the site unde non-stop satellite surveillance. They are massive and can't be moved, so they are sitting ducks.

As for launching, you are guaranteed to produce a thermal signature in the first few seconds of flight, since you hit the high density atmosphere at a 3-5 Km/s speed. You will leave a distinct, large and highly detectable infrared signature and the enemy will be alerted: https://youtu.be/JAczd3mt3X0?t=274

Scott Manley has made a video about it https://youtu.be/JAczd3mt3X0

⬐ usefulcat

This is fascinating, but I can’t believe he didn’t really address the elephant in the room (for me anyway). The instant the payload is launched, the launching mechanism will still be rotating at several hundred RPM but will no longer be balanced. I don’t see how it wouldn’t proceed to immediately and spectacularly tear itself apart. So they must have figured out how to rebalance it almost immediately. THAT is what I’d really like to hear about; that seems like the hardest aspect of the whole process.

⬐ p1mrx

The idea I heard was to just yeet a counterweight straight into the ground. Their system does not appear to have symmetrical exits though.

⬐ bagels

Seems like the simplest solution, throw it in to a hole in the ground.

⬐ jhgb

It could work, assuming you can shield yourself from the inevitable explosion once that mass impacts something.

⬐ stevesearer

Maybe they can redirect the ejected mass away from the launch site with a huge curved underground tube Mythbusters' style: https://www.youtube.com/watch?v=73FFitene58

⬐ dvdkhlng

Scott Manley talked on youtube about the centrifugal force on the wheel being around 10 thousand g (in the full sized version). So how do you build something that touches a tunnel at hypersonic velocity with many thousand tons of force without disintegrating? It's not like you can just add wheels or skates to your ejected mass (or the tunnel).

⬐ scoopertrooper

You got me curious, so I dug up their patent. This is as close as they come to addressing it.

> Although not shown in the previous figures, the circular mass accelerator structure 150 may comprise a second exit port directly opposite the exit port 115 to capture the counterweight 135 that is released simultaneously with the launch vehicle 105 to minimize an imbalance on the motor at the time of release. The counterweight 135 may be a solid material, or a liquid such as water.

The use of a liquid is a curious idea. Perhaps it could be dispersed in such a way as to spread the force of the counter weight being released across a wide surface area? Like a small explosive forces the liquid out in all directions?

https://patents.google.com/patent/US10202210B2/en

⬐ dvdkhlng

Whether liquid or not, running the formula for kinetic energy of the counterweight, I'm getting something around 1 GJ (gigajoule) for a weight of 1 ton at 1500 m/s [1].

According to this site [2] that's equivalent to around 200 kg of TNT. Even with the counterweight being mostly water, that's quite a lot of energy to disperse. How does one evenly spread out the water to a surface the size of a football field? Would that even be enough area to prevent a shock wave being reflected back at the launch equipment?

[1] https://calculator.academy/joule-calculator/#f1p1|f2p0

[2] https://www.convert-me.com/en/convert/energy/tntkg.html?u=tn...

⬐ mgsouth

There's a slide in Manley's video that says gross vehicle weight is 11,000 kg. And 450 RPM @ 100 m diameter, so 2 km/s. Kinetic energy for vehicle is 22 GJ. Equivalents:

* 5 metric tons TNT

* 1/3000 Little Boy atomic bomb

* 4 barrels of crude oil (!)

* Boil 2,300 gallons of water

* 0.25 mg of matter converted to energy

* Enough energy to melt two 11,000 kg iron counterweights, with 2 GJ left over

* A magnitude 3.7 earthquake [1]

[1] https://www.volcanodiscovery.com/earthquakes/energy.html

⬐ aww_dang

Perhaps it would be possible to use liquid carbon dioxide. The change from liquid to gas inside the vacuum chamber might help disperse the energy.

⬐ neltnerb

Yeah, I didn't see any explanation for that either. With that much kinetic energy around I wonder if it's designed to simultaneously launch a portion of the counterweight.

It's got a lower lever so the overall momentum might be low enough to make that recoverable. Maybe if it's 10% of the rocket's momentum, going into... yeah, it's hard to imagine that being recoverable but maybe it's just weights and that's good enough.

I'd love to see a real explanation.

⬐ ap11071

I was guessing, its water in a container with bomb bay like doors, when the payload is released the doors open and the water goes into some complex structure that takes the energy out of the water. but only a guess.

⬐ londons_explore

Isn't the simplest solution to just always launch things in pairs?

⬐ alexisread

If you take the simplest design then the second object would be launching into the ground, which is basically what they're doing with the counterweight. Alternatively you could have a contrarotating system, but I'd then be worried about two high speed objects travelling close together. The best solution would probably be a metal counterweight, so that you can regeneratively decelerate it from it's exit port.

⬐ darkscape

Build the thing on a sea platform. Launch the counterweight into water. Make it sharp-nosed like the payload, so it could potentially survive impact with water and be recovered.

⬐ Havoc

>so it could potentially survive impact with water and be recovered.

Doubtful even if pointy. Water is way denser than atmosphere

⬐ dtgriscom

Hey! Deep sea and space exploration at the same time! (You just have to get complementary mission designs.)

⬐ geerlingguy

Something like 10,000g to 0 in an instant—it does seem to be the largest engineering problem with a full-scale design.

⬐ bufferoverflow

You can just launch a dummy weight in the opposite direction into a body of water.

⬐ IshKebab

He did mention that in some detail.

⬐ finnh

He mentioned it toward the end, but did not describe the solution. I'm thinking the counterweight on the other end would need to move a very precise distance in effectively zero time.

EDIT: hmm, or a supplemental weight on the payload side, moving outward the right distance as the payload releases.

It seems like you'd generally want the non-payload rotating bits to vastly outmass the payload, so its release perturbs the whole system to the least amount possible. And then you use regenerative braking to reclaim the energy .

⬐ jessriedel

You'd need to reclaim a lot of energy very quickly because after the projectile's exit the atmospheric pressure is going to slow you down right quick

⬐ mgsouth

You could slam a blast door closed behind the exiting projectile. It should be possible to place it in the exit tunnel so that it is fully closed before the inrushing atmosphere gets to it.

⬐ jessriedel

Plausible. Do you know how fast such doors can close?

⬐ avereveard

I wonder why they don't just have an inert concrete mass on the other side and an exit port that opens into a sand bunker, sure it's a lot of energy but they don't have to contain it, only limit back splash from the mass hitting the sand. Doesn't even need to be enough sand to stop the mass completely, just enough to catch fragments, the mass can continue into the earth with no consequences

⬐ bufferoverflow

Sand will melt with all the energy absorbed. Water is much better.

⬐ dvdkhlng

Yes, that's an intriguing idea.

What I came up with was this: the launch arm has a second mass inside it, that will move (via centrifugal force) away from the center, in the same moment the payload is released.

Of course, just having two payloads launch in opposite direction as you propose maybe has much less implementation problems (though I wonder how you stop that second dummy payload in a way that does not cause an earthquake or explosion :)

Per Scott Manley[1] release velocity was Mach 1, they're targeting Mach ~7 for the final version.

[1] https://www.youtube.com/watch?v=JAczd3mt3X0