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Comment by gchadwick | Hacker News Reader

Like many others I was very skeptical of SpinLaunch's claims. Even with their successful demo launch you wondered if you'd be able to build a viable payload (especially one with a rocket motor, not just solid state electronics).

Though if NASA have chosen to enter into a contract them that gives a big credibility boost. It'll be very interesting to see how it goes.

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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

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.

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

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.

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.

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.

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.

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

It cannot be a coincidence that spinlaunch’s first stage (the spin) is designed to release at a speed equal to trans-earth injection from the lunar surface, and with a total mass equal to what a starship can deliver to the lunar surface. They’re playing the long game.

Very interesting. Maybe you're right! One of the complexities of SpinLaunch is that the centrifuge needs to be inside a vacuum chamber, which just completely disappears if you're launching from the moon.

What's currently worth mining on the moon and sending back to earth? Most resources are great for building more things on the moon, but valuable enough to send back.

Helium-3 is the obvious one, but that is also betting on fusion reactors becoming viable in the near future.

Some "rare earth" minerals might also be economically viable.

Rare, but industrially useful metals (cobalt, lithium, etc.) should be present in localized concentrations of high-grade ore on the lunar surface, along with platinum-group metals. We didn't use to think so, but our understanding of regolith and impact dynamics has come pretty far in the last few years and we now expect that a lot of the small impact craters on the moon asteroid cores that survived and are either dispersed in the crater floor, or for metallic impactors buried a few 10's of meters underground. So basically everything you would go to the asteroid belt to get, you can find on the lunar surface, far more accessible to humans in the decades to come.

But beyond that, the moon will no doubt export large amounts of volatiles from the permanently shadowed craters in the poles, and structural building materials for construction in Earth orbit or elsewhere in cis-lunar space, or the fueling of expeditions to the rest of the solar system. You'd just have to tilt the spin launcher to a different angle and adjust the throw velocity to send payloads on other trajectories through cis-lunar space.

The economics of all of this totally collapses when you can launch 150 tons of whatever fully reusable to earth orbit.

What's cheaper, mining infrastructure on moon, with a launch system on the moon to transport it back to Earth?

Considering you need potentially 100 launches from the moon to match one Starship launch. And the capital cost for the moonining and launch is absurdly high. And the only way we will ever even be able to build such a system will require a Starship type vehicle anyway.

That doesn’t affect the economics (and environmental impact) of mining the moon vs the earth for industrially useful metals.

The actual cost for Starship is unlikely to be the crazy low numbers space nerds like us are hoping for. No space launch system (including Falcon) has ever reached its theoretical minimum cost. It will be transformative, but not too cheap to meter.

By that logic building a mining base on the moon would also be far more expensive. You see how this makes no sense?

We will never build an industrial base on the moon unless we have a full reusable launch system and if we have such a system mining things on earth is just far, far, far, far, far, far cheaper.

The only reason you would mine on the moon is to build things ON THE MOON.

It's quite possible that the expense can be made comparable. Many resources available in the solar system exist in non-oxidized forms that just aren't available on Earth. Mining already reduced, pure metal nuggets is a huge reduction in energy costs and eliminates the need for refining steps with hugely toxic side products. Also have you seen how we mine many resources on Earth? Going to the moon (or near-Earth asteroids) and sifting out nuggets a few meters under the powdery surface regolith is way easier to do than drilling 2 miles underground for increasingly harder to find deposits.

The actual energetic cost of going from the moon to an Earth-capture orbit is only about 1 kwh/kg. Or about $150 per metric ton. Obviously real costs will be higher than physical limits, but you still might want to check your intuitions about just how costly mining the Moon really could be.

Ultimately we need to move our heavy industry off-earth to save our planet's biosphere. In a hundred years when there is a vibrant interplanetary economy, its possible we could eliminate toxic heavy industry on Earth entirely.

The cost from the moon to earth orbit isn't really the issue.

The problem is that to do mining you need a huge industrial base. Mining starts with prospecting. Then you need to develop the resource. You need to refine the resource at least a little. Then you need to mine that resources. Then you need to transport those resources to wherever your cheap launch option is. And then you need to launch it.

Building up such an industrial base on moon is incredibly difficult and would for sure require a massive Starship like rocket at the very minimum.

> Ultimately we need to move our heavy industry off-earth to save our planet's biosphere. In a hundred years when there is a vibrant interplanetary economy, its possible we could eliminate toxic heavy industry on Earth entirely.

Ok, in 100 years, but predicting that far ahead is pretty much useless. My point is that for any foreseeable future launching resource from earth is far more practical.

And from a money perspective it might never make sense, specially from the moon.

If its about the environment, then maybe but then you might capture asteroids instead.

Water, Oxygen, Hydrogen, possibly aluminium. Not to send back to Earth, but into Earth orbit to use as consumables and fuel. And these bulk materials aren’t going to be bothered by G forces.

Ah yes. I forgot that you might want consumables in earth's orbit itself.

Silicon could be useful in orbit for building solar panels.

> Though if NASA have chosen to enter into a contract them that gives a big credibility boost. It'll be very interesting to see how it goes.

NASA also funded experiments into the microwave engine thing [1], and that turned out to be bunk [2].

The point is, these are just tests. They give them a fair shake and see what happens. I highly suspect there are simply too many problems with flinging stuff into space for it to be practical.

[1] https://www.nationalgeographic.com/science/article/nasa-impo...

[2] https://en.wikipedia.org/wiki/RF_resonant_cavity_thruster

Plus the soul of NASA is innovating material and techniques for doing what can't yet be done -- even attempting the plainly impossible is likely to give engineers a fair shot at inventing something novel just trying to make it work.

Launch conditions are already very harsh. Rockets vibrate a lot.

I have no doubt that useful payloads could be designed to withstand the spinning as well as later rocket thrusts. (source: a couple of years on a satellite design project in university)

One other detail I've learned is that the G load increase is incremental, not all at once. Which apparently is very significant according to the company.

The G load increase is comparatively slow, but the release is pretty sudden.

Lots of things "bounce" in funny ways when you put them under very large loads, then release that load suddenly.

OK, so my knowledge of physics is lacking, but wouldn't the decrease of non-centrifugal G-load also be a bit slow as it takes the atmosphere some time to slow down the speed of the projectile?

The radial load/unloading is (approximately) instantaneous at the moment of release and does not vary in proportion to wind resistance.

Edit: this is, btw- fixable. Like other commenters mentioned, a trebuchet/sling like release mechanism would slow that radial unloading and reduce stress on the spinning arm too. It’s a lot more complicated to achieve though (as if this prototype/trial weren’t complicated enough!)

During spin-up the lateral force on the projectile increases slowly until it reaches maximum. When it's released, this load disappears almost instantaneously and the object is effectively in free-fall ... effectively 0g.

Then it hits the atmosphere and is subjected to significant drag, but that onset is reasonably slow (by some metric) compared with the release mentioned above, but it's along a different axis. What's more, the projectile has spin along its long axis ... I don't know how that's imparted.

Yeah, there are some huge forces that change rapidly in lots of directions.

This is probably only good for bulks. At least initially. Propellant, water, food, et cetera.

There is no launch contract, just a planned test.

Hopefully NASA watched this video, before making the contacts public instead of first examining the claims privately.

"Spinlaunch: BUSTED!": https://youtu.be/9ziGI0i9VbE

"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.

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.

FYI I'm a Spinlaunch invesetor.

Just watched this video. His argument for why Spinlaunch won't work is basically:

1) in the video of their first test chamber (12m diameter) there's some dirt and rust, therefore they don't know anything about vacuums

2) in their first ever test fire of a projectile leaving their 33m chamber, the projectile is wobbling, therefore they don't know anything

3) in a mock up video they made of a future launch system the headquarters is close to the launcher, which might explode if there's a misfire, therefore they don't know anything

4) the founder has an uninspiring resume when you look online

'Add these up and there's no chance they'll succeed. What they've done isn't as impressive as 50+ year old gunships.'

Give me a break. Their rate of progress is exceptional. They've already overcome so many challenges. These are weak arguments. Doesn't mean they'll be successful. But these arguments are weak. Some quick counter-arguments

1-) the 12m test chamber was a demo chamber. they were constantly spinning it up and letting people go inside. doing tours. stress testing new materials and arms. blowing stuff up. if anything the fact that it was so reliable even with the imperfections is a positive

2-) when someone is learning to throw a football there's tons of wobble. spinlaunch needs to figure out a perfect spiral. these videos were from their first couple attempts ever out of a chamber. what they're showing is very hard. this team has shown an ability to innovate and improve. those were images of their first few attempts to "throw the football"

3-) give the team some credit. these videos are designed for the general public. what they built already has an incredible amount of kinetic energy. they stress tested many tethers (past their limits) before going to this scale. when you're picking on things as small as "they're going to kill themselves by sitting right next to the system" you clearly don't have much left to nitpick

4-) jonathan is an absolute genius. just because he has a spartan online bio and unorthodox background doesn't mean he's not an absolute force of nature. thunderf00t is a very smart dude. but i'd bet anything that in a debate -- on basically any topic -- jonathan would absolutely decimate thunderf00t

cheers to the builders

>thunderf00t is a very smart dude

I just saw one of his videos on why Falcon 9 will never be economically viable so I would strongly disagree with this assessment.

I think his argument about Falcon 9 was about reliability vs reusability and he partially acknowledged he was wrong:

https://nitter.net/thunderf00t/status/961312911393218560?lan...

About the claim if he is smart or not, you might want to watch this then reevaluate your opinion:

https://youtu.be/5Hyy1zRZPiQ

The last video I watched of his was a debunking of flat earthers that was so bad it almost gave the flat earthers some credibility. Many of his 'debunkings' consisted of 'no, because science that's why' where the flat earthers had actually raised interesting questions where the answers provide a great jumping off point to explore things in more depth.

Taking ten years to come up with some simple experiments to debunk someone who is reasonably frequently publicly wrong and then labouring the point and being really condescending isn't a sign of someone being especially smart (although it's hardly stupidity either).

Its the typical build credibilty with debunking total nonsense and then use that to generate views on videos where he is suposidly depunking a lot more viable stuff.

Combine that with serving on the Anti-Musl wave and you have surefire way to be reddit famous.

Smart people make mistakes all the time. He has correctly debunked a lot of scams, it is easy to get jaded and carried away. Since he isn't an investor and doesn't have the inside scoop it is plain to see how his nitpicking, based on the publicly available information, potentially led him to a wrong conclusion.

SpinLaunch is a rather out there. I've actually had this idea and I'm sure many others have as well. I happen to think it can work but I was still skeptical when I first heard of them. You can only infer so much from the outside.

Thanks for the additional info blackholesRhot and for throwing money into this, the sort of bets we should be making. Godspeed. :)

The only thing that’s valid (and I didn’t really understand if the video maker understood it bc he wastes so much time on the wobble) is that if you spin sth up to, say, 200 /s, then your rocket will spin, with its full length, at 200 /s. I don’t know how they want to address that.

Cold gas thrusters.

That's barely enough for attitude control, do you have numbers how that could be used to despin a large rotating mass, as it is exiting the launcher?

I think you mis-understand the basics of how Spinlaunch is intended to operate.

The mass isn't rotating as it exits the launcher.

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

How could it not? The angular momentum is just disappearing?

Edit: Here's a link to an illustration, as your link provides zero information in that regard.

https://www.youtube.com/watch?v=TGO4LtCctTk&t=141s&ab_channe...

I clearly see their rocket rotate around its center of gravity, with the same angular velocity as the arm it's sitting on, while the center of gravity is moving on a circular path.

So, again, how is it not spinning? Where does the angular momentum go?

No, the better question is where it came from. The launcher spins the payload like a bucket on a rope. So upon exiting the launcher it isn't spinning. But by setting the guide vanes at a slight angle the payload can be made to spin to give it more stability (since this is essentially unpowered flight for the first bit) and it can be de-spun in the same way.

The launcher does not spin the payload around the long axis.

I can tell you exactly where it came from, it's being spun up in that launcher thing, obviously, that's the whole point of spin launch. You can see it for yourself in the video. Is the pointy end of the rocket always facing in the same direction, e.g. upwards? No, it's changing its orientation continuously, it's always facing 90 degrees from the arm of the launcher, which, you guessed it, spins.

It is indeed exactly like a bucket. And the bucket changes its orientation throughout you spinning it, that's the whole thing, that's why the water stays inside. The top side of the bucket is always facing you. For that to happen, it has to rotate around its COG with the same rate it's rotating around.

A different example: the moon is tidally locked to the earth (like the bucket to you, or the rocket to the spin launcher) - very obviously, it needs to spin around its axis to achieve that, and it does so at exactly the same rate as it is rotating around the earth.

That momentum doesn't just disappear.

SpinLaunch's website claims: "To date, we’ve conducted tests over 6x the speed of sound."

However, that doesn't seem possible because the centrifuge is not in a decent vacuum (as Thunderf00t points out in his second video) due to the whooshing sound of the centrifuge 'blade', and the speed can be estimated as just less than the speed of sound. If they have the ability to do hypersonic tests already, why would they not show it in their promotional video?

The fact that they intentionally blurred the data on the screens during the demo is also odd.

---

Regarding your final point, it's much easier to pretend to be a genius than to actually be one; Elon Musk is a master at it. Additionally, debating skill is a very misleading measure of intelligence.

Ah of course it's thundrfoot.

His phosphine "debunking" video was high on "hot takes" but low on actual intellectual honesty

There are ways of criticizing and going about that don't involve patronizing and shallow dismissals

I can't tell if you're joking.

I really hope NASA is making better use of taxpayer dollars than paying their decision-makers to watch clickbait trash on Youtube. How any serious person could take this sort of thing seriously is beyond me.

Richard Woolley springs to mind.

https://en.wikipedia.org/wiki/Richard_van_der_Riet_Woolley#V...

Well I would hope NASA is doing their due diligence.

Perhaps though there's a big push to invest in private space and they're not looking too closely at lower value/more speculative prospects.

Never ever recommend Thunderfoot for anything. He is an embaracing.

Your argument would be stronger if you would address the technical challenges he commented on.

I have years ago stopped watching his videos. He has long ago discredited himself and should not be promoted.

He should improve his video making skill beyond 2003 and stop making insulting people a core part of his message.

I have no interested in addressing his arguments, whatever they are on SpinLaunch. And I don't want to defend SpinLaunch anyway as it is terrible idea.

I think you are taking him too seriously and being maybe being a bit harsh. He is a mix of John Oliver and Johnathan Colbert with a bit of more precise shades of Veritasium.

He is primarily producing entertainment, and there is no harm in that. But he does it with a correct scientific background and some humorist tones not everybody appreciates. It's not a purely scientific channel, sometimes he get's some things wrongs, mostly on his opinions about the economics of projects.

The only thing I found too many, easily dismissing in this thread, is that when he makes one these busted videos he is also daring to make a statement and they are not random ramblings.

For example his first video of SpinLaunch, if you ignore the tone is a much better analysis than the one from Scott Manley, even if Scott Manley is a much better source for anything else related to Space.

Can you point me one of those egregious errors he made? Because I looked at this whole thread out of curiosity, and every single commentator criticizing him, did not provide a single concrete example.

It's a new genre...Scientific Entertainment ( bit still scientific) Not sure everything in this short life of ours, needs to be taken so seriously:-)

His fans believe any video by him is the god given be all and and all statement on any topic.

He employs a large number dishonest lines of arguments. Drawing large conclusions for limited unrepresentative data. Not actually fairly representing the things he is arguing about. What he does is build narratives to lead viewers to the conclusion he want them to reach.

> Can you point me one of those egregious errors he made? Because I looked at this whole thread out of curiosity, and every single commentator criticizing him, did not provide a single concrete example.

I have not one of his videos in a long time. I remember watching his videos on Falcon 0 and struck by him clearly have no understanding of the issues with his driving goal seeming to be to gather all possible evidence and building a 'Busted' narrative while ignoring any evidence that points into another direction.

In general, looking at his videos he seems to have made a career out of calling Musk an idiot. To be fair their are a lot of low equally low quality channels that made a career out of calling Musk a genius but those are equally stupid.

He even attacks some of those channels in his own videos, but its very telling that those are the kinds of channels he interacts with. Because that the level he is playing at.

> It's a new genre...Scientific Entertainment ( bit still scientific) Not sure everything in this short life of ours, needs to be taken so seriously:-)

You don't have to be serious but I very much get the vibe that he thinks he is very serious and his fans think he is very serious as well. A also think he is deeply unfunny and his videos are pure cringe to watch. Somehow he is a genius who knows everything about everything and yet his videos production quality is worse then a 8 year old on Instagram.

His channel is the kind of channel that is designed around making online interactions worse for any topic, not better.

This is the kind of video that I find actually helpful:

https://www.youtube.com/watch?v=d43ckxS8gJY

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