Can We Throw Satellites to Space? [video] | Hacker News Reader

Can We Throw Satellites to Space? [video]

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102 pointsraasdnil149 comments

We've had many discussions on HN about SpinLaunch, but Brian real goes through and answers several of the questions that were left unanswered, love it.

I don't know why this system is such a magnet of internet skepticism.

Of course the system is extraordinary, but it's an engineering project. An engineering project with a lot of "knowns", vs "known unknowns". It's mostly a materials science project.

It's a complicated integration problem with all of the engineering associated with that, but, to be fair, they're not making up a lot of stuff out of whole cloth, they're utilizing known things in new ways.

Simply, much of the concept can be simply tested after the napkin math is performed. Tested to the point of either "yea this will work" vs "no way".

As far as I know, there's no real government money in this, they don't seem to be running in to a lot of administrative red tape (like, high speed rail is not an engineering problem, it's social and governance problem). So, doesn't seem to be some swamp land boondoggle.

Can it fail? Of course it can fail. Is it inevitable? No, I don't think so. I don't think it's a bill of goods sold to investors to fund a few engineers in the middle of the desert.

Any reasonable version of it (what must look very different from the prototype) is an incredibly expensive investment, that must be diluted into what is currently an outrageous number of launches to pay for itself. Besides, there are some very problematic known unknowns involved on submitting things that want to explode to high g.

All of it looks patently possible, given enough money and engineer-time. It's the kind of project that may change the relation Humanity has with space, but has huge odds of bankrupting the entity doing it even if it succeeds in reshaping Humanity.

So yeah, it's either government built or it won't get built at all.

> it's either government built or it won't get built at all

This is a false dichotomy. Falcon Heavy is not government built. It nevertheless benefits from American largesse. SpinLaunch is in effect building the world's largest rail gun. If the proof of concept works they won't have trouble lining up grants.

Oh, man. If you think you can get it done in a single billionaire's budget, all power to you. But developing a Falcon Heavy looks like a much smaller marginal project than a launch rail.

I'm sure the US military will be interested in a launch platform that can quickly get a payload into space.

There’s always military uses.

> I don't know why this system is such a magnet of internet skepticism.

Because even if it works, it's still bonkers. Any proposal that involves extreme engineering never done before is going to illicit a lot of skepticism.

And this proposal also catches all the general (often unfounded) skepticism people have regarding space. And it catches the skepticism people have for startups proposing radical new technology. And being a space startup, it catches the skepticism inherent to being Musk-adjacent. Spinlaunch is a perfect storm for raising eyebrows.

The frustrating thing is that the skepticism always centers on basic physics/engineering problems that clearly have been solved before such a design would break ground. Nobody builds a giant centrifuge and says "Oh I didn't expect such high g forces!"

The areas I'm skeptical about are whether customers will be able or willing to design for 10,000G loads, and what market remains once Starlink can bring 120,000 kg to LEO at once. that fits a lot of small satellite ride shares.

I wonder if ICBMs will ultimately be a use case. I'm no fan of nuclear weapons, but the governments of the world are willing to throw money at them and weapons are generally easier to harden against g forces than an undergrad cubesat.

I'm amazed that radar circuits (for proximity fuses) can be fired out of a flak gun and survive and work, so maybe this is possible.

The US has had (for several decades) guided artillery shells, both optical and inertially guided. These get launched from battleship cannons and deploy fins to guide them to the target. The inertial guidance is almost more surprising, it means the IMU can not only survive being launched, but has enough sensitivity to double integrate accurately through both the launch and free fall.

> Nobody builds a giant centrifuge and says "Oh I didn't expect such high g forces!"

Nobody build a satellite and expect such high g forces, they don't build satellite to accommodate to launch system, it's the other way around.

Maybe I misunderstood what you wrote, but satellites are built to accommodate launch systems. They have to tolerate the temperature, vibration and acceleration of the launch system, even if it is a rocket.

Actually a lot of satellite engineering is based around reducing weight to lower launch costs.

> Because even if it works, it's still bonkers

Is thinking you can throw something into space really a priori any more bonkers than thinking you can get to space by strapping a seat onto a bunch of explosives? Because that's what rockets are.

"Bonkers" is a classification only for concepts that haven't yet been normalized.

I’m inclined to say there’s a lot of priors for throwing things really, really fast.

Also a lot of priors for what happens to things near explosives that go off. I'm not sure naive extrapolations from such experience is sound.

> Any proposal that involves extreme engineering never done before is going to illicit a lot of skepticism.

FYI this is "elicit" and not "illicit". The latter has negative connotations.

The video stresses that this has been done before at similar energies, and modern materials can vastly improve reliability and reuse.

Project HARP attempted to do this in the 1960s.

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

As Elon said about Starship - "We're not breaking any laws of physics here, so it should work".

Sure, it's super expensive and massive, but that doesn't mean it won't work.

I think we can assume Brian McManus read over the past HN thread (April 2022) with the skeptical comments about the feasibility because he puts a screen shot of that thread in the video. Deep link to the HN cameo appearance: https://www.youtube.com/watch?v=yrc632oilWo&t=39m48s

Related. Others?

Can We Throw Satellites to Space? – SpinLaunch - https://news.ycombinator.com/item?id=32375464 - Aug 2022 (5 comments)

An Inside Look: SpinLaunch Flight Test #7 - https://news.ycombinator.com/item?id=31098021 - April 2022 (4 comments)

NASA to Test SpinLaunch, a Giant Slingshot for Launching Satellites into Space - https://news.ycombinator.com/item?id=31010244 - April 2022 (1 comment)

NASA will test SpinLaunch's ability to fling satellites into orbit - https://news.ycombinator.com/item?id=30996665 - April 2022 (199 comments)

SpinLaunch completes first test flight with rocket-flinging launch system - https://news.ycombinator.com/item?id=29198589 - Nov 2021 (219 comments)

Spinlaunch completes suborbital launch without engine - https://news.ycombinator.com/item?id=29175912 - Nov 2021 (6 comments)

SpinLaunch is building a centrifuge to launch satellites into orbit - https://news.ycombinator.com/item?id=25204660 - Nov 2020 (143 comments)

SpinLaunch raises $40M to build a machine to catapult objects into space - https://news.ycombinator.com/item?id=17317688 - June 2018 (105 comments)

Space catapult startup SpinLaunch comes out of stealth - https://news.ycombinator.com/item?id=16439835 - Feb 2018 (110 comments)

Instead of spin I would be leaning more towards rails on a mountain but this requires more space but should be much more easier on payload

Yeah. With a few kilometers of track you're looking more at a thousand times less acceleration though still more than a human could take. Though emerging from a track kept at a vacuum and slamming into the atmosphere is going to be quite a jerk in any event.

Your forgetting the evacuated tube. The issue with rail launch on earth is dealing with the atmosphere

Just musing from intuition: but could gravity and magnetic rails come close to the potential energy of a spinning system?

If you have enough mass, and enough change in height, sure. Doesn't mean you have a practical way to use that potential energy though.

Is a centrifuge considered to have potential energy, or kinetic energy?

Sorry, my use of potential was a bit of wordplay on my part. I should have stated my question differently.

Kinetic.

That was a very interesting question to which you gave a very definite answer, but why do you say kinetic? Maybe I don't understand what potential energy is.

from wiki <https://en.wikipedia.org/wiki/Potential_energy> "In physics, potential energy is the energy held by an object because of its position relative to other objects, stresses within itself, its electric charge, or other factors"

but a spinning disc in a vacuum would maintain energy indefinitely, taken as a whole, and the spinning disc is a stress in itself.

From Wiki: https://en.wikipedia.org/wiki/Kinetic_energy

"In physics, the kinetic energy of an object is the energy that it possesses due to its motion."

The spinning disc has energy because of its movement. If it stops spinning (moving) it has no more energy. That is what people refer to when they say kinetic energy.

> In physics, potential energy is the energy held by an object because of its position relative to other objects

That would be when you put the disc on a high shelf and it falls on you.

> stresses within itself

When you take the disk and you bend it into an S-shape and it is trying to spring back.

> a spinning disc in a vacuum would maintain energy indefinitely

Assuming frictionless bearings perhaps. But what does that have to do with anything?

> spinning disc is a stress in itself.

Not in the way physicist think about it. On the other hand, watching a spinning disk is full of stress! Just think of the last scene of Inception.

>> a spinning disc in a vacuum would maintain energy indefinitely

> Assuming frictionless bearings perhaps. But what does that have to do with anything?

Thanks for this, let me elaborate. First, yes, magnetically suspended. That given, take a box containing some quantity E of energy in the form of petrol or TNT, whatever. Chemical energy.

Next take a box containing aforementioned disk, spinning with an energy also of E.

From the outside there is no observable difference if both they are left sitting on a warehouse floor untouched, however the box with E of chemical energy is potential energy, the box with the spinning disk has kinetic energy, according to your definitions. Yet they are indistinguishable from without. That's my puzzle.

(I'm being slowposted so replies may take a while)

> That's my puzzle.

Sorry but I don't see the puzzle. Are you expecting some "different things need to be able to be distinguished when left sitting on a warehouse floor inside a box, untouched" principle?

> I'm being slowposted so replies may take a while.

No worries. And sorry that that happened.

You can't distinguish the boxes externally (just by looking anyway).

Therefore you can't say which one contains kinetic energy (the box with the spinning disk) and contains the potential energy (the box with petrol in it).

If you can't distinguish kinetic from potential in this circumstance, does the definition of 'kinetic' and 'potential' have any rigorous meaning? I'm fine if they don't, I'm just trying to understand.

> If you can't distinguish kinetic from potential in this circumstance, does the definition of 'kinetic' and 'potential' have any rigorous meaning?

They're still different forms of energy even if you can't see which is which from the outside of a (non-transparent) box. Like, if you have a red ball in one and a blue ball in the other, you can't see from the outside which colour ball is in which box either. Does that mean "the concept of colours doesn't have any rigorous meaning"? No, it just means the concept of being in a non-transparent box has the rigorous meaning that you can't see what's going on inside it.

I dunno. If you can't see the ball's colours you can't meaningfully say that one is red, the other blue. It doesn't mean they aren't red/blue, you just can't infer which is in which box.

Same here. Energy E will hang around for unlimited time until you extract it. I dunno. Anyway, thanks.

> You can't distinguish the boxes externally (just by looking anyway).

You know what else can't be distinguished when they sit in boxes in a warehouse (just by looking)? Bricks and teddy bears.

Do you find that they also lack a rigorous meaning? :)

To desphericalize the cow a bit, the spinning disk would have /some/ potential energy associated with the tension the material experiences to keep itself from flying apart, but yeah, I don't think I'd bother keeping track of it most of the time.

This is what I thought. My physics is a little rusty so I tried to fit it to a potential energy just based off that comment, haha. Like if we look at the rotating (so, non-inertial) frame of reference, then maybe we could define a potential energy off the centrifugal "force..." but that would be illusionary.

What if you attach the payload to the projectile with a bungee cord, at exactly the moment it is released?

I suspect it'd be hard to find a tether material that could take that kind of force without breaking. There could also be some strange dynamics as the projectile and payload would become like bolas[1].

1: https://en.wikipedia.org/wiki/Bolas

You're probably right. I would love it if someone could put it in a physics simulator, though.

You will loose lot of energy on bungee cord aerodynamics, heat, etc

True, but the question is: will the payload suffer less?

You'd need an awfully long rail. Where does the energy come from for this idea?

Just for fun, accelerating on a rail to appreciable first stage velocities of 2000 m/s at ~3g (for humans): 60 seconds of acceleration along 60 km of rail

I think creating cannons along the designs of Gerald Bull would be more promising. Just huck cube sats into orbit. Obviously you'd probably want a cube sat with no moving parts or something that could withstand what I'd assume to be like 10K G's.

You can't fire anything into Earth orbit. Once propulsion is complete, you are in an orbit. Orbits repeat. So if your orbit starts from the ground, your orbit will intersect the ground which is... undesirable.

Instead, you have to fire a rocket motor to alter the initial orbit into one that doesn't intersect the ground. Now you have a new problem: you have to design a rocket motor which can withstand the launch. A solid rocket almost certainly will spontaneously RUD when heavy acceleration is applied. A liquid rocket has pumps and pipes which are likely can't survive the acceleration.

This is the reason spin launch is nonsense: you've traded a solved problem (make big rocket motor) for an unsolvable problem: make a rocket motor which can withstand absurd acceleration.

The other red flag with spin launch is that genuinely new approaches to problems do not come from unqualified randos thinking about a problem. For example, if a company has a crazy new idea for blood testing, it's really bad if the crazy new idea came from someone with zero experience and zero domain knowledge.

> https://www.freethink.com/space/low-earth-orbit-satellite

Seems like there is already a mechanism, sans moving parts, of generating force post-launch. Not saying it is sufficient to correct a ground-launched, ballistic projectile though.

> A solid rocket almost certainly will spontaneously RUD when heavy acceleration is applied

I am skeptical that there is no chemical propellant capable of resisting the initial acceleration. That seems like a bold claim.

What about gas-based thrusters(i.e. ion drive with xenon or even just nitrogen gas)?

The LEO post-launch force you link to is for minor orbital changes. Or large changes over a large amount of time. The problem with an orbit that begins at the ground is that you have exactly one orbit's worth of time in which to convert it into a real orbit. Magnetic or ion propulsion won't cut it.

My comment about solid rockets is due to the fact that they include fully combustable fuel in a ready-to-use mix. Solid rockets don't require much input to get them to combust. I assume no one is considering solid rockets for this application; I only mention it as part of assuming they would need a liquid rocket so I could explain the problem with liquid rockets which rely on pumps and pipes.

Fill a tank with nitrogen and cap it with something akin to an explosive bolt. When attitude is favorable, blow the bolt and let nature take its course. Sorry it's late here and I'm just spitballing. Seems feasible though.

I guess the problem then becomes designing an explosive bolt that can survive the 10,000G launch without exploding.

Rocket assistance is common among artillery rounds, and several militaries have been trailing next generations of these rounds that may reach performance ranges similar to intermediate ballistic ranges. So it's not that out there of a concept. I share the skepticism about a high performance liquid engine however.

You keep using "likely" and "almost certainly", suggesting uncertainty, but then somehow arrive at a strong conclusion that such a rocket is an "unsolvable problem". The latter does not follow from the former.

Doesn’t this ignore the fact that earth has an atmosphere? Couldn’t you fire something that would have an escape trajectory but then decays though air resistance into an orbit?

Suppose you have an object that has just left the atmosphere, and suppose it is in an orbit. You have the same problem again: every orbit repeats, so the object's orbit, having just left the atmosphere, will repeat into the atmosphere.

Let's put this another way: every orbit is an ellipse. If you do not alter your orbit, you will only travel on the ellipse. The moment you stop interacting with the atmosphere, you are on a fixed ellipse. The problem is just behind you on the ellipse is the atmosphere, and if you continue forward on the ellipse you will inevitably come back to the part of the ellipse that is still in the atmosphere.

I know how orbital dynamics work with the absence of non-gravitational forces.

But it's not a point that you suddenly stop interacting with the atmosphere, it's a gradient, with asymmetric forces on the forwards and down directions from gravity/air resistance that are smeared over time, a bit like a non-instantaneous burn around the fast end of the ellipse; I'm not sure how well the "free motion in a vacuum" intuition holds in this case; but especially when your delta-v from the atmosphere is smeared nonlinearly over your ascent period.

Yes, you end up at the same height or lower the next time round, and will incur drag from that, but shrug, that's just regular orbital dynamics.

I had to google this myself but for others who may be unfamiliar

RUD = Rapid Unscheduled Disassembly

Seems to be popularised by Elon Musk [1] but I managed to find a page which links to evidence [2] going back as far as the 70s.

[1] https://www.theguardian.com/technology/2015/jan/16/elon-musk... [2] https://space.stackexchange.com/questions/10022/who-coined-t...

Even if something is rated on i.e. 1000G it is rated for a very short time, like a shock or a fall on the ground. Which from my perspective is the problem of whole concept described in the video.

In 5:55 minute mark, video is describing force applied on the payload will reach from 1G to 10000G, but how long does this take? 10 minutes? 30 minutes? An hour? Can you have a payload which will be able to withstand 1000G+ for minutes?

Contrary to big cannons, like [0] there would be forces of 10000G only for few milliseconds as shells are accelerating only during the time of being in the barrel.

[0] https://en.wikipedia.org/wiki/Project_HARP

One advantage this has over guns is that jerk (https://en.wikipedia.org/wiki/Jerk_(physics)) is lower.

I don’t know whether it makes a difference in survivability, but it seems to me that it would, at least somewhat, for some materials.

But then, what do I know? Impact resistance typically is reported in gs, but that might be a simplification because, typically, the higher order time derivatives of position correlate well with acceleration.

I would invest in more rockoon research. More of an elegant way to sidestep the thick atmosphere we're straddled with rather than brute force it with cannons and such.

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

Makes a lot of sense to me — make the atmosphere do a lot of the heavy lifting rather than fuel.

The rate of change of acceleration is going to be massive in a cannon though. That intuitively feels worse than very high acceleration but with a more gradual increase in the rate of change.

I would guess you'd do something like try and cast any electrical components in something like a resin so it's just a solid brick that can handle the stresses. But 10k G is a lot.

Militaries have been shooting working electronics out of guns since WWII. The earliest versions were vacuum tube proximity fuses. The U.S, military has been shooting guided weapons out of guns since the 1970s. They work pretty well.

This technology seems to be suited for launching moderate numbers of small satellites. It's not a huge win on launch cost over filling up a Falcon 9 with racks of small satellites.

This competes with the Pegasus air-launch system, where a rocket is carried to high altitude by an aircraft. That works fine, and launches have been going on since the 1990s. But it's not a huge financial win.

It's good to have a few competing technologies. Keeps the price down.

10k G should be doable, during WW2 the allies had radio proximity fuzes for artillery shells that exceeded that: https://en.wikipedia.org/wiki/Proximity_fuze

The problem is that this thing is supposed to throw a whole second stage rocket, with plumbing, turbopumps with moving parts, and fuel that sloshes around.

> fuel that sloshes around

Pressure and ballast balls.

That was one design that was extensively tested and then copied. Weight was no concern.

Most satellites are unique, so the same can't be done. Besides being weight critical, every failed satellite becomes space junk.

If a satellite thrown by this system fails, it won't make orbit, so it won't become space junk. Even if it did make orbit; space junk in LEO isn't such a huge deal, it will fall out of the sky within a few months/years. Kessler syndrome is a popular but frequently overstated meme.

With regard to weight, they say this system works best with very dense payloads. But that's only for the spin/toss stage; it doesn't account for the rocket booster needed to actually bring the satellites into orbit.

As for testing, engineers don't need as much empirical testing anymore, since we have very good computer simulations now. Most of the satellites launched with this would probably be variations on a handful of designs. But I don't understand where the demand for such a launch system comes from anyway. There is only so much demand for school project cube sats; communication satellites launched this way seem dubious (not least because you can launch dozens/hundreds of them at once with a rocket like Falcon 9 or Starship)

What about the rest of the satellite? Solar panels, antenna, engines?

It all seems generally dubious to me. But I think solar panels could survive that force if they were firmly supported inside the vehicle before launch; I don't think the acceleration itself would break the panels if they were prevented from flexing. For an engine, maybe solid fuel but the fuel itself would be structural. A pressure-fed liquid fuel engine might be easier, if you could get valves (and actuators for those valves) to survive that kind of force.

Well problem is that this concept is supposed to replace 1st stage as it can reach only to 70km. What kind of 2nd stage rocket engine can survive such Gs? Solid booster which you can't control?

They have the significant advantage that they get pretty much free mass before the fairing opens (since more mass reduces drag and they aren't fighting the rocket equation until they are out of the atmosphere). As such they can do things like heavily brace the inside of the nozzle without it hurting their payload capacity.

There is lengthy discussion at the end of the video on design changes, primarily for the reaction wheel.

They conclude by placing a digital camera in their lab mockup and taking it to 10,000g.

This probably would not have worked for a phone, but they seem quite confident.

Or a closed magnetic rail which you unlatch when you fire. The idea that you should use an actual spinning arm is needed is what everyone has a problem with.

A sane solution will be something that's closer to a large water mains pipe supported by a roller coaster frame.

A practical railgun of that kind is several kilometers long last I heard.

It has to withstand exactly the same forces as the torsion arm used here.

That’s not true? The problem with spinning is the pulling to the outside, not the going faster. With a straight track/tube you only have the go faster forces not the pull to the outside

Earth might be little too thick for this but should work great on Moon, Mars.

If you don't launch to escape velocity, you launch to an elliptical orbit that intercepts the launch altitude.

That's why you basically always need a rocket engine anyway.

...thus the small rocket contained in every spin launch.

The initial velocity just replaces a rocket's booster stage, not a whole rocket.

The problem is drag and heating. The booster phase of a rocket moves slowest in the thickest part of the atmosphere so it mostly avoids this. Usually at the end of the booster phase a rocket is going 2-4 km/s but it's also at 60 km above sea level. (All these numbers vary somewhat by launch vehicle.) To travel at that speed even at jumbo jet heights, ~15km, would generate insane amounts of heat and drag; the front of the craft would be white-hot and there would be massive loss of energy to friction. And it would still need to have the fuel and engines to accelerate another 5 km/s to stay in orbit.

It's physically possible but the engineering is insanely difficult, much more so than a traditional rocket, which is already no cakewalk.

The video covers this.

The nose is copper and aluminum that do melt under these temperatures, but this is prevented by two elements.

Only the first five seconds of the launch will deliver the majority of heat, and this heat can be dissipated by thermal conductivity.

I think they have this covered.

is the total heat delivered as a function of height for each design known publically? could it make sense to replace the bulk of the mass with water, turning into steam to partially recuperate thrust? like a continuous steam explosion to keep the nosecone cool while providing thrust?

You know, they do the math in the video. You aren't in the lower atmosphere to loose a significant amount of your initial velocity. I have lots of other questions about the feasibility and cost competitiveness, but this just isn't a credible one.

Any craft which starts from sea level (and the top of a mountain or a rail system is basically sea level) will indeed lose a significant amount of its energy to heat. Check out the Sprint missile, which was chemically rather than kinetically launched but faced a similar challenge: https://en.m.wikipedia.org/wiki/Sprint_(missile)

I'm not saying it's impossible, just that to pull this off while still having a craft capable of reaching orbital speeds is an immense challenge.

As discussed in the video, the SpinLaunch has the advantage that the acceleration to launch velocity is done in vacuum without reaction mass, so they can use a relatively heavy vehicle. The heavy vehicle obviates the issue you discuss, since there is more kinetic energy stored in the heavier vehicle than in a chemically-launched vehicle (which in this case needed to be light enough to be accelerated to velocity in 5 seconds). Thus, the fraction of energy lost as heat will be lower.

Again, this is because the vehicle can be accelerated electrically under vacuum until it reaches the required velocity. The heavy mass (in the vehicle’s nose cone) is not part of the orbital vehicle.

From a quick skim of the article, I don't believe deceleration or energy loss calculations are given. TFA gives a figure of 150 m/s of aerodynamic losses which is fairly tiny compared to the roughly 2km/s launch or the 1km/s gravity losses.

150 m/s seems insanely low, only slightly higher than a regular rocket launch which moves much more slowly through the lower atmosphere. I don't think a vehicle which still has the mass to reach orbital velocity could attain that. There are smarter people than I working on this, but I remain a skeptic.

Also, economic viability: per the Tsiolkovsky rocket equation, for a 100kg payload (almost microsat territory) and an orbital-insertion engine with a generous ISP of 320, you'd still need over 500kg of propellant to accelerate the "second stage" 5km/s to orbital velocity. This ignores the mass of the tank and engine and electronics (which have to survive 10,000g!). If you remove the latter from the payload you're looking at just a few kg remaining for the sat itself and you've massively raised the cost for the upper stage due to the exotic materials required to hold up under such acceleration. Then even if SpinLaunch or another team pulls off said engineering, you have to compete against a traditional rocket which could launch ~100 equivalent satellites to low-Earth orbit in one shot—at a known cost, with high reliability—using only materials and design widely in use today.

Edit: The same numbers with a 1,000kg payload are ~6,000kg at launch. How are you going to design a 6,000kg craft which can survive 10,000g?

I think the main flaw with this analysis is assuming that 320 is the upper bound ISP. There are plenty of upper stage engines that are getting over 450 (eg RL10). Obviously making a high quality second stage that is small and durable enough isn't easy, but it's not obvious to me that it's impossible to make cost competitive. (that said they obviously are something like 95% likely to fail)

For that kind of ISP you need hydralox. Now you've got to accelerate cryogenically cooled hydrogen at 10,000g! Also if it ruptures during spin-up you've probably destroyed your launch mechanism (not that keralox would be much better). At least you wouldn't need much insulation on the tank since it only has to spend ~6-7 minutes in flight.

> that kind of ISP you need hydralox

Merlin 1D and Rutherford get close to 350 in vacuum with RP-1. Hydralox would need to be insulated during spin up, which probably makes it prohibitive. In any case, if anything goes wrong in spin-up or deployment, the entire facility is toast. Whether there's a bit of extra chemical energy added to the mix is likely a rounding error.

Oh yes, the casing to let it go through the atmosphere at hypersonic velocity is definetly a significant engineering challenge. But it's a solvable one, unlike trying to get through troposphere at orbital velocities.

not a criticism or a confirmation, just a remark:

> [...] the front of the craft would be white-hot [...]

To the extent heating is inevitably experienced, a conventional way is to get rid of it by radiative cooling. Complaints about the visual appearance of a radiative cooling subsystem visibly doing its job is a bit weird.

Related: Spinlaunch: BUSTED | https://www.youtube.com/watch?v=9ziGI0i9VbE

While there may be some valid critique in this video, it’s oozing frankly disgusting amounts of pompous dismissal and consequently I cannot trust its motivations.

Somehow I knew it would be Thunderf00t from the title alone.

I used to watch this guy religiously (lol) back in the day, and while I still occasionally see what he has to say about certain topics, I find him hard to watch because of what seems to be a lack of humility. Last year I unsubbed.

Yeah, some of the stuff he critiques is really stupid (ex. solar roadways), especially when it comes to Kickstarter scams, but his general attitude suggests that no one should ever test insane ideas for the sake of it. I get that reusable rockets have already been achieved, for instance, but Thunderf00t seems to think that's a reason to dismiss the efforts of SpaceX, as if nothing could have possibly been improved upon since the 1990s. He has a real bias towards governmentalized academia, and he's even admitted it more or less in the past, which is why he frequently criticizes commercialization of technology.

It's too bad, because he's a really smart guy, and used to make very good points against organized religion. He could be inspiring more people to get into science, but he's now in the business of mocking, which isn't a compelling reason to actually become scientifically literate.

The really odd thing about his critiques is that he doesn't actually attack the heart of the problem, which is the media. As long as the mainstream media is scientifically illiterate and is so bereft of ethics that it just wants to sell attention, people will invent cockamamie ideas like the "sky hotel."

> It's too bad, because he's a really smart guy

Is he really? I've yet to see a single video where he applies a significant amount of intellectual rigour.

I've seen him make so many basic mistakes in his reasoning that he's either incredibly lazy, intentionally misleading (a real possibility since "debunking" gets him views) or just not that smart.

I dont understand why so many people take him seriously. I suspect too many people get a kick out of feeling smart/smug from "debunking" videos.

Explain the wrong reasoning and flaws in these videos:

https://m.youtube.com/watch?v=DXpLAB5219A

https://m.youtube.com/watch?v=LmlAYnFF_s8

https://m.youtube.com/watch?v=Mwbd1qGvTeQ

https://m.youtube.com/watch?v=GJ4KoxeTu-8

https://m.youtube.com/watch?v=9g3eXLwH9J8

I will take your words by face value and assume that none of these videos used or needed any amount of intellectual rigor and that he is not very smart. Okay, but if the bar is that high, then it appears that whatever scam kickstarter he debunks wasn't even on the scale of intellectual rigor or smartness.

He announces a set of physics exercises relevant to spin launch on Brilliant at the end of the video.

I wouldn't discount his STEM knowledge.

Caution. The "he" you are referring to (the one who announces the Brilliant exercises) is Brian McManus from the Real Engineering youtube channel.

The "he" audunw refers to in the comment you are responding to is Thunderf00t.

You guys are talking by each other.

I’ve been assuming when I see those promotions that the content creators involved have pretty minimal real involvement signing off and maybe making suggestions. It is at the end of the day just an ad

The problem with his channel is that there are lots of fraudulent kickstarters and projects out there where a debunking video is as easy as taking a kid's lolly away.

The real problem is that a lot of people buy into this crap.

As you get further and further away from dehumidifier scams, the debunking becomes more speculative because there is a non zero chance that the project delivers something even if the hype and marketing are all wrong. Debunking hype and reigning in expectations isn't the same as debunking the concept. If spin launch is only ever going to deliver tiny payloads to orbit it is guaranteed to find some underwhelming niche and become just another boring business among hundreds of thousands of others.

People just hate him because he destroyed Musk

I've tried to listen to this guy in other contexts, and you're right. So much cynicism and arrogance of his supposedly grand intellect. It's just such a turn off.

You’ve got great intuition: https://youtu.be/SpgBkpb7xlU

What the hell is that & how is it relevant to satellites?

'He's wrong about feminism so he must be wrong about everything else.' I guess?

There's no denying the guy is a blow-hard loudmouth with an obnoxious style and some dumb opinions, but that's no reason to blindly believe the inverse of everything he says. Personally I ignore his videos; not because he's always wrong, but rather because he's always annoying.

I agree I find thunderfoot's attitude off-putting but in general I trust his take on these things

Lots of things from that "debunking" were well covered in the original post. Other than ad hominem attacks, I've not seen anything substantiative from Thunderf00t that address this new video.

If you want to know if this has any chance of working, you should probably ask somebody who is an expert in this field and ignore the youtube videos. This goes for both Real Engineering and Thunderf00t

Being an expert or not doesn't make basic physics go away.

Criticism can be valid even without credentials, especially in an area where the only people with relevant credentials are putting their hand out and seeking startup funding.

I can judge whether a honey is good or not, but I'm not a bee and I can't make any myself.

Yeah, I dont understand this "You are not an expert" bullshit.

This is 7th grade physics, centrifugal force, newtons laws, kinetic energy and a small amount of materials science.

People just get swayed by fancy CGI

What about the basic physics suggests SpinLaunch is impossible?

and part 2: https://youtu.be/ibSJ_yy96iE

Real Engineering always does such an amazing job on all their content, although I can't help but fixate on what the release mechanism looks like since it wasn't revealed in this video.

This comment was inspired by another commenter saying something about shooting the rocket off the side of a mountain.

I'm theory-crafting here without any specialized knowledge on the subject, asking strictly out of a mix of curiosity and fun. Is there an online community where I could pose this question and get a well-informed response about its viability?

What if you dug a very deep hole, created a near-vaccuum, and you shot the rocket out like a rail-cannon?

Here's a quick and simple sketch [0] of what I have in mind.

[0] https://imgur.com/bmHiMdq

> What if you dug a very deep hole, created a near-vaccuum, and you shot the rocket out like a rail-cannon?

What would happen is your payload would follow a ballistic trajectory up through the atmosphere into space, then it'd fall back down and hit the ground somewhere west of the hole because earth rotated under it while it was in flight.

As XKCD puts it, "The reason it's hard to get to orbit isn't that space is high up. It's hard to get to orbit because you have to go so fast." https://what-if.xkcd.com/58/

Also the way 2-body orbits work, you will always return to the point you last changed your velocity. That means your hole-launched spacecraft's flight path is actually an elliptical orbit that's so extremely narrow that it looks more like a straight line up and down, and then the ground prevents the vehicle from continuing on its orbit around the Earth's center of mass. So if you want to "circularize your orbit" you have to increase your sideways velocity by thrusting at the top of your orbit, so you can as Hitchhiker's Guide puts it "throw yourself at the ground and miss." That way the ellipse is mostly a circle around the Earth and you'll return to that thrust point in space rather than returning to hole's entrance.

So you'd want to make the hole more like a train track running just under the surface (or an evacuated tube just above the surface). That's sort of what SpinLaunch and other non-rocket space launch systems like mass drivers and Project Babylon.

How do you produce a near vacuum with a hole on one end?

Presumably with a rapidly opening door. Of course now you have to design your rocket to slam into an atmosphere at launch velocity.

You might have to install enormous compressed air tanks at the end to pre-accelerate the air right as the door opens just to make it less like hitting a brick wall of onrushing air.

Can't you do something similar to what the engineers in the rocket throwing video are doing?

By extending the cannon's end to space.

Oh no, now the vacuum of space is leaking into the base of a mountain!

What if it leaks out to sea level and kills us all?

A door.

> we ended up doing it for less than a couple of million dollars

That's a nice way to make a couple of million dollars sounds less than it is:-)

Hacker News is shown as example of naysayers: https://youtu.be/yrc632oilWo?t=2401 :=)

I’ve wondered this about airplanes. Couldn’t we launch an airplane into the air and it spends the rest of the time gliding back down to earth? It would make things a lot simpler and the chance of something going wrong is much less since it’s in a perpetual state of gliding back. Is this even possible?

I don't know.

Gliders are a thing, dragged into the air by a propeller driven plane, untethered they fly for quite some time.

https://en.wikipedia.org/wiki/Glider_(sailplane)

I estimate, speculatively that the energy to bring it to altitude, condensed into an impulse only imparted at launch, would destroy such an aircraft and kill any occupants.

Sure, but no modern airport would be able to accommodate these as the wingspans would have to be huge compared to a propelled jet.

What? Gliders fly out of "modern airports" every day. Not to mention large flying wings like NASA Sunglider, B-2s and wide-winged aircraft like the A380 and An-124. Heck, the Mriya was able to operate at many major airports, although with some disruptive considerations when taxiing.

> Gliders fly out of "modern airports" every day

Sure, carrying one or two people. What wingspan would you need to carry 200 people and their luggage? That's what the OP was talking about.

Think there also a middle ground in this debate that is overlooked. Perhaps it might not work for chucking humans into space. If you can do some with component part of liquid fuel that is in isolation inert that would be a massive win.

I think you've misunderstood the field of this debate. With regard to manned flight, there is no debate at all; 10,000 Gs isn't compatible with human life. Nobody, not even Spinlaunch, is proposing this for manned flight.

Putting a human on the spinlaunch is how you create human soup. Human tissues cannot withstand those accelerations.

I cant believe anyone with basic physics knowledge can be serious about this.

Its the sign of the times where anything thats pitched big tends to be seen as "revolutionary"

Incredibly well produced video

I could be wrong, but I got the sense watching it it was a long form paid advertisement?

That seems to generally be the way with space journalism; flatter the companies/personalities to get the best access for filming/interviews.

Wow.

This will definitely work. I can't say how I know, but someone in the intelligence community told me they are banking on it.

> can't say how I know,

Sorry to say, but you just told us how you know. :)

Only a little.

Someone in the intelligence community told me the opposite.

That's uniquely interesting. Curious.

Now you've got me thinking that it isn't for satellite launches, but for kinetic or nuclear bombardment.

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