Spinlaunch... Can it succeed? - Page 1
Forum section: electronics / general

author: BrianHG
author_rank: Super Contributor
timestamp: November 17, 2021, 07:53:37 am
content: Spinlaunch... Can it succeed?Do you think they will ever get a payload to low Earth orbit?Do you think they will ever achieve their claimed multiple launches per day?

author: Nusa
author_rank: Super Contributor
timestamp: November 17, 2021, 11:33:49 am
content: Quote from: BrianHG on November 17, 2021, 07:53:37 amDepends on your definition of success. Technically, probably. As a business, I don't know. Being limited to payloads that can tolerate high G is a bummer.Probably. But at what cost?If they can do one launch, they can do two. Second launch 23 hours after the first on the same day would satisfy the question.

author: Marco
author_rank: Super Contributor
timestamp: November 17, 2021, 11:58:48 am
content: You could imagine it being used for bulk materials for a space station. The containment structure can be a heavy steel construction and then you just fill it with liquid oxygen or water or whatever you need up there.I don't think satellites will like the G and tidal forces.PS. the video makes a point about the shift in the centre of gravity the moment the rocket is released, you'd think the other arm would have a similar weight which gets launched and disintegrates into a pool, but maybe I'm underestimating the strength of the materials.

author: jpanhalt
author_rank: Super Contributor
timestamp: November 17, 2021, 12:26:18 pm
content: @MarcoI agree with you. Ultracentrifuges that get a little unbalanced are known to go through walls. Of course, launching an identical projectile simultaneously in the opposite direction will have its own set of problems.

author: Nusa
author_rank: Super Contributor
timestamp: November 17, 2021, 12:51:08 pm
content: Quote from: jpanhalt on November 17, 2021, 12:26:18 pmDoesn't have to be identical at all, just the same mass. Opening a water chamber on the opposite side could do it.Alternately, a replacement mass could fall down the firing arm as the projectile is released. Or could even be part of the release mechanism when it arrives.

author: Marco
author_rank: Super Contributor
timestamp: November 17, 2021, 12:54:36 pm
content: Too much of a mess, if you're going to release it, firing something solid into a pool is the obvious solution, just need an explosive shutter so it doesn't splash back into the centrifuge chamber.You probably want an explosive shutter on the launch tube too so you don't lose all your vacuum.

author: Algoma
author_rank: Frequent Contributor
timestamp: November 17, 2021, 12:55:28 pm
content: Better chances if they get higher. It's still a rocket, just getting a different type of boost.. plane launched rockets seem more practical, heat stresses through the lower atmosphere is still the biggest problem.. especially if you want to launch at nearly orbital speeds...Not much use if you only launch a plasma ball at full power.

author: Marco
author_rank: Super Contributor
timestamp: November 17, 2021, 12:56:34 pm
content: Planes don't go high enough.

author: Haenk
author_rank: Super Contributor
timestamp: November 17, 2021, 01:05:52 pm
content: I smell utter BS.Let's assume this works properly, for now. Haha, no.Watch the video at 4:30 - the center of the "breakthrough" area needs to stay perfectly in the same spot. However, the center of the breakthrough area moves quite a lot, which means, the projectile is not launched straight, but sideways, so there is a loss of control and massive increase in friction to start with.Second, the launch requires pure kinetic energy - enough to still surpass exit speed after all that friction happening in the air. That energy amount must be insane. And other than a conventional rocket, you have to have the highest speed at the highest media density. Not a great idea, considering stuff falling from the sky is way slower, but still starts to glow hot red in the upper atmosphere.Then we have the acceleration. Unless you have massive blocks of metal, most stuff will crumble.And then the counterweight problem, to make the release of your rocket+payload irrelevant to the fastly rotating slingshot-machine, the whole launcher has to be a massive construction. Way larger than shown in the video.

author: mc172
author_rank: Frequent Contributor
timestamp: November 17, 2021, 01:36:47 pm
content: Is it even worth drawing a vacuum or are they just doing it because it's the in thing at the moment? *cough* Hyperloop BS *cough*woooo it uses vacuum technology, invest in us!The expense of drawing and maintaining a high vacuum vs the work to overcome the air resistance encountered...? If left at ambient pressure, the air inside the disc isn't going to be stationary relative to the moving parts for long as it'll be stirred around by the rotor arm so won't really be an absolute air resistance per se, like it will be once the projectile leaves the launcher.

author: SiliconWizard
author_rank: Super Contributor
timestamp: November 17, 2021, 06:37:16 pm
content: A number of issues that make it look fishy for any practical use.Thunderf00t also has doubts:

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 17, 2021, 07:44:48 pm
content: Quote from: mc172 on November 17, 2021, 01:36:47 pmMore to the point, it would be emitting a continuous shock wave. It would get very hot indeed in there.What's interesting about this, to me, is it's sort of a single contained scale model of more adventurous proposals, like a launch loop. It's a lot of stored energy, moving mass; but not the truly stupendous amounts of a full loop. The price paid is the considerably higher g-forces, and, obviously, the smaller capacity. As long as it doesn't destroy itself too often, it should be fairly cheap, and being wholly electrical, it does a huge part towards reducing environmental impact (carbon footprint, raw materials (rockets, chemicals and processing), ozone layer depletion).Tim

author: bdunham7
author_rank: Super Contributor
timestamp: November 17, 2021, 08:04:33 pm
content: Quote from: mc172 on November 17, 2021, 01:36:47 pmOh dear, at those speeds? I've worked with vacuum systems in the past, things like turbo-molecular pumps, and yeah, you want the air out of there before you wind that thing up. Having it circulate with the rotor isn't any sort of solution because it will be a very turbulent flow, which means you lose energy and thus the air will never keep up with the rotor. And if you did manage all that, you'd still have to cover the launch tube part on the inside because otherwise you'd have a resonance there--a sort of hypersonic pipe organ. It's not a hyperloop type of situation, you need a vacuum. And the vacuum is probably the easiest problem to solve out of all the complications in this scheme.I don't know why everyone thinks this is necessarily a scam. You can already launch artillery shells a good way out of the atmosphere at 3000G+ and those can contain complex electronics, nuclear weapons and optics.

author: Marco
author_rank: Super Contributor
timestamp: November 17, 2021, 08:26:33 pm
content: It's a shame quicklaunch sunk, it seems the more realistic option for a space gun.

author: Circlotron
author_rank: Super Contributor
timestamp: November 17, 2021, 09:15:27 pm
content: What would the centripetal g force on the payload be compared with simply shooting it out of a very large gun pointed skyward?

author: Stuart Coyle
author_rank: Contributor
timestamp: November 18, 2021, 08:14:02 pm
content: They can fix the issue of a sudden change in the centre of mass by simultaneously launching two rockets, one straight up and one straight down. Can do some geology at the same time as launching a satellite.

author: SiliconWizard
author_rank: Super Contributor
timestamp: November 18, 2021, 08:22:44 pm
content: Quote from: Stuart Coyle on November 18, 2021, 08:14:02 pmNice.

author: Haenk
author_rank: Super Contributor
timestamp: November 18, 2021, 09:59:15 pm
content: Quote from: Stuart Coyle on November 18, 2021, 08:14:02 pmReleasing a counterweight at the same time (let it crash into the floor) might at least solve the imbalance-issue after launch. However the impact will be enormous, as the object has the same kinetic energy as the rocket, enough to launch it into space.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 19, 2021, 01:18:05 am
content: The least that comes to mind, is releasing a second counterweight in the same end as the load. The counterweight is allowed to shift to a higher radius, giving the same moment as before. This keeps it statically balanced. The dynamic imbalance lasts between the instant the load is released, and the counterweight smacking into its final position. Which should be about a quarter rotation, I would guess. The catch (literally) is, the bearings still need to withstand that 1/4 cycle of massive imbalance, and, the counterweight will be accelerated (radially, i.e. in the rotating frame) very rapidly, then decelerated EXTREMELY rapidly as it catches the end stop. This can all be designed for, but a good question is which is harder: doing a supersonic baseball pitch and catch in the span of a few feet, or just letting the fuckin' thing bang itself around for a few -- whatever it takes to servo it more slowly, or brake the rotor down to safe levels -- maybe tens, hundreds, thousands of cycles?I suppose these are even high enough forces that we'd have to consider the flex of the shaft, even as thick as it is, with respect to the clearances of the bearing, and whatever bearing surfaces there are. What would a high speed vacuum bearing look like anyway, would it be a simple hydrodynamic (oiled) journal bearing? Ball bearings surely won't be used here; roller bearings perhaps. Some kind of lubrication is still needed, I think? (Vacuum bearings aren't new for aerospace; they're well understood...at least, sometimes.) I don't know offhand what they use for these things; some kind of vacuum grease would be necessary to avoid loss and contamination (spreading / condensation of oils on all surfaces in the sealed environment), but at the same time, vacuum greases are generally quite goopy. And graphite and MoS2 work by basically grinding themselves up, and in a completely dry environment would make more dust and thus contamination. So, I don't know, but it's a thing that's been done, however they've done it.Tim

author: Marco
author_rank: Super Contributor
timestamp: November 19, 2021, 03:20:30 am
content: Quote from: Haenk on November 18, 2021, 09:59:15 pmOr a big pool of water at the end of a tunnel, with air cushions on the side and bottom to give the shockwave something to heat up rather than turn the walls to dust and a second tunnel for pressure to escape from, rather than the steam going through the centrifuge room.

author: BrianHG
author_rank: Super Contributor
timestamp: November 19, 2021, 04:49:44 am
content: Quote from: Stuart Coyle on November 18, 2021, 08:14:02 pmThe counterweight could actially be a liquid holding object, IE a sealed container of water which would get released into the chamber at the opposite/down vector at release. The inside of the vacuum chamber can have a fins and pipes pattern to gradually disperse the trajectory of that water at multiple angles over a vast distance, all within/part of the vacuum chamber. Basically, a huge pipe straight down which has many gradual Y splits eventually hitting shock absorbers.(Yes, I know water boils in a vacuum, but not instantly and not at all while sealed inside the counterweight release holding device.)We can also do the same trick with a far smaller amount of liquid mercury, though, that stuff will hit the dispersal fins like solid metal.

author: fourfathom
author_rank: Super Contributor
timestamp: November 19, 2021, 05:56:04 am
content: When the rocket is released from the flywheel it is going to travel along the tangent line, but doesn't it also have rotational momentum (or whatever you call it) as well? As I see it, the rocket will be tumbling as it is released, and this is going to cause a lot of drag before the fins stabilize it. Or have I got the simple physics all wrong?

author: bdunham7
author_rank: Super Contributor
timestamp: November 19, 2021, 06:09:31 am
content: Quote from: T3sl4co1l on November 19, 2021, 01:18:05 amThe change in angular moment during that transition would result in an abrupt slowdown of the whole rotating arm. It might not seem like a big problem intuitively, but these machines are dealing with huge mechanical energies and I think anything abrupt is going to put some stresses on arms.QuoteI'm pretty sure it will be a hydrodynamic bearing, either plain or tilting pad, with an adequate sealing system. The bearing won't be in the vacuum part.

author: bdunham7
author_rank: Super Contributor
timestamp: November 19, 2021, 06:24:59 am
content: Quote from: fourfathom on November 19, 2021, 05:56:04 amThe angular momentum will be separated into three components at release--the spinning arm, the linear motion of the projectile off-center from the spinning arm and the rotation of the projectile about its own center of mass. You can actually see the last one in the video of the projectile coming through the cover--it isn't perfectly straight. I'm sure they'll learn to deal with this, perhaps by carefully tuning the release mechanism, or even counter-spinning it at the end of the arm.

author: hex4def6
author_rank: Newbie
timestamp: November 19, 2021, 06:29:23 am
content: Could you put a rocket nozzle on the launch side of the arm, facing inward (towards the axis of rotation). At the moment of launch, you start that nozzle firing, which should stimulate the centripetal force of what the vehicle was exerting.You would need the nozzle to basically fire instantly. Not sure if some sort of cold gas type thing would be quick enough.You could have the counter balance be the tank of propellent potentially.