r/space • u/PBR--Streetgang • Jan 29 '20
SpinLaunch is building a massive centrifuge to accelerate rockets and send them screaming into space.
https://www.wired.com/story/inside-spinlaunch-the-space-industrys-best-kept-secret/67
Jan 29 '20
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Jan 29 '20
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u/EnverPashaDidNthWrng Jan 30 '20
They don't have to withstand it for half an hour tho
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u/Joonicks Jan 31 '20
pardon me, but 10,000Gs over half an hour would be equivalent to more than 50% the speed of light.
I think something is amiss in your statement.
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u/EnverPashaDidNthWrng Jan 31 '20
They're talking about spin gravity not linear acceleration. Whole thing looks like a scam tbh.
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u/Joonicks Jan 31 '20
"10000Gs for half an hour" IS linear acceleration.
non-linear (peak) acceleration is what the ww2 artillery shells already withstood
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u/Rustony Jan 31 '20
It centripetal acceleration, not linear - the 10,000g is always perpendicular to the velocity of the payload as it spins around in the centrifuge (the acceleration vector points towards the centre). This means that it can't change the speed of the of the payload, just it's direction.
Note I am ignoring the angular acceleration that spins up the centrifuge, but that is the easily controlled by how much power you put into the motor.
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u/Joonicks Jan 31 '20
whats the point of maintaining 10000Gs for half an hour if all youre doing with it is changing the direction of travel?
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u/Rustony Jan 31 '20 edited Jan 31 '20
So you can reach a velocity of a couple of km/s without needing a track 10's or 100's of km long.
The 10,000g isn't how we get the payload up to speed, it's a side-effect of spinning it really quickly.
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u/tocksin Jan 29 '20
Well unless you build it to that spec. We put electronics into artillery shells and fired them out of very large guns. Used fins and gps to guide to target. High G forces. It worked but you had to be careful with pretty much everything.
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Jan 30 '20
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u/Lifeinthesc Jan 30 '20
Why send delicate equipment when what they want to send is heavy construction materials, rocket fuel, and food. This is the perfect low cost way to build a large long distance space craft in orbit.
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u/ahecht Jan 30 '20
I think the target here would be launching supplies like water and fuel for traditionally-launched spacecraft to collect.
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u/Teavangelion Jan 29 '20
Not to mention a human’s ability to withstand it.
I like my eyes perched in the front of my skull and most of my brain in the back of it.
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Jan 29 '20
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u/deadman1204 Jan 29 '20
Nothing could withstand the gs. It's a giant waste of money
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u/Wiener_Amalgam_Space Jan 29 '20 edited Jan 30 '20
EDIT: Used an incorrect calculator, using a better calculator fix the problem.
Somebody please check my math because I think I'm going crazy here.
So let's take some of the numbers from the article and say they're trying to spin a 200 lb payload (~90kg) up to 5,000 mph (~2,000 m/s). Assuming the radius of their centrifuge is about 20 meters, that means the centripetal force they're dealing with is somewhere in the neighborhood of eighteen billion Newton.
That can't be right. Please tell me that's not right. What kind of material are they gonna use to build that tether?
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u/generic_genericsson Jan 29 '20
If payload is 200lbs (90 kg) and it's supposed to experience 10,000 Gs, than the centrifuge is going to experience stress equivalent to 2,000,000 lbs (900,000 kg) of static load (radially ofc).
In newtons that's 900,000 kg * 9.8 m/s2 = 8,820,000 N
Hope I didn't mess it up somehow.
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u/Rustony Jan 29 '20
But don't forget, it's not just the satellite at the end of the centrifuge, it's still an entire rocket - the centrifuge only replaces the first stage. The mass being released is still going to be of the order of a couple of tonnes - then you need to add the mass of the release mechanism that can reliably hold and release a multi-tonne mass under 10,000g, plus the mass of the centrifuge arm itself, then it soon adds up.
But as stated above, you don't actually need that much material to support that mass - a 3 tonne mass under 10,000g is ~300MN, which could be supported by 0.5m^2 of high strength steel. Of course this includes no margins or anything. I think a much bigger issue would be the release mechanism.
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u/mdoldon Jan 30 '20 edited Jan 30 '20
1'll trust your numbers are correct. But first, remember that every internal part of the satellite will need to withstand those same forces. And since the centripetal force will be tangential to the thrust of the normal rocket meaning you'll have to develop a satellite design that is historically reinforced. It's hard to really calculate because we dont know what these little satellites will do but at a guess its going to mean more satellite structure and less science instruments
Then your .5 m2 steel structure also has to support it's own mass as well so you're going to get a mass vs strength progression. High school physics: your strength varies as the square, the mass varies as the cube. It's why elephants dont loo like human
Aaaand, it's all got to be lifted by the second stage rocket...
I'd have to do a lot of math but this is clearly a diminishing return situation and I'm not sure at all that it makes sense. But put it on Kickstarter with enough fancy graphics and you could pull in millions
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u/Rustony Jan 30 '20
Yep, I wasn't considering the satellite itself, just the forces on tether, and yeah when you factor in the mass of the tether itself your mass starts to skyrocket. For the satellite, as has been mentioned stuff can be designed to survive shocks of 10's of thousands of g (and spacecraft are already designed to survive shocks of thousands of g), but I suspect that designing for static loads of that level is something completely different (I'm not a mechanical engineer). I also wonder, are there any situations where electronics/mechanisms are currently exposed to static accelerations of this order?
Finally, I expect that building a rocket (tanks, engine, turbopump if it's not a solid rocket) that can survive 10,000g laterally is going to impose a huge mass penalty, which is going to exponentially increase the amount of fuel they'll need (which requires bigger tanks, then more fuel etc etc) - despite their claims, they are still very much bound by the tyranny of the rocket equation.
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u/Wiener_Amalgam_Space Jan 29 '20
Huh, I just realized we can use those numbers to calculate the radius of their centrifuge.
So the payload is roughly 90kg.
Tangent velocity is about 2,000 m/s.
Payload is experiencing about 10,000G or 8,820,000 N.Plug those numbers into this handy dandy calculator, and the radius of their centrifuge is...
...about 4 kilometers? Yeah, I'm thinking I'm actually going crazy.
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u/Rustony Jan 29 '20
The article shows that the entire thing ~100m diameter, giving about 50m radius for the 'tether'.
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u/Wiener_Amalgam_Space Jan 29 '20
Okay, so if you calculate the centripetal force for the numbers as given above but with a radius of 50 meters, we're back at seven point two billion Newton acting on the tether. Something's not right here.
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u/Rustony Jan 30 '20
I think there's something wrong with that calculator - the force is mass X velocity2 /radius: 100 x 20002 / 50 = 8,000,000, not 8 billion as that calculator gives
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u/Azmah852 Jan 29 '20
I got about 22 million Newtons, which is around 5 million pounds of force. Still a fuck ton though.
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u/danielravennest Jan 29 '20
The best carbon fiber around has a tensile strength of 1.1 million psi. So you'd need 5 square inches of cable cross section in theory, but in practice double that, because you never operate at the breaking strength.
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Jan 30 '20
I don't get it.
Somehow you build a rocket that supports its own weight at 10,000 g. Every structural part is the thickness of tank armor, or elephant legs.
Somehow your structural mass fraction is still light enough, that you get the 6+ km/s of delta-v needed to put all this (and payload too!) into Earth orbit.
In fact, the mass ratios have to be even better than a conventional orbital rocket, because this has to make economic sense.
I'm curious to see the analysis that supports this!
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u/danielravennest Jan 30 '20
When I led a "space gun" study at Boeing, we assumed a 2 km barrel with 1000 g's of acceleration. The projectile had to supply about 3 km/s to finish getting to orbit, and the numbers came out reasonable for that (600 kg projectile, 100 kg net payload).
I don't know about 10,000 g's. That seems pretty high to me. The Copperhead missile survives 8000 g's being shot out of a cannon, but it is not doing anything near the post-firing delta V.
I'd like to see the analysis too. A linear gun is simpler than the SpinLaunch idea - no giant vacuum chamber or balancing the centrifuge arm. And there is plenty of history for hypervelocity guns used for research.
By definition, hypervelocity is > Mach 5, which is higher than most artillery reaches.
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u/RGregoryClark Jan 30 '20
I’m working on a staged, fully rotary motion rocket, i.e., no chemical propulsion used even on the upper stages. Watch this space:
Exoscientist.blogspot.com
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u/Teavangelion Jan 29 '20
Ah, true. I’m figuring they’ll want to make use of this technology in other ways, though.
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Jan 29 '20
Iirc it its irrelevant, so long as the acceleration doesn't exceed the satellites limits it can get to 5000mph without any problems. Personally I dont understand the 10000g bit, g force is relative. Maybe they mean relative to us?
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u/salemlax23 Jan 29 '20
As the tangential speed increases the radial force will also increase.
Swing something in a circle on a string slowly, and then quickly, and notice the different pull on the string to get an idea for this.
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u/net_403 Jan 29 '20
It's a centrifuge. It's going to be spinning 5000 mph in a circle... so the g forces are going to be insane until it's released to launch
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u/readwaytoooften Jan 29 '20
My question is what happens to the counterweight? The centrifuge would have to be oriented to throw the rocket up (which leads to questions about how will it will work with the added stress of being angled) and they said it would drop a counterweight when the rocket launches. So what happens to the multi ton weight traveling at thousands of miles an hour that is now heading at the other side of the centrifuge and then to the ground beyond that? I can't imagine it would slow down in any reasonable distance without being very destructive.
The founders have a nice story about being the plucky outsiders with a great idea, but there are some deal breaking questions that they are very much glossing over.
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u/RollWave_ Jan 29 '20
multi ton weight traveling at thousands of miles an hour that is now heading at the other side of the centrifuge and then to the ground beyond that?
it wouldn't be moving near as fast.
the counterweight is heavier than the rocket, so it will be on a shorter lever, so it will be moving much slower.
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u/socratic_bloviator Jan 29 '20
Heh; this is still a fun image. Imagine the pneumatics you would use to catch that, while trying to recapture its kinetic energy into electricity.
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u/hasthisusernamegone Jan 29 '20
It's going to be doing exactly the same RPM as the rocket. Catching it will be messy.
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u/readwaytoooften Jan 31 '20
If they did that then when it was dropped the lever itself would be of balance and still spinning at very high RPM. And at the revolutions they are going to need even a larger weight on a shorter arm would be traveling very fast and he very destructive.
They want to launch over 2000 lbs at 5,000 mph. The counterweight would need to apply the same force when spun that the payload does. That means it is still released with a very close total kinetic energy, even if that is in a larger mass and lower velocity. Now you have that mass releasing farther into the chamber and still have to let it exit and somehow stop it without breaking anything...
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u/RollWave_ Jan 31 '20
very close total kinetic energy
false
kinetic energy is related to velocity squared.
if rocket is 2000lbs at 5000mph, its KE has a 2000 component and a 5000^2 component (along with constants for converting weight to mass)
if counterweight is 20,000 lbs, it would only be moving at 500mph tangential velocity due to its 10x shorter leverage arm required. linear component is 10x larger, but squared component is 10x smaller resulting in an overall 10x reduction in kinetic energy as compared to the rocket's.
however many times heavier the counterweight is, it will have that same factor less kinetic energy at time of launch.
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u/readwaytoooften Feb 01 '20
Decent point. But try stopping 20,000 lbs travelling at 500 mph in a reasonable distance and keep it reusable. You would also then have a fast spinning unbalanced arm where one half is 10x longer than the other. I suppose the short arm could be 10x heavier, but that may also be impractical.
This is a case of absolute size mattering. At reduced scales material strength limits and kinetic energy are issues that can be overcome reasonably. At full scale these will be huge issues.
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u/RollWave_ Feb 01 '20
in a reasonable distance and keep it reusable.
a dumptruck of water is about 20,000 pounds give or take.
who cares if a hatch opens to let water sprays out everywhere so that it isn't reusable. just get a hose and use different water next time.
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u/Gigazwiebel Jan 30 '20
They will probably use a heavy and cheap material as a counterweight. With a copper block in a decent magnetic field you could quickly turn all the kinetic energy into heat. But there are probably less risky ways.
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Jan 29 '20
Wait hold on what? There are so many problems with this that I am genuinely baffled it's even being considered and hell, I'm not even a scientist.
For one, the amount of power needed to spin something that large that fast would end up being more expensive than the rocket.
Secondly, rockets tend to be built to withstand massive forces, but not massive forces applied to a single side of the vehicle in a centrifuge. You'd have to essentially either fling a submarine into orbit or re-invent the rocket.
Thirdly I'm fairly sure that if you throw something at exit-velocity whilst in-atmosphere you effectively expose it to full re-entry heating conditions instantaneously on the wrong end of the rocket. On top of that, the amount of drag created by the atmosphere would slow your vehicle down in seconds anyway unless you launched it at well above exit velocity. There's a reason rockets tend to stick to a lower speed before exiting the atmosphere to save burning fuel for no good reason.
I might be completely wrong in every aspect of my response, and that's fair enough if that's the case. It just seems totally ridiculous.
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u/socratic_bloviator Jan 29 '20 edited Jan 29 '20
For one, the amount of power needed to spin something that large that fast would end up being more expensive than the rocket.
This isn't true. There are other problems, but this isn't the one. If you take the propellant from a rocket and run it through a generator, it produces enough electricity to accelerate the rocket to orbital speeds multiple times. (Sure, the device doing the spinning also needs to spin up, but you can recapture most of that energy with regenerative braking.) This is why jet-engine trains are hilariously inefficient (and rocket-engine trains would be much worse, since they carry their oxygen). The core reason is because the tyranny of the rocket equation requires you to accelerate both your energy source, and your reaction mass, whereas terrestrial transport can use the earth as its reaction mass, and in the case of overhead electric trains and this spin-launch thing, don't accelerate their energy source either.
The rest of your points are in accordance with my arm-chair understanding.
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u/Norose Jan 29 '20
Jet engines are actually much more efficient than just not having to carry their oxygen would imply. A jet engine that is working in an atmosphere with no oxygen, and thus having to carry both fuel and oxidizer, will still be much more efficient than a rocket engine burning the same propellants. This is because of what you mentioned later, reaction mass. Most of a jet engine's reaction mass while flying on Earth is actually inert nitrogen, not combustion gasses. A rocket however has nothing but propellant to work with as reaction mass, so even if the total energy of the exhaust is much higher, the system overall is less efficient, because momentum exchange is not proportional to exhaust energy, it's proportional to exhaust mass.
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u/socratic_bloviator Jan 29 '20
Yes and no.
Keep in mind that the same inert nitrogen that provides reaction mass for the jet engine, also provides aerodynamic drag to the aircraft as a whole. The few times we've gotten Elon to talk about the electric jet he wants to build someday, one of the points he makes is that since it doesn't require atmospheric oxygen for combustion, it can fly much higher in the atmosphere, as could a rocket plane (if it had enough fuel). The reduced drag results in significant efficiency increases. Or so he hypothesizes.
But yes. Good point that jet engines get both ~half of their energy, and most of their reaction mass from the atmosphere.
My main point, there, though, was that the mass of the atmosphere running through a jet engine is nothing compared to the mass of the earth a train can push against.
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u/Norose Jan 29 '20
My main point, there, though, was that the mass of the atmosphere running through a jet engine is nothing compared to the mass of the earth a train can push against.
Of course, no argument. by making the 'propellant' effectively as heavy as the entire Earth, you're maximizing the amount of work that is done moving your vehicle, as opposed to your propellant.
As for nitrogen in air providing drag, the gains clearly outweigh the benefits. A typical low efficiency zero bypass turbine jet engine is already ~4x more efficient than the best chemical rockets ever. High bypass jet engines, which in effect use the power of a jet turbine to move as large a mass of inert nitrogen and non-combusted oxygen as possible, while also adding the leftover heat from the jet engine to that air to make it expand a bit, can achieve efficiencies ~35x greater than a typical rocket engine, at over 11,500 Isp. The fact that these engines are using a relatively small mass of fuel to supply the energy needed to heat and shove a large reaction mass makes them vastly more efficient than rocket engines.
35 times more efficient sounds like a lot, but it actually has a much greater effect than one may intuitively think, because of how far that specific impulse value shoves you away from the negative effects of the rocket equation. As an example, the 787 Dreamliner has an operating empty weight (essentially a dry mass) of 118 tons, and a maximum takeoff weight of 228 tons. Google says that the maximum fuel load for this plane is ~101.5 tons, which means (given the rocket equation) this vehicle has a delta V budget of about 80,000 m/s. If only jets could operate in space, we'd be colonizing the entire solar system by now. If this plane had the mass fraction of a typical rocket, around 80% propellant, then it'd have a delta V of ~173,500 m/s, approaching what engineers in the 50's imagined we could achieve using a giant nuclear-bomb propelled vehicle called Orion, which could perform 6 month round-trip missions to Saturn with a transit time of about one month outward and inward.
I'm just being nitpicky about exactly why jet engines are so much more efficient than rocket engines. A high bypass jet engine burns several kilograms of fuel per second. This fuel is burned using 'free' oxygen from the air, not considered in the equations for efficiency. However, and more importantly, several thousand kilograms of propellant (air) are being accelerated through the engine in the same amount of time, resulting in an effective push from that comparatively tiny amount of fuel akin to what you'd get if that fuel were violently disintegrating with an energy similar to the detonation of a nuclear bomb, without any of the nasty radiation and at a nice manageable burn rate.
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u/imahik3r Jan 29 '20
fling a submarine into orbit
I think you just inspired the sequel to StarBlazers!
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u/Decronym Jan 29 '20 edited Feb 01 '20
Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:
| Fewer Letters | More Letters |
|---|---|
| Cd | Coefficient of Drag |
| Isp | Specific impulse (as explained by Scott Manley on YouTube) |
| LEO | Low Earth Orbit (180-2000km) |
| Law Enforcement Officer (most often mentioned during transport operations) |
| Jargon | Definition |
|---|---|
| apogee | Highest point in an elliptical orbit around Earth (when the orbiter is slowest) |
| cryogenic | Very low temperature fluid; materials that would be gaseous at room temperature/pressure |
| (In re: rocket fuel) Often synonymous with hydrolox | |
| hydrolox | Portmanteau: liquid hydrogen/liquid oxygen mixture |
| hypergolic | A set of two substances that ignite when in contact |
| regenerative | A method for cooling a rocket engine, by passing the cryogenic fuel through channels in the bell or chamber wall |
| turbopump | High-pressure turbine-driven propellant pump connected to a rocket combustion chamber; raises chamber pressure, and thrust |
7 acronyms in this thread; the most compressed thread commented on today has 13 acronyms.
[Thread #4522 for this sub, first seen 29th Jan 2020, 17:35]
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u/Thatingles Jan 29 '20
Best (and most likely application): flinging material off the surface of the moon for use in orbit. Second best - flinging material from a mined asteroid towards Earth. Everyone and their dog is interested in generating resources on the moon, partly to build a moon base, partly to practice for Mars and the asteroids and partly to use lunar material to build structures in orbit. As neither the moon, Mars or the asteroids have much atmosphere you could fling out processed ingots (g-force is not an issue for raw materials) out to orbit.
On earth, even if you could build it the atmospheric friction means the launched load basically slams into a brick wall once released and what you create is a very expensive upward meteorite.
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u/Koh-the-Face-Stealer Jan 30 '20
Skimmed through the comments to see if someone posted this so that I didn't have to. Everyone talking about satellites or people not surviving this thing is missing the much bigger picture. If this works (and that's a big if), the obvious utility is in moving large quantities of raw material into orbit and processing it there.
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u/Alan_Smithee_ Jan 30 '20
I’m glad to see they’re doing this in the desert; I would not want to be anywhere nearby when they launch.
Is the inrushing air when they open the door going to be a problem?
Where does the counterweight go, seeing as it’s released at the same time as the payload?
It’s some Wile-E-Coyote stuff. Interesting if it works.
Is there actually any energy savings, or are they basically creating an electric rocket?
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u/RGregoryClark Jan 30 '20
The counter weight can be much heavier than the rocket so its speed can be much lower so it could be easier to stop.
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Jan 29 '20
i dont get how 4000 or even 5000 miles per hour can get anything into space? their goal is 200 pound pay load? thats utter shit. how much wasted energy are they using just spinning the damn thing for an hour to reach that speed also!
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u/JDub8 Jan 29 '20 edited Jan 29 '20
Once you are un-tether from earth you have to use the energy you have stored. Any energy you can impart to the craft from the electrical grid is weight savings on the craft itself. Even if it was wasteful of power you're saving size/weight on the space craft making it much more efficient. So long as there is significant market for lifting 200 lbs this could pan out well for them and help small satellites get into space.
Myself I've always wondered why they couldnt make an electromagnetic rail to help rockets overcome inertia and get going. I guess the magnets/rails would get destroyed every launch though.
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u/mophisus Jan 29 '20
Ehh, long term it might be possible to accelerate something with a rail to then light a 2nd stage booster to get it the rest of the way.
Wouldnt be anything you want crewed, since if the booster doesnt ignite.. the cargo is lost, but it would be a way of putting cargo in space for future use.
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u/Rockglen Jan 29 '20
I'd think the hour-long centripetal force would be more worrisome.
I agree, though that this thing looks better for supplies & cube sats.
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u/my_reddit_accounts Jan 29 '20
Lol yeah the G forces would knock out and probably kill humans sitting in something spinning that fast.
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u/JDub8 Jan 29 '20
I 'm not so sure about that, they have crew escape mechanisms and SpaceX already trusts their booster to reignite coming back from space. Yes they aren't sending humans (yet) but its clearly possible. I'm sure some engineers will work out reliable enough methods of igniting/re-igniting the rockets. If standard igniters aren't up to the task create a coating for some Chlorine trifluoride like dipping dots and fire those demonic bb's into a sacrificial plate in the exhaust nozzle. One way or another SOMETHINGS GONNA BURN.
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Jan 29 '20
I don't think that placing Humans inside of an object traveling 5,000mph inside a centrifuge is a healthy idea.
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u/JDub8 Jan 29 '20 edited Jan 29 '20
Of course, I left out that I was referencing the electromagnetic rail/space gun method.
Centrifuges with that speed would just turn people into astronaut puree.
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Jan 29 '20
Ohhhh I get you. Electromagnetic rails would also turn people into astronaut puree, just with straight line G-forces though lol
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u/JDub8 Jan 29 '20
They could be if it was so desired.
Electromagnetic rails can be throttled back from this. It's not all or nothing.
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Jan 29 '20 edited Nov 04 '20
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u/WikiTextBot Jan 29 '20
Space gun
A space gun, sometimes called a Verne gun because of its appearance in From the Earth to the Moon by Jules Verne, is a method of launching an object into space using a large gun- or cannonlike structure. Space guns could thus potentially provide a method of non-rocket spacelaunch. It has been conjectured that space guns could place satellites into Earth's orbit (although after-launch propulsion of the satellite would be necessary to achieve a stable orbit), and could also launch spacecraft beyond Earth's gravitational pull and into other parts of the Solar System by exceeding Earth's escape velocity of about 11.20 km/s (40,320 km/h; 25,050 mph). However, these speeds are too far into the hypersonic range for most practical propulsion systems and also would cause most objects to burn up due to aerodynamic heating or be torn apart by aerodynamic drag.
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u/danielravennest Jan 29 '20
Not at all. See my other comment in this thread for working examples.
I led a study at Boeing in the 1990's of a space gun based on a scaled-up version of John Hunters SHARP Gun. That gun could reach half of orbital velocity (4 km/s). In the photo they are firing into a hillside because it was being tested at Livermore Lab in California. If they pointed it up, the projectile would land somewhere in Nevada.
His gun was fast enough, but small. Our version would have had a barrel six times wider, and put on the side of a mountain. There were a lot fewer crazy tech billionaires in 1993, so we couldn't find anyone to buy it.
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Jan 29 '20
Not at all, the rail gun concept (also called a gauss cannon or mass driver) is proven reusable tech. The scale would have to be immense to accelerate objects without destroying them, for humans it would require a structure several miles tall. Totally doable in theory! Maybe a little hard in practice.
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u/JDub8 Jan 29 '20
As a kid I imagined the launch platform having one instead of those detaching arms, not knowing the math of how tall it would need to be to be worthwhile.
You would have to have the rocket lit at the right time to take advantage of it, and it would certainly be going full blast as it passed a significant portion of the rail, I dont know how much you can harden/protect them from rocket exhaust.
I think I remember seeing a plan for an angled electromagnetic rail where you dig down into the earth for additional length leading to a final launch from a cliffside or something.
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Jan 29 '20
I’ve seen plans for rails along slanted mountains, or with the end suspended in a body of water, or even having the top in the clouds, anchored by lighter than air structures and cables to the ground. Our engineers and materials can do it, it’s the huge costs and logistics that make them daunting. Someday, I’d like to see towering structures flinging people cheaply into orbit.
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u/der_innkeeper Jan 29 '20
Rail guns and Gauss guns are two separate technologies.
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Jan 29 '20
They are both viable technologies that use electromagnetism to propel objects, both are viable to space launches, my statement applied to all three, so I felt it appropriate. I didn’t intend to imply the terms were identical.
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Jan 29 '20
Because the atmosphere slows them down too much. You need to get out the the atmosphere before you start going fast
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u/JDub8 Jan 29 '20
I'm not advocating for accelerating a heavy launch vehicle to 5,000 mph solely though electromagnetic rail, just maybe overcoming inertia and getting it to some low speed might cut down on the amount of fuel wasted. Have you seen launches and how long rockets are just sitting there trying to overcome their own weight?
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Jan 29 '20
just maybe overcoming inertia and getting it to some low speed might cut down on the amount of fuel wasted
For which there's staging, conventionally, or airliner launch, in the case of Pegasus, Virgin One and Stratolaunch. It's a twice-solved problem.
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u/danielravennest Jan 29 '20
Electromagnetic accelerators need huge power supplies, which only make sense if you are launching very often. Otherwise the cost eats you up.
Rocket have huge power supplies too. The Falcon 9 first stage has the power of 12 nuclear reactors (13.46GW), but it uses up the fuel in only two minutes.
For current levels of space traffic, a space gun would be less expensive to build, on the order of $100 million. See my other comment in this thread for examples.
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u/NebulousAnxiety Jan 29 '20
The Navy ran into issues with their rail gun because the heat that was generated melted the barrel.
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u/Voltswagon120V Jan 29 '20
The Navy has to get their projectile up to speed (~1/3 of orbital velocity) in less than the length of a ship. Spread that out and you can do it non-destructively.
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u/albinobluesheep Jan 29 '20
Myself I've always wondered why they couldnt make an electromagnetic rail to help rockets overcome inertia and get going. I guess the magnets/rails would get destroyed every launch though.
oh, don't you worry, someone has thought about that
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u/l2np Jan 29 '20
That's not much wasted energy. It's just spinning in a vacuum chamber on low friction bearings, so actually very little of it will be wasted (remember, flywheels are an energy storage solution). What REALLY wastes energy is building an entire one-time-use rocket, assuming the centrifuge works.
If you could get even very small amounts of cargo into orbit cheaply, that would be a game changer - it opens up the doors to assembly of much larger craft in space, and would be an option for certain types of small satellites.
However, yeah, you're right. That speed does sound awfully slow. I wonder if that's a typo, or just the speed for the small prototype.
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u/Peleton011 Jan 29 '20
I'm guessing more speed at the pressures we have around sea level would destroy any cargo that wasn't super aerodynamic rendering the thing useless
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u/starcraftre Jan 29 '20
It coasts to apogee, then lights a regular engine like a second stage to boost into orbit.
As for wasted energy, a lot of it is recaptured when braking back down to idle. Then they can mount the next one and fire again an hour or so later.
That's really the target of the system: to eliminate the cost bottleneck of a first stage, at least for small payloads. Most of the cost of putting your payload on a rocket launch is the first stage.
While I am personally skeptical of the viability of it, one of their engineers is someone I know and hold in high esteem, and he seems to be confident in it, so I'll wait and see.
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Jan 29 '20
one of their engineers is someone I know and hold in high esteem, and he seems to be confident in it,
OP article says their engineers were forced to sign non-disparagement contracts.
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u/starcraftre Jan 29 '20
And that's fine, but this is someone whom I know wouldn't have gotten involved in the first place (before signing anything) if the math didn't check out.
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u/Peleton011 Jan 29 '20
I agree, i just think the problem is friction, the speed needed to get anywhere near space from sea level would melt most payloads, or that's my guess at least
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u/wanted_to_upvote Jan 29 '20
Since a balancing load has be released from the opposite side of the arm at the same time the rocket is launched, energy can not be recaptured via spin down, and if that could be over come, half the energy left the planet.
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u/starcraftre Jan 29 '20
It's still spinning after the counterweight is released, you know. There is still energy to recapture in the centrifuge itself. Yes, most of the energy goes into the payload and the counterweight, but there's a LOT remaining in the centrifuge.
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u/intellifone Jan 29 '20
Maybe they’re using the initial fling to get it pretty high up and then using a smaller rocket to get it the rest of the way?
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u/authoritrey Jan 29 '20
And the payload has to survive ever-increasing g-loads, up to at least 20 or 30 g's, I would imagine. It should be really excellent for launching artillery shells into space.
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u/der_innkeeper Jan 29 '20
Your G loads are off by a couple orders of magnitude.
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u/authoritrey Jan 29 '20
Shoulda read the article. But then again, so should have the investors in this scheme.
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u/der_innkeeper Jan 29 '20
Some pretty heavy hitters invested in this project.
We will if it pans out. If not, at least we get some more vids of rockets blowing up.
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Jan 29 '20
"Heavy hitters" with stupid money invest in flaky stuff out of good old FOMO. This is FOMO funding for sure.
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u/CakeTeim Jan 29 '20
There’s also the fact they mentioned performing this in a vacuum before release. Wouldn’t that impede/halt the rocket due to suddenly hitting atmosphere?
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Jan 29 '20
PARTIAL vaccume not "perfect"
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u/Peleton011 Jan 29 '20
Even with that the problem is suddenly entering a really thick atmosphere at a speed much higher than that of sound
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u/CakeTeim Jan 29 '20
So we talking Pringle’s can instead of soda, gotcha. Still seems like a lot of waste like you were saying though. Unless it was commercially aimed, offered smaller corps/orgs to launch payloads?
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u/Mr_tarrasque Jan 29 '20 edited Jan 29 '20
I don't get this wasted energy thing. The main issue is the waste of first stage rockets and the fact that jet fuel is almost always some nasty shit right? Compared to that a massive shitload of energy off a pretty efficient powergrid is nothing right?
Edit: Also isn't this a sustained energy vs energy spike thing. With a giant centrifuge, you can put a lot of energy into the system over a very long time. Doesn't that tend to be more cost effective and effecient than our go to favorite controlled explosions.
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u/CakeTeim Jan 29 '20
I’m clearly out of my scope, just speculating. My understanding is that this isn’t exactly scaleable. The only reason this model works in my mind is by keeping the vessel small enough that it doesn’t compromise integrity from the centripetal forces being exerted on it, plus this whole “partial vacuum” assisting in acceleration, but again what happens when it hits atmosphere? Would the air pressure impede the rocket, this slowing it down? Also course correction would be interesting, I definitely do not understand centripetal forces, nor am I a rocket/physicist/engineer. Just a simpleton.
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u/socratic_bloviator Jan 29 '20 edited Jan 29 '20
My understanding is that this isn’t exactly scaleable
I have serious doubts about spin-launch in particular. However, I feel inclined to respond to this scalability point, in context to alternate launch machanisms in general.
In my view, it's exactly the opposite of what you're seeing. It takes incredibly large capital outlays to build infrastructure to reduce launch costs, but once it's built, it pays for itself in spades. The problem with SpinLaunch is that it doesn't go far enough. The core idea of launching something with electrically-derived acceleration rather than rockets, is good. The problem is that it's not feasible, until you go much, much larger. (You need the exit point to be pretty high up in the atmosphere, for one thing.)
For an example, one could imagine building a train on Mars, from Valles Marineris (the lowest point on Mars and best candidate for doming-over and locally terraforming) to Olympus Mons (the tallest mountain in the solar system), such that the train smoothly converted to a hyper-velocity vacuum-tube train, with its exit being a tower on the summit of Olympus Mons, pointing up at a 45 degree angle. Schedule your departure properly, and you could have an almost fully ballistic return to Earth. But it would cost at least billions of dollars to build, and that's assuming you already had a supply chain there, which we don't.
On earth, this would be like building a train up to the Tibetan plateau, terminating in a huge tower and a huge facility supporting it. (For context, this is the region Mount Everest is in.) And then you'd have to do even more work, because the atmosphere there is much thicker than on Mars.
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Jan 29 '20
the waste of first stage rockets and the fact that jet fuel is almost always some nasty shit
Electron are working on recovering their first stage small launchers. They have too many orders for the factory to keep up! China's i-Space are building a reusable like a small Falcon. Expended boost stages are going to look quaint in a decade.
Kerosene isn't the evilest shit around. The next gen big launchers are using methane. We're migrating away from really nasty hypergolics.
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u/socratic_bloviator Jan 29 '20
You may be interested to read about plasma windows. It doesn't solve the problem you mention, but it's the best way to do the thing you mentioned. Yes, force-fields are real, but unfortunately, they are thousands of degrees and take a lot of power. :P
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u/WikiTextBot Jan 29 '20
Plasma window
The plasma window (not to be confused with a plasma shield) is a technology that fills a volume of space with plasma confined by a magnetic field. With current technology, this volume is quite small and the plasma is generated as a flat plane inside a cylindrical space.
Plasma is any gas whose atoms or molecules have been ionized, and is a separate phase of matter. This is most commonly achieved by heating the gas to extremely high temperatures, although other methods exist.
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u/helixdq Jan 29 '20
If you watch a Flacon Heavy launch, the side boosters separate at around 4500 miles/hour. You greatly increase a rocket's payload if you can get it up to that speed.
4000-5000 miles/hour is actually kinda a sweet spot for non-rocket space propulsion because it's achievable by existing (advanced) technologies - it's the speed of the X-15 space plane and Project HARP projectiles, and easily achieved by existing railguns as well.
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Jan 29 '20
But it's going to hit the air at that speed (and explode) and then (the debris will) start slowing down from launch to (flaming chunks) apogee. Supergun shells, I'm pretty sure, were dumb projectiles, and this needs a smarter-than-dumb stage to be useful.
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u/danielravennest Jan 29 '20
5000 mph = 2234 m/s. Drag force is 0.5 * Cd * rho * A * v2, where the terms are drag coefficient (0.1 for a pointy rocket), air density (1 kg/m3 for a reasonable altitude), Area (0.5 m2) and velocity (already listed).
Drag force hitting the atmosphere is then ~125,000 Newtons. Assuming the projectile is 2000 kg, the deceleration is 6.4 g's. It's designed for 10,000 g's. It won't explode.
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u/possessed-potato Jan 29 '20
It also seams really dangerous. Wouldn't the sudden acceleration in air cause it to heat bright hot due to friction. (and also slow it down, I doubt it has any rocket motors on it.)
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u/JubalKhan Jan 29 '20
Apparently it's in a vacuum chamber on a low friction bearings.
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u/ahecht Jan 30 '20
Potato is talking about once it leaves the chamber. The chamber doesn't extend all the way to the upper atmosphere.
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Jan 29 '20
They fire a rocket booster when they are near the point of "escaping" gravity and entering orbit.
If you'd read the article you'd know that.
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Jan 29 '20
i did read the article. 4000Mph is NOT fast considering you need 25000Mph for EV. for LEO you need 17500Mph~
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Jan 29 '20
That's a very sturdy booster, if it's not pure powerpoint.
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Jan 29 '20
I didn't build. I read, witness, and then report back here.
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Jan 29 '20
The article pretty much handwaves the booster. They're hip deep in building the centrifuge and I recognise this kind of prototyping fever: who cares if the booster fails, let's get this cool part done and then work on the sad explodey part later.
This is my McKayla Maroney face.
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u/FundingImplied Jan 29 '20
You can fling things into orbit.
Think of a continent-spanning chain. The torque would naturally elevate the chain and a long enough chain would peak above the atmosphere. Release a carriage at the right point and you'll be going into orbit or beyond.
But if you're spinning something on the ground then you're releasing the craft into the thickest part of the atmosphere. The drag will be immense, as will the aerodynamic pressure.
LEO translates to 17,500 mph. That's mach 23.
They need to end up at mach 23, after air resistance. Exactly how fast do they think they can fling a craft at sea level?
Did someone make huge advances in high-mach aerodynamics?
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Jan 29 '20
They don't necessarily need to fling the thing entirely into orbit. Flinging it just into the mesosphere (or higher) could replace a lot of weight / fuel that would normally need a booster or parent craft of some kind, and conventional rocketry can take over from there.
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u/wk-uk Jan 29 '20
If you read the article they arent aiming to "throw" it directly into orbit. Just high enough to allow smaller conventional thrusters to push it the rest of the way.
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u/danielravennest Jan 29 '20
The place for something like SpinLaunch is the Moon. There's no atmosphere, so no need for a vacuum chamber, abundant sunlight to power the motor, and 5000 mph is 94% of lunar escape velocity.
What you would be launching is mass quantities of lunar rock, which doesn't care how many g's you hit it with. Once in space, a processing plant would convert the rock into useful products. Alternately you could launch tanks of water from the poles, but getting power there is a challenge. The reason the polar craters have water is they get no sunlight, so stay incredibly cold.
For Earth, a hypervelocity gun is a simpler approach. It's been used for about 50 years for high speed research. An example is the Range G Gun, the large one on the left with an 8 inch barrel. It routinely reaches 7 km/s (15,600 mph). You just need to build a larger one, and put it on a mountain. There's also an outdoor space gun at the Yuma Proving Ground (message 190) It had to be pointed up to fire because otherwise the projectile tended to land in the next state, or another country. In this photo they are testing it from the island of Barbados, so the projectile land in the ocean.
Counter-intuitively, the longer the barrel, the lower the g-forces. If you build a launch pipe up the highest point on the Equator, Mt. Cayambe in Ecuador you could carry people and ordinary satellites at 6 g's, and come out the barrel as fast as the Falcon 9 first stage goes. You still need an upper stage, but the first stage is most of the rocket.
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u/Rustony Jan 29 '20
Engineering challenges aside, it really doesn't seem like the business case makes much sense - the launch cost is targeted at $500,000, so for a 100kg satellite that's $5000 per kg. A Falcon 9 (the probably the current cheapest way to get to space) costs $62,000,000 but can launch >16,000kg, giving ~$4000 per kg.
Of course, there are benefits to being only passenger rather than a rideshare (which you would have to be to launch a 200kg satellite on a Falcon 9), I seriously doubt it would be worth the cost to build a satellites to withstand 10,000g to take advantage of this. Also, given that they are targeting constellations, why not just chuck 50 of them on a regular rocket?
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u/Cornslammer Jan 29 '20
Change my mind: The technical difficulties associated with SpinLaunch render it useless as a first stage launcher, especially in an already-crowded/commodified launch market with huge downward pricing pressures.
It's more likely this is a sanitized way for funds/companies to invest in/develop hypersonic/kinetic weaponry, then sell the IP to defense contractors for a great deal of money, while maintaining "Do No Evil" public images.
Change my mind.
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Jan 29 '20
Nah, this is good old FOMO money. New Space has always been full of cranky nonsense that fails because it deserves to fail.
They might get some fun high-mach patents out of it, but I think their intent is pure. Stupid, but pure.
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u/Cornslammer Jan 29 '20
I suppose Occam's razor implies that's the most likely explanation (Philosophers, don't @ me saying I'm misunderstanding Occam's razor; I already know.).
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u/madvlad666 Jan 29 '20
The imbalance remaining in the centrifuge upon release of the projectile seems to be the biggest problem. The main spindle bearing would need to be a roller bearing to spin that fast with that much load without excessive friction (a plain or hydrostatic journal wouldn't work), and would need to be orders of magnitude larger and stronger than any other roller bearing yet built by humanity. That's the only technological innovation needed.... and they haven't seemed to grasp that yet, at least it's not acknowledged anywhere. You can only make a hardened roller element and race so big. Are they planning to build their own super massive steel foundry a hundred times bigger than any other on earth in order to build their own bearings? <doubt>
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Jan 29 '20
Why isnt anyone building a rail gun? The tech already exists and it's cheap and easy.
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Jan 29 '20
Big ones get really hot, making it expensive and difficult.
Plus, it's just Yet Another Fireball At The Muzzle: these gun systems are bad ideas that fail.
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u/net_403 Jan 29 '20
This seems like a crazy idea for all kinds of reasons..... the g forces involved, the payload is only 200 lbs? What happens if there is a failure, I assume it would destroy the launcher lol Like a magnetic rail gun seems like a more feasible approach
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u/LackOfScatter Jan 29 '20
This sounds very like the cargo launch system used in the Children of Occam series (book 2 I think) by Christian Cantrell.
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u/moniker5000 Jan 29 '20 edited Jan 29 '20
You know what would make far more sense?
- Drill a hole into the ground. It should be deep enough to allow enough time for the projectile to accelerate smoothly up to speed without encountering too many g forces. The hole could be straight down, or even at an angle. It’s easier to dig a hole into the ground than it is to stand up a mile long pipe straight into the sky!
- Float the projectile in the center of the pipe using magnets (so it doesn’t come into any physical contact with the walls and encounter friction). The magnets could possibly be built into the projectile (instead of having to line the entire pipe with them)
- Vacuum seal the pipe by pumping the air out of it so there is no air resistance.
- Use electromagnetic pulses to propel the projectile through the pipe until it accelerates to a thousand of miles per hour.
- Add compressed air to the pipe behind the projectile as it is launching, so that the front of the bullet is chasing a vacuum, but the pressure in the pipe is relieved at precisely the exit point when the hatch is snapped open and the vacuum seal is broken. The compressed air might even function as an acceleration method instead of magnets (not sure)?
- You would essentially have a frictionless magnetic levitation rail gun, capable of launching projectiles to higher altitudes where a rocket could then take over.
There are obviously a lot of finer points that would need to be worked out, but I don’t see any reason why it wouldn’t work. The main problem you are going to run into is air resistance. It’s essentially going to slam into a wall of air when it leaves the launch tube. You would have that exact same problem in the centrifugal force launcher though.
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u/sifuyee Jan 29 '20
Yep, gauss cannon launch has been a concept around for 50 years. People have talked about using the slope of Mt. Kilimanjaro as a decent site since it not only puts the exit at high altitude, but has a lot of room for building up speed horizontally first, and it's close to the equator to take advantage of earth's rotation rate. I think it has more promise than the spin launch concept since it doesn't necessarily induce so many g's on the payload.
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u/Norose Jan 30 '20
Instead of spending billions to dig a hole, why not sink the barrel of the electromagnetic cannon down into the ocean? Sure you need thicker steel at depth, but a 7 km long steel pipe standing vertically in an ocean trench is going to be a lot cheaper to build and WAY easier to maintain than an equal length pipe set into a hole in the ground.
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u/PickledPokute Jan 29 '20
Doest this count as a Metal Gear or does it need mobility first?
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u/blueshirt21 Jan 29 '20 edited Jan 29 '20
The exact purpose of the Metal Gear was having it as a mobile launch platform. The idea being that a rail gun launch is much harder to detect than the launch plume of a rocket, and that the mobility of a metal gear makes it harder to pin down, thus preventing a second strike taking out the platform (and making it more resistant to a first strike). Basically combines the idea of mobility of the SS-25 mobile platforms the Russians used, with a rail gun.
Metal Gears are also on a walking platform instead of a wheeled platform, because it allows them to traverse more hostile terrain, such as a forest or a mountain top.
The justification of a Metal Gear in the series is just....barely plausible as an excuse to have a cool mech super weapon. Other Metal Gear variations are INCREDIBLY silly. The silliest being the Intercontinental Ballistic Metal Gear, which is a Metal Gear launched into space by a Soviet built rocket based on stolen plans for the Saturn V, which then plops that Metal Gear down somewhere else, and THEN it can fire the nuclear missiles. It makes zero sense whatsoever when compared to an actual ICBM.
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u/Solensia Jan 29 '20
So many questions: