A Space Cannon That Might Actually Work 432
Unequivocal writes "Chalk another one up to Jules Verne. Physicist John Hunter is proposing a space cannon with a new design idea: it's mostly submerged. 'Many engineers have toyed with the [space cannon] concept, but nobody has came up with an actual project that may work. Hunter's idea is simple: Build a cannon near the equator, submerged in the ocean, hooked to a floating rig ... A system like this will cut launch costs from $5,000 per pound to only $250 per pound. It won't launch people into space because of the excessive acceleration, but those guys at the ISS can use it to order pizza and real ice cream.' Though it won't work on people, with launch costs that low, who cares?"
atmospheric stresses (Score:5, Interesting)
If you try to launch an object from the surface of the Earth using a "cannon" the projectile won't be doing anything other than decelerating throughout its flight and this means bringing the projectile to very high velocities where atmospheric heating and stresses become major problems. Then again, launch its self may be a problem as the Hydrogen propelling the projectile is detonating at an extremely high temperature and pressure. Small nitpick as well from TFA:
A big reason space food is what it is instead of the Earthling food we're all accustomed to has to do with keeping the station reasonably clean and experiments doubly so. Crumbs and fluid loose in the station can cause problems.
Re:We need more ideas such as this (Score:3, Interesting)
For most ideas, feasibility lay entirely on the hands of engineers.
For example, building a skyscraper 2km tall is merely an engineering problem. A space elevator is merely an engineering problem. A script to automatically discard redundant comments is merely an engineering problem.
Still, parent's comment is obviusly not discarded.
More wildly optimistic cost estimates (Score:3, Interesting)
In the end, once you've figured up the total cost of the system it's often more than just using rockets, even though rockets are so terribly inefficient.
Re:Hunter should watch his back (Score:1, Interesting)
A super cannon of this scale is unlikely to be useful to any non-superpower since the sheer scale of the device seriously limits its mobility. Limited mobility means it would be easy for an enemy to take the device out, assuming the enemy has superior air power.
So a weaponized version of this might benefit the US since they would be able to defend it, but for a country like Iran it would just be an expensive easy to hit target.
Duh, we bomb the shit out of those who have them.. (Score:5, Interesting)
http://en.wikipedia.org/wiki/Project_Babylon [wikipedia.org]
Yes gents, Saddam Hussein could have given us cheap access to space ensuring new area of prosperity for mankind, and era of space colonization...and we killed him!
PS. If a supergun has a basic design similar to German V-3, it might be almost bearable to humans...
Re:atmospheric stresses (Score:1, Interesting)
If you really want to see crazy go look up base bleed rocket artillery. http://en.wikipedia.org/wiki/Base_bleed They use a rocket merely because it can generate a lot of exhaust to fill the void in the back of an artillery shell so said shell can stay at a higher velocity longer. The rocket is NOT installed for its impetus. It is a rather elegant solution to the problem.
Re:Velocity (Score:5, Interesting)
Min orbital velocity = 7.6 km/s
Earth Escape Velocity = 11.2 km/s
Funny coincidence, world record for hydrogen gun == 11.2 km/s
These guys plan to have the gun propel the projectile to 6.0 km/s, and then the projectiles themselves are rocket motors that will add an additional 3.0 km/s. That gives them enough acceleration to reach orbital velocity and take into account friction/gravity losses.
The reason they plan to limit the gun to 6.0 km/s is because that requires the hydrogen gas to only reach 1700 kelvin, which after taking into account heat exchange with the barrel, it ends up being a few hundred kelvin below the melting point of steel ( the barrel ).
Cheaper (Score:2, Interesting)
Commercial space flight here I come!
Re:We need more ideas such as this (Score:4, Interesting)
Most reputable materials folks I know still claim its a fundamental technology problem, not merely a funding one. While the expected stresses are nominally within what an ideal carbon nano-tube structure can handle, the purity required for that is well beyond what we can manufacture.
In order to feasibly build a space elevator, we would need much improved nano-technology. Not that I feel that its necessarily an idea-killer -- I'm not terribly knowledgeable on nanotech, but its one of those fields that always surprises me with how fast its going.
The longer the gun, the lower the Gs. (Score:5, Interesting)
Make it long enough and it CAN launch people. (You'll need good streamlining to avoid nasty deceleration when it leaves the muzzle, though.)
The ocean is DEEP. Something that's roughly neutrally buoyant (i.e. a gun barrel supported by floats distributed along its length) needs to spend negligible structural strength supporting itself. (It only needs to be strong on any part that protrudes from the water - which might be a lot to avoid sinking it when it recoils.) You might want to put "helper combustion chambers" along it periodically to boost and smooth the acceleration if you want to launch live stuff though.
Also you can make it larger diameter and put sabots on the projectile while it's in the barrel to reduce the internal pressure variations or fire very dense loads. (Doesn't really help the materials strength issues, though, because the curvature lessens as diameter rises.)
Recoil? By being submerged it's an inside-out hydraulic shock absorber. B-)
Propellant is cheap. Guns wear out. (Score:3, Interesting)
I don't see the benefit of floating the cannon (Score:3, Interesting)
Sorry, but I don't see the benefit of floating the cannon in the ocean. You have a very long structure that must be kept really close to perfectly straight that is subject to currents, waves, coriolis effects, etc. Worse, you are stuck with the projectile emerging into the densest part of the earth's atmosphere.
It would make a lot more sense to build a fixed structure on an appropriate, high mountain near the equator. Places like Peru or Ecuador come to mind as well as Mauna Kea on Hawaii. I'm sure there are more places that would be "developable" and logistically acceptable.
Cheers,
Dave
Re:The longer the gun, the lower the Gs. (Score:2, Interesting)
Re:Duh, we bomb the shit out of those who have the (Score:4, Interesting)
First of all, you can't get into stable orbit ballistically; you have to use a rocket motor at apogee of ballistic trajectory, at the least.
Also, we do have clear examples of electronics (from the 60's...) surviving launch to half of orbital velocity from a modified big naval cannon (Project HARP). And that's more or less a "normal" cannon, very short, very high acceleration. Look up V-3; such design can maintain almost constant acceleration, close to average one, and be hypothetically several kilometers long.
So why don't we go totally overboard, and assume a barrel length of 30km; and close to half of orbital velocity (so it will be easier, since there's ^2 in this part of equation ;p) - 3.5 km/s. From simple calculations that gives 20 g. Definitely bearable, as far being launched from a cannon into space goes. With 5 km/s you have 42 g.
Yes, widely unpractical and even...stupid. But I didn't actually suggest using it for humans, just said that it might be almost bearable.
A few questions for the engineers in the crowd (Score:3, Interesting)
If this launcher is anchored at the surface, how will they compensate for the motion of the waves at the surface? Does that eventually become a non-issue due to the weight of the launcher?
How would they 'catch' the cargo once it was launched into orbit?
How rigid would such a structure need to be, and are there currents in the ocean that would cause bending stress issues between surface and the deepest parts of the structure?
Re:Duh, we bomb the shit out of those who have the (Score:4, Interesting)
You are misinformed (and here you didn't even need to perform any basic calculations...)
http://en.wikipedia.org/wiki/G-force#Human_tolerance_of_g-force [wikipedia.org] // I would venture a guess they were breathing and their brain was supplied with blood // without loss of consciousness or apparent long-term harm. The record for peak experimental horizontal g-force tolerance is held by acceleration pioneer John Stapp, in a series of rocket sled deceleration experiments in which he survived forces up to 46.2 times the force of gravity for less than a second. Stapp suffered lifelong damage to his vision from this test //"this test" likely means eyeballs-out
Early experiments showed that untrained humans were able to tolerate 17 g eyeballs-in (compared to 12 g eyeballs-out) for several minutes
(emphasis mine)
In my hypothetical scenario with 20 g that acceleration would last only 17 seconds, quite bearable. In the overboard example with 42 g, it would last 12 seconds (eyeballs-in!), which still might be survivable (and with eyeballs-in, which stresses eyes less, perhaps even without long-term damage)
Re:We need more ideas such as this (Score:3, Interesting)
Even if a 1.5 light second long cable were feasible you'd still have to deal with the fact that, as far as I understand, the anchor would have to be in geosynchronous orbit. Since the Moon isn't in geosynchronous orbit, the surface moves relative to the Moon you'd end up winding the cable around the planet.
no, no! they would simply make the base of the elevator mobile, and put it onto a train that constantly runs around the equator at the speed of the earth's rotation, plus or minus (as appropriate) the speed of the moon's orbit.
think of the money we'd save getting things into orbit!
Re:We need more ideas such as this (Score:4, Interesting)
For one thing we need a big counterweight, and the 'easiest' way to do that is to tow an asteroid into Earth orbit. I'd say building a space tug is an engineering challenge.
I don't think towing an asteroid is the easiest way; it would be much easier to just start with a very small counterweight (e.g. a rocket stage, or even nothing). That would give you a very low-payload-capacity cable. No problem, you send a very small/light elevator-car up the cable, and when it gets to the end of the cable, it stays there and becomes part of the counterweight. Now you send a slightly larger/heavier elevator-car up the cable, and when it gets to the end, it stays there too. Repeat as necessary until you have enough mass at the end of the cable to support whatever payloads you want to bring up.
Re:We need more ideas such as this (Score:2, Interesting)
I have to agree. I'm not sure how stating the obvious "that this is "merely an engineering problem at this point" qualifies as insightful.... but I guess the bars been set a lot lower on SD of late ;)
What is important about this is NOT the obvious. It's that this should have been SO obvious. The problem with a cannon is one of "runway" if you will. Building a cannon above ground introduces huge amounts of engineering hurdles, much like building bigger and bigger buildings so oh on the scale of 3x what we have now. Put a cannon in the water however! Wala, relative density starts working for you, you can feasibly build a device that can be sustained at long lengths that can build acceleration in the package over the tube distance.
What I want to know is why we didn't think of this before.
Re:I don't see the benefit of floating the cannon (Score:3, Interesting)
Re:Duh, we bomb the shit out of those who have the (Score:3, Interesting)
My undergrad thesis supervisor back then worked in the field and actually met this guy at a conference a year or two before he was assassinated.
Re:I don't see the benefit of floating the cannon (Score:3, Interesting)
As some people have pointed out, most of the things you mention aren't problems. Loss of speed, straightness of barrel etc. Plus, as they say, you get to aim for different orbits in one platform
One thing they didn't point out which is significant: Logistics.
You go ahead and bring huge supply train up the side of Mauna Kea - I'm sure none of the neighbours will mind. As someone else pointed out, I'm sure they wont mind when something goes tits up and you send shrapnel towards them at a km/s.
Logistics are a killer though. With an ocean platform, you already have your base on the harbour. You have plenty water for all types of uses, like desalinate for drinking, use in flushing, cooling etc., and you only have to make sure your installations are protected against sea water. If you need a big housing base for staff etc. you can float in every thing you need by buying a small cruise ship. Park an oil tanker next to it for fuel and gas needs and retrofit it for ship to ship refuelling.
Compare all those advantages to the minor inconvenience of losing a small bit of initial velocities, and you end up with a massive conclusion of ocean based vs nailed to the side of a mountain.
Re:Duh, we bomb the shit out of those who have the (Score:3, Interesting)
Well yes. We still have the receipts for some of those. But he didn't have them at the time. As to conventional forces... I don't think it would have made much difference. The USA had air support. Every time the Iraqis tried to put something in the air or looked like they might, the US blew it to pieces. And anyway, the Iraqi army was never defeated. They just took their uniforms off and the US is still fighting them.