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The Science Behind Building a Space Gun
An anonymous reader writes "Astronomer and gamer Scott Manley (more famous for his Kerbal Space program coverage) has created a fantastic video explaining the science behind building guns that could one day be used to launch payloads into space. It's not as easy as simply making a bigger gun, there's a whole host of unorthodox 'gun' designs which work around the limitations of garden variety propellants."
before the Mossad kills this guy...
In honor of the time before xkcd, but in the style of such:
http://en.wikipedia.org/wiki/From_the_Earth_to_the_Moon
I think it's called a mass driver
they have, but it's impractical as in taking up airspace which causes it to act like a wall in the sky preventing airplanes to pass through.
it's easier and cheaper to just build a space elevator in the long run.
it's not economically interesting to prevent airplane traffic.
Why not scale down the LHC and build something that is capable of accelerating something relatively small say 10-100kg fast enough to make it to orbit instead of accelerating atoms to nearly the speed of light.
The problem with conventional rockets is you need to carry the fuel to get in to orbit as well as the fuel to go where you need to. The bigger the ship the more fuel you need to carry to overcome the weight of the fuel.
If you can split the carrying of fuel for your journey from getting your rocket in to orbit you would not need to waste as much fuel lifting itself.
You could set up an automated system that would fire a 10kg payload of fuel every 10 minutes and get what you need over time far cheaper than one big launch.
http://en.wikipedia.org/wiki/Launch_loop
Much better than a cannon, and finally a place where we can put all of that electricity from our power plants that we don't use during trough times to be used again when you get a spike. Just gloss over the energy of a small nuclear device in a moving cable over a 2000km area bit. That's not going to bother anyone...
Science advances one funeral at a time- Max Planck
Oh Scott Manley. I wish you had gotten your PhD. Dr. Manly would be pretty much the best name ever. You could say you have a PhD in Manlyness.
Marianas trench is 11km deep. A neutrally bouyant gun barrel inclined at about 20 gives a barrel length of 30km and is relatively cheap to build (a couple of billion for a few meters diameter).
If you immerse the astronauts in water (body hugging 'bath') they can easily withstand 10-20g for 15-30 seconds. That gives you 2.5-3.5km/s muzzle velocity, and a relatively simple rocket to prvodie the additional 5-6km/s - similar to current rocket second stages.
The gun can also be used at higher g to launch inert payload to orbital speeds without less rocket propulsion.
Guns are ok for lower speeds (up to perhaps 2-3km/s) but ram - accelrators are better than light gas guns for higher speeds.
Everything is expensive. As to what to do with a gun, just launch water into space. It provides fuel, air, food, and of course water.
This would be ideal for sending inert things like oxygen, water, rocket fuel, or some kinds of food. It would even work for structural parts or electronics if they could take the accelerations without damage.
For that matter, one of the problems of a Mars flight is having adequate shielding against the radiation the craft would encounter between Earth and Mars. With a system like this, the cost of getting the shielding up would be as cheap as possible. (I guess the mass of the shielding would affect the accelerations the craft could make and thus affect the length of the trip.)
One problem, as I understand it: a projectile launched from a big space gun would need to have its orbit adjusted or it will return to Earth. Either you need to catch it while in orbit (you get one chance) and add additional acceleration to put it in a stable orbit, or else the projectile needs to have rockets or something to adjust its speed. The video mentioned this issue briefly (the part about Newton figuring out that the projectile would return to the point of launch if no other forces acted upon it).
P.S. I saw proposals for an Apollo-style mission from Earth to Mars: a single giant rocket launches everything in one launch. Why is anyone even looking at doing it that way? Send the craft to space without fuel or consumables; send it up in parts even and assemble it in space. Then, as it is in orbit, fuel it up, load it with consumables, and then when it is ready send it on its way.
We don't really need giant space guns to make space access more affordable; we just need practical, reusable craft that can carry a small load to orbit, return, and do it again soon. It must not need man-decades of work to completely overhaul it, as the Space Shuttle needed. Single stage to orbit, two stage to orbit, whatever... but not single-use rockets. Rockets that fall into pieces as they ascend, where you never get a test flight because each flight uses up one rocket, will never give us cheap access to space.
According to Jerry Pournelle, the fuel cost of putting something into orbit is similar to the cost of flying it most of the way around the world on an aircraft. Because the aircraft isn't consumed by the flight, we can do this for much less than the cost of sending something into orbit. Practical, reusable transportation would be a total game-changer.
lf(1): it's like ls(1) but sorts filenames by extension, tersely
you turn in your geek card. in a multi-body system, such as the earth-moon one, there ARE trajectories to orbit from a "space gun"
A baseball, per google search, weighs about .142kg and a 120mph baseball is going about 53m/s.
0.5 * mass * velocity^2 gives about 200J.
200J / 1.6e-19 gives around 1.24 x 10^21 eV.
The LHC's protons top out at around 7TeV, or 7 x 10^12.
Your estimate of the LHC's proton energy, sir, is off by a factor of something like 1.78 x 10^8, or in words, by a factor of 178 million, depending on what you think of as a "fast" baseball! (Unless you think of a baseball moving at .009mph as fast?)
Perhaps you were thinking of some cosmic rays, which are reputed to have that much energy? There are cosmic rays that have had 50J of energy, or about energy of a 60mph baseball. But the LHC has about a factor of 10 million to go to reach that class of energy!
--PM
At those speeds you need the barrel, track, or rail straight to extreme precision. Any deviations will set up a wave in the track that will destroy it.
We built a 1000 ft light gas gun and had it happen. A couple hundred feet down the track the projectile existed through the wall of the tube and the tube was bent into a sin wave.
I love Jesus, except for his foreign policy.
What would be interesting is if a 3D printer were used to fabricate the gun.
a whole bunch of magical technology to do so?
You mean an electrolysis tank and a power source? Ok, granted there's some engineering to do there but considering the kinds of engineering that would go into building a spacecraft, it's a pretty trivial amount.
Really?!
The Israelis are bad for killing the guy that was going to give Saddam a GIANT GODDAMNED GUN to lob poison gas shells at Tel Aviv ?!!
Bull was pulling a Von Braun and just didn't have the luck of getting a buyout offer at the end.
the preceding comment is my own and in no way reflects the opinion of the Joint Chiefs of Staff