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The Science Behind Building a Space Gun

Posted by samzenpus on from the acme-approved dept.

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."

17 of 131 comments (clear)

  1. I estimate it will be about a week by Anonymous Coward · · Score: 3, Insightful

    before the Mossad kills this guy...

    1. Re:I estimate it will be about a week by Anonymous Coward · · Score: 5, Interesting
      LOL no kidding. Paging Dr Gerald Bull!

      http://en.wikipedia.org/wiki/Gerald_Bull

    2. Re:I estimate it will be about a week by F34nor · · Score: 3, Interesting

      The bones of the space gun are rusting in the Bahamas. The biggest problem is A LOT OF MOTHERFUCKING Gs. That's why I say we just launch barrels of water.

  2. Obligatory by Kylon99 · · Score: 5, Interesting

    In honor of the time before xkcd, but in the style of such:

    http://en.wikipedia.org/wiki/From_the_Earth_to_the_Moon

  3. I think it's called a mass driver by Joe_Dragon · · Score: 3, Interesting

    I think it's called a mass driver

    1. Re:I think it's called a mass driver by roc97007 · · Score: 3, Informative

      Some of the techniques resemble a mass driver, but many do not. It's actually an interesting video.

      --
      Oliver's law of assumed responsibility: If you're seen fixing it, you will be blamed for breaking it.
    2. Re:I think it's called a mass driver by Grayhand · · Score: 3, Insightful

      I think it's called a mass driver

      By any other name the gee force issues are the same. The problem with mass drivers would be the expense. Imagine building a 500 kilometer CERN collider. Mass drivers are practical on the Moon because of the low gravity and no atmosphere.

  4. Scaled Down Particle Accelerator by dns_server · · Score: 4, Interesting

    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.

    1. Re:Scaled Down Particle Accelerator by crtlaptop · · Score: 3, Insightful

      Orbital speeds in atmosphere means bleeding off speed and part of the payload being vaporized. Its the same forces acting on re-entry. As far as I know (not very far) this makes it harder to send smaller objects.

    2. Re:Scaled Down Particle Accelerator by Grayhand · · Score: 3, Informative

      It's the g-force involved. The benefit of a long barrel is lower g-forces. A short barrel would be possible but when you start talking a million Gs the only thing that could survive would be solid metals. It's a balancing act of barrel length as opposed to G-Forces involved. There's nothing special about how the LHC is built, magnets or explosives it's still converting energy into motion. Most gun launch systems plan on using explosives to cut costs. Explosives are cheap, magnets and electricity are expensive. If you could do it efficiently one gallon of gasoline would orbit a couple of kilos. The trick is not wasting the energy. As the projectile moves down the barrel the gas expands exhausting it's energy. Say you have a mile long barrel you'd likely run out of gas expansion before you reached the end then add in friction and a projectile that could reach orbit doesn't even make it a mile. Instead burn a cup of vaporized gasoline spaced out every ten feet along the barrel and you might need a few hundred gallons of gas to reach orbit but it's still dirt cheap. Watch the video and he explains why that wouldn't work either. The real solution is lower density gases like hydrogen that have a higher Mach speed. The best bet is watch the video. It's one of the best I've ever seen and explains the problems in laymen's terms.

  5. Revive the lofstrom loop! by Cryacin · · Score: 3, Interesting

    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
  6. Dr. Manley by crtlaptop · · Score: 3, Funny

    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.

  7. Re:This is all well and good, but... by F34nor · · Score: 4, Insightful

    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.

  8. Inexpensive way to send up inert objects by steveha · · Score: 3, Insightful

    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
    1. Re:Inexpensive way to send up inert objects by currently_awake · · Score: 3, Informative

      Reusable rockets must be fully overhauled after every single flight and must be more rugged to survive repeated use, they therefore cost more than a disposable rocket. The Saturn 5 was much cheaper than the space shuttle. Using chemical fuels means 95% of the rocket must be fuel. To get usable launch weights you have to use every trick in the book to save weight. All those weight savings make rockets fragile, they wear out quickly and need everything rebuilt after each flight. The only way to make space cheap is by having the power source separate from the rocket/payload (gun, mass driver, loop, skyhook, tractor beam).

    2. Re:Inexpensive way to send up inert objects by DerekLyons · · Score: 4, Interesting

      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. The video mentioned this issue briefly

      All gun schemes mention this 'briefly', if they mention it at all (most don't) - mostly in hopes that nobody will notice. The mass of the engines and fuel needed to circularize the orbit dominates the payload, and is *very* difficult to make resistant to the shock and acceleration. It's pretty much a showstopper all by itself, without even mentioning the need for (the currently non-existent) heat shielding needed to protect the payload on ascent. As the vehicle bleeds off energy to atmospheric drag and gravitational forces as it coasts upward, it has to leave the muzzle of the gun at considerably more than orbital velocity... essentialy exposing the payload to re-entry conditions at launch.
       

      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?

      Nobody that I'm aware that's even remotely serious is proposing to do it that way.

  9. he was sort of asking for it by Thud457 · · Score: 3, Insightful

    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