Half a croissant, on a plate, with a sign in front of it saying '50c'
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Centripetal Space Junk Drive

Trash thruster, frog blender
(+1, -1)
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I just thought of this this morning and haven't spent too much time thinking about it and apologize if it plagiarizes someone else's work. So there's all this space junk floating around out there (mmm mass), I suggest we grab it, accelerate it and chuck it out the back of our space ship. Here is how it works, say you have 2 counter rotating centrifuges configure like a figure 8 (one on top of the other) that are 10 ft in diameter running at say 100 rpm. The outside wall (where the junk get pressed up against due to centripetal force) resembles venetian blinds, that is, any section could be opened to release said junk in the appropriate direction. A computer would monitor the location and mass of each of the objects inside the centrifuges so the release timing could be balanced between the two centrifuges. Now that I've completed my experiments on frogs in space and collected all the data I don't need the frogs anymore. So, I take my 1 oz. frog and chuck it in my centripetal blender, at 10 ft. dia. and 100 rpm that frog can produce 75 pounds of force (that is if my Moms math is correct). And that at only 100 rpm, just think! This would be a "dockable" engine that would be left in space spinning when not in use. Once up to speed it would take very little to compensate for new mass pick ups. Junk mass could be collected from stuff floating around or waste produced by our spacecraft.
plonk, May 29 2003

(?) frog in space video http://content.funv...ent/froginspace.asf
[thumbwax, Oct 04 2004, last modified Oct 21 2004]

(?) almost epic cartoon strip http://www.nsfg.cwc.net/fisep1.html
[thumbwax, Oct 04 2004, last modified Oct 21 2004]

scavenger Scavenger_20satellite
also uses captured space junk for propulsion [the great unknown, Jun 28 2007]


       However you go about it (centrifuge or cannon), you are propelling your spaceship by chucking things off it. Do a thought experiment: if you want to propel your, say, 5,000 ton spaceship by an extra, say, 10 meters per second, just how fast are you going to have to throw that frog in the opposite direction?
DrCurry, May 29 2003

       Ok, so I'll need to throw in all four of my frogs and increase my rotation speed to 10000rpm and my diameter to 20 ft. to get a 5000 ton spacecraft to move just over .5 m/s. There only little frogs, what about when I catch a pound of iron.
plonk, May 29 2003

       Now, figure out how long it's going to take you to get to Mars at .5 m/s. And before you go, tell me how much energy you've used up to get the two 2,500 ton halves of the spaceship spinning at 10,000 rpm, and how the heck you're going to dock the thing at the other end.
DrCurry, May 29 2003

       Ok, so I left out that I could throw out their entire frog habitat and I was figuring on collecting trash from the ISS. So if I had 2 tons collected I could use 500 of it to get 1214 m/s. To dock the venitian blids would open such to chuck another 500 pounds in the opposite direction. I just pulled that trash weight from thin air, what if were really 10 tons? And it was you [DrCurry] that said the spaceship weighed 5000 tons, the centrifuges don't have to weigh that much. Power and spin up... heck one could take a month to spin them up while they're preparing more frogs. Time to spin up doesn’t matter, once it's spun up it just keeps going (with a little power for mass pick ups.)
plonk, May 29 2003

       Umm yeah [dag] I was thinking 10000rpm as a practical number... but heck if you could reach 500000rpm in space or shoot, a cool mil. then we're on our way.
plonk, May 29 2003

       The trouble is, you'd use up 1000 pieces of space junk as propellant just to get to piece number 1001. You can't just put your hand out and pick these things up, you know. They are traveling in all sorts of orbits and at all sorts of velocities.
pluterday, May 29 2003

       Your centrifuge, at 10000 rpm and 20 feet in diameter, suddenly becomes imbalanced by so much as a frog... I think it will instantly commence autodisassembly into a far larger quantity of junk. Controlling the tangential release points of the resulting debris could be helpful, but difficult.   

       Only the frog is safe.
lurch, May 29 2003

       How are you getting these fogs to last a trip to anywhere? You can't breed enough
dickity, May 29 2003

       Don't worry, nobody's thought of it before (-)
FloridaManatee, May 30 2003

       [dickity] Rabbits then ;-)   

       I'm still hanging out for the Bussard Ramjet, I'm sure it will be figured out before breeding a multitude of frogs in space.
gnomethang, May 30 2003

       Further to lurch's note, I had thought the absurdity both of spinning major portions of your spacecraft at 10,000 rpm, and of trying to exactly time ejecting a large object from something spinning at 10,000 rpm, was obvious. But I guess we need to spell it out: THIS THING CANNOT POSSIBLY WORK!   

       If you want to propel your spaceship by ejecting frogs, vaporize them and emit them as a directed particle beam. Much, much easier to manage.
DrCurry, May 30 2003

       gnomethang, when I was reading Zorben's (sp?) "Earth to Mars", he discussed anti-matter prop. and mentioned a guy who trid to devolop a Bussard Intake for plasma, but failed. That did trun into a nifty way to slow a craft though ;) I can't remember how that worked, I think it was the attraction system couldn't ditect the matter, so the bussard collector would actually slow it down.
dickity, May 30 2003

       Ok how about I don't use frogs (it's hard on them), suppose prior to start up of the centrifuges they're filled with sand (or trash is ground) each of the "blinds" have portioned amounts to keep it balanced and I just release a few grains at a time.
plonk, May 30 2003

       Just re-reading it a bit...   

       // have 2 counter rotating centrifuges configure like a figure 8 //   

       Could this actually be like one of those two-wheel things that pitches baseballs? No worries about centripetal forces/imbalance, just feed the frog into the interface and he gets a large *linear* acceleration.
lurch, May 30 2003

       *thinking of fun*   

       WOW, thats fun
dickity, May 30 2003

       Yes indeed. What happens when there is no more space junk to be found? I simply assumed that this would be good for flights in an asteroid belt and nowhere else: A slow moving asteroid chunk is sucked in the front of the ship thenn accelerated out the back, producing thrust. Frogs don't really weigh enough.   

       And you can't really acrry the space junk with you, becuase all that does is give you enough power to push the weight of the space junk around.
Macwarrior, May 30 2003

       space junk engine : lots of weight, uses electric energy to push off frogs & bits of russian space stations. Nuclear rocket engine : less weight, uses radio active pellets in porceline to heat up hydrogen and pushes off that.
LED Prism, Jun 18 2003

       It's amazing how much better the Centripetal Space Junk Drive seems when compared to a nuclear rocket engine.
bristolz, Jun 18 2003

       There are a lot of fundemental problems with this idea, but let me point out the most obvious. This device (let's call it the frog pitcher) works on the basis of friction. The contact points of the rotating accelerator wheels are traveling at about 100 fps (70 mph). Let's say about 2 inches of the wheels (1 angular degree) will be in contact with the frog at any given time. Imagine if you will, accelerating a 1 oz. frog to 70 mph over a space of 2 inches.   

       As someone already pointed out, vaporization of the frog, ionaztion of the resulting mist, and pushing it out of the ship through a liniac (Linear Particle Accerator) is really the most effient utilization of the frog given today's technology. Specific impulse per ounce of frog is going to be at mininum an order of magnitude higher.
netmanakre, Jul 16 2003

       What would be the effects of passengers on a ship spinning at 500000 rpm? Your frogs (and pilots) would all be conveniently turned into liquid fuel.
zindog1282, Aug 08 2003

       Specific Impulse is what makes a good space drive. Specific impulse is pounds of thrust divided by mass ejected per second. Specific impulse is proportional to the square root of temperature divided by molecular weight. (i.e., sqrt(T/Mw). Frogs have a very high molecular weight; much higher than, say, hydrogen. Plus, the effective 'temperature' of your chucker is very low. Therefore it has abysmal specific impulse and is totally impractical as a space drive.
boris, Aug 09 2003

       It would take a couple thousand passengers for each one's contribution to even add up to a newt-ton.
lurch, Aug 09 2003

       I think this was the first halfbakery idea I ever saw.
DesertFox, Jun 21 2004

       Surprised nobody pointed this out:   

       //To dock the venitian blids would open such to chuck another 500 pounds in the opposite direction. //   

       Are we chucking debris at the craft to which we intend to dock? Our host will NOT be pleased!   

       Also, space debris is going to be a problem as orbital space becomes more crowded. Hurling it about in new crossing orbits at higher speeds makes the problem worse, not better. (-)
gardnertoo, Jun 27 2004

       Why does this remind me so much of the hobos and the shop owner haggling about the dollar:frog exchange ratio in Steinbeck's Cannery Row? Still cracks me up, that part of the story.   


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