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Space Rail and Pacman Rocket

Moon based mass driver shoots iron "stepping stones" into space...
  [vote for,

... which the spacecraft takes into the front and shoots out the back utilizing another on-board magnetic mass driver. The advantage is that since the spacecraft isn't carrying any fuel, other than the nuclear power plant generating the electricity for the mass driver, it can continue accelerating until the line of iron pellets shot into space runs out. This line of cannon ball size iron pellets could extend thousands or tens of thousands of miles which would provide a lot of mass for your rocket to use.

Problems are keeping that line of pellets straight and being very accurate with this rocket. The Moon is a moving platform so a static rail gun aimed in one direction won't be shooting a straight line of pellets. Plus you can't be off in your accuracy by even a few inches. Hitting a 10 pound cannon ball in space at 50,000 miles per hour could really ruin the party. Still, the concept might find it's place for use in a very high speed probe that was maneuverable enough to hit each iron ball exactly spot on. Good news is it's easy to see things in space and you know where it's going to be by the time you reach it.

Another, possibly more realistic alternative would be to have the iron and power mechanism embedded in a long rail, say 2,000 miles long. The rocket would just take this rail in the front and shoot it out the back. It could receive it's electricity from the rail further lightening it. Such a rail could be put in orbit around the earth, aimed and re-used easily. Each launch would slow down it's orbit a bit so you'd just have to freshen up it's velocity from time to time. However if you just shot your next spacecraft in the opposite direction that would "replenish" it's orbit.

Might be a way to get people to mars in weeks instead of months. A several thousand mile long rail weighing a million tons would provide a lot of mass for a one ton spacecraft to use. You'd need another on on the Mars side to slow down with as well.

doctorremulac3, Oct 15 2013

Neat acceleration calculator http://www.smartcon...ion_calculator.aspx
Fun toy for all you amateur astro-nuts like me [doctorremulac3, Oct 16 2013]

G-force effects on people http://hypertextboo...ipAndriyevsky.shtml
Working backwards from this to see how many balls you'd need. [doctorremulac3, Oct 16 2013]

NASA's new venture https://www.nasafcu...inancing-promotion/
One giant leap for flexible and affordable mortgage solutions [doctorremulac3, Oct 16 2013]

The Moon has lots of iron http://www.ncbi.nlm...gov/pubmed/17840628
Essentially atmosphere free so it's easy to throw stuff up there [doctorremulac3, Oct 17 2013]

Space Fountain http://en.wikipedia...wiki/Space_fountain
[MisterQED, Oct 17 2013]

What the orbital chain version launch might look like http://www.youtube....watch?v=TjgsnWtBQm0
Go to 1:38 for the launch part [doctorremulac3, Oct 17 2013, last modified Oct 18 2013]

Don't let the quest for physics bending propulsion mechanisms turn you into this guy http://www.youtube....watch?v=c-nTHdlB28M
[doctorremulac3, Oct 19 2013]

The first countdown. Real space-flight concept as movie star http://www.youtube....watch?v=CaVLaD4vfBc
Fast forward to 8:30 [doctorremulac3, Oct 21 2013]

MagBeam http://en.wikipedia...d_plasma_propulsion
Similar, but using many more much smaller cannon balls. [scad mientist, Oct 21 2013]

Replace iron pellets with a fuel rod https://www.youtube...watch?v=Lfwg6nQqv-0
Astrojet space scramjet [notexactly, Mar 21 2016]


       You know what, [doc]? This is a bloody brilliant idea.   

       Electrical power can be had cheaply in space, but reaction mass is exponentially expensive. This is an awesome idea!   

       I think the rail idea is unfeasible for the time being. But a series of cannonballesque reaction masses would work. The only drawback is that all of the delta V has to happen in the short time it takes the spacecraft to pass around the cannonball, which means that large delta Vs are going to need lots of small reaction masses rather than a few big ones, if only to spare the crew from violent accelerations.
MaxwellBuchanan, Oct 15 2013

       Thanks Max.   

       The concept is, since you can move that magnetic "wave" from one side of the spacecraft to the other at up to the speed of light, (or faster really) you would shoot each ball out at a higher rate than the last one. If you had enough balls, it would let you get up to a pretty big chunk of the speed of light in theory. Of course it might take a 100,000 mile long trail of trillions of balls but in THEORY it would work.   

       The longer the ship the better, you'd be able to grab onto that mass for a longer time and have less of that "bumpy" acceleration you referred to. There would have to be a balance though between length vs weight since every pound on the rocket vs static mass side slows you down.   

       Might be best for an unmanned shock resistant probe. At least at first.
doctorremulac3, Oct 15 2013

       // best for an unmanned shock resistant probe. At least at first.//   

       I dunno. Strikes me that if you've got the technology to get all your balls in the air (metaphorically and inaccurately speaking), you could use the same method to launch a shock- resistant probe in the first place. I see this as being more of an option for manned spacecraft - the cannon balls can survive the high G of launching, whilst the manned spacecraft uses many of them to achieve a staged acceleration.
MaxwellBuchanan, Oct 15 2013

       You could also have a ring of these orbiting Earth so you could use each ball several times. Sort of like winding up for a pitch, the craft could gobble up and spit out each orbital ball, come around the Earth and gobble accelerate off those same balls again. This could happen several times until the ship was going fast enough and it would just tangent off into space. If you changed the orbit of the balls by accelerating them, you'd have the next ship go the other way to put them back where they were.
doctorremulac3, Oct 15 2013

       Or, why not take this idea to its logical extreme: use your lunar railgun to fire out a stream of iron filings along your desired trajectory, and then use them in much the same way as you suggested using a rail?
MaxwellBuchanan, Oct 15 2013

       As usual, I have nothing of value to contribute at this time. However, I am compelled to annotate if only to agree that this is absolutely a bloody brilliant idea. By the time I got to // which the spacecraft takes into the front and shoots out the back // I was having one of those Halfbakery monents where you're a little surprised you're not reading Popular Science.
Alterother, Oct 15 2013

       [+] All the cannonballs could have solar-sails on them for stationkeeping.
FlyingToaster, Oct 16 2013

       Cool idea although the rocket is still carrying 'fuel' in the sense of nuclear fuel but you don't have to carry your reaction mass with you. The tolerances would have to be very fine for the reasons you mention. It also inspires a comical vision of the spacefarers finally landing at the distant planet only to be bombarded by a few spare iron cannonballs that the moonbase fired along their trajectory 'just to be safe'.
AusCan531, Oct 16 2013

       //a stream of iron filings along your desired trajectory//   

       I think you might have problems with stray bits that would become an issue at those high speeds.   

       //rocket is still carrying 'fuel' in the sense of nuclear fuel//   

       You could just use solar panels, but I think you'd get more bang for the buck with an onboard nuke reactor.   

       //you don't have to carry your reaction mass with you//   

       Better name might be "external reaction mass space vehicle concept" Sounds more NASA/sciency.   

       See links for a pretty neat acceleration calculator and g-forces info.
doctorremulac3, Oct 16 2013

       //Better name might be "external reaction mass space vehicle concept" Sounds more NASA/sciency. //   

       No, if it were NASA, it would have an acronym like "SUNBURST" or "TIGER", until it was either shelved or became routine, at which point it would get a TLA.
MaxwellBuchanan, Oct 16 2013

       Depressing fun fact: NASA's latest breakthrough is getting into the loan business. See link.   

       And yes, I checked, it is THAT NASA. Not some cute play on words like National Ameriloan Solution Agency. It's the National Aeronautics and Space Agency's credit union. They run regular ads on the local radio stations, I'm assuming that the add campaign is nationwide.   

       What the hell, they gave up the premise of exploring space a long time ago anyway. Gotta make a living.
doctorremulac3, Oct 16 2013

       I suspect there is a limit to how far out you could project your pellets and still have them where you expected them to be when the ship gets there (n- body problem). Practically speaking, if you're dealing with iron pellets, build radar corner reflectors into them to make them easy to find, and give your shipboard mass driver the ability to add some side acceleration so you can adjust to pick up the next one in line.
MechE, Oct 16 2013

       The idea is a little far fetched for space flight, but an airliner that is propelled by migratory birds would be more practical. The birds could be factory farmed and released on migratory routes, the airliners suck them in and shoot them out the back golden roasted in a little oil and glaze and they fall to earth over impoverished nations into outstretched hands.
rcarty, Oct 16 2013

       Fly with Rcarty Airlines and your goose is cooked.
AusCan531, Oct 16 2013

       One way to straighten the balls out is to put them on a cable and put thrusters on either end to pull the string straight.   

       You assemble sections on earth, fly them into orbit, assemble them and when you've got a few thousand tons of mass, pull them taut and viola, space rail. Move the thruster units that you used to pull the thing straight out of the way, put your Pacman rocket on one end and let 'er rip.   

       If the vehicle pulling on the thing caused it to oscillate you could leave that forward thruster on for the duration of the launch. Just make it skinny enough to fit through the input of the rocket and get spit out like the rest of the mass modules.   

       I wonder if, alternately, you can line up a row of balls in space with 4 lasers sort of corralling them, sort of like a laser containment cage.
doctorremulac3, Oct 16 2013

       This is a reasonably cool idea and the name of it is a space fountain (link). I've never heard of using it in any type of orbital mechanics for a very good reason, the first ship would disturb the pebbles and kill everyone coming after. Think about it, if the first ship gives one of these balls even a slightly angular velocity, the next ship will be destroyed. If gravity or solar radiation mis-aligns one of the balls, you are dead. Better to do it with particles that won't kill everyone, photons. For the energy you are expending you could just power a laser that would push a light sail and then you would be giving the ship both propulsion and power, so you can cut the weight way down.
MisterQED, Oct 17 2013

       //This is a reasonably cool idea and the name of it is a space fountain (link).//   

       Well, might want to go back and read the idea. This has nothing to do with putting things into space. It's a way to get around the limits of the Tsiolkovsky rocket equation and take a stab at accelerating a vehicle to some mentionable percentage of the speed of light.
doctorremulac3, Oct 17 2013

       Another approach would be to chain these together in orbit around Earth or the moon and have a big ring that you'd go around and around on, building up speed each pass until you shot out on a tangent. Problem is you could only fly out on one plane and you'd have to burn a lot of conventional fuel to change your course to go someplace located outside that plane.
doctorremulac3, Oct 17 2013

       I like that spin, [doc]. Like some kind of demented orbital flywheel. And I don't think the tangent limits you with good planning re future slingshot course changes.   

       Also, as you speed up, the balls are going to speed up oppositely and the orbit is going to get larger (hopefully at the same rate as you do). Er, I think.
the porpoise, Oct 17 2013

       Yes, you're right, that's why I'm thinking you could chain them together, then any speeding up of the orbit wouldn't result in a larger ring, just a faster spnning ring. Also, the mass of such a ring would be so huge a tiny little spaceship wouldn't make much of a change in it's speed. Even so, you could launch the next ship in the other direction to counter any changes to the velocity imparted by the previous ship.   

       It seems the practical limit to this would be the centrifugal force that would be pulling you away from your launch ring. It would be easily reusable though.   

       See link and fast forward to 1:00 to see what such a launch might look like.
doctorremulac3, Oct 17 2013

       This is a really interesting idea!   

       However, regarding the 'orbital ring' idea in the comments - it simply doesn't work. Every time the spacecraft gobbled up a pellet and shot it out the back, the spacecraft's orbital velocity would increase - after all, that's the point- and the pellet's orbital velocity would decrease (action and reaction, y'know.) Due to the laws of orbital mechanics, this would mean that the spacecraft would move into a higher orbit, and the pellet into a lower orbit - and so when the spacecraft came a full circle around, it would find that the same pellet was no longer aligned with the entrance point. Each pellet is usable strictly once only.
Hive_Mind, Oct 18 2013

       Yea, the ring thing would need them to be chained together to be practical, (as practical as a 50,000 mile long chain of metal balls would be.)   

       Then you could just have the ring spinning faster and faster or go the other way on the next launch. Not that the light little spaceship would have much effect in a hundred million ton chain.   

       I think the most intriguing incarnation of this is the first if you can figure out how to keep your space balls straight enough to have your super high speed spaceship gobble them up and spit them out without slamming into them.   

       100,000 mile long chain of ten pound balls would be 1 million tons, (?) about the same amound of iron India imports in a month. You get a one ton spaceship spitting these things out at the top speed of a mass driver, maybe 6000 m/s and you could really set some records.
doctorremulac3, Oct 18 2013

       //the top speed of a mass driver, maybe 6000 m/s and you could really set some records.//   

       Hang on a moment. Is that 6000m/s relative to the spaceship? If so:   

       (a) As the spaceship accelerates, it's going to have less time to apply force to the cannon balls   

       (b) Shirley the spaceship's speed will then be limited to 6000m/s plus whatever speed the cannon balls were travelling at beforehand?
MaxwellBuchanan, Oct 18 2013

       (God, I hope somebody doesn't check my math)   

       Wait, did I type that or just think it?   

       You'd increase the velocity of the mass driver with every new ball. It's my understanding that there's no limit to how fast you can send that magnetic wave down the tube since it's just switches. At these speeds though you probably would be getting into the theoretical limitations of a mass driver.   

       Anyway, I think the 6,000 m/s number would apply to each shot, you'd just have to increase the speed by whatever speed you're going. So if you were already going 6,000 m/s, you'd have to have your mass driver shooting at 12,000 m/s.   

       I think.
doctorremulac3, Oct 18 2013


       Assume the cannonballs start out stationary (relative to, say, the sun).   

       Your spaceship starts from a standstill, and accelerates the first ball to 6000m/s. This gives the spaceship a forward speed of something - let's say 1m/s (if the mass of the ship is 6000 times that of the cannonball). If the mass driver is (for ease of calculation) 300m long, then it has roughly 0.1 seconds in which to accelerate the cannon ball.   

       This continues, let's assume, until the ship is travelling at 6000m/s. But now it encounters a stationary cannon ball. Even if the mass driver is turned off, the cannon ball will pass through it in just 0.05 seconds.   

       Therefore, to achieve any additional acceleration, the mass driver's peak power must be more than twice as high as it was before.   

       Moreover, the acceleration from 0 to 1m/s will be 10G; that from 6000 to 6001m/s will be 20G.   

       Or something.   

       The big difference between a rocket carrying its own reaction mass, and one which picks it up en route, is that in the former case the unused reaction mass has a lot of kinetic energy, some of which it gives up to the rocket.   

       For example, if 1kg of reaction mass is carried on a rocket travelling at 10,000m/s, it has a kinetic energy of 50MJ, which is roughly as much as the chemical energy in the same mass of a typical propellant. If that the reaction mass can be ejected at 10,000m/s (relative to the rocket), then it ends up with no kinetic energy - all its KE has been transferred to the rocket (as well as all its chemical energy).   

       So, to get best value out of this system, you actually want to have your cannonballs travelling in the same direction as the rocket, and at various speeds, so that the closing speed of the rocket with each cannonball is as low as possible.
MaxwellBuchanan, Oct 18 2013

       hmm, the way I picture it, (if the balls are tethered at equal distances), is much the same as a chain grabbing a gear. As long as the frequency of interactions increases with speed then it would only require a faster and faster distributor-cap. Why the exponential increase in power?   

       No, no increase in power necessary. Just an increase in frequency. With each ball you get forward momentum by that push you're giving the ball when you kick it to the rear. You'd get the same kick with each ball, but you just have less time to do it.   

       Picture riding a skateboard. Your first kicks are pretty slow but as you get moving they're faster and faster, but your'e putting the same amount of energy into each kick. So you're not kicking the balls any harder, just kicking them faster because you have less time with each one. But since you're in space, you get to keep all that forward momentum so even if it takes hours or days to get through them all, you get all that momentum added up without any loss unlike the skateboard with all it's friction.   

       Hmm. The skateboard might be confusing because to kick it faster you WOULD have to put more energy into moving your leg. This isn't like the leg though, it's just an energy wave putting a set amount of kick on the ball at various segments of it's path through the vehicle. It hits point A it gets a kick, it hits point B it gets a kick. When you're going faster you just give that same kick to A and B at different times, a faster rate.   

       I'm not even going to try to read my long rambling answer that I'm sure makes no sense. Had an exhausting day and I'm actually typing myself to sleep. I can imagine reading it would probably give the same effect.   

       'night all.
doctorremulac3, Oct 19 2013

       //No, no increase in power necessary.//   

       //You'd get the same kick with each ball, but you just have less time to do it.//   

       That's what I meant by "more power" - the same kick has to be applied in progressively shorter times. It alse means that the acceleration will be higher (if you get the same delta-V for each interaction, but the interactions get shorter).
MaxwellBuchanan, Oct 19 2013

       I suppose we do lay roads to make it easier to travel but it still seems a bit flintstonish . In my mind all motion is about gripping the environmental medium to lever off. More knowledge is needed on the fine grain, rainy structure that is space. Hopefully there are some unique sets of interactions that can be purified into a FTL engine and humanity can open pandora's box.
wjt, Oct 19 2013

       I see what you're saying Max, but (I think) you're getting the same amount of push out of every ball without any extra energy expenditure because these are just magnets that you're switching on and off and for our purposes, they're pretty much on all the time. But I think, if I understand you correctly, you're saying when you have less time to push that ball with X amount of force you're getting less work out of it. Hmmm.   

       Well, put it this way. I don't see the "brick wall" where your set amount of energy stops accelerating you because you are unable to get the balls shot through your tube any faster. I guess you could put it this way, you're getting less time to push that ball through to get useful work from it but since that next ball is coming in faster, you're requiring equally less work from it since you're going faster.   

       And since that didn't make any sense, how about this? You're kicking that ball at point A, Z and all points in between with the exact same amount of force. This energy is going somewhere. Since you're in space, it's not getting eaten up by friction so it's all accumulating in the form of velocity, there's nowhere else for it to go.   

       You can pretty much tack on "I think" to every statement I make here.   

       The core concept behind this is that you actually do have an engine that's generating forces at the speed of light. Not saying that those forces will be able to move matter at close to the speed of light, but that's because the limitations to doing so are practical, not theoretical. At some point you'd be running into issues with those damn slow semiconductors and their sluggish switching characteristics. Not to mention the previously mentioned job of ball management. (Insert tight slacks joke here)   

       In theory, if you've got a line of ten pound balls ten million miles long and some way to keep them perfectly straight ignoring that space does actually have forces and a sort of "weather" with photons and gasses and such that would actually become a factor at these speeds, if you shoot along accelerating 20,000 miles per hour per hour with this thing in about 4 years you'd reach the speed of light. At which point you'd stop for some reason because smarter people than me have said so. Although then I'd have to ask the brainiacs like Einstein "Then where does the energy from my caterpillar drive go after that?"   

       Anyway, ok, not super likely that we'd be shooting all the Moon's iron into space just to say "Wow! Look at 'er go!", but can this idea be used practically to significantly increase the pathetic 40,000 mph top speed of our current probe launch technology? I think it might. (Maybe it's 25,000 mph without slingshotting stuff around planets, I forget) Right now we're basically using aerospace technology that's almost a thousand years old to launch our probes. It shouldn't be too hard to increase this speed, I don't know.. 100 fold?   

       Don't know how well this would work in the real world, but the job at hand is to start probing these earthlike worlds around us for habitation and getting there by lighting a can of chemicals on fire isn't going to cut it.
doctorremulac3, Oct 19 2013

       //lighting a can of chemicals on fire isn't going to cut it//   

       I was wondering; if two opposing gyroscopes or flywheels were mounted to the same framework in micro-gravity, would suddenly stopping them both simultaneously cause the entire framework to jerk in a given direction due to the opposing precession?.. and could a series of these interactions result in linear movement in a vacuum without a chemical propulsion system?   

       No hidden bootstraps in space.   

       Everything goes equal and opposite. It's maddening but there you are. I don't like these rules any more than you do but it's what we've been given.   

       It's like every time we try to cross that bridge into brave new worlds of space travel or perpetual motion the laws-of-physics-troll is there making sure you're not getting anything out that you didn't put in. Since better men than me have given up trying to fool him, I quit trying to outsmart him a long time ago. I "designed" a gyroscope drive when I was a kid. Don't really remember the design but finally realized it would just ended up spinning and jerking back and forth comically.   

       Oh yea, I remember now. Two gyroscopes slam to a stop and the energy shoots out a marble on a string that pulls the whole thing along while the reaction opposite the marble is dissapated by the whole gyroscope mechanism spinning, kept separate from the marble by a string on a pivot. So dissapate your reaction in spinning but use your opposite reaction to make the whole thing move. Don't spend too much time trying to visualize it. The troll shook his head and I decided that rather than overturning the basic laws of physics I'd take up bass guitar instead.   

       Bottom line, it's probably best to try to solve these problems with what we've got on hand McGyver style so we don't end up looking like McGruber. (see link)
doctorremulac3, Oct 19 2013

       Power: yes, that was my point, [doc]. You're delivering energy to the cannonball, and you have less time to do it in. Power is energy divided by time.   

       One final point: you do need to ensure that the cannonball is given a backward velocity relative to space, not just relative to the spacecraft.   

       If your switching circuit didn't operate fast enough (not saying it won't, but if it didn't) then you run the risk that the cannonball will actually be set moving in the same direction as speeding the ship. If that happens, you have subtracted momentum from the ship rather than adding to it.
MaxwellBuchanan, Oct 19 2013

       //you do need to ensure that the cannonball is given a backward velocity relative to space, not just relative to the spacecraft//   

       I think the way it would work is that, after a while, almost all your energy would be going into the spacecraft and the balls would be just sitting there having barely been moved. That's because I think you're right about the time/power thing since even though you're kicking these balls with the same force, you're hitting them for a progressively shorter and shorter duration.   

       But you're still kicking away from those balls and continually accumulating the forward motion from doing so. Does the duration get so short that even with the same kick it's not moving the spacecraft forward in a useful fashion? That's your question and my answer is a decidedly sheepish: Uhh... I don't think so?   

       Anyway, triggering is the easy part. Ball breaks a light beam, the magnet for that section turns on. The light beam/magnet point is always to the rear of the ball. So ball breaks light beam - interrupted light beam turns on magnet 12" behind ball to pull it - ball moves 12" till it hits second light beam - that magnet turns off, next magnet turns on and the next and so forth till it exits the ship.   

       The tube on the ship might be more of a notch at the bottom by the way so you could ease onto and off of the "rail" as necessary. Sort of like the Disneyland monorail. I know that's not the main design concern though. Sort of like pondering what color the carpet should be in a time machine, but a notch would probably be better than a hole.
doctorremulac3, Oct 19 2013

       //Another, possibly more realistic alternative// [marked-for-tagline]   

       what does straight line mean in this context? Wouldn't every object you pre-position in this manner actually immediately (even during initial "positioning flight" start orbiting around its nearest center of mass?
theircompetitor, Oct 19 2013

       You've got a little velocity on these things to keep them straightish, but yes, nothing you throw into space isn't going to be un-effected to some degree by gravity of objects around it.   

       Good news is, space is pretty big, you could probably get away with a line of these that was "straight enough". For starters you'd shoot it perpendicular to the solar system plane to keep it away from the planets. You could maneuver your ship to follow curves in the line as well as long as they were shallow enough.
doctorremulac3, Oct 19 2013

       //I think the way it would work is...//   

       Ultimately, the easiest way to model it is in terms of momentum. However much backward momentum you can apply to the cannonball, that's how much forward momentum your ship will gain.
MaxwellBuchanan, Oct 19 2013

       Well, relative movement between ball and ship is the factor here. I don't think you'd be much budging the balls later in the flight hitting them with those magnets as you are for only a microsecond, but if the ball is essentially still sitting in the same place because the ship passed over it so quickly, that doesn't mean that some forward motion wasn't transferred to the ship as it passed over. Enough to be useful once the speeds get really high? Don't know.   

       You might get more bang for your buck with the first balls, but the lack of push you get in the faster passing balls might be made up for by the fact that there's so many of them later in the flight. In other words, you might get 1% of the power from a ball in section D as you would a ball in section A, but you're hitting 100 times more balls per second in section D than in section A. And with that I'm speculating on how many angels can dance on the head of a pin since, sorry to say, the ability to preform such calculations are not within my grab bag of expertise.   

       Anybody good at computer modeling out there?
doctorremulac3, Oct 19 2013

       //but if the ball is essentially still sitting in the same place because the ship passed over it so quickly, that doesn't mean that some forward motion wasn't transferred to the ship as it passed over.//   

       If you mean that the ship leaves the ball basically as it found it (ie, with the same velocity) then no, nothing gets transferred to the ship. This would be the case, for example, if the ship just had a hollow tube down the middle, with no magnetic jiggery pokery.   

       //you might get 1% of the power from a ball in section D as you would a ball in section A, but you're hitting 100 times more balls per second in section D than in section A.// That's a valid point.
MaxwellBuchanan, Oct 19 2013


       Why are you all so hung up on the concept of Newtonian reaction drives ?   

       Conservation of momentum, blah, blah blah. How fast, even with a small ship and a very big, heavy rail, are you going to go ? Relativistic velocities ? We think not ...   

       And there's that "stopping at the other end" thing to solve, too ...   

       Proxima Centauri: 4.2 light-years. So, if your system can accelerate the vessel to 0.1 C (optimistic) then it's a mere 42 year trip.   

       Your crew are probably going to be college graduates, or have completed a period of military service. And there's all the psych and medical evaluations to do ... so, at best, they'll be at least 25 years old on launch.   

       So, on arrival, they're 67 - about ready to retire, grumpy, slightly deaf, out of touch with "today's youngsters", having bladder problems, and wondering where they left their keys.   

       Sounds like a great mission profile to us ...   

       To sum up:   

       1. Your propulsion system needs to achieve high relativistic velocities without killing the crew.   

       2. Implicit in (1), the journey time needs to be short enough that the crew are still no more than middle aged on arrival.   

       3. There has to be a way to stop the vessel when it gets where it wants to go. Running into something solid is not a good option.
8th of 7, Oct 19 2013

       Not even a little forward movement? That's the thing. If you traverse a thousand miles of these balls getting a little forward movement from each, you're going to continue to accelerate.   

       What you're saying is it would just hit a top speed, (maybe it would) and just top out like your car or any other vehicle. I'd like to know though how it can suck a thousand tons of mass through it's slot and not move any faster in the direction of the sucking.   

       And if there is a top speed, entirely possible, I'd like to know what it is.
doctorremulac3, Oct 19 2013

       8, you're talking about the coctail service on this spaceship when we don't even know if it will go any faster than a standard chemical rocket. Might not even be worth putting people on.   

       I'm thinking probe first, then take it from there. (not something you want to say on a first date)   

       Besides, our bodies are crappy for long range spaceflight. They're designed to eat/breed/die/repeat. We'll have to loose the meatbags if we expect to do something useful with our lives. At least when it comes to traveling to other star systems. Once we get there we can thaw out the reproductive machinery and get sexy again, but for long trips we need to go in something a little more sturdy. Don't know if it will be pod shaped or more of a cube, but it won't complain about aching joints and hair loss.
doctorremulac3, Oct 19 2013

       Force = mass x acceleration.   

       There is no velocity term. The initial velocity of either object is irrelevant*. What matters is the force applied.   

       * As are "freedom" and "self-determination". You will be assimilated. We will add your technological and biological distinctiveness to our own. You must comply. Lower your shields and prepare to be boarded. Resistance is futile.
8th of 7, Oct 19 2013

       //Not even a little forward movement? That's the thing. If you traverse a thousand miles of these balls getting a little forward movement from each, you're going to continue to accelerate.//   

       No, that's not what I meant. What I said was that if you do *nothing* to the ball as you pass over it (responding to your //if the ball is essentially still sitting in the same place because the ship passed over it so quickly//), then you do nothing to the ship's velocity. But perhaps by "essentially" you meant "almost"?   

       If you can push the ball backward as the ship passes over it then, yes, the ship will gain some forward speed.   

       //Why are you all so hung up on the concept of Newtonian reaction drives ? // I seem to recall a certain member of a hegemonizing smarm expending considerable efforts on extolling the advantages of an improved canal boat propulsion system.
MaxwellBuchanan, Oct 19 2013

       Ok smarty pants, (talking to 8)   

       Does this thing have a speed limit? Will it move at all? Max thinks it has a speed limit while I'm almost positive it either will or won't although I can't say for sure.   

       And didn't the Star Trek guys regularly kick the Borg's collective butt? Don't know not being a fan of the next generation stuff.
doctorremulac3, Oct 19 2013

       //But perhaps by "essentially" you meant "almost"//   

       (As I move uncomfortably in my chair, nod my head and try to appear not at all totally confused.)
doctorremulac3, Oct 19 2013

       //Max thinks it has a speed limit//   

       Not necessarily. We're looking at two potential problems here:   

       (1) The faster the ship is moving, the less time it can interact with any one ball, and therefore the less acceleration it can get. For example, if it passes a ball in a microsecond, then even if it could interact sufficiently to accelerate the ship by 1m/s, this would be a momentary acceleration of 100,000G. However, as [doc] pointed out, a faster-moving ship can encounter more balls per second, and therefore get useful acceleration in many small packets.   

       (2) The balls must always be pushed backwards relative to free space. In a simplistic case, suppose each ball is captured by a grabber at the front of the ship; and the grabber then zips backwards along the ship before releasing the ball. If the grabber cannot move backwards (relative to the ship) faster than the ship is moving forwards, then in fact the ball will be given a forward velocity (relative to free space) and the ship will be slowed down. With a magnetic drive, you might be able to do this - I don't know enough about magnetics.
MaxwellBuchanan, Oct 19 2013

       Well, I'm at the limit of my ability to evaluate this further without adult supervision.   

       Maybe I'll do that weird thing where I write college professors and ask them questions about obscure science stuff. The weirder thing is that they usually write back. NASA's not busy, maybe I'll give them a call. They're actually right there in the next town, maybe I'll just drop by.
doctorremulac3, Oct 19 2013

       I do that too. Every time I've written to a professor (usually opening with 'I am a fiction writer doing research for my next story') I've gotten a positive response.
Alterother, Oct 19 2013

       I use the "I'm a hot blond co-ed who loves balding professor types who can answer this question:..." line.
doctorremulac3, Oct 19 2013

       //I use the "I'm a hot blond co-ed who loves balding professor types who can answer this question:..." line.//   

       So, since bald heterosexual female professors are extremely rare, you seem to be restricting yourself to bald gay male ones.
MaxwellBuchanan, Oct 19 2013

       Hey, if they know the answer I don't judge.
doctorremulac3, Oct 19 2013

       //No hidden bootstraps in space.// Yet to be discovered or told about, is always hidden.   

       Aside. Is a charged weight heavier than an uncharged one? I always imagined a spaceship to have self laying tracks of some description.
wjt, Oct 20 2013

       I guess a negatively charged weight would be heavier by the small mass of the excess electrons.
MaxwellBuchanan, Oct 20 2013

       Ok, I think I got it without having to stalk any professors.   

       There's X amount of iron being pulled on by Y amount of magnetic force for Z amount of time. It doesn't change.   

       The only difference as velocity (and ball frequency) increases is that X amount of iron under Y amount of magnetic force, (per minute let's say) might be made up of 100 balls, then 1,000 balls, then a million balls, but X amount of iron per minute is always being pulled on by the magnets.   

       In other words, that first ball weighs ten pounds. It's under magnetic pull for, call it a hundreth of a second.   

       That last ball is also ten (cumulative) pounds under magnetic pull for that same hundreth of a second. The only difference is that last ball is made up of a million balls stretching over 10,000 miles.   

       Unless I'm missing something, I think that's what's going on here.   

       If that IS the case, then your limitation is the speed of your switches.   

       Now I can go watch football without being distracted.
doctorremulac3, Oct 20 2013

       I think that's a good thought experiment.
MaxwellBuchanan, Oct 20 2013

       If there was a long metal wire rope, the space craft could follow that, and then use it to slow down as well. However, someone else can lay the rope in advance, 'cos I'm a bit busy right now.
Ling, Oct 20 2013

       A nifty way to do this would be to use knowledge of the orbital paths and alignment of various space objects, then use pre-existing masses as your cannonballs. Some of them are big, which is nice as regards mass to push against but troublesome as regards getting your rocket around them. So maybe all of the rails in space should be used to make a big hoop for the ship. The hoop could be tightened or relaxed to accomodate the size of the next object en route. Hotshot pilots would make the loops as close fitting to the obhject as possible, to maximize the propulsive force thus obtained. Every now then then they would catch the loop on the object, and so these "loose hoop" pilots would have the hoops barely attached to the ship as they approached, but then grab them harder as the hoop engaged and began to deliver propulsion. Every now and then the hoop would not be grabbed firmly in time and would break free and shoot off by itself, leaving the rocket adrift.   

       In the scifi in which this concept appears, a hotshot loose hoop pilot would use other space ships as propulsion - approaching freighters and competitor ships from behind and leapfrogging around and past them, while disrupting all electronics going on within.
bungston, Oct 21 2013

       Funny that you should mention scifi application because that's exactly what I was thinking could be the next step for this. Lots of real science gets it's start as entertainment. The countdown first appeared in Fritz Lang's "Woman On The Moon" in 1939. (see link)   

       I'm not sure of the real world application of this launch method but it's absolutely ready to take it's place in Hollywood superstardom alongside greats like balloon aero-breaking in 2010 (the 2001 sequel) and the Nutrimatic beverage dispenser in Hitchhiker's Guide.   

       Hard science? Maybe. Hard science fiction? Absolutely. I'm getting a little sick of wormhole travel premises written by the same people who think space travel should include a holo-deck so you can pretend to be going places more interesting than boring old new planets while Woopie Goldberg mind melds with you to see if you're suffering from un-groovy space vibes.   

       I declare myself official manager of Hollywood superstar to be: The Space Rail. "Bubula, who loves ya? Don't worry, I'm telling those fat cats you don't roll out of bed for less than a hundred gs. That transporter from Star Trek that gets all the big roles? Over rated smoke and mirrors baby. You're the real thing."   

       The chance of me making any money off of this? Those numbers are what we call "In the noise".
doctorremulac3, Oct 21 2013

       //Proxima Centauri: 4.2 light-years. So, if your system can accelerate the vessel to 0.1 C (optimistic) then it's a mere 42 year trip. //   

       Assuming linearity, it would actually have to accelerate it to a peak of 0.2 C before starting deceleration, so that the average speed of the trip was 0.1 C.
the porpoise, Oct 21 2013

       Stopping is another problem though. Onboard nuke pellets maybe?   

       But as the song says: "Vunce ze rockets are up, who cares ver zey come down? Zat's not my department." Says Wernher Von Braun.   

       V2 jokes: Too soon?
doctorremulac3, Oct 21 2013

       It occured to me that you might get a similar effect using a particle accelerator to fire a continuous stream of relativistic-speed particles at the spacecraft. Something like the PSI Ring cyclotron that can generate a beam power of 1.3MW with protons traveling at 0.8c seems like it would be useful for a small craft. It turns out that this variation is already proposed as a system called MagBeam [link]. The Wiki article mentions having the particle accelerator in earth orbit, but taking the cue from this idea and putting it on the moon seems like a better idea to me. On the moon you don't need to worry about disturbing the orbit of the particle accelerator when is fires, and there's plenty of area to deploy a large solar array to power it.
scad mientist, Oct 21 2013

       I was thinking of methods to slow down that involved spinning around and around the inside of your portable giant metal hoop, or pushing off against it. None of that kind of deceleration will be worth much at space travel speeds.   

       So maybe slow down the same way you sped up? One can use the hoop in reverse! Brake by flying thru a nebula and accelerating gas and other encountered matter forward thru the hoop. Of course a fast ship will not really accelerate the matter encountered, just magnetically transfer some kinetic energy of the ship to the gas. Nebulas are big. You will have lots of space to slow down.   

       Hopefully where you are going is on the other side of a nebula. Close to the other side. That sounds like scifi too - a space base sites to take advantage of a big nebula interposed between the base and earth. "It was the only place the ships could reliably come to a stop, and so that is where they did."
bungston, Oct 21 2013

       Instead of just plain old Mass out there to be harvested by your spaceship, wouldn't it be more reasonable to fling fuel? Some sort of capacitors which could be quickly harvested before rapid excretion out the back?
AusCan531, Oct 21 2013

       brilliant idea.
ixnaum, Oct 22 2013

       //wouldn't it be more reasonable to fling fuel?//   

       My first idea was to throw out a row of nuclear bombs and then sort of "surf" them as they went off. That got an immediate "Naaa" since if you have a million nuclear bombs you might as well just throw them out the back Orion spaceship style and eliminate the problem of lining them up. Then I thought of conventional explosives but that wouldn't work because at some point the explosions would be too slow to be of any use.   

       The problem with laying out fuel is you don't have any time to catch it at those speeds. You'd get slowed down every time you slammed into the first fuel containers, pellets or whatever and destroyed by them as you got going faster.   

       My first passive fuel idea was to just shoot out lunar regolith which is something like 10 or 15% iron but it seemed unlikely that you'd be able to keep a stream of dust contained. At the speeds being attempted dust particles become micro bullets that would shred your spacecraft if even a few floated outside the column. So it seems like the most plentiful reaction mass that's handy is the iron on the Moon, and this is the best way to use it.   

       I do like the idea of connecting them though so they can be re-used. As discussed earlier, connecting them allows you to keep them in line easier, straighten them out and even change the direction you're sending your probes. The ability to add onto it incrementally doesn't hurt either.   

       At tens or hundreds of thousands of miles long it would be the largest man-made object ever which would have the added benefit of being totally awesome, total awesomeness being something we don't shoot for enough in modern society in my opinion.   

       I think you could park it at the L5 or equivalent point and get to it with the smaller Earth ring space rail. Use this for your real high speed stuff and use the much smaller Earth ring space rail and matching Mars ring space rail to get back and forth between those two planets while you're developing Mars. Or "New Earth" as I think it should be called. The matching rail rings would be used to both "throw" and "catch" spacecraft.   

       As an aside, a very small Moon rail could be built without even having to orbit it since there's virtually no atmosphere on the moon. You just put these iron balls on sticks and line them up around the Moon. Aim it at Mars I guess. You could make 1 shot a month for supplies or whatever. Seems like less of a hassle to just skip the moon though and build the Earth Rail.
doctorremulac3, Oct 22 2013

       ^ I disagree. I'm totally awesome.
AusCan531, Oct 22 2013

       That's the right attitude Aus! Awesomeness starts with the self.   

       If we're going to colonize any planets the first step is to up our collective awesomeness levels. I try to do my part every day.   

       Mars will not be colonized by pussies.
doctorremulac3, Oct 22 2013

       //Mars will not be colonized by pussies.//   

       Oh. That's a bit of a disincentive then. MARS NEEDS WOMEN!
AusCan531, Oct 23 2013

       Yea it does.   

       Question: How much power can I get to a 100 square foot solar panel in space from a Moon based laser? What I'm obviously getting at is, if you could dump the onboard nuke you could start thinking about a space probe that's just a few pounds burning through tens of thousands of tons of reaction mass.   

       I see no reason why this wouldn't be the fastest manmade object by several orders of magnitude over flying chemical tanks. I'd be very surprised if you couldn't, with real world practicality, hit a million miles per hour plus with this.
doctorremulac3, Oct 23 2013

       //The balls must always be pushed backwards relative to free space.// ([MaxwellBuchanan])   

       What is this //relative to free space// of which you speak? There is no absolute inertial reference frame. All that matters is the change in the ball's momentum, from before to after the ship's interaction with it, since the ship's momentum changes by the same amount (with opposite sign).   

       So if the ball is moving at 1,000 m/s relative to some arbitrary point (such as the sun, or the moon, or the destination) in the same direction as the ship's motion, and the ship leaves it moving at 999 m/s, the ship is still accellerated in the desired direction. If I wish to increase my canoe's speed while moving downstream, I only have to push some water back relative to the current, not relative to some external reference frame (such as the bank).
spidermother, Oct 24 2013

       Because it is so important to have them in a row, they should be ducks.
pertinax, Mar 11 2016


       " (God, I hope somebody doesn't check my math) "
normzone, Mar 11 2016

       Re: Replace iron pellets with a fuel rod post.   

       I tried to watch the video but the music made me want to blow my brains out. I turned the soundtrack off but was still so agitated and cranky due to this sonic horror that I was subjected to that I now hate the inventor and his stupid idea.   

       Whatever it may be.   

       (notexactly, I'm just kidding if that's your invention. If it's not, the previous comment still applies.)
doctorremulac3, Mar 21 2016

       It's not mine, but I think it's a neat idea. I didn't remember the music being annoying—I watched it long ago and didn't rewatch it when I added the link.
notexactly, Mar 30 2016


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