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# Circular Spaceship Accelerator

Basically, the mother of all merry-go-rounds...
 (+3, -2) [vote for, against]

Astrophysics is not my core interest, so I hadn't given space travel much thought. But Larry Niven's book "Lucifer's Hammer" and the interesting discussion on [pmboy200]'s "Electron Propulsion Engine" stimulated me to ponder this matter.

The key problem, it seems, is how to get mind-boggling amounts of sustained accelaration with a finite amount of fuel. The larger the fuel tank, the heavier the spacecraft, which in turn requires a larger fuel tank, etc.

Therefore, the solution is to allow unlimited refueling, by having the spacecraft stay essentially stationary, and accelerate while in the proximity of the Earth (where it can easily be supplied with fuel). Instead of going straight out to space and accelerating en route, the spaceship will swing around in a circle. I envisage a setup which looks similar to those devices designed to torture fighter pilots with high G's. When the spaceship reaches the desired speed (I should think somewhere in the vicinity of the speed of light) it is released and sails towards its destination.

All this would be happening somewhere in space, not too far from the Earth, but also not too close (because if something travelling in a circle at 250,000 km/h is realeased 0.001s too late, it's going to go in the opposite direction and plow into the Pacific).

You have an axis, an arm attached to the axis by frictionless means (using maglev technology?), and the spaceship, attached to the arm by means of a release mechanism. Since there is near-zero drag on the spaceship, something near the speed of light can be achieved (in theory). The whole thing is rather big, perhaps as big as the particle accelerators down on Earth. There is a fairly large mass attached to the axis -- perhaps an asteroid -- to prevent the spaceship from flying off with the arm attached. Conventional rockets mounted on the spacecraft burn fuel, which is ferried up from Earth, or perhaps even manufactured in space.

It might be an idea to first just have the spaceship accelerate to high speeds and see if it is true that time passes slower when you're moving (really *really* fast).

 — Dr Furtz, Jun 19 2001

G info! http://www.hq.nasa....onghand/fig15d5.gif
This may be helpful... [my-nep, Oct 06 2004]

[Klaatu, Oct 06 2004]

Launch RIng http://www.newscien...com/article/dn10180
Circular railgun [BunsenHoneydew, Oct 04 2006]

Spin Launch https://techcrunch....8/02/22/spinlaunch/
[theircompetitor, Feb 22 2018]

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Annotation:

 The problem is that acc_n is a change in velocity which is in a specific direction. If you if you are in orbit you are always accelerating as you have to keep changing direction to move in a curve. I may not of explained it very well though... someone else may have to clarify it.

I realy like the idea though.
 — RobertKidney, Jun 19 2001

You know how you get mashed to the side of your car when ever you take a tight turn at high speed? Make the turn a thousand times wider, but make your speed a hundred-thousand times higher. If your seat were made of bread and your clothes made of peanut butter, you'd make a nice sandwich.
 — centauri, Jun 19 2001

Disclaimer: Physics is not my strong suit. Having said that, is it correct to say that bodies in orbit need constant acceleration and route correction to remain that way? Why does this not apply to the moon, which does not appear to be powered at all?
 — snarfyguy, Jun 19 2001

 [PeterSealy] is right. With linear acceleration your body has a chance to 'catch up' with the vehicle if under (relatively) low acceleration. With the orbital acceleration being discussed your body will have greater and greater centripetal forces working on it making you heavier and heavier until you're just a grease stain in the cabin.

I haven't a clue as to the math, but I wonder if this would be worth pusuing for unmanned spacecraft?
 — phoenix, Jun 19 2001

[snarfyguy], the moon is moving away from the earth, but the reasons for it are more complicated than just that it needs to fire its booster rockets. The moon is slowing down the earth with the tides' friction; we're losing about 1 1/2 milliseconds per century, and the moon moves a little less than 1 1/2 inches per year further away.
 — jutta, Jun 19 2001

 snarfyguy, the moon does have constant acceleration, keeping it in orbit. The earth's gravity provides this acceleration, just as it does for anything else in orbit. The space station, for instance, needs to be boosted in its orbit from time to time, because collisions with the superthin atmosphere up there continuously slow it down. As jutta pointed out, the moon has the opposite situation, as it is moving away.

In short, centripetal acceleration, be it tension on a line, friction on a road, gravity, or rockets, are required for objects to maintain a circular trajectory.
 — centauri, Jun 19 2001

The strength of the arm will be a key limiting factor. Remember, this thing is going in a circle, which means that on any given axis it will be accelerating from stop to full speed and back to stop again in half an orbit. If you can build a tether or arm capable of withstanding that much force in the first place, you can probably avoid the lengthy acceleration process, and just build a big space catapult.
 — egnor, Jun 19 2001

[centauri] & [phoenix] I see. So this would be for unmanned probes. [egnor] I'd think a catapult would mash the contents instantly with a whole load of G's. But -- as centauri hints -- I'd think the centrifugal force could be easily beaten, by aiming the rockets not straight ahead but at an angle towards the axis, so that in effect you have one force pushing you forward and one force pushing the spacecraft back into the circle.
 — Dr Furtz, Jun 19 2001

 I see the nearest existing representation of this idea to be the behavior of a ball on the roulette wheel. I don't think it could be done reliably with rockets.

Manned exploration of deep space requires a human to survive a sustained linear acceleration for an extended time. Is it possible to redirect movement from one angle to another instantly and gently? The challenge is to move an occupied vehicle linearly by the torque of a circular accelerator. The vehicle must match closely the outer rim speed of its attending circular driver without any interference that would tend to produce turbulence (>15G) or short bursts of acceleration (3G) that exceed a human's known endurance.
 — reensure, Jun 20 2001

Dr Furtz: I think egnor's point was that you will still have a similar amount of force mashing the ship whether it's going linearly all at once, or spread out around in a circle. Angling the rockets will probably just make it take longer to acheive full speed, but once you're there, there's still the same acceleration and deceleration that egnor spoke of.
 — PotatoStew, Jun 20 2001

Okay, dredging up my high school physics: if my math is correct, to go 250,000 km/h in an orbit with a 1000 m long arm requires a centripetal acceleration of 4.8*10^6 m/s^2, or roughly 500,000 times the acceleration due to gravity on the Earth's surface. Even if you could build an arm that wouldn't snap under that kind of tension, anything in the ship is doing to have to deal with those 500,000 G's.
 — bookworm, Jun 20 2001

bookworm's nailed it most succinctly. Think centrifuge on steroids. It's easy to build an earthbound centrifuge strong enough to seperate blood cells and plasma, and the machine under consideration is lotsa mucho mucho more powerful.
 — Dog Ed, Jun 20 2001

[mfd] Since I see now that this idea cannot be realistically baked, I will be deleting it shortly. Thanks to all you boffins who supplied feedback and calculations. It was a most interesting exercise, and I look forward to challenging you all with a better space travel mechanism in future.
 — Dr Furtz, Jun 20 2001

 [Dr.] While I'm relatively new here, I don't believe an idea has to be bakable to be good. This is a perfect example of a half-baked idea, raises some interesting points and made me think about something I probably wouldn't have otherwise.

Keep up the good work!
 — phoenix, Jun 20 2001

 > as centauri hints

Eh? I really hope I didn't hint that you could maintain a circular trajectory at a certain speed and not feel the full amount of inertial (or centifugal) force pasting you to the inner hull.
 — centauri, Jun 20 2001

Why don't you just speed the ship up and *then* get on, it the same way as if you step from a falling plane just before it hits the ground you will will survive with minor injuries.
 — CasaLoco, Jun 20 2001

[CasaLoco] LMAO! Tell you what CL, you go first...
 — phoenix, Jun 20 2001

Have you considered the exponential increase in mass as you approach the speed of light? I think a quick check of relativity would prevent this particular scenario from working. Even if you kick out the "arm" theory and go back to the Mag-Lev in a tube, the power required to keep the ship from running through a wall would be astronomical.
 — Reverend D, Jun 20 2001

Just like my mother told me when I started skydiving: "don't worry if your parachute doesn't open, just remember to jump up just before you hit the ground". Try and step onto the already fast-moving ship after it's been accelerated? Try to step onto the front bumper of a semi truck at highway speed. Now imagine trying to do essentially the same thing with a ship moving and many thousands of times that speed. Somehow, I don't think that would feel too good.
 — Freefall, May 21 2002

Well if u know the force that the walls can cope with then just make that the max velicity and release at that point, and use the onboard fule to accel from there on out (asumming dule acceleration is being used)
 — LittleBigIdeas, Aug 30 2002

Related to the difficulty of acceleration at near-light speeds, remember that the propellant will increase in mass as well as the spacecraft, and provide more thrust in exactly the same proportion as the mass increase of the spacecraft. So essentially, for the purposes of calculating acceleration, Special Relativity can be ignored. <edit>(for mass-based acceleration systems like ion propulasion and all rockets. Mag-lev to lightspeed is ludicrous IMHO.)</edit>
 — dunwitch, Feb 10 2003

 The propellant increasing in mass would not be a problem if the speed were attained by solar propulsion.

As to instantaneous acceleration; what if the capsule were filled with oxygenated water like some deep sea diving suits? Breathable, (once you get over the terror of breathing water), and since the occupants would be suspended in a liquid, no splat.
 — 2 fries shy of a happy meal, Feb 11 2003

 Forget about relativity, and acceleration and tension on the line, there's a simpler reason this is not practical.

So first, we need an asteriod. Nothing could be simpler, there are asteriods in the belt, right? We go out and expend the energy required to move an asteriod mass into earth orbit. (Nothing you couldn't do if you had 10 years and 30 million pounds of H and LOX out in the asteroid belt (the energy required to move 30 million pounds of anything out to the asteroid belt is an exercise left to the reader)) So now that we've got our asteriod in earth orbit, let's use it to slingshot something into deep space. Think back to high school physics, the part about every action having an equal and opposite reaction. Oops... when the spaceship went one way, the asteriod went the other. Well, let's just go get some more rocket fuel to put the asteriod back into earth orbit. See where I'm going here? Even if you don't take into consideration that any space drive that lets you move around asteriods at will obsoletes the slingshot drive, you're still using twice the fuel to move the asteriod back into position every time you use it.
 — netmanakre, Jul 16 2003

I wrote a story once that had a conveyor-belt around the Moon's equator as a launching device.
 — Mogo, Aug 18 2003

The roulette wheel analogy got me thinking. Suppose you took a tube (say, one lined with a linear accelerator) and spun it on its center of gravity, as if it were a propellor. You leave a hole in the middle, and drop/slide/kick your cargo inside. It goes flying out one end, hopefully up and in the right direction. The rpms give it an added boot. nb I suspect if you could dispense with the need for even a fraction (maybe a large fraction, but a fraction) of the weight with a catapult you could more easily build a single-stage-to-orbit rocket. Also by waiting until you were "spun up" to add the cargo pod you would avoid the need to figure out a strong release mechanism. Still, you'd pull ya some Gs there, on your way out the window, you bet.
 — cloudface, Sep 10 2003

I feel that I should comment - fore short times, high Gs are acceptable hear is a old chart. <link>
 — my-nep, Jan 02 2004

Hey, NO FUEL TANK. Use MagLev concepts! You will be able to go at the fastest possible speed for the craft's mass.
 — empty89, Jan 08 2004

just seen a television program (discovery) about floating magnetic train. A sience dude said that in vacum its no end how fast a train like that can go. its a very good idea, if u ask me :) build a track in circle, and accelerate the space ship / satelite up to speed and the realese it. A track in orbit, can also be used for all future missions. Am not thinking of light speed and speed up to that. If am not wrong i think all spaceships that enter orbit have a speed on about 24-27 000 km/h. Use the track to speed it up to 60-70 000 +. A good kick off. sorry my english.. NASA wake up, try this :o)
 — gimbo, Jan 10 2004

well...this circularaccelerationdevice...is something i also have processed in my mind.. the best way to get a good interplanetary infrastructure, i think is to build a maglev around the moons ekvator. there are all energy you can wish for, solarpanels beside the maglev all the way around. you could "throw" whole trainsets wherever you want hehe. of course the moon will move slightly in the opposite direction to your payload...but it will even up in the end when you throw stuff in different directions...and btw, the moon is allready moving out from earth. what i dont have the skills to figure out is what the Gforce will be when you travell in very fast around the moon. the moons gravity, and the very big circle your turning, will get down the Gforces somewhat... so hey mathfreaks;) how fast can we go around tha moon with passengers?
 — psychoticus, Mar 26 2004

 If the vehicle considered were in orbit, despite the fact that it is going in circles, anyone inside would be gravitationally attracted to the bottom, not flung out to the side. Imagine a fusion ramjet orbiting the sun, scooping up hydrogen into a fusion reaction and flinging the helium out the back. As speed increases, the rocket would either need to move closer to the sun and/or fire an upward facing rocket to stay in orbit. It seems to me that centrifugal force would not be an issue to occupants - athough you would need some radiation shielding. Eventually the outward facing counterrocket would be firing as much or more as your propulsion rocket. When you are whipping around the sun at high speed - turn off your counterrocket and away you go.

 As I think about it, the thing to do is orbit a gas giant, not a star. Then just orbit lower and lower as your speed increases. Heat is less of a problem.

The nice thing about this system is that you can do the same thing to come home, if you can find a suitable star at your destination.
 — bungston, Mar 28 2004

 netmanakre: We can solve the equal and opposite effect on our asteroid base by pivoting an arm with two ends and launching a sacrificial mass from the end not used by our payload. Picture a discus thrower with a disc in each hand instead of in only one hand. Releasing simultaneously, he throws one downrange in the direction he really wants, and one behind him into a wall of dirt or haybales. Obviously we will have to orient the device so that the sacrificial mass goes somewhere harmless.

 Come to think of it, since this proccess would be a good way to launch interstellar probes, we could pick two stars in opposite directions and launch two probes at once, without any waste mass.

Gotta give a +, since I was trying to articlulate this exact idea. (Glad I searched before posting!!)
 — gardnertoo, Jun 27 2004

 This is nearly baked.

Moment exchange tether, which can fling payloads into a higher or lower orbit. It's not quite as spectacular as an interplanetary sling, but if you look at the rest of their website, you'll see that they have ideas for those, too.
 — arglebargle, Jun 28 2004

 Some really rich (marked-for-tagline) ore in the first few annos.

 " I may not of explained it very well though... someone else may have to clarify it "

" Physics is not my strong suit. Having said that ... "
 — normzone, Feb 22 2018

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