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# Mutually-Repulsing Rockets

Make objects push against each other to opposite directions, and avoid the tyranny of the rocket equation.
 (+3) [vote for, against]

Traditional rockets work by expelling mass at high velocity, which is scattered into space. What if we could avoid scattering?

To avoid the scattering, take two non-overlapping beams of collimated particles or light that shines into black-box-like setup inside another of them, and use the collected energy to power the collimated particles projector back to the source.

The idea is that the process set up this way would accumulate the intensity of particle beam as we add more energy, in a way similar to how would how wave interference creates increasingly stronger standing waves between two surfaces, creating increasing pressure as we do not let the energy scatter.

This would mean that the rocket pair would avoid having to be subject to the tyranny of the rocket equation.

 — Mindey, Dec 25 2019

Unwinese https://en.wikipedi...(comedian)#Unwinese
Englyness speakyfied in bestwell comprhedibode - deep joy ! [8th of 7, Dec 27 2019]

solar system engine https://futurism.co...e-move-solar-system
[theircompetitor, Dec 31 2019]



 Well, at least you haven't proposed a reactionless drive, or posted it in Other:General.

 Apart from that ...

 Well, the "rocket equation" is not one equation but many. We refer you to the work of Newton and Tsilkovsky.

 Maintaining a collimated particle beam inside a vacuum chamber is challenging enough; achieving it over even modest distances (for example, between your planet and its moon) is not possible. There is an innate tendency for the beam to diverge.

 For the particles to transfer substantial momentum, they need to be traveling at a substantial fraction of C. Applying the equation F=BeV, if there is any magnetic field (either from your planet itself, or its primary) which the beam cuts, then the components will be subject to a force according to what you call Fleming's Rule. Since the population will not be monoenergetic, and the force varies with velocity, scattering will inevitably occur.

 If the particles are neutral - e.g. complete, unionized hydrogen atoms - then there will be less scattering, although the dipole moment due to the proton-electron doublet will generate a reaction. However, there will still be the tendency for simple diffusion - i.e. the gas molecules will, despite their velocity, bugger off in all sorts of random directions long before they reach your "catcher's mitt".

We will not bone this for "Bad Bhysics" (altho we are sure others will), but merely criticise it for "Poor and inadequate understanding of Physics" which is unfortunately not an actual crime (yet).
 — 8th of 7, Dec 25 2019

//unionized hydrogen atoms// They're the worst sort. Always striking for pay and conditions.
 — MaxwellBuchanan, Dec 25 2019

 ... longer holidays, health care plan, sick pay ...

Ungrateful, we call it.
 — 8th of 7, Dec 25 2019

 // Maintaining a collimated particle beam inside a vacuum chamber is challenging enough; achieving it over even modest distances (for example, between your planet and its moon) is not possible. There is an innate tendency for the beam to diverge.

 That's super difficult for sure, especially with electrically charged particles. However, we had been getting increasingly better at precision, so, it doesn't mean we can't gradually increase the distance, with iterative improvements, like we did in transistor technology.

 The principle of building pressure between objects by increasing the amount of temperature trapped between them also may hold for set-ups without collimated particles, such as long tubes in outer space for simultaneous releases of rockets to opposite directions by reusing each other's push that does not scatter for a few initial kilometers, or even getting extra kick from fuel burned at the center of the tube. Such kind of descattering is known to work pretty well in gun barrels.

 // //unionized hydrogen atoms// They're the worst sort. Always striking for pay and conditions.

The scattered ones are worse, they contribute more to the heat death of the universe.
 — Mindey, Dec 25 2019

(+) 'cause stuff wuz learned.
 — 2 fries shy of a happy meal, Dec 25 2019

What [2fries] said.
 — Voice, Dec 25 2019

 // it doesn't mean we can't gradually increase the distance, with iterative improvements, like we did in transistor technology. //

 That's precisely what it does mean, because the improvements in semiconductor technology were achieved by making devices smaller and thinner - so that quantum effects predominate. You're trying to do something where the path length is near-infinite compared with the particle size and wavelength. Quantum behaviours don't scale to macroscopic applications.

 You would need a region of "ideal" vacuum - one free from electrostatic, magnetic, and gravitational fields, and where the mean free path for gas molecules is close to the separation between the two parts of your system. Some portions of intergalactic space come close to this. Then you need the ability to emit particles, or gas molecules, with monoenergicity approaching the Planck limit. For that, you need an Interocitor with Electron Sorter. They're expensive, and quite bulky and heavy, plus the lead time is very long and even then you have to assemble it yourself from a kit,

Good luck.
 — 8th of 7, Dec 25 2019

 // You're trying to do something where the path length is near-infinite compared with the particle size and wavelength. Quantum behaviours don't scale to macroscopic applications.

 With increase of distance that is increasingly true, and even more, we'll find quantum randomness effects large when magnified by distance, but at least to certain distances it may be possible, while things like warp drive require exotic matter, and are therefore not yet possible for any distances.

 // an Interocitor with Electron Sorter. They're expensive, and quite bulky and heavy, plus the lead time is very long and even then you have to assemble it yourself from a kit,

So, not getting an engine to depart to M31 on this 2020 eve just yet?
 — Mindey, Dec 25 2019

 No, we've been invited over to [MB]'s place for drinks, dinner and the traditional Buchanan New Year's Eve party games, including Snail Jousting, Cripple Mr. Onion, Mornington Crescent (Sturton cheats, you know) and the hilarious yet inevitably tragic Blindfold Rattlesnake Catching.

Rather than subatomic particles, or gas, you'd be better doing this with dense, inelastic, non-magnetic projectiles - literaly, billard balls, or bowling balls. They would transfer momentum without significant energy loss because of a relatively high coefficient of restitution, then could be captured and returned using a captive-piston pusher, akin to a steam catapult. But you'll still struggle with accuracy even at moderate ranges, despite being in vacuum and free-fall.
 — 8th of 7, Dec 25 2019

I can see day when chocolate factories will achieve making Mars bars, almost infinitely smaller and thinner, their technology will adopted by a grateful semiconductor industry etc
 — not_morrison_rm, Dec 26 2019

 "VLSI: the only field of human endeavour in which 'shrinkflation' is seen as a good thing ..."

Is there a version of Moore's Law for confectionary ?
 — 8th of 7, Dec 26 2019

 If the aim is for as efficient a rocket as possible, then surely the answer is to eject the reaction mass only at the same speed as the rocket is already going? i.e. if the rocket is going at 100mph, you eject your mass backward at 100mph, so that it ends up static relative to (hmmm - something). If the rocket is going at 1000mph, you eject the mass at 1000mph, again leaving the ejected mass stationary.

 In this way, the ejected mass is always stationary and hence has no kinetic energy, meaning that all the work has been transferred to the rocket.

The only problem is when the rocket is initially stationary.
 — MaxwellBuchanan, Dec 27 2019

It's not actually the only problem, but it is certainly a significant one.
 — 8th of 7, Dec 27 2019

//if the rocket is going at 100mph, you eject your mass backward at 100mph//
That only works if the ejected mass has the same mass as your rocket. If your ejected mass is smaller, it must go faster to conserve momentum. I suppose a sequentially-bifurcating rocket COULD work...

 // If your ejected mass is smaller, it must go faster to conserve momentum.//

I don't think that's true. If the rocket (weighing say 10000kg) is moving at 100mph, it will still require an effort (force) to throw a 1kg mass out of the back at 100mph relative to the rocket (ie, leaving the mass stationary), and that force has to go somewhere.
 — MaxwellBuchanan, Dec 27 2019

 Your units are inconsistent; 100 mph is 44.7 m/s.

 Applying the Law of Conservation of Momentum, it is possible to calculate the increase in velocity of the vehicle. Now, who is going to favour the class with an answer ?

<Looks round to see who has hand up/>
 — 8th of 7, Dec 27 2019

Is it "22.8°C"?
 — MaxwellBuchanan, Dec 27 2019

 No.

 What have we told you about listening to that stupid brother of yours ? No, which one is irrelevant - they're as bad as one another.

Try again.
 — 8th of 7, Dec 27 2019

3.6, for some Unit.
 — MaxwellBuchanan, Dec 27 2019

Nice, a vertical kilometre expulsion trail from the escape engine's, launch pad embedded, other half. Double the launch celebration.
 — wjt, Dec 27 2019

//a vertical kilometre expulsion trail from the escape engine's, launch pad embedded, other half.// So reminiscent of English, and yet...
 — MaxwellBuchanan, Dec 27 2019

... more like Unwinese ...
 — 8th of 7, Dec 27 2019

If everyone had perfect grammar, it would hide clues to their logic processes. It would only be down to what words were used.
 — wjt, Dec 29 2019

We were introduced to [MB]'s grammer last year, and though she's far from perfect, she seems a lot more likeable than many of his other relatives. Grampa Buchanan does seem to have some singularly repulsive personal habits...
 — 8th of 7, Dec 29 2019

The particles could be any material. I propose launching a stream of croissants at the ship via an orbital mass driver and bakery. The croissants would be inedible (i.e. not fresh or warm) due to vacuum freezing and radiation burn, so the ship would use its own onboard mass driver to return them to the bakery for replacement. To avoid croissng the streams, perhaps the buns should be launched in bursts, i.e. at "local breakfast time" which is of course many hours different between the ship and orbital bakery.
 — sninctown, Dec 30 2019

Being a boomerang-like shape the croissants are going to have an interesting, if not complex, trajectory along the repulsing path.
 — wjt, Dec 31 2019

No, because they are in vacuum - the shape is therefore irrelevant. A boomerang needs air to operate.
 — 8th of 7, Dec 31 2019

There is no such thing as a perfect vacuum, though. So boomerangs will still curve, but on a much, much larger scale of distance.
 — MaxwellBuchanan, Dec 31 2019

 // no such thing as a perfect vacuum, //

A close inspection of the 2019 Christmas TV schedules will soon disabuse you of that misconception.
 — 8th of 7, Dec 31 2019

Charge distribution, mass density, reflective surface, there are quite a few dimensions forces can act on. Shape does matter.
 — wjt, Dec 31 2019

You could have a sensible person, and a bot that trawls the HB archive at regular intervals and broadcasts the idea and annos. The sensible person would be repulsed by the stream of idiotic information, and would soon accelerate to super-relativistic velocities in every direction.
 — pocmloc, Jan 02 2020

 // a sensible person //

Sp. "Unobtanium" ...
 — 8th of 7, Jan 02 2020

Until it is partially obtained. Given we have gone from the Wright Flyer to a space shuttle in under a 100 years, another few hundred, at exponential human and machine logic, what seems magic and impossible may become commonplace.
 — wjt, Jan 03 2020

 // If the rocket is going at 1000mph, you eject the mass at 1000mph, again leaving the ejected mass stationary. In this way, the ejected mass is always stationary and hence has no kinetic energy, meaning that all the work has been transferred to the rocket. //

That's nonscience. There is no such thing as absolute position in space, which means there can be no such thing as absolute velocity or kinetic energy (which is dependent on velocity) either. All positions, velocities, and kinetic energies are relative to external objects.
 — notexactly, Jan 03 2020

Yep, that was a flaw in my reasoning. I guess, if anything, you'd worry about the velocity relative to the rocket (in which case the whole argument falls apart).
 — MaxwellBuchanan, Jan 03 2020

Wouldn't quantum foamed virtual particles pairs be fixed in space? The further, energetically speaking, away from returning to the natural foamy balance, the harder the position would be to move. A fleeting space-time fabric spike. if such a thing could be generated.
 — wjt, Jan 03 2020

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