# Alternatives to rocket engines

Discussion in 'Science and Technology' started by Jadzia, Sep 27, 2008.

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Conventional rocket designs rely on "Equal and opposite forces" exerted between the ship and propellents in the engine exhaust. Because the exhaust emissions are relatively low mass compared to the ship, the momentum is balanced through a relatively high velocity.

But high velocity means that the exhaust emissions take most of the kinetic energy from the engine, and relatively little kinetic energy is taken by the ship.

If the exhaust emits mass m at velocity v, then a ship is of mass M and gains velocity =mv/M.

Looking at how the energy is distributed:

Total energy in the exhaust emission:
E = (1/2) mv^2 + (1/2) M (mv/M)^2
= (1/2) mv^2 + (1/2) m^2 v^2 /M = (1/2)mv^2 . [M+m]/M

Proportion of energy taken by the exhaust: = M/(m+M) = Most.
Proportion of energy taken by the ship: = m/(m+M) = Hardly any.

Is there any way we can imagine accelerating a ship without using a conventional rocket engine design?

For example, What if we fired a highly collimated beam of accelerated particles at the ship from a planetary station, to push it along?

What if the ship fired a particle beam out of the back of the ship, but the beam swung around a star and returned to the ship. So the ship gains the propellent back, AND double momentum.

The energy liberated on recapture of that energetic particle beam could also be fed back into the fired beam.

Any other thoughts? And nobody mention warp engines.

Last edited: Sep 27, 2008
2. ### LindleyModerator with a SoulPremium Member

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I'm trying to figure out how this would fit into action/reaction......the star's participation *might* let you get around that. But keeping a beam coherent enough while passing it that close to a star seems a bit iffy.

3. ### sojournerAdmiralIn Memoriam

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4. ### All Seeing EyeAdmiral

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Something that could directly convert electrical energy to forward kinetic energy wouldn't violate the laws of nature, but doing it without needing to throw mass out the back of your ship is the real trick.

Say it takes 1 joule of energy to add .000001 m/s to your spacecraft. Well it may take less energy to use that joule to push a milligram of matter out the back of the ship using electricity, but when you run out of stuff to throw out the back of the ship you are screwed.

But, if you could convert that 1 joule of electricity to momentum without having to throw mass out the back of the ship you could power you ship with a nuclear reactor and never have to worry about running out of reaction mass, but you would still have to worry about running out of fuel.

If the conversion of electrical energy to inertial energy could at least 50% efficient it would revolutionize space travel.

Someone was working on a microwave cavitation chamber that cailmed to be able to affect inertia without throwing out reaction mass. hmmm..

EDIT: I read up on this and some scientists are bitching about how the microwave drive would violate the laws of physics.

I agree but only if the kinetic energy the device generates exceeds the electrical energy dumped into it.

Isn't electricity and photons moving kinetic energy in particle form, vs. a solid object moving which it a bunch of bonded particles moving the exact same thing.

Energy is energy whether it be potential energy in a batter being dumped out and converting into kinetic energy via a microwave cavitation chamber.

All you are doing is taking the potential energy in something like nuclear reactor in a space craft and applying it directly into kinetic energy which is making the craft move and attain kinetic energy equal to the potential minus conversion loss, electrical conversion loss, thermal loss and any other losses not accounted for.

Last edited: Sep 28, 2008
6. ### All Seeing EyeAdmiral

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check out my link dude. That's all the technology we need.

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Yeah I did, I guess I was on the same wavelength, I added an edit to the bottom of my post.

8. ### KaziarlCommodoreCommodore

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Warp Drive....

Sorry, couldn't resist...

9. ### All Seeing EyeAdmiral

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QUESTION: Hypothetically speaking, if I designed an engine that didn't require any fuel and only required electric current and this engine could pretty much propel a spacecraft to the outer solar system pretty quickly how would I go about selling such a design? would i even be allowed to patent it?

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I don't see why not. I mean, it's obviously just the sort of invention that is eligible for patenting (all-new, gonna change people's lives, immediate applications, the works) and probably would have to be protected ASAP, too. The costs of obtaining the patent would be considerable but not overwhelming - I think you could get plenty of good loan if you had a few big names vouch for the validity of the basic concept. And there would probably be very little in the way of competition, prior claims, legal ambiguities and such.

As for the black helicopters paying a visit, that's rather unlikely. The thing wouldn't have weapons applications or anything like that - it would be a pipe dream for the next fifty years anyway, until humans could build a credible space presence and invent some sort of a mission for this type of propulsion.

Timo Saloniemi

The only place where an immense amount of power is required is achieving escape velocity from a planet's gravity. Beyond that, a large amount of thrust is not required. Low power and utilizing a sling-shot method around large bodies can enable fast travel.

12. ### DeckerdFleet ArsePremium Member

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Which brings the interesting prospect that the patent holder may well be dead before any application for the device could be built.

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...Although if you rigged up enough of these low-thrust devices to give you 1 gee or so, you could go to space from Earth's surface at a not-so-brisk walking pace. The propellant-less design in this case wouldn't be necessary for defeating the rocket equation and allowing for a high terminal speed - but it would be great for bringing forth all the advantages of scaling up. You could build a launcher the size of a small city, and it wouldn't suffer from the vicious circle of increasing propellant requirements and consequently decreasing payload.

But you could cash in nevertheless, as aerospace companies would be able to think 50 years forward on something like this, and would buy the invention from you.

Now, 70 years forward... Probably not.

Timo Saloniemi

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Put it in a car and call it the green machine and get it widespread as a new type of electric motor.

Electricity cannot be generated without utilizing some type of fuel source.

What about using giant rubber bands to slingshot a vessel into space?

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Well no duh, use batteries, and use the kinetic device to impart movement, aka. thrust to the car.

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Batteries are basically just chemical reactions, and in terms of this "energy released per kilogram of fuel/battery", there is much more energy released in 1 kilogram of hydrogen burning than what 1 kilogram of batteries could ever give out.

Fuel cells are the way to go, imo. Batteries will be phased out at the fuel cell design is refined and miniaturized.

Last edited: Sep 30, 2008