Antigravity idea

[Chirios]

Based slightly off'f Mass Effect.

There's a material, let's call it X, you pass a current through it and it accelerates away. If on Earth this would be at 9.81m/s^2, on Mars 3.78m/s^2 etc. What would the possible uses for this material be?

[StarSword]

Physics guys, feel free to correct me, but I think that if "X" maintains that acceleration for as long as the current flows, the main use would be launching objects into space a la the repulsor cage used by Lusankya to escape Coruscant in X-Wing: The Krytos Trap.

To use it for, say, a hovercraft/landspeeder/whatever, you'd have to turn the current on and off at a rate that would make it maintain an altitude but not continue to climb.

[Eternal_Freedom]

If the current causes X to accelerate at 9.81 ms^-2 on Earth it will counteract the pull of Earth's gravity for the mass of X. Now if you incorporate X into a rocket (in the rocket body itself) then you make the rocket effectively weigh nothing (when the current is flowing). That means your rocket thrust is only working upon the payload, not the rocket, meaning you can launch more mass of payload for the same amount of rocket fuel.

Of course, that depends how much current it takes to make X do it's thing, and how much that will all cost, and how much weight will be added to keep the current flowing in X. If that extra cost is more than the saving in rocket fuel, then X will remain a curiosity as far as rocket scientists are concerned.

[Imperial528]

So if I get this right, X generates an acceleration in the opposite direction and of the same magnitude as the nearest source of gravity if a current of Y is applied to it?

The possibilities are endless.

For one, this could make nuclear aircraft much more appealing, since all the engine needs to do is move the rest mass, not move the rest mass and resist gravity's pull. It also makes any conventional aircraft it is applied suddenly much, much different in design, as it only needs to be aerodynamic in a way to have the least drag, rather than produce constant lift and have less drag. This means that aircraft would become extremely efficient. It would also make landing, well, anything on any surface much, much easier, since you essentially have an electric gravity-based parachute that would cancel out the acceleration of the object you mean to land on.

Also, a question:

If X creates an acceleration of gM, M being the nearest and largest local gravity source (E.g., gearth would be -9.8m/s^2, etc), at a current of Y, what happens if a current of <Y is applied to X? Does it accelerate at <gM? Likewise, would the opposite occur if a current of >Y were applied? This opens up even more possibilities, and it practically becomes a reactionless drive.

[Simon_Jester]

Can you control the effect by varying the strength of the current? If not, landing is gonna be a bitch.

The best answer I can think of would be to have multiple blocks of the stuff and selectively run current through only some of them.

Another problem is that of necessity, an aircraft that relies heavily on this antigravity metal will need to be half antigravity metal by mass. We already have cargo aircraft that can carry roughly the weight of the unloaded airplane in cargo; if you made a C-5 out of an equal weight of antigravity metal, it wouldn't actually be able to carry more cargo, and I'm not at all sure it'd need less fuel than a normal C-5 would (weight of fuel would then eat into cargo weight).

The main difference would be in space applications, where they effectively replace chemical rockets as the means of choice of putting something to orbit altitude. If you want it to remain stable with the current turned off, you still need some kind of engine to accelerate the object to orbital velocity and not just altitude, but you can use low mass-fraction, high-efficiency drives for that, and then gently lower the antigravity part of the craft down to the ground... I think.

It'd be very tricky to use properly, though, because all it gives you is lift- you have no lateral control.

For one, this could make nuclear aircraft much more appealing, since all the engine needs to do is move the rest mass, not move the rest mass and resist gravity's pull.

The problem with nuclear aircraft is more that it's hard to pack a useful nuclear reactor on an airframe without irradiating the crew.

It also makes any conventional aircraft it is applied suddenly much, much different in design, as it only needs to be aerodynamic in a way to have the least drag, rather than produce constant lift and have less drag.

Yeah, but it's now half antigravity metal by weight, and you still need big tanks of jet fuel to keep the plane moving through the sky if you want to go anywhere.

[Patrick Degan]

There's a material, let's call it X, you pass a current through it and it accelerates away. If on Earth this would be at 9.81m/s^2, on Mars 3.78m/s^2 etc. What would the possible uses for this material be?

Look up "cavorite". It's an antique SF idea.

[Imperial528]

The problem with nuclear aircraft is more that it's hard to pack a useful nuclear reactor on an airframe without irradiating the crew.

Very true. From what I have read though projects where the desired shielding requirements could be reached for the reactor were scrapped because the sheer mass of it would severely prohibit the plane from moving much else beyond itself and crew, and that prototypes never reached the desired shielding requirement.

Yeah, but it's now half antigravity metal by weight, and you still need big tanks of jet fuel to keep the plane moving through the sky if you want to go anywhere.

Which is why I asked the OP if the material stays at a constant force regardless of current or not. If the material's output is always at the local gravity, it becomes more limited in application. But if doubling the current going through X doubles the force, you only need 1/2X as you would with the standard current, and so on with 4 times as much current, etc.



I believe the material that the OP is describing differs a bit in operation from cavorite, IIRC in H.G. Wells' book cavorite was used by exposing the craft to it through the use of shutters, without need for running a current through it. But then it's been a long time since I read the book.

[Purple]

So this thing once applied turns every craft into an airship? That in it self could be an application for SF enthusiasts. Make airships viable again.

[Chirios]

Let's say no. If you have a sample of X, you need to apply a current of >=Y for the antigrav properties to work. But using >Y will not produce larger antigravity effects.

[Imperial528]

Hm...

Then what are the rough physical properties of X? Would it be useful as a structural component, or is it frail or brittle such that it can't support much at all?

[Feil]

First law requires it to consume energy equivalent to the mechanical work it does, like an electromagnet. This will hamper its utility as a launch mechanism, since electric power is not very weight-efficient compared to chemical power. If it can only be used when it is going at g upwards, its utility is virtually nil. No large-scale current technology can output enough power to lift itself at that rate. If it just makes the sample of X have its weight be negative while it is under current, it could be extremely useful (although still not as a launch vehicle). If it doesn't require energy when it isn't doing work (which is perfectly reasonable, physics-wise: the electric fields keeping you from sinking to the center of the earth aren't expending any energy to exert a constant upwards force equal and opposite to your weight), then that is something really interesting.

[lordofchange13]

First law requires it to consume energy equivalent to the mechanical work it does, like an electromagnet. This will hamper its utility as a launch mechanism, since electric power is not very weight-efficient compared to chemical power. If it can only be used when it is going at g upwards, its utility is virtually nil. No large-scale current technology can output enough power to lift itself at that rate. If it just makes the sample of X have its weight be negative while it is under current, it could be extremely useful (although still not as a launch vehicle). If it doesn't require energy when it isn't doing work (which is perfectly reasonable, physics-wise: the electric fields keeping you from sinking to the center of the earth aren't expending any energy to exert a constant upwards force equal and opposite to your weight), then that is something really interesting.

It doesn't necessarily have to follow the Law's of physics, as most examples of this technology/unobtainium in scifi don't.

[Simon_Jester]

The problem with nuclear aircraft is more that it's hard to pack a useful nuclear reactor on an airframe without irradiating the crew.

Very true. From what I have read though projects where the desired shielding requirements could be reached for the reactor were scrapped because the sheer mass of it would severely prohibit the plane from moving much else beyond itself and crew, and that prototypes never reached the desired shielding requirement.

It's not just mass, it's bulk. There's a feasible limit on the size of an aircraft you can build without having to make the structure very strong and heavy, at which point costs will go up quickly. They go up quickly even with antigravity metal, because it's a good bet that antigravity metal is expensive. If you have to use many tons of it to hold up 100 tons of airplane, then at some point it's no longer cost effective to pile extra tons onto the airplane to make its nuclear reactor safe. Not unless you build the plane to be roughly the same size as a nuclear submarine, which has its own problems.

Which is why I asked the OP if the material stays at a constant force regardless of current or not. If the material's output is always at the local gravity, it becomes more limited in application. But if doubling the current going through X doubles the force, you only need 1/2X as you would with the standard current, and so on with 4 times as much current, etc.

It also depends on structural properties- can you build a significant fraction of the airframe out of the antigravity metal? Can you do so safely, given the need to pass current through it?

What happens if a plane made partly of antigravity metal gets struck by lightning? That doesn't happen often but it is a safety issue.

And, of course, there's the standing issue I mentioned with landing: the plane will have trouble landing if its lifting force is supplied by an "all or nothing" block of antigravity metal.

So this thing once applied turns every craft into an airship? That in it self could be an application for SF enthusiasts. Make airships viable again.

A big bag full of hot air or helium is probably going to be cheaper than a block of antigravity metal (well, I don't know about helium, as helium is actually a lot more expensive than we might think). What makes airships impractical is mostly that they're slow, not that they're expensive. A 200-ton C-5 cargo airplane can carry 200 tons of cargo, flying it several thousand kilometers in a period of twelve hours or so. A 200-ton antigravity skyhook-type airship may carry 200 tons of cargo, but it probably won't be as fast as a C-5, which is a significant disadvantage in both passenger and freight aviation. You usually don't put things on an airplane unless you care about how fast they get there.

First law requires it to consume energy equivalent to the mechanical work it does, like an electromagnet. This will hamper its utility as a launch mechanism, since electric power is not very weight-efficient compared to chemical power. If it can only be used when it is going at g upwards, its utility is virtually nil. No large-scale current technology can output enough power to lift itself at that rate. If it just makes the sample of X have its weight be negative while it is under current, it could be extremely useful (although still not as a launch vehicle). If it doesn't require energy when it isn't doing work (which is perfectly reasonable, physics-wise: the electric fields keeping you from sinking to the center of the earth aren't expending any energy to exert a constant upwards force equal and opposite to your weight), then that is something really interesting.

Yes, but you still need lateral propulsion, which is kind of a limiting factor on the value of the design.

There are lots of applications, but I'm not sure if there's any one really big Killer App that makes it vastly better than existing technology- except, perhaps, for space launch applications where you can use antigravity metal to lift yourself to orbit altitude, then use ion thrusters or the like to get the payload up to orbital speed over a long period of time.

It also vastly simplifies the problem of creating a working space elevator, because you no longer need one huge cable with the tensile strength to support its own weight. All you need is to have segments of cable interspersed with chunks of antigravity metal that hold up the weight, plus the power lines to run it all... and once the antigravity metal parts are in place, they probably don't consume much energy. Except for resistive heating, of course, but if this really is a "metal" that is not a large power drain.

[Feil]

It doesn't necessarily have to follow the Law's of physics, as most examples of this technology/unobtainium in scifi don't.

If you throw out the first law (or the second, for that matter), you throw out physics, and there is no point in discussing this any further. Every formalism of physics depends on ΣΔE=0.

[Patrick Degan]

I believe the material that the OP is describing differs a bit in operation from cavorite, IIRC in H.G. Wells' book cavorite was used by exposing the craft to it through the use of shutters, without need for running a current through it. But then it's been a long time since I read the book.

Yes, it involves a different mechanism than the substance of the OP, but it's still the same basic idea: an antigravity mineral.