[Spaceships] Your preferences regarding plausible/playable Reactionless Drives

Anthony · 10-06-2010, 01:44 PM

As a side note, something that behaves in a way similar to a reactionless drive doesn't really require any violations of GR, it just requires some forces that don't exist as far as we know. In particular:

If you had some sort of tractor/pressor beam, you can simply grab hold of the nearest large object and pull yourself around. This isn't fundamentally different from using a pole and a rope, other than the fact that you're using invisible beams rather than physical objects. The following constraints apply:

Force can only travel through your beam at the speed of light; thus, if you're pulling on an extremely distant object, it will take quite a while to start or stop accelerating.
Force can only be applied towards or away from an object. Thus, if you want to accelerate sideways, you have to basically push on one edge of you anchor, pull on the other. This will multiply acceleration by 2*sin(angular size/2); at long distances this can be approximated by multiplying by (size/distance).
You're subject to power constraints -- the power requirement of your drive is at least (force applied) * (velocity relative to anchor). For objects in orbit around the earth, accelerating 'forward' requires about 70 MW per ton per G. 1 EP appears to be on the order of 100 kW/ton, so even there your acceleration would be 0.0014G, and it will go down as speed increases.

10-06-2010, 01:44 PM	#6
Anthony Join Date: Feb 2005 Location: Berkeley, CA	Re: [Spaceships] Your preferences regarding plausible/playable Reactionless Drives As a side note, something that behaves in a way similar to a reactionless drive doesn't really require any violations of GR, it just requires some forces that don't exist as far as we know. In particular: If you had some sort of tractor/pressor beam, you can simply grab hold of the nearest large object and pull yourself around. This isn't fundamentally different from using a pole and a rope, other than the fact that you're using invisible beams rather than physical objects. The following constraints apply: Force can only travel through your beam at the speed of light; thus, if you're pulling on an extremely distant object, it will take quite a while to start or stop accelerating. Force can only be applied towards or away from an object. Thus, if you want to accelerate sideways, you have to basically push on one edge of you anchor, pull on the other. This will multiply acceleration by 2sin(angular size/2); at long distances this can be approximated by multiplying by (size/distance). You're subject to power constraints -- the power requirement of your drive is at least (force applied) (velocity relative to anchor). For objects in orbit around the earth, accelerating 'forward' requires about 70 MW per ton per G. 1 EP appears to be on the order of 100 kW/ton, so even there your acceleration would be 0.0014G, and it will go down as speed increases.