Re: Reactionless Redux

"Knobby" <knobbynobbs@xxxxxxxxxxx> wrote in message
news:1174518222.449974.210940@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Hello to all the regulars and irregulars from this humble newbie.

I was prompted to sign up and post here from the discussion on
reactionless drives and energy costs thereof that was linked to from
the excellent Atomic Rocket site.

Sorry if this dead horse has been beaten so much as to have been
reduced to it's constituent atoms, but if I may be indulged, I'd like
to re-visit the question of what the hypothetical energy cost of a
reactionless drive might be.

I would also like to apologize in advance if this has been asked and
answered elsewhere, and similarly would like to thank any who deign to
chime in for putting straight my admittedly meagre knowledge /
understanding of physics.

It's been asked many times, but that's no reason it can't be addressed
again. At least given a reasonable down-time between discussions.

Anyhoo, on with the show...

It is my understanding that, regardless of frame of reference,
relativistic effects on a mass are the same. IOW, if two space craft
moving at relativistic velocities are pacing each other side-by-side,
looking from one to the other, one will be able to observe a length
contraction in the other, while not noticing seeing it in one's self.

So, if I've got this right, and relativistic effects on a body are the
same regardless of frame, why not use a spacecraft's relativistic mass
(the extra) and the grand ol' equation of E=mc^2 to figure out the
energy costs associated with having moved that spacecraft?

Relativistic effects of velocity are the same in every frame, but velocity
is not. If two space craft are pacing each other side-by-side, it doesn't
matter how fast they're travelling with regard to anything else, neither one
will see relativistic effects in the other.

For instance, if the spacecraft's velocity is such that due to
relativistic effects it's mass (in kg) has increased by 1%, the energy
it would have taken to achieve that velocity would be (at 100%
efficiency) 0.01*mass*c^2 joules.

Okay, that's it. Hack away.

The trouble is that in some frames (such as one which is moving at
relativistic velocities wrt the launch site in the same direction as the
space craft is accelerated) will appear to be slowing down and losing
energy, and other frames won't see the same magnitude of increase or
decrease. Reaction drives make up for this by putting the balance in
whatever it was that you pushed off against.

-l.
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