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starship-design: Wild thoughts

Antonio C T Rocha writes:
 > Just fantasizing, of course, but :
 >    Counter-rotating masses of superconducting stuff (a condensate?) carrying
 > static circular current. Compensating for one another.
 >    Gues I'll toy with that one for a while.
 > Antonio C T Rocha

Superconductors have this problem where a magnetic field above a
certain strength breaks down their superconducting properties.
This puts a limit on how much current any superconductor can
carry, since the current creates a magnetic field around the

One amusing feature of relativistic kinematics is that while one
photon is massless, two or more photons treated together as a
system usually aren't (unless they are all traveling in exactly
the same direction).  So, for example, if you could create a
fiber-optic ring and pump a large amount of laser light into it,
you would make it heavier; the sum of the energy-momentum vectors
of all the photons in the ring would add up to an energy-momentum
vector that has a mass.  The ring also has to exert a centripetal
force against all the photons bouncing around its outside to keep
them contained, so eventually you could rupture the ring by
putting enough photons into it.

In any case, stored energy _is_ mass.  If you can somehow cram a
tremendous amount of energy into any kind of container, it gets
more massive.  Normally the amount of stored energy in things
like chemical batteries or warm objects is too small of a
fraction of the total mass to measure, but there's really no way
to make an exotic battery that can hold an amount of energy on
the order of its own mass where it won't get more massive as you
charge it up.