--- In space-elevator@yahoogroups.com, "William Haught" <wlhaught5873847@...>
wrote:
>
> So how does the induced force of lauching say, 10, let alone the 70
> metric tons the StarTram proposal calls for at 2.5 gs over 1250 km
> compare to the force required to launch .8 metric tons over probably
> something like 2 km at much higher gs? The paper I downloaded a long
> time ago says that the "acceleration drive power" is 28 GW.
>
To be feasible, both StarTram and coil gun will need to be designed in such a
way that the energy needed during launch is first stored in the system, as
magnetic field energy. In other words, the coils get charged comparatively
slowly to full (super-) current, and then get depolarized/deenergized very
quickly by the passing vehicle/projectile.

It is easy to have the approaching projectile depolarize the coil and get
accelerated, but it is hard to turn the coil off fast enough to avoid it getting
recharged (and the projectile slowed back down) afterward. Especially near the
muzzle, where this needs to happen VERY fast.

The best way seems to be quenching of superconductivity, but at near orbital
speed the electromotive force in the wake of the projectile gets so large that
any known coil materials will evaporate from the induced current. What is needed
is a superconducting material that instantly becomes a good insulator when
quenched. I don't think a suitable material is known at this time, and there may
well not be one.

If the problem is solved, though, the process is quite energy efficient, i.e.
the actual electrical power needed is not much more than the kinetic energy
passed to the projectile, and because of the built-in energy storage ability of
any plausible system it will not need to be pulsed.

Andreas