Slingatron questions.

Copied from space.tech because it seems the moderator left and it died.

Supposedly the slingatron is one of the more sound and more thoroughly
reviewed of potential hypervelocity systems, but there are a few
problems I can't figure out a way around.

Suppose you use conventional or gas bearings. The best I've seen is
..001 for a friction coefficient. At a few km/s (below which why
bother!) because the projectile makes many trips the heating seems to
be unacceptable and destroys the projectile. Also gas bearings
obviously introduce gas into the track.

On to magnetic levitation. Type 1 superconductors and rare earth
magnets seem to be too weak for reasonably sized slingatrons. All of
the type 2 superconductors I know of, even single grain YBCO, seem to
have magnetization losses such that the losses of the track
superconductors as the projectile electromagnet approaches and leaves
are unacceptably high, requiring overly high track speeds and leaving
very low efficiency. These losses go down with projectile length but
not really enough.

Further, as a projectile moves around a track, it exerts an outward
force of the track at a point that moves around the track, and the
track bends in response. Are people designing variable resonance masses

that cancel this out and move with the gyration? Planning on very
massive stiff tracks? Both? Otherwise you lose a bunch of energy.

So are people planning 100m projectiles on a 1km diameter fast moving,
massive, stiff, ring, with large amounts of well cooled
superconductors, and active vibration cancellation handling variable
frequency and exerting thousands of tons of force? And still being
inefficient, with power supplies and motors scaled accordingly? Doesn't

seem so cheap...