On Sun, Feb 25, 2018 at 10:43:08PM -0500, Richard Aiken wrote:
> A straight and level stretch of track, a governed speed of 100 mph, a big
> hook and an even bigger V-shaped hook funnel (like on the front of planes
> used for Fulton extractions) . . .

I'm not sure what you mean by the "straight and level stretch of
track".  This is all happening high in the atmosphere, probably at
least 50 km from the ground and more likely 100-150 km.

Or maybe it's a misunderstanding about the direction of the tether?
For the "momentarily stationary" proposals, it shoots in essentially
straight down from space, and zooms back out straight up, not
horizontally.  The points where it dips into the atmosphere will be
spaced out depending upon the period of rotation vs orbital speed, and
will also vary somewhat over time.  A track doesn't really help
anything that I can see.  Being in the right place at the right time
will require precise planning.

Even for the slower tether rotations where the tip never gets slower
than 4 km/s or so relative to ground, its height above ground will
still vary a lot even during its lowest second.

> According to wikipedia (admittedly not the best source), we're about
> halfway there (3.5 km/s with off-the-shelf materials)

It's closer to quarter of the way there since the tension depends upon
v^2 rather than just v, but yes we are a reasonable fraction of the
way there.

> Still, I believe the OP was willing to assume working hot fusion as a
> common technology, so I think 7+ km/s not unattainable in his TU.

Yes, it should be doable with even relatively near future materials.

- Tim