On Sun, Feb 25, 2018 at 11:36:55PM -0500, Richard Aiken wrote:
> > 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.
>
> Why so? The hub of the system is capable of maneuvering, even in the
> real-world examples given.

It's just the nature of circular motion that the tip is under constant
acceleration.  That means near the lowest point, the tip's altitude
changes as described.

Now it might be possible for the tip to have some automated high-speed
retraction mechanism so that the length of the tether's lower end
changes to exactly counterbalance the altitude variation.  Then it
could maintain a relatively constant altitude for some longer period
of time, but this plays exactly into the comment about needing either
good automation or very steady nerves.  Automation capable of
extending and retracting a tether tip of many kilometres length at
speeds comparable to the speed of sound, to within a few tens of
milliseconds timing so that it can sweep along a horizontal track for
pickups qualifies as pretty good in my book.

- Tim