Orbital Elevator

On Aug 24, 2006, at 02:50 UTC, Matt Gallimore wrote:

> It is true that a rotating tether should be able to fling an object
to a
> higher orbit or even escape velocity.

Rather than thinking of it as flinging, just think of it in terms of
delta-V. The bottom of the tether is moving at a certain velocity with
respect to ground; when the tether is rotating (in the proper
direction), this is slower than the tether's own orbital velocity. At
the top, the tether is moving at a different speed, faster than orbital
velocity. The difference between these speeds is the delta-V that the
tether can impart to the craft.

> Is that not also true for a vertical tether?

Yes, but in this case the delta-V is very small, unless your tether is
ridiculously long. Perhaps this is hard to see unless you actually
work through the numbers.

> Or did you mean the tether would have to be really long to be
beneficialt?

Yes, exactly.

> Now, if the system were shorter, 200 km or so, then I'd agree that
the
> potential difference in orbit boost might be minor. It might not be
worth the
> difficulty of docking vs just carrying the extra fuel.

Right. The radius of its orbit is at least 6400 km (the radius of the
Earth) already; an extra 200 km just doesn't amount to much.

> Would a shorter structure be worthwhile if it wasn't used for orbital
> transfers but just the small gravity on a station?

Yes, I think there may be some value in that. Even having enough
gravity to make stuff tend to settle to the floor might be useful.

Cheers,
- Joe

Joe Strout -- joe@...