Vincent Cate wrote:
VC The same device gets a different name depending on
VC where it is?

You did not read the web page which explains the difference:
http://www.islandone.org/LEOBiblio/SPBI122.HTM

The name depends on whether the device picks up
its cargo from the surface of a planet or a moon. If it
can do that, it is called the rotovator. If it cannot,
it is called the bolo. I have seen the rotovator term in
several publications.

AN The rotovator hurls the sacks filled with regolith
AN (Moon dust) towards the Earth.

AN In order to do this more than once, it needs to get
AN momentum back from someplace.

No, it does not.

VC The next problem is that your sack will need some
VC guidance and thruster control to get exactly where
VC it needs to go to. You can not fling something 1/4
VC million miles and have it get within a few meters
VC of the spot you were aiming for at exactly the right
VC time.

You did not read the web page about GPS accuracy:
http://gipsy.jpl.nasa.gov/igdg/syste....html#accuracy

VC With the mass of the tether and payload on a 200 km
VC lever arm you would need a *really* huge greenhouse
VC to store up an equal amount of angular momentum.

VC For a similar idea I like 2 hotels in GEO connected
VC by a 20 km tether and rotating fast enough to get
VC 1/6th G. This is 131 m/sec tip speed which is so
VC low that the tether can be like 0.8% of combined
VC mass of the 2 hotels. Of course my hotels would have
VC greenhouses, but they are mostly hotels.

I agree. The first, small system of this kind can be any
large spinning object. Note that the system can "bootstrap"
itself, which means that a small, one ton system can lift
into space a much more massive system.

AN When a winch reels its cargo in, the cargo moves
AN faster to conserve its angular momentum. This fact
AN makes it possible to increase the orbital energy
AN of the rotovator and the greenhouse without the need
AN for any external thrust.

VC You conserve both your angular momentum (around own
VC center of mass) and your tether systems momentum
VC around the moon. Since you picked up something that
VC was not moving, your overall orbital speed is slower
VC (more mass and less speed for same momentum). So the
VC opposite side of the orbit from where you pick up
VC gets lower. Depending on how high it was to start,
VC you can only do this a few times before you hit the
VC moon. Why do you think you don't need thrust?

The lunavator picks up cargo from the Moon, reels it in
and hurls it backward before it gets to the other side
of the Moon. Its orbital energy is increased, but its
angular momentum about its own center of mass is
decreased. This is why the arm is needed to adjust the
angular momentum of the lunavator. When you run out of
the angular momentum, you have to reverse the angular
velocity of the lunavator before you release its cargo.
(If you reverse the angular velocity of the lunavator,
you cannot pick up anything from the Moon unless you
reverse it again.)

AN When the cargo is captured by the terrestrial bolo,
AN its velocity relative to the bolo is 4.3 km/s.

VC For spectra-2000 you would need a tether like 600
VC times as heavy as your payload to handle a 4.3 km/s
VC tip speed.

You did not read the web page which explains it:
http://www.islandone.org/LEOBiblio/SPBI1SL.HTM

The characteristic velocity of Spectra 2000 is 2690 m/s,
so the minimum tether mass is about 40 times greater
than the cargo mass.

AN It is easy to design a reusable sounding rocket which
AN lifts the payload to the altitude of 100 km and accelerates
AN it to the velocity of 2.5 km/s. (When the payload separates
AN from the rocket, its total energy is equivalent to the
AN kinetic energy of only 3 km/s.)

VC I think it is easy to get a reusable sub-orbital rocket
VC going much faster than 2.5 km/sec. I think you are
VC putting too much work on the tether and not enough on
VC the rocket.

We could argue about that point for ever. I prefer to use
the tethers because they use almost no propellants. The
only consumables are Xenon gas used by the ion engines
and the cargo sacks.

VC In order for your LEO tether to pickup something every
VC 90 minutes, I think it has to be in an Equatorial orbit.
VC But the moon only crosses the equatorial plane every 2
VC weeks, so you can not toss to it all the time from an
VC Equatorial orbit.

No. The bolo orbit must be in the same plane as the Moon
orbit. This means that the sounding rockets are launched
from a different latitude in summer than in winter.

VC Have you tried things on tether simulator?
VC http://spacetethers.com/spacetethers.html

Yes, but it is too simple to simulate the system we are
talking about (lunavator bolo exchange). The system
is a complex celestial ballet of 3 rotating tethers. There
is a great need for a simulator that explains the ballet,
and you are the best guy to make such a simulator!

PS. I made another sling improvement: terrestrial cargoes
are attached to both ends of the sling when the sling is
released from the bolo. I also made a drawing of the
lunavator. It is posted at:
http://www.islandone.org/LEOBiblio/S...M/SPBI1324.JPG