Re: This is the most important CATS post ever!

Andrew Nowicki <[EMAIL PROTECTED]> wrote in message news:<[EMAIL PROTECTED]>...
> The technology described in this post has not been tested, but
> it looks trivial when compared to rocket launchers, and it
> may reduce the cost of space access to a few dollars per kilogram!
> 
> The technology is based on GPS, a reusable sounding rocket,
> cheap terrestrial bolo, cheap lunar rotovator, cheap cargo
> sacks, and a small Zylon sling.

A suborbital rocket and some kind of a space tether does seem like
a very good way to reduce the cost to orbit.

> The bolo and the rotovator
> are useful terms defined by Robert Forward. They are described
> here: http://www.islandone.org/LEOBiblio/SPBI122.HTM
> (Robert P. Hoyt calls lunar rotovator "lunavator.")

It seems funny to call a space tether with a tip speed of 1.6 km/sec
a "bolo" if it is orbiting Earth and a "rotovator" or "lunavator" when
it is orbiting the moon.  The same device gets a different name
depending on where it is?   There is no distinction in what a 
simulator computes for either.  Also, if you search for "rotovator" 
in Google, most of what you get has nothing to do with "space tethers".
Anyway, I think it is better to just use "space tether".

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

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

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

>It is mounted on a rotating arm which is
> attached to a large, rotating, toroidal greenhouse. The arm
> rotates independently of the greenhouse, so it can easily
> change the angular velocity of the rotovator. The maximum
> length of the rotovator is about 200 km. 

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

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

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

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

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

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

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

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

In order for your LEO tether to pickup something every 90 minutes,
I think it has to be in an Equatorial orbit.  But the moon only
crosses the equatorial plane every 2 weeks, so you can not toss
to it all the time from an Equatorial orbit.  So I like the idea
of tossing to a lower tip speed tether at GEO which can toss 
large collections of objects to the moon every 2 weeks.  You save
huge in reducing the mass of your LEO tether because you can get
by with a lower tip speed tossing to GEO instead of the moon.  
Think of it as a two stage tether system where the total mass 
is less than a single stage tether system because of the exponential
tether mass problem.  This is very much like the TSTO vs SSTO
problem.  If you have equal mass going both directions (i.e.
as much regolith coming back from the moon as payload going to
the moon), then you don't need thrust on LEO-tether, GEO-tether,
or Lunar-tether.

But getting a setup working with the moon seems like a more costly
way to start than some others.  

We like an EDT to boost momentum for the LEO tether and a solar sail 
to boost momentum for the GEO tether.  The mass for the solar cells 
for the EDT or the solar sail for the GEO tether are not all that bad.
And once you have this infrastructure in place you could do a 
reasonable sized payload (we work with 4,000 kg) every 90 minutes.  
This looks like CATS to the Cates. :-)

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

   -- Vince