My father (Henry Cate) and I have come up with an initial tether project
that might be fun, affordable, and profitable. The idea is to use a
rotating tether to pickup some Lunar samples, bring them back to Earth,
and sell them.

The Apollo Lunar Orbit Rendezvous was a big win because they did not need
to land their return vehicle or fuel on the moon, just the lander. With a
rotating tether we could win even more by only having a small scoop at the
end of the tether touch the moon.

Since there is no landing vehicle, we can also use a high ISP ion drive the
whole time. By lifting a small scoop of regolith (probably under 10 Kg,
maybe under 1 Kg) many times we could lift a reasonable total mass of
lunar regolith using a small tether. For the 1.6 km/sec tip speed of a
tether for lunar pickup, the tether only needs to be like 3 to 10 times
the payload mass. The ion drive has to replace the momentum before the
next pickup.

The Dnepr at $10 to $13 mil for 9920 lbs (4500 Kg) to LEO seems like a
good deal.

http://www.spaceandtech.com/spacedat...nepr_sum.shtml

Starting with a 4500 Kg vehicle in LEO we use an ion-drive to go to the
moon, spin up a tether (probably winching in and out 2 tethers), and start
picking up samples when the end of the rotating tether touches the moon.
After picking up enough that it is running low on fuel, it could head back
to earth and have a capsule reenter with the samples.

The question of how many Kg of lunar sample you could bring back depends
on a lot of things, like ISP of thruster, watts/Kg for solar, ratio of
capsule mass to payload mass, how long the mission can be, etc. To really
get a detailed answer would take some real work. You can also trade off
time and mass returned to some extent (higher ISP can bring back more but
takes longer). Our initial guesstimate is that you could return between
1,000 Kg and 10,000 Kg in something like 1.5 to 4 years.

All of the Apollo missions combined returned 381.7 Kg. The Apollo costs
have been estimated at $100 billion in 1994 dollars (next URL). If this
project can be done for $50 million (not by NASA for sure) then this would
be like 2000 times cheaper and return 2.5 to 25 times as much. :-)

http://www.asi.org/adb/m/02/07/apollo-cost.html

In a more fair comparison, the Artemis people were going to start with
44,000 lbs in LEO (so 4.4 times as much as us). They would return between
200 lbs (95 Kg) and (227 Kg) of lunar material (we return ~4 to ~100 times
as much).

http://www.asi.org/adb/04/03/10/05/returned-mass.html

If you think of the investment cost as scaling with the lbs to LEO (a
reasonable first approximation) and the financial return value as the Kg
of Lunar material returned (not totally fair as the price goes down with a
bigger supply), then the tether method is 16 to 400 times better. Artemis
was sort of marginal as an investment, but this could be a reasonable
investment.

It is of course hard to estimate what people would pay for lunar regolith
once there was a real supply. If it was $1,000/gram and you had 2,000 Kg,
that would be $2 bil. Probably be hard to get that much, but it could
really be a good return on investment.

Additional missions would cost much less than the first, since you would
not have the development costs again. You could even design the vehicle
to be resupplied for a new mission (more xenon, new reentry capsule, etc).

This would be able to pick up samples from many parts of the Moon, any
part that passed under the orbit. If it was in a polar orbit it would even
be possible to get a sample from a dark crater at the North or South pole
to see if there was water ice.

Most of the regolith is very fine dust. You might get more money selling
lunar rocks. It might be possible to have a computer guided harpoon on
the end that could target small rocks.

Another interesting option is to use the tether to toss small reentry
capsules from the Moon in such a way that they fall back to Earth. One
nice thing about this is that you could start selling your product much
sooner. The other nice thing is that and if at some point their was a
catastrophic failure you would at least have what had been returned so
far. People bidding on what you had so far would not know how much more
would be coming. So concern that your vehicle might fail at any time
might keep the price of Lunar material high longer.

We have not seen this idea of using a rotating tether to pick up lunar
samples anyplace else and think it looks very promising. What do you
think?

-- Vince