In most of the lunar resource utilisation projects that I have heard about, a
mass driver is used to deliver material to L2. Each payload must rendezvous with
a mass catcher in L2. It must do this with exceptional accuracy. If the payload
misses the catcher by 1 metre, it has missed. Unless our lunar mass driver is
super accurate, we must find a way of guiding the inert payloads into the mass
catcher. How can this be done without a complex guidance system in each payload?

Tony

In most of the lunar resource utilisation projects that I have heard about, a
mass driver is used to deliver material to L2. Each payload must rendezvous with
a mass catcher in L2. It must do this with exceptional accuracy. If the payload
misses the catcher by 1 metre, it has missed. Unless our lunar mass driver is
super accurate, we must find a way of guiding the inert payloads into the mass
catcher. How can this be done without a complex guidance system in each payload? T. A. Heppenheimer came up with what he called "achromatic trajectories". These werepaths where small variations in launch speed result in small variations in trajectory, but the payloads still passing through the exact same point at L-2. It was also proposed that the payloads be electrostatically charged so that, after leaving the mouth of the launcher, one could arrange for the payloads to pass through down-range course-correcting structures which used electrostatic deflection plates to make minute adjustments in trajectory: http://www.ssi.org/assets/images/astronaut_at_lunar_mass_driver.jpg Also, I'm thinking the mass-catcher was envisioned as having an opening many 10's of meters across. Getting the payloads to hit the catcher was not considered one of the more difficult things to do in the overall system.
Regards,

Mike Combs

>>>>T. A. Heppenheimer came up with what he called "achromatic trajectories".
These were paths where small variations in launch speed result in small
variations in trajectory, but the payloads still passing through the exact
same point at L-2.

It was also proposed that the payloads be electrostatically charged so that,
after leaving the mouth of the launcher, one could arrange for the payloads
to pass through down-range course-correcting structures which used
electrostatic deflection plates to make minute adjustments in trajectory:
http://www.ssi.org/assets/images/astronaut_at_lunar_mass_driver.jpg
http://www.ssi.org/assets/images/astronaut_at_lunar_mass_driver.jpg>

Also, I'm thinking the mass-catcher was envisioned as having an opening many
10's of meters across. Getting the payloads to hit the catcher was not
considered one of the more difficult things to do in the overall system.>>>>

Did the original study team produce an estimate of the incoming velocity of
the masses? If this velocity is too high, then it may be necessary to use a
reverse mass driver to decelerate the masses to handlable speeds.

How would the payloads be transported from L2 to L5? Using chemical fuel is out
of the question. The only option that I can think of is some sort of nuclear or
solar electric device. What is the required D-v to get from L2 to L5?

Tony

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Did the original study team produce an estimate of the incoming velocity of
the masses? I'm sure it did, but don't know the number off the top of my head. I think it was in the 10's of miles an hour range. The spheres would lose a lot of speed ascending the lunar gravity well. I know that aconical fabric catcher was considered adequate to stop them. If this velocity is too high, then it may be necessary to use a
reverse mass driver to decelerate the masses to handlable speeds. I don't think such a thing would be needed for this specific purpose. But at the 1999 SSI conference, there was a comment that we also needed an "anti-mass-driver", a device which would slow payloads down and convert the kinetic energy back into electric. I was tickled, as I had written a short story which peripherally involved just such a system launching ice from the South Pole of the moon to an equatorial location, where it was subsequently launched away from the moon. http://members.aol.com/howiecombs/tnbttbt.htm How would the payloads be transported from L2 to L5? Using chemical fuel is out
of the question. The only option that I can think of is some sort of nuclear or
solar electric device. You're right in thinking that chemical would not be the way to go. It was assumed that the mass catcher would have an associated mass-driver reaction engine, and would use a percentage of the mass gathered as reaction mass for the trip. What is the required D-v to get from L2 to L5? Don't know off the top of my head, but it's pretty modest. But know that later studies indicated that the best orbit would not be L-5 but a circular orbit about halfway between the Earth and lunar orbit. The answers to some of your questions might be found here: http://lifesci3.arc.nasa.gov/SpaceSettlement/75SummerStudy/Design.html

Regards,

Mike Combs