Mass Drivers

There have been many suggestions for mass drivers on Luna for the exportation of
raw materials and other purposes, notably by Gerard K. O'Neill (God rest his soul)
and the Space Studies Institute.  Plans can keep the power requirement low by
calling for a low payload size.  Higher acceleration rates allow shorter track.  
High firing rates keep the investment actively earning its return.  

I consider here a circular mass driver or mass accelerator which would keep power
requirements low by spreading the acceleration out over many laps of a circular
track.  The payload could be about 200 kilograms.  If there are passengers or
cargo available every 110 minutes for rendezvous with a catcher satelite, it can
keep constantly busy.  Suitability for passenger service requires a low radial
acceleration, I specify 30 meters per second squared (about 3 g's).  This in turn
requires a large diameter (about 120 miles).  The shape of the device is like a
very regular volcanic mountain peak with gently sloping sides and a circular
crater on top.  The accelerator track would run along the vertical wall of the
circular crater.  When the payload and carrier reach orbital velocity (1680 meters
per second), the payload is dropped radially outward over the top of the wall.  A
counter weight may be required on the carrier near the base of the wall to
ballance the carrier.  Since the diameter of the track is 120 miles, there is
about one and two thirds miles bulge of the curvature of Luna interfering with
line of sight communication from one side of the track to the other.  The plane of
the circular track makes a 3.2 degree angle with the surface of Luna.  Payloads
launched tangentialy from the track, however, deviate from that plane by curving
downward toward Luna in a orbital path.  This makes it more likely than otherwise
that a payload would smash into a mountain peak.  So the accelerator track should
be built up on fill as high a practical and care should be taken in choosing the
exact dirrection of launch.  The circular accelerator should be centered at the
North pole while the catcher satelite would orbit about once per 110 minutes at an
inclination of about 86.8 degrees.  So it would pass over one or another spot on
the circular track with every orbit as Luna rotates under the orbit.  It could
catch a payload whenever a mountain peak did not interfere.  Troublesome peaks
could be razed.  

The specifications would require 43 kilowatts average power put constantly into
payloads plus power to accelerate the carrier and allow for the losses in magnetic
levitation.  Unfortunately, the carrier can not constantly accelerate because it
must come to a stop to be ready to pick up the next payload.  Two tracks, one of
10 meters less radius and 2 meters more altitude than the first would allow one
track to accelerate while the other uses regenerative braking.  As long as we
consider developments that must be many years in the future, there is a capability
of adding carriers in a train as there is increased available power and  need for
cargo tonnage.  The whole 370 mile circumference of the accelerator could be
filled with one train of carriers.  The payloads could be connected by rope and
launched from one point on the cicomference into one orbit as 5 minutes and 53
seconds go by. --Farred 23:34, 23 April 2008 (UTC)