Space Transportation - mmmt_transportation.pdf - Moon Society

A Cislunar Ferry
Gordon Woodcock(1) and Joe Hopkins, SLUGS (Seattle Lunar Group Studies)
We propose a vehicle be developed to utilize swing orbits (Woodcock, 1). The vehicle would be designed to
travel in the lunar plane between Earth and Luna, providing frequent and regular access to both bodies.
This vehicle could be viewed as a cislunar ferry. In its initial form, the orbiter would be a small, no gravity,
passen-ger/freight carrier. The cycling orbiter could be configured to provide radiation shielding for the passenger
section. If gravity becomes necessary, it could be simulated by spinning equal massed compartments opposite each
other on a tether.
[Actually, it is not necessary that both opposing components be equal in mass - unless equal levels of artificial
gravity are required at both ends. If this is not required and the two components are unequal in mass, the center of
gravity or fulcrum simply lies proportionately closer to the heavier mass while the gravity felt in the lighter more
distant component will be the greater - Editor.]
Regular, inexpensive transportation between the Earth and Moon is the main purpose of the orbiter. Cargo and
passengers would be transported on and off of the orbiter in specially designed taxi modules. Passengers would
generally remain on board for only one leg of the trip at a time; three to five days.
Over time, with a system like the cislunar ferry, transshipments from the Moon to low Earth orbit would
become cheaper than such shipments from Earth. Early shipments could include oxygen, unprocessed lunar rock (for
shielding) and agricultural products. As lunar bases develop, processed metals and glasses could be included.
Shipments from Earth to the Moon would be precision tooling equipment and electronic supplies. Organic
waste generated onboard the cislunar ferry and in low Earth orbit could be sold to Moonbase farms. The orbiter would
also be valuable as a research facility.
(1) Woodcock, Gordon R., Transportation Networks for Lunar Resources Utilization, Space Manufacturing 5;
Engineering with Lunar and Asteroidal Materials, American Institute of Aeronautics and Astronautics, New York,
Proceedings of the 7th Princeton/AIAA/ Space Studies Institute Conference, May 8-11, 1985
Magsail Asteroid Survey Mission
(SEI & Stafford) by Stan Love and Dana G. Andrews
The asteroids, lying principally between the orbits of Mars and Jupiter, have long been considered
one of the best potential sites for near term access to extraterrestrial resources. To fully assess the value
of asteroids for commercial use, and also to gain scientific knowledge about them which is critical to our
understanding of the formation of the solar system, it is necessary to examine a large number of them a
very close range, perhaps even collecting samples of their surfaces for analysis on Earth. Such a mission is
unthinkable with current chemical rockets, however. Each flyby would require a few km/s of velocity
change (hence approximately doubling the initial mass of the spacecraft) and no surface landings could
occur without expending a prohibitive amount of propellant.
The magnetic sail (Andrews, D.G. and Zubrin, R.M., "Progress in Magnetic Sails," AIAA Paper
90-2367, 1990) suggests a solution to this problem. It would derive its thrust from the interaction of the
solar wind with the magnetic field around a loop of super conducting cable several dozen km in diameter.
As long as current flows in the cable (once set up, it will continue to flow indefinitely) the sail would
develop a small amount of thrust, which could be directed by altering the orientation of the loop or by
changing the current, easily accomplished with a modest-sized solar array. Since it would produce a
continuous force without expending any propellant, a magsail could orbit the sun in the asteroid belt
indefinitely, visiting tens or hundreds of objects at a relative velocity of a few km/s.
Asteroids possess no magnetic fields to hinder the use of a magsail. Neither do they have strong
gravitational gradients, which are difficult for any low-thrust vehicle to overcome. If the mission profile
allowed the necessary deceleration time, the spacecraft could rendezvous with asteroids to take samples
of their surfaces. Proper alignment of the sail and the asteroid could be arranged so that the sail force and
the gravitational attraction of the asteroid exactly balance one another, allowing samples to be taken of
the surface from a motionless spacecraft. After sampling a number of asteroids, the spacecraft could
return to Earth to drop off material samples and undergo routine maintenance. It could then return to the
asteroid belt for further exploration.
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