I'd appreciate any comments and suggestions, and would be happy to answer any questions.

Long Space Transportation Tethers


by James Edward David Cline SSN# 525-82-1047

Originally part of my presentation to the SSI Space Studies Team in July 1989, in El Segundo, CA, a small, informal group. Two of my topics are presented below:

The MOONCABLE PROJECT, a captive form of tensile structure, or tether, attached to the surface of the lunar body and supported by an adjacent gravitational well such as the Earth's. The tether supports electrical power conductors along its length that couple kinetic energy between the two gravitational wells, across the Libration-1 balance point between earth and moon.

The TWO-BODY-ORBITING SKYHOOK, a free spinning tether shuttling back and forth between two unequal gravitational wells, along two abruptly changing trajectories.

But first I would like to remind you that space, extraterrestial space with its abundant resources, is essential to a continued expansion of a civilized human population while taking the load off of the environment that gave us life. Indeed, it might be said that Mother Earth is very pregnant with humanity, and must give birth soon or both Mother and child will perish! Perhaps it is fitting that the form and function of the following proposed supply links resemble umbilicals. In that service, then, the following inspirations are offered you.

THE MOONCABLE CONCEPT: Reference figure 1.

The Mooncable concept is a very long (about 180,000 miles long!) tensile structure balanced across the L-1 libration point between the Earth and the Moon, and attached to the lunar surface at one end. With essentially equal weights in either direction from L-1, it hangs in place, forming an energy tunnel from the lunar surface to a slightly lower gravitational energy level 1/6 the way into the Earth's gravitational field.

The structure is made of fiberglass, which has a strength of 500,000 lbf due to being made and used in a hard vacuum...there is no air to force its way into the surface microcracks that are the primary breaking mechanism on Earth. The structure is tapered to provide a constant-stress-crossection, thickest where it passes through L-1. Conductors along the length of the structure couple energy generated by payload braking down the Earthside of the cable, over to the Lunarside of the cable to lift more payload up to L-1, in a process analogous to a siphon.

In the initial version of the concept developed in 1971-72, lunar nickle-iron meteoric debris was to be hauled up to the manufacturing site at L-1, where solar furnaces melted this natural stainless steel and foamed it into molds casting it into re-entry glider shapes. After being dropped off the earthside end of the Mooncable, and remote-controlled atmospheric entry and gliding to near seaports, tugs would go out to retrieve the floating glider, haul it to port and saw it up for use in building freeway crash bariers, fireproof homes, and impact absorbing car bodies, for example. Pockets cast into the gliders would transport smaller amounts of other exotic materials and devices, such as hollow ball bearings, to Earth markets.

Large spacecraft would have been built at L-1 for manned exploration of the solar system in relative comfort.

It was to be built in a bootstrap process, where one of the remaining Saturn V boosters would be used to launch a craft to L-1, where a micro-diameter Mooncable of fiberglass would be despooled in both downward directions, and in the process soft-landing a robot glass-factory on the lunar surface at that end of it. From the solar furnaces in that robot fiberglass plant, up would be lifted fibers to gradually increase the girth of the Mooncable, until reaching operational transportation capacity.

This Mooncable project would have involved moving something less than 0.6 cubic mile of lunar-source fiberglass into balance across L-1. But once built, and the energy pump primed, it would thereafter provide free transportation energy (analogous to an ordinary liquid siphon's function) between lunar surface and earth-dominated gravitational space, enabling massive and highly efficient materials transportation thereafter.


This is a modified Moravec-Skyhook useful for transferring payload from the urface of a moon to a point dominated by the parent planetary body, using the greater gravitational field of the nearby planet as an energy pump to sustain the process. A permanently orbiting spacecraftwould dangle a long tether to briefly touch the farside of the Lunar surface as it passes by, grabbing awaiting payload. Then the combined whirling masses would continue on around the Moon in an orbit that passes near the Earth. At the precise instant that the whirling tethered mass pair has the payload deepest in the Earth's gravitational field, the payload would be released, restoring the kinetic energy to the spacecraft that was given up when the pickup was madeoff the Moon. The tether would be reeled in or let out before release, to compensate for varying payload mass when restoring kinetic energy to the spacecraft... letting the whirling payload drop deeper into Earth's well before release would give the orbiting spacecraft extra energy, such as for compensating for having some of the payload move aboard the spacecraft, for example. The tether attachment on the spacecraft would have to loosely spin around its CG, like a yo-yo with a loose string, or a "Y" fitting to eitherside of craft's CG, unless it was unmanned and didn't care if it wobbled erratically. The spacecraft-skyhook would then continue on back to pick up another payload off of the Moon. Reference figure 2.

This concept I feel the least comfortable about. Energy-wise, it seems plausable, being able to freely supply its own transportation energy, like the siphon-like Mooncable concept. However, the orbital mechanics is very shaky; Kepler's laws are not yet fully in my conceptual working grasp. It must cycly shift between two orbits, due to the abrupt energy transfers at the pickup and release points. It may be limited to a single spacecraft/payload mass ratio to enable the moon-to-planet path. It may require unmanned operation, due to the abrupt accellerations at the pickup and release points...or at least crews chosen for iron-gut qualities!

A supply of reaction engine fuel would be needed on the spacecraft, to be used in case of ever missing a payload pickup, to return to Earth vicinity and again to go back to Lunar pickup point for another try. If the clockwork never fails, this seems to provide extremely energy-efficient payload transportation from Moon surface to an energy level somewhat less than 5/6 of Earth's gravity well.




Copyright C 1995 James Edward David Cline

I can be contacted at:
Dave Cline, 9800-D Topanga Cyn Blvd #118, Chatsworth, CA 91311, USA
Telephone 818/886-8059 E-mail at: jedcline@earthlink.net
E-mail also at: j.e.d.cline1@genie.geis.com