Bringing up Phobos

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  • If there is any fear of Phobos falling on a Mars colony, the possibility exists to raise Phobos to a higher orbit using its own orbital energy. Glass-glass composite cable manufactured out of the stuff of Phobos should probably be strong enough to hang the cable one thousand miles Marsward from Phobos. Stuff lowered to the Marsward end of the cable and dropped will leave Phobos in a higher orbit, eliminating the need to worry about Phobos falling on a Martian colony. The tether would go up from Phobos in the Marsward direction about 17 kilometers to the Mars-Phobos L1 point and then down in the Marsward direction another 983 kilometers. The tidal force at the lower tether tip would be 0.17 meter per second squared. The cable could vary in cross section area to be close to its design stress over the entire length. Two sheets of glass film could encircle the cable as micrometeoroid protection with at least three inches between the two sheets and between the inner sheet and the cable. Bogies carrying the wheels and electric motors would be encircled with the cable while the cars would be supported by structural connections to the bogies that would extend through slots in the micrometeoroid shield, one slot for upward bound cars and one for those downward bound. The shield would be attached to the cable by numerous curved glass whiskers. These whiskers would be like a glass slinky streched out in the space between sheets and welded with a lower melting point glass wherever the slinky touches a sheet or the cable. The slot in the shield would be angled to avoid a straight line path for micrometeoroids to the cable. The cable would be shaped to include two rail-like portions of its cross section so upward bound empty cars could run on one rail and downward bound cars full of Phobos stuff could run on the other. Regenerative braking would produce electricity from the downward bound cars to drive the upward bound ones. Excess electricity would be used to toss the Phobos stuff to the rear to raise Phobos' orbit more than would be the case by simply dropping the stuff. This would be accomplished by an electric accelerator at the Marsward tip of the tether. The direction of the thrust could be varied in phase with Phobos' orbit to reduce the inclination of Phobos to the equator. Its orbit is presently inclined slightly more than one degree to the equator. When Phobos' orbit has been raised to synchronous altitude, high strength to weight ratio materials could be used to extend the length of the cable as far as people find practical at that time.
  • Phobos stuff dropped by this means would be ground up so that either the particles would burn up on contact with the Mars atmosphere, or the surviving remnant cinder would be so small and light as to cause no unacceptable damage to Mars installations. To insure this, Phobos stuff would need to be ground to particle sizes that would cause not much more damage than the dust that is blown about Mars in occasional high velocity winds.
  • If a tether from Mars' surface to orbit is someday constructed, it would be better to use Phobos for the low strength requirement central portion of the cable than to crash Phobos into Mars to avoid its bumping into the tether.