2209-013 Pai TH
Rotating Tethers hold bicycle wheels together. They are like such a spoke, in tension. But they can be a lot longer and a lot stronger with new high tensile strength-weight ratios. As in Supercord and Staggeringly stronger with carbon nanotubes and CCTs just as the wheel end of a spoke makes contact with the ground at zero speed, for a fraction of a turn, even though the bicycle and wheel hub is travelling forward. That contact point, half a turn later is travelling at twice the speed of the bicycle, and another half a turn later is at the bottom, stationary with respect to the ground, though one turn of the wheel forward.
If a spacecraft has a long enough “spoke” objects on the ground could be picked up or put down at a precise spot and time. For Planet Earth that radius needs to be thousands of Kilometres long, and the object being “spun” would still endure high (spin) gravity. Though more practical than a fixed tether – at least 50,000Km long, the orbiting “hub” has to travel 7.5Km/sec to stay in orbit. With a 100Km tether the circle (rim circumference) of 600Km takes 80 seconds -and the delta-v of (6x7.5) 45Km/sec takes 80 seconds about 500m/s.s or 50 gravities. For a 1000Km tether, 5 gravities, but the spacecraft has to orbit at 1000km and the top of the “wheel” is at 2000Km. Space junk forbits either the fixed tether, or such a long one.
However, at a lesser speed, and “spin gravity” loading, some assistance can be provided in capturing a precisely positioned mostly accelerated package. … or dropping something off at less than orbital speed. Mainly, however, such a rotating-tether can precisely release a package from a low orbiting craft to be similarly captured (by a second rotating-tether) at a higher orbit... this not only “delivers a package” but also transfers inertial momentum from one craft to another.
UnitedSpaceAgency uses this method to transfer goods and momentum between LEO-Port and Haven1 - and to send and receive space-junk collection craft ( www.Plasma-tugs.com ) on and from their various missions.
This is not “free energy” if packages are accelerated, the ship (and package) is slowed down, and the same (reaction mass x velocity) has to be supplied by rocketry – or by a similar (or larger) mass “coming back”. But more effective “rockets” (VASIMR) can be used at low thrust, High S.I. setting over a longer period.
A third ship in a higher orbit such as GEO – 36,000Km where live and dead commsats orbit (needing repair/ refuel / replace / removal) may be reached in a similar way, perhaps with intermediate steps. From higher still, a ship can take a “pumping orbit” of earth-moon gravitation “slingshot” acceleration, decelerated by package exchange to the lower orbits, reducing rocket propellant usage.
From 100Km Lunar orbit a 100km tether can pick and place objects from and onto the surface with about 3-4G “spin gravity”, and the acceleration required in pick up can be obtained from “pumping orbit” ships package exchange. Materials so lifted from the moon gain a lot more in the descent to LEO.. materials arriving there boost LEO-Port's orbit perhaps to the extent of needing a retro-burn! (or assisting AscentCraft to carry a greater load.