Design of tether sling for human transportation systems between Earth and Mars

Abstract

Human transportation systems between Earth and Mars might benefit greatly from the construction of a tether sling facility on Phobos. A tether sling has the potential to launch vehicles from Phobos to Earth with little or no propellant expended because it is solar powered. For current trajectory designs and tether materials, we show that a tether sling facility is superior to chemical propulsion systems when multiple launches from Phobos are considered. A performance index of the ratio of tether mass to chemical-propellant mass is used to compare various mission scenarios. Ratios less than 10 are considered desirable. The most advantageous application of the tether sling occurs during a Hohmann transfer from Phobos to Earth where the mass ratio is 1.8. Next are semicyclers (ratios of 1.9 and 2.4) and a three-synodic-period cycler (8.7). Unfortunately, the Aldrin cycler does not benefit from the tether sling because the high hyperbolic velocity at Mars drives the mass ratio to infinity. For cases with desirable mass ratios, we also account for fluctuations in the cross section of the tether as a result of manufacturing uncertainties