Conditions at the interface between the space elevator tether and its climber

Abstract

A simple space elevator consists of a single tether extending well beyond geosynchronous altitude and a payload-carrying device which grips and climbs the tether. A friction-based, opposing wheel climber was judged most likely to be constructed with present-day technology and it appears that mass-production of the tether material is also within reach. The physical conditions at the interface between the climber wheels and tether determine first of all the possibility of climbing and then the design parameters of the tether. Conditions such as lifting torque, tensile, compressive and shear strength, friction, interface temperature, thermal conductivity and radiative cooling were examined and used to set minimum requirements for the tether material. Graphene superlaminate (GSL), consisting of layers of single crystal graphene, appears to be an excellent tether material with a sufficiently high tensile strength. An increase in its inter-layer cross-bonding and a larger mutual coefficient of friction with the climber wheel material would allow it to satisfy the climbing conditions. A final determination of the suitability of GSL requires the measurement of a number of, as yet unknown, material properties. A list of such measurements is proposed and a partial list of trade studies and iterations of design for the tether are provided.