The Climber-Tether Interface of the Space Elevator
International Space Elevator Consortium
Routine, simple, low cost access to space
International Space Elevator Consortium : Spring 2023
Authors:
Preface
In order to increase the knowledge base in the field, the International Space Elevator Consortium (ISEC) undertakes each year the study of an issue important to the development of Earth-anchored space elevators.
At the inception of this study in 2020, recent advances in strong material technology made it clear that an in-depth examination of the state of the art of such materials would be useful. Enough was becoming known that the physical conditions at the interface between the space elevator climber and tether could be identified and used to determine the requirements of the strong materials. In the process, the study evolved into a multi-disciplinary effort, ranging from atomic physics and chemistry to aerospace and mechanical engineering to orbital mechanics. As a result, more than two years were required for its completion.
The goals of the study were to identify the physical conditions that must be met in order to allow climbing, to set forth the current state of the art in tether materials, to demonstrate by conceptual design that a payload-carrying climber could be built with today’s technology and to outline the research necessary for future development of tethers and climbers.
It is hoped that the results of this study will convince the reader that advances in strong material development and climber design have brought the space elevator much nearer to reality.
Dennis Wright
ISEC Vice President and Director of Studies
31 January 2023
Executive Summary
The “climbability” conditions of a space elevator climber, and those imposed by payload and speed requirements, determine the design of the climber and tether. For an Earth-based space elevator a frictional drive with opposing wheels gripping the tether and providing traction was chosen as the most feasible configuration. The physical conditions at the interface between the space elevator climber wheels and the space elevator tether determine whether or not climbing is possible.
These conditions were used to set limits on critical design parameters such as the coefficient of friction between tether material and wheels, the range of allowable climber wheel radii, the minimum torque to be supplied by drive motors or drive train, the minimum strengths (tensile, compressive and shear) of the tether and wheel materials and the amount of waste heat to be rejected by radiators.
Because mass production of single crystal graphene and graphene super-laminate (GSL) seems near at hand, GSL was selected as the tether material. While GSL has sufficient tensile and compressive strength to support itself and climbers, its shear strength may be too small. Cross-bonding graphene layers within GSL during production is one possible way to increase shear strength.
A conceptual design of the climber was conducted assuming that only present-day technology would be used. It showed that a system of ten wheel-pairs and twenty electric motors could not lift a 20 t climber, even without payload, but that five wheel-pairs and ten high-torque electric motors could lift a climber of 20 t having 9 t of payload.
Extrapolating current trends showed that many improvements in motor and material technologies are feasible and will allow reductions in climber mass with corresponding increases in payload. It thus seems possible that a 20 t climber with a 14 t payload will be achieved. These improvements include higher-torque, low-mass motors and tether materials specifically designed for better shear strength and higher coefficient of friction.
A number of unknown or poorly understood properties were identified which need to be studied or measured. A program of molecular modeling should be carried out so that the GSL manufacturing process can be understood and modified to provide the type of tether material needed. Because GSL is expected to be orthotropic, many of its elastic response parameters, along with its stress-strain curve, will need to be measured. Friction measurements will also be required.
Further improvements of the tether and the climber require a multi-parameter optimization of the climber and the tether designs. This is typically handled in a trade study for which a list of trades is provided.
Despite the challenges to friction-based tether climbing identified in this study, methods of overcoming them have been proposed and no roadblocks to the process have yet been found
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2 年Greetings Experts, could someone tell me what that ciam colored cylinder that surrounds the climber represents???