The Hoytetherâ„¢: A Space-Survivable Tether Structure

Long-life, damage resistant tether system for extended-duration, high-value, and crew-rated missions.
The lifetimes of current single-line tethers are limited by damage due to meteorite and orbital debris impactors to periods on the order of weeks. Although single-line tether lifetimes can be improved by increasing the diameter of the tether, this incurs a prohibitive mass penalty. The Hoytether, illustrated in Fig. 1, is a tether structure composed of multiple lines with redundant interlinking that is able to withstand many impacts.


Figure 1. a) Section of a tubular Hoytether ("Hoytube"). b) Schematic of undisturbed Hoytether. c) Secondary lines redistribute load around a failed primary line without collapsing structure.

Research Results:
Analytical modeling, numerical simulation, and ground-based experimental testing of this design indicate that this tether structure can achieve lifetimes of tens of years without incurring a mass penalty. Moreover, while single-line tether survival probability drops exponentially with time, redundant linkage in failsafe multiline tethers keeps the tether survival probability very high until the tether lifetime is reached. The survival probability of a failsafe multiline tether is compared to that of an equal-mass single line tether in Fig. 2.


Figure 2. Lifetime comparison of equal-weight single line and failsafe multiline tethers for a low-load mission.

Tethers Unlimited has successfully developed a method of fabricating long lengths of Hoytethers. Using this process, we have fabricated over fifty kilometers of Hoytether prototypes suitable for use in electrodynamic and momentum-exchange tether missions, and tested them succesfully in several tether deployment systems.

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