Horizontally-Configured Ground-Test Method for Tethered Satellites

Abstract

Two configurations of ground tests may be envisaged to provide experimental data to enhance dynamic modelling of tethered satellite configurations: (a) a vertically suspended tether and (b) a horizontally suspended tether. This paper describes the design and implementation of the horizontal configuration used during design of the BOLAS (Bi-static Observations with Low-Altitude Satellites) rotating tethered satellite configuration. The merits of the horizontal and vertical configurations, in the context of rotating tethered satellites, are compared. Large-scale, room-temperature experimental tests emulating the in-orbit dynamic state are described, in which a SPECTRA-1000®/acrylic tether is suspended horizontally and attached to a pendulum-supported sub-satellite mass. Tension variation due to gravitational cable sag effects is reduced by supporting the tether at intermediate points. The stiffness and structural damping properties are deduced from a cable model that accounts for tether tension variation due to gravitational cable sag effects. Small-scale laboratory tests of tether samples at cryogenic temperatures are conducted to establish the temperature dependence of the tether-material properties. Tether stiffness and damping properties at orbital temperatures are estimated using the experimental data from both large- and small-scale tests. The in-orbit loss of rotation rate of the BOLAS mission due to the gravity-gradient-induced longitudinal stretching of the tether is estimated by applying the experimentally determined tether stiffness and damping properties to previously determined equations of orbital motion.