Design and Testing of Reduced-Stiffness Umbilicals for Space Station Microgravity Isolation

We detail efforts on minimizing power electrical umbilical stiffness on the International Space Station active rack isolation system to improve system performance. The effects of wire conductor material, winding configurations, electrical insulation materials, and umbilical geometry were investigated. Dynamic sine-sweep measurements were made on a special test rig having an extremely low coefficient of sliding friction value of mu = 5 x 10 exp -6 . Transfer function analyses were used to assess the stiffness of current configurations and various alternates. Because of the very low stiffness of some candidates, the effect of 1-g umbilical sagging on the measurements had to be considered. A detailed comparison is provided of the properties of the different umbilical candidates tested. Several candidates provided dramatic dynamic stiffness reductions.