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 configuration s, electrical insulation materials, and umbilical geometry were investigate d. Dynamic sine-sweep measurements were made on a special test rig having a n extremely low coefficient of sliding friction value of mu = 5 x 10(-6). T ransfer function analyses were used to assess the stiffness of current conf igurations and various alternates. Because of the very low stiffness of som e candidates, the effect of I-g umbilical sagging on the measurements had t o be considered. A detailed comparison is provided of the properties of the different umbilical candidates tested. Several candidates provided dramati c dynamic stiffness reductions.