Study of the effect of static/dynamic Coulomb friction variation at the tape-head interface of a spacecraft tape recorder by non-linear time response simulation

NASA's Voyager 1977 mission to Jupiter-Saturn utilizes a magnetic digital tape recorder (DTR) on each of the two flyby spacecrafts. It has been experimentally determined that about 97% of the total output torque of the drive motor of the Voyager DTR's is required to overcome the static/dynamic Coulomb friction at the tape-head interface while the remaining 3% of the torque is utilized to overcome other bearing and aerodynamic frictions. Needless to say, the accuracy of the analytical simulation of the DTR servo depends to a very great extent on the fidelity with which the analytical model of the highly non-linear and piece-wise continuous static-dynamic Coulomb friction represents real life. In order to demonstrate the power and flexibility of graphic interactive simulation in time domain, three aspects of a realistic Coulomb friction model (viz., the static component, the dynamic component and the general shape) were interactively adjusted with a view to determining the sensitivity of the system behavior to such perturbations. A number of stable system configurations were arrived at, which had significantly different static/dynamlc components of Coulomb friction than current (nominal) design values.