Spacecraft wiring harnesses can fundamentally alter a spacecraft's structural dynamics, necessitating a model to predict the coupled dynamic response of the structure and attached cabling. While a beam model including first-order transverse shear can accurately predict vibration resonance frequencies, current time-domain damping models are inadequate. For example, the common proportional damping model results in modal damping that depends unrealistically on the frequency. Inspired by a geometric rotation-based viscous damping model that provides frequency-independent modal damping in an Euler-Bernoulli formulation, a time-domain viscous damping model with terms associated with the shear and bending angles is presented. This model demonstrates a much weaker dependence on frequency than proportional damping models. Specifically, the model provides modal damping that is approximately constant in the bending-dominated regime (low mode numbers), increasing by at most 6% for a particular selection of bending and shear angle-based damping coefficients. In the shear-dominated regime (high mode numbers), damping values increase linearly with mode number and are proportional to the shear angle-based damping coefficient. A key feature of this model is its ready implementation in a finite element analysis, requiring only the typical mass, stiffness, and geometric stiffness (associated with axial loads) matrices as developed for an Euler-Bernoulli beam. Such an analysis using empirically determined damping coefficients generates damping values that agree well with existing spacecraft cable bundle data.