This paper illustrates a procedure to calculate the response of a tethered spherical aerostat to gusts, including the effect of structural nonlinearity and accounting for some of the fluid - structure interaction between the aerostat and tether line. The procedure developed and presented here is based on a full three-dimensional dynamic finite element model, with aerodynamic loads calculated from the relative velocity between a time-varying input airflow and resulting structural velocities. Exact solutions for the static response and a simplified dynamic model, both developed to validate the results of the procedure illustrated in this paper, are also derived and described in detail. The dynamic responses to gusts are compared with the equivalent steady-state solution to assess the approximations of the static solutions. Particular emphasis is placed on the output rotation of the aerostats to quantify disturbances on the pointing stability produced by gusts.
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