Analysis and design of aerocapture tether with accounting for stochastic errors

As an alternative to conventional aerocapture spacecraft, a system comprising two vehicles (a probe and an orbiter) connected by a long thin tether has been proposed. In this tethered system, the probe provides the necessary atmospheric drag while the orbiter remains high above the sensible atmosphere. The results of a sensitivity analysis of the aerocapture tether are presented. Errors in knowledge of the atmosphere and in control of the initial conditions are considered. A result of the analysis is the discovery that the tethered system possesses a self-correcting mechanism that partially compensates for these errors. This intrinsic characteristic can be enhanced with a simple guidance algorithm that implements a change in the tether length to minimize the effect of off-nominal conditions. Design rules are developed to accommodate stochastic errors without violating the constraints, i.e., breaking or compressing the tether, subjecting the orbiter to atmospheric effects, crashing, or failing to capture. The final design consists of a 68-km tether with a mass of 381 kg and a probe and orbiter of 1000 kg each. It is capable of achieving a 99% success rate for aerocapture at Mars.