On the Deployment of a Tether from an Elliptical Orbit

Abstract

A two-phase deployment scheme has been studied for a tethered system being deployed from a spacecraft in a circular orbit. With the proper choice of the ejection parameters-angle and speed–the tether can be left at rest, aligned with the local vertical, in less than one orbital period, regardless of length. For a circular orbit, this position is a relative equilibrium configuration. When the tether mass is small, a perturbation method allows it to be included in the second and higher terms of a power series, whose first term corresponds to the end body and a massless tether. This analysis is extended here to the case of an elliptic orbit. Two new parameters appear: eccentricity and ejection anomaly. Taking only the first term allows a wide and fast scanning of the acceptable ranges for these parameters. It is found that, for most values of the anomaly, there are combinations of initial speed and angle for which the deployment is hardly affected by eccentricity. Initial anomaly always affects the process, but a combination of parameters can still be found to achieve the desired effect. A tether can be completely deployed while in the highest part of the orbit, avoiding the effect of drag in the area around the perigee, for eccentricities of 0.1 and higher.