Sensitivity Analysis of Tether-Mediated Orbital Injection

Abstract - This paper investigates the injection of a satellite from lower to higher orbit by means of the tether sling-shot technique. This technique utilizes the increment of velocity (Delta-v) imparted by a long librating tether, attached to a suitable orbiting platform (e.g., the Space Shuttle), for changing the satellite's orbit. With a scheme that mirrors a two-impulse orbital transfer, the tether is cut twice: the first time on the platform side when the tether crosses the local vertical after deployment and the second time on the satellite side at a convenient apogee passage. The two cuts increase the apogee and the perigee heights, respectively. Issues addressed in this paper, which are essential for an accurate and effective orbital injection, are the maximization of the first Delta-v and its sensitivity to uncertainties associated with tether unmotorized deployers (e.g., the Small Expendable Deployment System). The initial conditions that minimize the sensitivity to variations of the deployer's model parameters and the optimal timing of the second cut are evaluated. A specific numerical case is made for the injection of the SEDSAT satellite in order to prove that the orbital altitude after injection can be maximized and made insensitive to unpredictable variations of the deployer's tension model.