Speaker
Mr
Thomas Peters
(GMV)
Description
COBRA is a contactless concept for de-tumbling and controlling the attitude of a target space debris object that exploits the torques generated on the target by the plume impingement of a thruster facing the target to impart torques on the target. The control strategy for de-tumbling is based on a switching strategy for the de-tumbling thruster and a pointing strategy for aiming the de-tumbling thruster at a specific region of the target. This control strategy has been developed in a previous study of the concept. This article discusses several refinementsfurther developments of the original strategy and examines the general applicability of the COBRA concept, mainly in Active Debris removal missions in line with Cleanspace. The applicability of COBRA concept is investigated by examining several scenarios, namely, de-tumbling and attitude control of debris objects of varying configurations in terms of object geometry and mass parameters and in various initial rotation states. The main targets examined in this study are Envisat and Cryosat PROBA 2.
Simulation results described in a previous article have shown that the simple pointing and switching strategy for COBRA can successfully de-tumble a large space object such as Envisat in a relatively short time and using only a modest amount of ΔV, namely from an initial rotation rate of 5°/s to 0.5°/s in under one orbit. These simulations assumed a relatively favourable rotation state of Envisat, which allowed pointing the thruster at the Solar panel. The normal of the Solar panel was perpendicular to the rotation axis, such that a large torque could be generated. In the current article, new simulations will be presented for less favourable rotation states of Envisat. In addition simulations will be presented for a different target, PROBA 2. PROBA 2 is a roughly cube-shaped object, which means that there is no particular geometry (location plus orientation) of the thruster with respect to target that generates high torques.
Previous results have indicated that the ΔV required ΔV required could be improved, in part by updating the thruster layout of the chaser and in part by updating the control strategy. The thruster layout is updated to include thrusters in the direction exactly opposite to the de-tumbling thruster to limit cosine losses. The control strategy is improved in a number of ways.
Previous results indicated that the ΔV overhead (that is, the ΔV not directly contributing to de-tumbling the debris) was higher than expected based on the ΔV required to compensate for the activation of the de-tumbling thruster. A part of the overhead can be explained by the cosine losses, but a substantial fraction was due to attitude control. The pointing strategy and the attitude control of the chaser are improved to reduce this overhead. In addition some effort is spent in improving the pointing strategy of the chaser. The current strategy uses a very simple model to predict the torques imparted on the target. The prediction model is improved such that the torque imparted on the target is closer to the desired torque.
| Applicant type | First author |
|---|
Primary author
Mr
Thomas Peters
(GMV)
Co-author
Mr
Diego Escorial Olmos
(GMV)
