Attitude dynamics and thrust control for short tethered sub-satellite in deployment

Abstract

Dynamic characters and control strategy for short tethered satellite system in deployment are studied in this paper. Tether elastic oscillation and sub-satellite attitude motion are considered in the dynamic model. Sub-satellite releasing method with an initial velocity and a negative acceleration is proposed for fast deployment. It is indicated that the short dimension and fast deployment make dynamic characteristics of both the tether and the sub-satellite different from those of the long-tether systems. Control strategy is designed based on these dynamic characters. Thrusters are considered to provide active control for the tether and the attitude of the sub-satellite. Variable structure control is adopted, taking into account the nonlinear dynamics of the system and the on-off output of the thrusters. Numerical simulation shows that the tethered sub-satellite can be deployed to designed direction in or out of the orbit plane with thrust control. The tension of the tether is positive during deployment. The in-plane angle of the tether is controlled within 0.1 . The out-of-plane angle passively keeps near its initial releasing value. In addition, the attitude angles of the sub-satellite are controlled or passively remain within 0.5 . This fast deployment provides flexibility for tether assisted space operations.

Pure-tension non-linear sliding mode control for deployment of tethered satellite system

“…Proof. Considering system dynamics (4), disturbance observers (9) and (10), adaption (20), desired sliding surface (18) and control law (22), we select the Lyapunov function candidate for the overall system that includes the components mentioned above as…”

“…The fast and high-precision convergence to the desired sliding surface benefits from the related controller parameters, and they are k 2 ¼ 10, k 3 ¼ 1, k 5 ¼ 0:01, while k 1 and k 4 can be chosen as some big enough parameters to satisfy equation (36) or the statedependence parameters like equation (37) with1 ¼ 2 ¼ 10. After the system states arrive onto the desired sliding surface s ¼ 0 with acceptable precisions, the whole system dynamics is handled by the reduced system (18), and the related parameters can be arranged as c 1 ¼ 16, c 2 ¼ 3 and " ¼ 9:8. To compensate the input constraint, the initial value of adaption can be selected as 0 ¼ 100.…”

“…3,[15][16][17] In the existing control schemes, a type of popular thruster-aid approaches utilizes thrusters to convert the underactuated issue into an oversimplified actuated problem, i.e. Liu and Zhou 18 constructed the specified thruster system imposed on the load to maintain the tension along the space tether, and applied the variable structure control scheme to achieve the stabilization of short distance deployment of space tether. Huang et al 19 studied the combination of tethered robots by the means of thruster control, which provided constant force to make the entire system stable.…”

Dynamics modeling and model selection of space debris removal via the Tethered Space Robot

“…A simplest, but reasonable dynamics model of the TSS has been derived by several researchers, by treating two end-bodies as massive points, the connecting tether as rigid and uniform in mass, and assuming a circular Keplerian reference orbit for the center of mass of the system. 6,7 This simplest model can be extended directly when the longitudinal flexibility or elasticity of the tether is taken into account, 8–10 and it is also can be used for momentum exchange 11 and orbit transfer. 12 These models are widely used for dynamics analysis and control scheme design during deployment and retrieval because of the well description of basic characteristics of the system, and the simplicity in mathematics.…”