###### Abstract
As shown in Figure 1, the time for data communication can be drastically increased by using an inter-orbit communication link through a data relay test satellite (DRTS) in a geostationary orbit (GEO), instead of using direct communication [6; 7]. Owing to these reasons, it has become important to ensure that small Earth observation satellites use a data relay system in order to increase the time of data communication. In conventional operation, first, satellite maneuvers using linear state feedback controller. After that the data relay satellite communication (DRC) antenna is driven [8; 9]. However, in this operation, there is loss of time between the completion of the attitude maneuver and the start of data communication. Therefore, we need to shorten the time between the start of attitude maneuver and the completion of the antenna motion. Accordingly, the purpose of this study is to increase the time of earth observation and data communication by carrying out satellite maneuver and antenna motion concurrently, as shown in Figure 2. Since a small satellite mounted with DRC antenna has a large mass ratio of the antenna, we cannot ignore the time variability of the moment of inertia of the whole system that is caused by antenna motion. In addition, a reaction torque generated by antenna motion is increased. In view of these points, we formulate the optimization problem that is subject to a state equation for the whole satellite system; the optimization problem is solved in order to design a satellite attitude controller by taking the influence of the antenna motion into consideration. On the other hand, a small satellite mounted with DRC antenna has the nonlinear equation of motion. Thus, it is difficult to design a linear state feedback controller. In recent years, the development of calculators is effectiveness in studying direct solvers that calculate approximate solutions, because it converts an optimal control problem active into a Nonlinear programming problem (NLP) [10]. Therefore, this study converts the optimization problem of minimum-time attitude maneuver and antenna motion into an NLP, and applies the sequential quadratic programming (SQP) method to obtain an optimal Feedforward (FF) control torque. We assume an operation scenario as shown in Figure 3. In assumed scenario, first, we calculate the optimization problem of minimum-time attitude maneuver at a ground station. Second, we send the optimal FF control torque command to the satellite. Third, satellite carry out attitude maneuver and antenna motion. After that satellite can start missions. However, it is considered that model uncertainty of antenna [11; 12] and unknown disturbance exists in real space. Thus, we have to design Feedback control to secure robustness in model uncertainty and unknown disturbance. In order to propose a nonlinear control method for carrying out Minimum-time satellite attitude maneuver and antenna motion which have robustness against model uncertainty and unknown disturbance, first, we calculate the reference attitude \(x_{r}\) by the application of optimal control input torque \(u_{FF}\) to the ideal model. Next, we design servo controller in order to track time-variant \(x_{r}\) as shown in Figure 4. [PERSON] and [PERSON] use the state-dependent Riccati equation (SDRE) control method to control position and attitude of two satellites in formulation flight. They design integral type servo controller to track a reference command [13; 14; 15]. Referring to [13; 14; 15], we design servo controller by using SDRE control method in order to track the time-variant reference attitude \(x_{r}\). In addition, SDRE control method has typical characteristic in that weighting matrix can be designed depending on the state. This means we can change the characteristic of controller depending on the state. Using this typical characteristic, we design state dependent weighting matrix in order to shorten the satellite attitude maneuver and antenna motion. The paper is organized as follows.