This paper presents a method for three-dimensional attitude stabilization of a satellite. The pitch loop of the satellite is controlled by a momentum wheel; whereas the roll/yaw loops are stabilized using two magnetic torques along their respective axes. In order to design an efficient controller, the stability conditions are considered based on a nonlinear model of system. An adjustable adaptive fuzzy system is proposed as the method to design the controller. The span of membership functions are tuned using errors of fuzzy inputs with respect to their references. Results show that fuzzy sets cover all variations of fuzzy inputs and optimal fuzzy output is gained. The Lyapunov synthesis method is used to prove the stability of the closed-loop system. The efficiency of the controller in converging of the position error to close to zero is also shown using some numerical simulations.
This paper deals with the stationkeeping control for halo orbits at EL1 in the Sun-Earth/Moon system, and proposes an effective adaptive robust controller for the unknown spacecraft mass and perturbation boundaries. The controller has to deal with two divergence sources: one is the instability of the halo orbit, and the other is the perturbation imposed by the natural model onto the nominal model. The former source is displayed by the Floquet multiplier from the Poincaré mapping. However, the latter is revealed by the difference of Hamiltonian functions between the nominal reference model, the circular restricted three-body problem (CR3BP) and the natural simulation model, the spatial bicircular model (SBCM). Firstly, the algorithm of backstepping control theory is employed to generate the initial controller in the nominal reference model of CR3BP. Some improvements are then implemented for the estimations of the unknown parameters as the perturbation boundaries and the spacecraft mass, which may cause the failure of the initial unimproved controller in stationkeeping. The controller proves to be effective in terms of adaptive robust estimation and asymptotic stability from Lyapunov's stability theory. Furthermore, further improvements of the triggers for the on/off schedule are proposed to remedy the weakness in the capability of estimating for excessively long (infinite) time required to converge. Finally, the controller developed in this paper is implemented in the natural simulation model of SBCM to evaluate its performance. In the numerical simulation, the mass and perturbation boundaries will converge only after approximately three iterations. The deviation of the estimating mass is 1 kg from its true mass, but 55 kg for the unimproved controller. The total velocity increment over five years is only 126 m/s, which is equivalent to the fuel consumption of 3.8 kg for the Hall thrust engine carried by SMART-1.
The flow past a capsule-shaped space transportation system (STS) is numerically analyzed using computational fluid dynamics (CFD) for different free stream Mach numbers ranging from 1.2 to 5.0, where a capsule is modeled by a cone, and a rocket by a circular cylinder. The objective of this research is to study Mach number effects on phenomena of the supersonic aerodynamic interference with periodic flow oscillations at supersonic regime. So far we have considered two models: model A (without disk) and model B (with disk). It was found from experimental and computational results that the flow around model A becomes steady, where aerodynamic interaction is not observed, while in model B, flow becomes unsteady with periodic oscillations. This flow oscillation is considered to be a potentially high risk in separation of the capsule and rocket. Therefore, the present study focuses on the unsteady case of model B. Numerical results at M=3.0 compared well with experimental ones, which validates the present CFD. Time-averaged results are employed to see the whole trajectories of shock waves and the variation in amplitude of flow oscillation during one cycle. Moreover, a fence is proposed as a device to suppress the flow oscillation.
The length of the boundary layer transition region is predicted by the conservation of momentum, based on the prediction method of the boundary layer transition by the mass conservation. The predicted length decreased in line with wall cooling and an increase of Mach number. Some calculated lengths agreed with experimental results, and others did not. To examine the insufficient agreement, the effect of the wall temperature on the length is discussed. Under the heated-upstream wall condition, which may appear in hypersonic wind tunnel experiments, the length of the transition region and the transition Reynolds number increased in line with the wall cooling in the prediction calculation. Most of the experimental data are in the region between the calculated results with this heated-upstream wall condition and those with the uniform wall-temperature condition. The similarity of the results predicted by the energy conservation to those predicted by the momentum conservation is also discussed.
A parametric study is conducted on a segmented flap system of a cranked-arrow wing in a low-speed wind tunnel. The objectives are to investigate the effects of a multi-segmented flap system on the aerodynamic performance in takeoff and landing conditions, and construct a database for designing a high-lift device of a supersonic transport configuration. To achieve better aerodynamic performance, the leading-edge flap is divided into four segments, and the trailing-edge flap into two segments. In this paper, the effects of the deflection angle of flap segments on drag reduction and lift-to-drag ratio improvement are discussed for lift coefficients of interest. Analysis of experimental data indicates that the segmented flaps are more efficient than the uniform deflected flaps and an optimal combination of flap deflection angles enables larger improvement of the aerodynamic performance.
This paper presents a modified Rodrigues parameter (MRP)-based nonlinear observer design to estimate bias, scale factor and misalignment of gyroscope measurements. A Lyapunov stability analysis is carried out for the nonlinear observer. Simulation is performed and results are presented illustrating the performance of the proposed nonlinear observer under the condition of persistent excitation maneuver. In addition, a comparison between the nonlinear observer and alignment Kalman filter (AKF) is made to highlight favorable features of the nonlinear observer.
A static aeroelasticity analysis is accomplished for an ONERA-M5 wind tunnel calibration model. The Reynolds-averaged Navier-Stokes (RANS) solution obtained using the cell-wise relaxation implicit discontinuous Galerkin (DG) computational fluid dynamics (CFD) solver is fed into the structural analysis method to iteratively determine the aerodynamic equilibrium configuration of the wind tunnel model. For the freestream conditions of M=0.84, α=-1.0°, Re=4 × 106, P0=220 kPa and T0=274 K, the aerodynamic equilibrium shape is successfully obtained within three iterations. The maximum deformation of 3.11 mm appears at the wing tip of the wind tunnel model, and the resulting change in aerodynamic force produces a nose-down effect. A detailed examination reveals that the deformation mostly causes pure bending which reduces the effective angle of attack for the present swept wing. Moreover, we attempt to split the change in aerodynamic coefficients into that due to the model deformation effect and that due to the Reynolds (Re) number effect. By comparing the computed results for Re=1 × 106 and Re=4 × 106, it is indicated that an increase in lift coefficient due to the Re number effect is totally offset by the model deformation effect. It is also shown that the amount of drag reduction can be overestimated due to the model deformation effect. In addition, a CFD-aided data correction method utilizing the wind tunnel data is discussed.