In future space infrastructure, missions for refueling and capturing inoperative spacecraft using an orbital servicing vehicle or a space robot have been considered. To realize these missions, six-degrees-of-freedom tracking control of a chaser spacecraft is required to approach the target spacecraft. Moreover, the stability of the system connecting the chaser and target must be ensured. It is also important to suppress position and attitude errors due to disturbances. In this study, our aim is to derive an adaptive proportional-integral-derivative (PID) controller that ensures the stability of a spacecraft system before and after capture, and that removes the state errors caused by a constant external disturbance. The effectiveness of the derived controller is verified by numerical simulations.
Kalman filtering-based in-flight alignment heavily relies on coarse alignment to obtain a sound initial attitude; otherwise the subsequent fine alignment cannot achieve a reliable and satisfying result. In order to strengthen the rapid response capability, it is necessary to have an integrated system combining an airborne global navigation satellite system (GNSS) with strapdown inertial navigation system (SINS) to implement coarse alignment on a moving base. Due to complicated flight dynamics and strict load constraints of UAVs, in-flight coarse alignment is much more difficult than ground coarse alignment. Moreover, the introduction of a low-cost micro-electro-mechanical system-based SINS (MEMS-SINS) with high noise, which is suitable for UAV applications with advantages in cost-effectiveness, lightweight, miniature design, low power consumption and survivability, makes it more challenging. In this paper, a novel in-flight coarse alignment aided by GNSS is derived to obtain the initial attitude based on quaternion. Velocity and its differential information from GNSS and specific forces from MEMS-SINS are compared to obtain an analytical solution for the initial angles. A flight test is conducted to test the new algorithm. The results indicate it can achieve 11.5 deg (1σ) accuracy for heading, and 5.7 deg (1σ) accuracy for level angles (i.e., roll and pitch). As a nice in-flight coarse alignment, it can guarantee accurate and reliable fine alignment afterward.
As is well known, the T-tail flutter speed depends strongly on the steady lift or dihedral angle of the horizontal tail plane. The unsteady rolling moment acting on the horizontal tail plane oscillating in yaw and sideslip plays a critical role in this phenomenon. In this paper, a numerical method based on 3D Navier-Stokes equations for computing the subsonic and transonic flow for a wing oscillating in yaw and sideslip is presented. By introducing a new coordinate system oscillating in yaw and sideslip, the existing 3D Navier-Stokes code is easily modified to account for the in-plane motions. The calculated rolling moments show good agreement with the existing experimental data obtained for incompressible flow, and the effect of compressibility, especially the effects of the shock wave in transonic flow, on the rolling moment are clarified.
The flutter speed of a T-tail depends strongly on the angle of attack or dihedral angle of the horizontal tail plane (HTP). The unsteady rolling moment acting on the HTP oscillating in yaw and sideslip, which is induced by the bending and torsion of the vertical tail plane, plays a critical role in this phenomenon. In this paper, a 3D Navier-Stokes code that takes into account the in-plane motion of the HTP is developed, and the unsteady flow features of transonic flow around an oscillating T-tail are clarified, especially, in relation to the mechanism generating the rolling moment.
The L1 and L2 points of the Sun-Earth system attract much attention for various space uses, such as observation and communication. Deploying the spacecraft just on L1/L2 is, however, not convenient, because L1 always overlaps with the Sun as seen from the Earth and L2 is hidden behind the shadow of the Earth. Adopting a small-amplitude periodic orbit around the L1/L2 points is one option to solve this problem. The orbit can be achieved by low continuous maneuvering. The required magnitude of acceleration is at a level that can be managed by solar radiation pressure. Utilizing solar radiation pressure has the possibility of saving maneuvering to keep the spacecraft near a L1/L2 orbit. Acceleration due to solar radiation pressure depends on the surface area of the spacecraft and thus the spacecraft should be equipped with a large flat surface. A spacecraft equipped with a solar sail is appropriate. This paper presents two station-keeping examples of solar sails in the vicinity of SE L1/L2 using acceleration resulting from solar radiation pressure. The orbit control laws are built into the linear system about the equilibrium, and we confirm that they are applicable in the non-linear system through numerical calculation.