Jianjun Luo

Robust inertia-free attitude takeover control of postcapture combined spacecraft with guaranteed prescribed performance

In this paper, a robust inertia-free attitude takeover control scheme with guaranteed prescribed performance is investigated for postcapture combined spacecraft with consideration of unmeasurable states, unknown inertial property and external disturbance torque. Firstly, to estimate the unavailable angular velocity of combination accurately, a novel finite-time-convergent tracking differentiator is developed with a quite computationally achievable structure free from the unknown nonlinear dynamics of combined spacecraft. Then, a robust inertia-free prescribed performance control scheme is proposed, wherein, the transient and steady-state performance of combined spacecraft is first quantitatively studied by stabilizing the filtered attitude tracking errors. Compared with the existing works, the prominent advantage is that no parameter identifications and no neural or fuzzy nonlinear approximations are needed, which decreases the complexity of robust controller design dramatically. Moreover, the prescribed performance of combined spacecraft is guaranteed a priori without resorting to repeated regulations of the controller parameters. Finally, four illustrative examples are employed to validate the effectiveness of the proposed control scheme and tracking differentiator.

Airborne pseudolite aiding BeiDou system to improve positioning precision in low latitude areas

The BeiDou System (BDS), which has three satellites in Geostationary Earth Orbit (GEO), is a regional satellite navigation system of China and its positioning performance is notorious in low latitude areas. The two mending plans using Airborne Pseudolite (APL) aiding BDS to improve navigation precision in such areas are put forward. Plan I uses three BDS satellites and one APS to supply navigation data and Plan II employs two BDS satellites, one APS and altimeter to work. Both of the plans adopt point positioning with code pseudo-range algorithm. Geometric Dilution of Precision (GDOP), which is calculated by Positioning Error Transfer Coefficient Matrix (PETCM), is used to evaluate the positioning performance of new plans. PETCM is predigested when user is in low latitude areas. The key elements of predigested PETCM that effect the Geometric Dilution of Precision (GDOP) are analyzed. The character of GDOP is forecasted easily with the predigested PETCM. The simulations show that the precision of plans are expected to be hundreds of meters except some region where the latitudes of user and APL are close to each other and Plan II is better than plan I. The phenomenal consists with the theoretical analysis.