This paper addresses observer-based optimal zero-sliding midcourse guidance for missiles with thrust vector control (TVC) and a divert control system (DCS) for the interception of a theater ballistic missile. First, a three degree-of-freedom observer-based optimal zero-sliding midcourse guidance law is designed to minimize the control effort and to narrow the distance between the missile and the target. Then, the exponential stability of the overall system is analyzed thoroughly via the Lyapunov stability theory. Finally, successful simulations are developed to verify the effectiveness of the proposed guidance law.
Due to the difficulty in accurately predicting the limit cycle oscillation (LCO) generated by nonlinear unsteady aerodynamics in the transonic regime, neither the traditional system identification nor eigenmode-based reduced order model (ROM) are suitable for designing active LCO control law. A support vector machine (SVM) based ROM is investigated and an active control law design method based on the new ROM is proposed. A three-degree-of-freedom pitch and plunge aeroelastic systems in transonic flow is successfully demonstrated for the SVM-based ROM. The simulation results indicate that the active LCO control law can be designed and evaluated with good accuracy and efficiency by the SVM itself, without requiring intensive simulations of the CFD/CSD couple solver.
This paper proposes a real-time collision avoidance algorithm for midair unmanned aerial vehicles (UAVs). The algorithm is developed based on the geometry of the closest-point-of-approach (CPA) and a collision detection/resolution scheme. To deal with multiple aircraft, the avoidance velocity of one's own aircraft is expressed in an explicit form, where the avoidance velocity is a component of the safety boundary. The safety boundary is projected on the domain of the flight path angles, and sampling points are chosen along the boundary. The domain of the flight path angles provides directions along which the aircraft can move without collisions, which can reduce the computational load for real-time applications. A collision avoidance solution is obtained by examining possible collision cases involving intruders. The singularity of the geometric approach is also analyzed, and an additional boundary for the singularity is adopted to prevent unexpected maneuvers. The validity of the algorithm is demonstrated through numerical simulations for the non-cooperative and multiple aircraft avoidance problems.
Weak stability boundary (WSB) lunar gravity-capture transfers can save much effort (dV) on arrival at the Moon but there is a very narrow window of only a few days in a month to achieve these transfers. This is because WSB transfers require a specific orientation of the orbit with regard to the Sun, the Earth and the Moon to efficiently use the chaotic dynamics of the multi-body problem. In this paper, we propose controlling the orbit through small continuous acceleration. The results show that the window of the WSB transfer can be expanded up to a full month.
A signal-acquisition process using the fast Fourier transform algorithm enables parallel correlation based on the circularity of code sequences. If a bit transition exists in the received signal sample, the correlation peak does not represent the maximum value at the true Doppler shift. Although there has been some research to solve the bit-transition problem, an analysis of this research with a performance index does not exist. This paper analyzes and compares calculation time and the signal detection probability of two existing methods and a new method for single-period code acquisition. Simulation results indicate that although the zero-padding method shows the best performance based on signal detection probability, the calculation time of the new method is the fastest of the test methods.
The present paper sheds some light on simplified mechanical models in order to discuss the dynamic stability of slender flight bodies subjected to aerodynamic loads. Firstly, we discuss the nature of a suitable simplified mechanical model to demonstrate body divergence and flutter. A method leading to a rational mechanical model is presented. It is shown that a simplified model composed of three bars connected together by two elastic rotational hinges, having four degrees-of-freedom, is preferable to discuss both body divergence and flutter. Secondly, after having a duly simplified mechanical model, effects of mass distribution, stiffness distribution and location of a stabilizer fin are discussed. A perspective of body divergence and flutter of slender flight bodies is demonstrated on the basis of the proposed simplified mechanical model.
Throttled operation of turbopumps of liquid rocket engines is studied analytically. Two types of pressure drops in the propellant injector are examined, that is, the drop of gas injection and that of liquid injection. Circulation is examined in relation to throttling to operate the pump in the vicinity of the design condition. An enthalpy increase at the pump entrance is derived analytically in the circulation system. With the derived analytical relationships, throttled operating conditions are examined for imaginary LH2 and LOX turbopumps with a LH2/LOX property calculation code. The circulation causes gasification at the entrance of the high-pressure LH2 pump. This does not occur in the mid-pressure LH2 pump or the LOX pump. In the liquid propellant injection system, the unstable region becomes narrower than in the gas propellant injection. The ratio of the turbine flow rate to the pump flow rate decreases in line with throttling. Throttling does not degrade the engine specific impulse from the viewpoint of the turbine bleed ratio.