Missile autopilot design using quasi-LPV polynomial eigenstructure assignment

This paper presents the design of a missile autopilot over its flight envelop using quasi-linear parameter-varying polynomial eigenstructure assignment (PEA). The paper describes the extension of PEA to parameter-varying systems using a nonlinear missile model developed by Horton as an example. The autopilot is designed for a single-plane lateral acceleration control and a 5 degree of freedom (DOF) autopilot is also designed. Both lateral acceleration and augmented lateral acceleration outputs are considered. The lateral acceleration autopilot has nonminimum phase characteristics, and it is shown that the quasi-linear parameter-varying PEA approach can handle nonminimum phase systems unlike classic dynamic inversion techniques. Simulation results are presented over fast variations in Mach number and show that the design is robust.     

Nonlinear relative position control of precise formation flying using polynomial eigenstructure assignment

A nonlinear relative position control algorithm is designed for spacecraft precise formation flying. Taking into account the effect of J₂ gravitational perturbations and atmospheric drag, the relative motion dynamic equation of the formation flying is developed in a quasi-linear parameter-varying (QLPV) form without approximation. Base on this QLPV model, polynomial eigenstructure assignment (PEA) is applied to design the controller. The resulting PEA controller is a function of system state and parameters, and produces a closed-loop system with invariant performance over a wide range of conditions. Numerical simulation results show that the performance can fulfill precise formation flying requirements.     

Direct Intercept Guidance using Differential Geometry Concepts

This paper examines the application of differential geometry to the engagement of both nonmanoeuvring and manoeuvring targets. The kinematics of the engagement for both manoeuvring and nonmanoeuvring target are developed and expressed in differential geometric terms. Two-dimensional geometry is then used to determine the intercept conditions for a straight line target and a constant manoeuvre target. The intercept conditions for both targets are developed for the case when the interceptor missile guides onto a straight line interception. These two cases are shown to have a common set of core conditions such that it enables a unified guidance law to be developed. The guidance law is shown to be globally stable using Lyapunov theory, so that guidance capture is assured for any initial condition. The analysis and guidance law design does not rely on local linearisation and can be shown to produce guidance trajectories that mirror proportional navigation for the straight line interception of a nonmanoeuvring target for which proportional navigation was originally developed. The paper finishes with simulation in two dimensions, illustrating the convergence and solution properties of the approach.     

Electrophysiological, histochemical, and hormonal adaptation of rat muscle after prolonged hindlimb suspension

The perspective of long-duration flights for future exploration, imply more research in the field of human adaptation. Previous studies in rat muscles hindlimb suspension (HLS), indicated muscle atrophy and a change of fibre composition from slow-to-fast twitch types. However, the contractile responses to long-term unloading is still unclear. Fifteen adult Wistar rats were studied in 45 and 70 days of muscle unweighting and soleus (SOL) muscle as well as extensor digitorum longus (EDL) were prepared for electrophysiological recordings (single, twitch, tetanic contraction and fatigue) and histochemical stainings. The loss of muscle mass observed was greater in the soleus muscle. The analysis of electrophysiological properties of both EDL and SOL showed significant main effects of group, of number of unweighting days and fatigue properties. Single contraction for soleus muscle remained unchanged but there was statistically significant difference for tetanic contraction and fatigue. Fatigue index showed a decrease for the control rats, but increase for the HLS rats. According to the histochemical findings there was a shift from oxidative to glycolytic metabolism during HLS. The data suggested that muscles atrophied, but they presented an adaptation pattern, while their endurance in fatigue was decreased.