A Unified Approach to Model-Reference Adaptive Systems Part II: Application of Conventional Design Techniques

The use of linearized error equations in the design of model-reference adaptive systems developed by Part I is illustrated. Using standard control specifications on the system error (e.g., percent overshoot, rise time, etc.), a set of desired root locations on the root loci can be obtained. Then constants in the adaptive scheme can be chosen to obtain the desired root locations. Simulation results are given to illustrate the validity of the linearized error characteristic equation design procedure.     

Evaluation of Geometric Performance of Global Positioning System

The global positioning system (GPS) is a satellite-based radio navigation system to provide extremely accurate three-dimensional position fixes and system time to users anywhere on the Earth at any time regardless of weather conditions. The most significant performance parameter of the GPS is the degree of navigation accuracy which is strongly coupled to the choice of orbit configuration. The 3 X 8 orbit configuration has been considered as an operational GPS which consists of 24 satellites deployed in circular 63° inclined, subsynchronous 12-h orbits. In this paper, the geometric performance of several orbit configuration, including a 3 X 8 orbit configuration, is analyzed numerically by altering orbit period and elevation mask, respectively. It will be shown that 1) there are a few orbit configurations which are comparable to or better than the baseline 3 X 8 orbit configuration, and 2) for higher elevation mask, the geometric performance can be improved effectively by increasing orbit period to some extent.     

A Comparison of Numerical Methods for Solving Optimal Control Problems

Linear systems with quadratic performance criteria typically lead to two-point boundary value problems. The numerical solution of such problems is often difficult because of roundoff and truncation errors. In this paper numerical methods for digital computer solutions are considered for a system described by a given second-order linear differential equation and the results are compared. The results show that where accurate analytic solutions cannot be obtained, the invariant imbedding technique yields more accurate results, for a given integration grid interval, than the other methods considered.     

Optimum Linear Estimation of Stochastic Signals in the Presence of Multiplicative Noise

This paper considers optimum (MMSE) linear recursive estimation of stochastic signals in the presence of multiplicative noise in addition to measurement noise. Often problems associated with phenomena such as fading or reflection of the transmitted signal at an ionospheric layer, and also situations involving sampling, gating, or amplitude modulation, can be cast into such formulation. The different kinds of estimation problems treated include one-stage prediction, filtering, and smoothing. Algorithms are presented for discrete time as well as for continuous time estimation.     

Current views and future programs in cardiovascular physiology in space.

The volume shift of 2000 cm3 from the lower to the upper part of the human body during weightlessness gave rise to theoretical and practical questions which are addressed in this communication. The analysis revealed that the mobilized fluid reduced the interstitial fluid of the lower extremities by 40%. Applying the current ideas in the field of interstitial tissue physiology to these problems, one must conclude that the fluid displacement can only be brought about by a change of the interstitial tissue compliance. Based on the observations made by the astronauts and on our working hypothesis, a method was proposed to follow the fluid migration and to measure the tissue compliance in man. Results are reported from experiments under terrestrial conditions. They show that the tissue compliance indeed can be modulated. Applying the method in space can eventually help to clarify several concepts in terrestrial physiology.     

On Finite-Lag Receivers for Fading Channels

This paper reports some results on the development of finite-lag receivers for reception via fading channels. The receivers are given in discrete form and clearly show the additional complexity due to introduction of delay between the instants of reception and estimation of the signal. The channel noise has been assumed to have a multiplicative component due to fading. This results in the optimal demodulators being nonlinear and unrealizable. However, the receivers proposed are suboptimal, but realizable. Simulation studies evaluating the performance of the various receivers are also discussed.     

Surface, Subsurface and Atmosphere Exchanges on the Satellites of the Outer Solar System

The surface morphology of icy moons is affected by several processes implicating exchanges between their subsurfaces and atmospheres (if any). The possible exchange of material between the subsurface and the surface is mainly determined by the mechanical properties of the lithosphere, which isolates the deep, warm and ductile ice material from the cold surface conditions. Exchanges through this layer occur only if it is sufficiently thin and/or if it is fractured owing to tectonic stresses, melt intrusion or impact cratering. If such conditions are met, cryomagma can be released, erupting fresh volatile-rich materials onto the surface. For a very few icy moons (Titan, Triton, Enceladus), the emission of gas associated with cryovolcanic activity is sufficiently large to generate an atmosphere, either long-lived or transient. For those moons, atmosphere-driven processes such as cryovolcanic plume deposition, phase transitions of condensable materials and wind interactions continuously re-shape their surfaces, and are able to transport cryovolcanically generated materials on a global scale. In this chapter, we discuss the physics of these different exchange processes and how they affect the evolution of the satellites’ surfaces.     

On mapping a tracking algorithm onto parallel processors

The problem of mapping the tasks of a multitarget tracking algorithm onto parallel computing architectures to maximize speedup is considered. An asymptotically optimal mapping algorithm is developed and applied to study the effects of task granularity and processor architectures on the speedup. From the simulation results, it is concluded that task granularity and the parallelization of clustering and global hypotheses formation stages of the tracking algorithm are major determinants of speedup