Showing papers by "Computer Resources International published in 1988"

Tracking accuracy evaluation for data relay and user satellites

Abstract: The demand for almost continuous coverage for close Earth orbiting satellites necessitates the use of data relay systems. The European Space Agency is currently studying the in-orbit infrastructure and is preparing a European data relay system, not only to be used for telemetry and telecommand purposes but also for tracking support. This paper deals with the tracking aspects of the user satellites and derives the requirements on the position accuracy of the data relay satellites. This orbit accuracy requirement is about 70, 25, 10 m (along track, cross track, radial) and can be achieved in routine cases with a few ranging stations suitably distributed in the European area. However, the use of an additional ranging station outside Europe, preferably in the Southern Hemisphere would aid the determination of the orbit after manoeuvres, especially after inclination control manoeuvres. Adequate knowledge of the position could then be achieved after about 4 h of dense tracking.

Knowledge-Based Dialogue in Intelligent Decision Support Systems

Abstract: The overall goal for the design of Intelligent Decision Support Systems (IDSS) is to enhance understanding of the process under all operating conditions. For an IDSS to be effective, it must: (1) select or generate the right information, (2) produce reliable and consistent information, (3) allow flexible and effective operator interaction, (4) relate information presentation to current plant status and problems, and (5) make the presentation at the right time. Several ongoing R&D programs try to design and build IDSSs. A particular example is the ESPRIT project Graphics and Knowledge Based Dialogue for Dynamic Systems (GRADIENT) which addresses the problems of: (1) knowledge-based alarm handling with real-time state and fault identification, (2) prevention of incidents through monitoring of operator actions, and (3) increased flexibility of the graphics interface through abandoning the restrictions of pre-defined displays. The GRADIENT project regards the interaction between man and machine as a whole and integrates several specialised support functions through the common concept of a knowledge-based, graphical dialogue. The starting point is the analysis of the functionality needed for this purpose. The knowledge-based systems provides the content of the interaction, graphical expert systems provides the form, and the whole is controlled by a dialogue system. There are two categories of users for the GRADIENT system: the designer of a particular application, and the operator who uses it to control the process. In both cases the GRADIENT project considers the functions that are needed to support these user categories.

Parameterized Algebraic Domain Equations

Abstract: An algebraic analogue to domain equations as known from denotational semantics is presented. A set of mutually recursive algebraic domain equations is roughly speaking a set of parameterized algebraic specifications applying instances of each other in a recursive fashion. The solution to a set of algebraic domain equations can be constructed by using a new parameter passing technique called recursive parameter passing. The theory also covers the notion of parameterized algebraic domain equations and it is shown that the result of successive actualization and recursive parameter passing is independent of the order. The specification method makes sense under an arbitrary institution.