A study to investigate the interactions between space system cost-effectiveness and spacecraft reliability and redundancy.

This document contains a detailed account of a study to investigate the interactions between space system cost-effectiveness and spacecraft reliability and redundancy. It is submitted to the University of Surrey for the degree of MPhil by research (in collaboration with the Defence Research Agency). Currently there is a strong drive from within the UK to understand the cost drivers and minimise the costs of government funded space ventures. Present programmes are concerned with satellite communications systems and remote sensing satellite systems. The aim of this study is to investigate and improve understanding of the interactions between the cost-effectiveness of such systems and the reliability and redundancy of the satellites within them. A broad review of other work reveals that limited research has been carried out in this particular field and that there is scope for further investigation. To gain added insight into the process of optimising reliability and redundancy with respect to system cost a study of the failure histories of satellites is conducted. Failures of a wear-out nature are almost as common as random failures; and the AOCS, power subsystem and payload are found to be the most failure prone parts of a satellite. A model is constructed which relates satellite reliability and redundancy to system cost-effectiveness, after first making a number of simplifying assumptions. Results from using this model indicate that a cost optimum amount of redundancy can be found for the spacecraft in this type of system. Also an interesting and potentially useful algorithm is derived which allows satellite designers to make an objective choice between whether to use cheap low quality/ technology components or more expensive high quality/ technology versions in a satellite. A critical review of the model and results forms the basis of a series of recommendations for further research