On several engineering applications high Reliability is one of
the most wanted features. The aspects of Reliability play a key
role in design projects of aircraft, spacecraft, automotive,
medical, bank systems, and so, avoiding loss of life, property, or
costly recalls. The highly reliable systems are designed to work
continuously, even upon external threats and internal Failures.
Very convenient is the fact that the term 'Failure' may
have its meaning tailored to the context of interesting, as its
general definition refers to it as "any deviation from the
specified behavior of a system". The above-mentioned
'deviation' may refer to: performance degradation,
operational misbehavior, deviation of environmental qualification
levels, Safety hazards, etc. Nevertheless, Reliability is not the
only requirement for a modern system. Other features as
Availability, Integrity, Security and Safety are always part of the
same technical specification, in a same level of importance.
This paper intends to present the most important points to be
considered for building a Fault-Tolerant System applied to the
attitude control system of a spacecraft project. To accomplish its
intent, the paper starts by a theoretical review of definitions and
concepts. After that, the requirements of a spacecraft project will
be selected and/or written. Then, two possible solutions for the
requirements will be proposed, and then compared. As the conclusion
of this work, the key requirements for specifying a Fault-Tolerant
Systems will be highlighted. Besides, a comparison between the two
proposed architectures will be performed. Finally, possible
applications to the automotive system will be commented.