Electrical failures

[Geoff_H]

It is possible to get a fault tolerant control system.  You need three control systems, if two systems agree then they can remove the third from operating.  The third can be repaired with the system running and no engine output is lost.  These systems are used where loss of control would be a problem.  A company called August Systems (now taken over by ABB) designed the first of these systems for the US space craft.  There is also a four control system that works slightly differently but just as effective.