This question appears in Mumbai University > Satellite Communication and Network subject

Marks: 5 M

Year: May 2015

Once a satellite enters an orbit, there is little possibility of repairing components that fail or adding more fuel for station keeping. The components that make up a satellite must therefore have very high reliability in the hostile environment of outer space, and a strategy must be devised that allows some components to fail without causing the entire communication capacity of the satellite to be lost.

Space Qualification –

• Space qualification of every part of the satellite is carried out to ensure that it has a long life expectancy in orbit
• The first stage in ensuring high reliability in a satellite is by selection and screening of every component used. Past operational and test experience of components indicates which components can be expected to have good reliability. Only components that have been shown to have high reliability under outer space conditions will be selected
• Each component is then tested individually or as a subsystem to ensure that it meets its specification. This process is known as quality control or quality assurance

• Testing carried out on these components is designed to overstress the system and induce failure. It is an expensive process, and one of the factors that makes large GEO satellites expensive.

  Reliability –

  • We need to be able to calculate the reliability of a satellite subsystem for two reasons:
  • what the probability is that the subsystem will still be working after a given time period, and
  • the need to provide redundant components or subsystems where the probability of failure is too great to be expected
  • Reliability theory is a mathematical attempt to predict the future.

Bathtub curve for reliability failure

• The reliability of a component can be expressed in terms of the probability of failure after time t. For most electronic equipment, probability of failure is higher at the beginning of life – the burn-in period – that at some later time. As the component ages, failure becomes more likely, leading to a bathtub curve

• The aim of testing is to determine reliability, causes of failure, and expected lifetime.