ExoMars rover

Why is Dependability important?

There are no second chances in space missions. Getting something wrong has expensive and potentially unrecoverable consequences, especially as post-launch repairs are often impossible to carry out. The above constraints, together with the current trend of increased autonomy of space systems and the rapid and unpredictable rate of technological change, raises new challenges for dependability.

Unlike the aviation industry, the space industry can not typically follow the ‘fly-fix-fly’ approach. In fact, space programs are expected to work in one-shot, and thus imposing stringent dependability requirements. There are only a handful of exceptions to this approach, such as the shared NASA-ESA mission – the Hubble Space Telescope. Launched in 1990, Hubble continues to perform due not only to its robustness and built-in reliability but also to the new instrumentation installed during four servicing missions with the Space Shuttle.

Dependability is therefore an essential aspect in any space project and one of the key contributions to the overall quality of the final product. However it is not always perceived as such, due to schedule, cost, mass, volume and other constraints on projects. A dependability programme does not generate physical products like a breadboard or a solar panel. The outputs are essentially recommendations on design trade-offs, a statement of risk, a procurement choice, identification of potential design weaknesses, and so on. However, designing a space product without regard to dependability issues jeopardizes mission success and may lead to catastrophic consequences. Experience shows that mission failures are always more costly than proactive investments into quality, dependability and safety assurance.

Accidents are not due to lack of knowledge, but failure to use the knowledge we have. -- Trevor Kletz

The overall cost of a satellite and the cost of a kilogram placed into orbit together with the high levels of risk related to space operations are per se essential reasons for the development of reliable, highly available systems with minimal needs in terms of maintainability.

In space projects, dependability is essentially concerned with assuring the success of any space mission.

Last update: 30 September 2009

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