RISK ASPECTS OF A MISSION TO A COMET

Space science missions are rarely a repeat of a predecessor and thus i n the wider view they do not have the benefit of heritage-related stat istics. This paper discusses the cost and risk factors in gaining acce ss to space and describes the challenges of the forthcoming Rosetta mi ssion, which has the objective of conducting studies of a comet and it s increasing activity as it moves towards the sun. It will fly in form ation with the nucleus and later send a lander to its surface to condu ct in situ measurements. Reference will be made to the further challen ges for the scientific instruments faced by an eight-year period of in activity during the cruise phase after launch. Statistics have a part to play at the component and unit test levels but are increasingly les s relevant at instrument, spacecraft and mission levels. Ultimately th e designer is faced with a string of single-point failure possibilitie s, commencing with the launch vehicle and culminating with the unknown surface conditions that will greet the lander.