Mirce Science: Impact of Causing Mechanisms on Spare Parts Selection for Spacecraft Missions

Majority of spacecraft have been deigned to be “one shot devices”, which means
that they seized to exist at the end of the mission, or during the unsuccessful
missions, caused by any reason, whatsoever. However, today, there is growing
interest in designing satellites that could be refuelled in the operation by
replenishing on board propellants and other consumables. Even more, several
nations are planning to establish the permanent settlements of humans in space,
starting with space stations and later with bases on Moon and Mars. Hence, the
spacecraft of the future will inevitably experience failures of their consisting parts
during their missions. Spare parts are one of the most important resources
required for the spacecraft to be return to service. Thus, the main purpose of this
paper is to present Mirce science based method for calculating the number of
spare parts required for the successful completion of planned missions. It is
radically different from the currently well establish practise of the aviation and
defence industries, where the reliability departments collect failure data of
replaced parts and compute Mean Time Between Failures (MTBF) that logistics
departments convert it into failure rates =1/MTBF, which governs the number of
spares required for the given length of the mission. However, the Mirce science
method presented in this paper clearly shows that all failure causing mechanisms
do not posses a constant failure rate, hence, that not all spare parts calculations
can be accurately determine by applying current method. A simple, but not trivial,
numerical example presented clearly illustrates the ability of the Mirce science
methodology to quantify the undesirable consequences of the predictions made by
the constant failure rate method, as “Running out of spares during a spacecraft
mission is not an option”!