New Approach to Total Dose Specification for Spacecraft Electronics

The total dose specification of electronic piece parts in a space system should ensure that the system performs to its specifications in the total dose environment of space until the planned end of mission. This has... [ view full abstract ]

The total dose specification of electronic piece parts in a space system should ensure that the system performs to its specifications in the total dose environment of space until the planned end of mission. This has traditionally been accomplished by categorizing electronic parts for flight acceptability through the use of radiation design margin (RDM).  RDM is the ratio of the mean total dose failure level of a flight lot or lots of electronic parts to a fixed total dose level calculated for the mission.  The shortcoming of this approach is that both the failure level of the part and the total dose level for the mission are best represented as probability distributions, not fixed quantities.  The total dose environment, in particular, is very dynamic and must be evaluated years in advance in order to incorporate requirements into the mission design.  In this presentation a more complete approach is developed by evaluating and combining these two distributions.  The result is a probabilistic approach in which RDM for an electronic device is replaced with a calculation of total dose failure probability for the device during the mission.  This is applicable to both ionizing and non-ionizing (displacement damage) dose.

There are several advantages of the new approach.  First, the space radiation models for trapped protons, trapped electrons and solar protons are all used in a consistent probabilistic manner leading to the expected mission dose as a function of confidence level.  This gives the spacecraft design teams more information and trade space.  Second, the failure probability is less arbitrary than RDM and it better characterizes device radiation performance in space.  Thirdly, it allows direct comparison of total dose threats for different devices, regardless of whether it is total ionizing dose or displacement damage dose.  Finally, the probabilistic approach is more amenable to circuit, system and spacecraft reliability analyses.

In the presentation, example results will be given for devices selected for space missions and comparisons of the new and traditional methods shown.