Radiation tolerance of components for picosatellite on board computers

Abstract

Space has all kinds of radiation coming from the Van-Allen belts, the Sun or even background cosmic rays. At ground level, these do not pose a problem but as the altitude increases, the Earth's magnetic field gets weaker and the atmosphere gets thinner. This means that electronic devices in space receive a large radiation exposure. The On Board Computer (OBC) of a satellite has the task of supervising all systems and take decisions, which means that high reliability is required. To achieve this, triplex-redundancy is commonly used, whereby, three components performing the same task, utilize a voting system to cross check each other. Pre-radiation testing of these components is the key to reliability by providing insight into what the problems might be together with their symptoms, which can later be used to predict failure. This dissertation discusses some research into the radiation effects on electronic components, as well as designing hardware for evaluating the performance of devices undergoing radiation testing. The devices under test (DUT) included microcontrollers, memories and MOSFETs. The hardware was improved over multiple design iterations to improve reliability and extend functionality to test multiple components at one time. Latch-up protection circuitry was designed to cut off the power and isolate the DUT after exhibiting a latch-up condition for a fixed amount of time. The testing is performed to analyse the affects and symptims of radiation, in this case x-rays. Repeatability is ensured from one test to the next by varying only one parameter at a time -typically the only difference being the DUT itself. The DUT are subjected to x-ray while continually monitoring their power and storing the measurements every 10ms. Any functional errors captured during testing are stored on a text file alongside any available data like current, date, time and elapsed time since the beginning of the test. Details about the occurrence of any Latch-up event are saved on a separate text file. It is found that MRAM memory can handle much greater radiation dosage than the other memory technologies tested. Unpowered devices will survive longer in radiation. Heating electronic components will extend their life in a radiation environment, by reversing some of the deleterious effects of radiation.