This standard is applicable to all space systems. There is no space system in which radiation effects can be neglected.
In this clause the word “component” refers not only to electronic components but also to other fundamental constituents of space hardware units and sub-systems such as solar cells, optical materials, adhesives, and polymers.
Survival and successful operation of space systems in the space radiation environment, or the surface of other solar system bodies cannot be ensured without careful consideration of the effects of radiation. A comprehensive compendium of radiation effects is provided in ECSS-E-HB-10-12 Section 3. The corresponding engineering process, including design of units and sub-systems, involves several trade-offs, one of which is radiation susceptibility. Some radiation effects can be mission limiting where they lead to a prompt or accumulated degradation which results in subsystem or system failure, or catastrophic system anomalies. Examples are damage of electronic components due to total ionising dose, or damaging interaction of a single heavy ion (thermal failure following "latch-up"). Others effects can be a source of interference, degrading the efficiency of the mission. Examples are radiation "background" in sensors or corruption of electronic memories. Biological effects are also important for manned and some other missions where biological samples are flown.
The correct evaluation of radiation effects occurs as early as possible in the design of systems, and is repeated throughout the development phase. A radiation environment specification is established and maintained as a mandatory element of any procurement actions from the start of a project (Pre-Phase A or other orbit trade-off pre-studies). The specification is specific to the mission and takes account of the timing and duration of the mission, the nominal and transfer trajectories, and activities on non-terrestrial solar system bodies, employing the methods defined in ECSS-E-ST-10-04. Upon any update to the radiation environment specification (e.g. as a result of orbit changes), a complete re-evaluation of the radiation effects calculations arising from this standard is performed.
In order to make a radiation effects evaluation, test data are used, both to confirm the compatibility of the component with the environment it is intended to operate in, and to provide data for quantitative analysis of the radiation effect. In general there is one effects parameter for each radiation effect. Severe engineering, schedule and cost problems can result from inadequate anticipation of space radiation effects and preparation of the engineering options and solutions.
In some cases, knowledge about the radiation effects on a particular component type can be found in the published literature or in databases on radiation effects. It is important to use these data with extreme caution since verifying that data are relevant to the actual component being employed is often very difficult. For example in evaluating electronic components, consideration is given to:
• variations in sensitivity between manufacturers' "batches";
• variations in sensitivity within a nominally identical manufacturing "batch";
• changes in manufacturing, processes, packaging;
• correlation of measurements made on the ground and in-flight experience is far from complete.
As a consequence, and to account for accumulated uncertainties in testing procedures, component-to-component variations and environmental uncertainties, margins are usually applied to the radiation effects parameters for the particular mission. This document also seeks to provide specification for when and how to apply such margins.
Application of margins can have important effects on the engineering. Too high a level, implying a severe environment, can imply change of components (leading to increased cost or degradation of performance), application of additional shielding or even orbit changes. On the other hand, too low a margin can result in compromised mission performance or premature failure.