Electromagnetic Compatibility for Space Applications: Test Specifications, Standards, and Methods

Background

According to the definition found in the new and the older EMC EU Directive, but also in other relative contexts, “Electromagnetic compatibility” is the ability of equipment to function satisfactory in its electromagnetic environment without introducing intolerable electromagnetic disturbances to other equipment in that environment. This definition is valid for all systems and devices regardless of the operating environment (industrial, commercial, military or space).

Another useful definition is regarding “electromagnetic disturbance” which is any electromagnetic phenomenon which may degrade the performance of equipment or a system and may be electromagnetic noise, unwanted signals or changes in the propagation medium itself.

An important aspect of electromagnetic compatibility of systems or equipment is their “susceptibility” (immunity) which defines a measure of the ability to perform as intended without degradation in the presence of an electromagnetic disturbance.

In general, the assessment of the electromagnetic compatibility of a system or unit is performed by making specific tests based on methods described in relevant standards. Depending on the field of application different kind of standards applies. Some tests are similar or even identical. However, limits or performance criteria could be different for different application areas like between space and commercial systems or units.

Electromagnetic compatibility for space applications utilize test methods similar or identical to military ones, like MIL-STD-461-F/G. Differences are encountered in test limits or specific parameters of tests like for example frequency range or, in some case, in instrumentation. For systems used in commercial applications, like for example household devices, electromagnetic compatibility is assessed using test standards prepared from International Electrotechnical Committee. The test methods are similar; however, limits and performance criteria are in most cases different.

The most important difference in electromagnetic compatibility assessment between space and commercial systems is that in space systems the interaction between electrical, electronic, electromagnetic and electromechanical equipment within a space vehicle may cause performance degradation or problems in the functionality that could compromise the success of the whole space mission. Therefore, all equipment shall be characterized carefully and in detail to obtain the necessary data to allow the analysis of the interactions and to define mitigation measures, especially for sensitive or critical, for the space vehicle, equipment. In such cases, strict electromagnetic interference safety margins are defined. This matter is defined as intra-system EMC. On the other hand, in commercial systems these, interactions are less frequent as electronic or electrical parts are less sensitive. And, if such problems arise, these cause marketing or sales issues only.

Intersystem EMC is defined as interactions between external natural, induced or man-made electromagnetic environment and the space vehicle. An example of natural electromagnetic environment is the voltage building-up of a space vehicle when entered in plasma. External, man-made interference might result from radar beams during ground operations or in launching sequence. Interference could be also applied between the launcher and the space vehicle.