EMI is the interference caused by an electromagnetic disturbance that affects the performance of a device. Sources of EMI can be environmental, such as electrical storms and solar radiation, but more usually will be another electronic device or electrical system. If the interference is in the radio frequency spectrum, it is also known as radio frequency interference or RFI.

Electromagnetic interference often manifests as undesirable noise and may lead to disrupted function of electrical, electronic, and RF systems. There are four types of EMI:

• Conducted EMI – EMI that flows through wires and is caused by physical contact with the source of EMI.
• Common Mode EMI – A high-frequency EMI that flows in the same direction through one or more conductors.
• Differential Mode EMI – A low-frequency EMI that flows in an opposite direction through adjacent wires.
• Radiated EMI – The most common type of EMI, caused by radiating electromagnetic fields. Common manifestations of radiated EMI include static noise on AM/FM radio receivers and “snow” on TV monitors.

Common sources of EMI include:

• Power generating equipment and peripherals such as generators, power supplies, voltage regulators, switches and relays, battery chargers, and high voltage electrical transmission lines.
• Devices operating at high frequencies like oscillators, computing devices, radios, radar, and sonar equipment.
• Machines that use both high voltage and high frequencies, including motors and ignition systems.

EMS refers to the susceptibility of electronic systems to malfunction or performance degradation in the presence of electromagnetic interference. EMS can be triggered by various factors, such as environmental, such as electrical storms or solar radiation, high-power electromagnetic fields, conducted disturbances, and transient voltage events. Understanding and mitigating EMS is crucial to ensure the robustness and reliability of electronic systems, especially in environments with elevated electromagnetic activity or potential risks of interference.

High levels of radiated and conducted electromagnetic energy exist ambiently and has the potential to couple into susceptible electronics, degrading performance. Some examples of these sources are:

• Wireless communications like WiFi, Bluetooth
• Microwave sources including 5G small cells
• Magnetic fields from transformers, motors, appliances
• Electrostatic discharge events
• Lightning strikes creating intense transient energy
• Electric power line disturbances

EMC is a measure of a device's ability to operate as intended in its shared operating environment while, at the same time, not affecting the ability of other equipment within the same environment to operate as intended.

Electromagnetic compatibility of an electrical, electronic, or RF device has two facets:

• EMS = The ability to work properly in the presence of electromagnetic radiation.
• EMI = The ability to not generate additional EMI that affects the operation of other devices in its vicinity.

The Electrical Power System (EPS) of spacecraft typically consists of an electric power-generating source (e.g., generators, batteries, fuel cells, solar arrays, and distribution subsystems) including the associated cables, switches, protective devices, converters, and regulators.

Power quality is directly related to the effects produced by power generation, power conditioning, system impedance, and the interactions within the distribution system which includes loads. Interactions include electromagnetic interference (EMI), regenerative energy, and system transients resulting in power surges and spikes.

The EPS should remain stable over the entire range of power generation, energy storage, and load conditions in all operating modes, temperatures, and orbital phases or conditions over the power system's design life to maintain power quality.

Two shielded/anechoic testing facilities are available for conducting EMC tests.

These facilities meet electromagnetic performance requirements specified by MIL-STD-461, and support the performance of EMC tests specified by MIL-STD-461; the GSFC "Goddard Environmental Verification Specification" (GEVS); and numerous other EMC testing specifications.

The ambient electromagnetic noise level is verified to be at least 6 dB below test specification limits prior to testing.

Both facilities provide very low interior noise level ambient electromagnetic environments; excellent earth grounding; and have the ability to contain internally-generated, radiated electromagnetic waves.

All electrical power, communications, and other facility wiring are filtered, and the facility structures are bonded to earth ground, to minimize the introduction of external electromagnetic noise.

Both facilities feature ventilation and other apertures designed as waveguide-below-cutoff to prevent either ingress or egress of electromagnetic waves.

Both facilities are equipped with electromagnetic energy-absorbing panels allowing optimized anechoic performance.

Each facility also features wall-mounted ferrite tiles for absorption of incident energy at frequencies from 20-MHz to 1-GHz and the Small facility has ceiling-mounted tiles as well.

The Large facility has only a 10-ft x 10-ft anechoic target mounted on the ceiling. It is typically used for the absorption of intentionally generated, highly directional test article microwave signals.

Rohde & Schwarz spectrum analyzers/receivers systems are used for generated interference data acquisition, processing, and data reduction.

Peripheral equipment includes electric field and magnetic field antennas and line conduction transducers for testing in the frequency range 20 Hz to 40 GHz.

The Receiver/Analyzers are controlled by an ISO9000 controlled, Windows-based EMI measurement software package.

Susceptibility tests are performed using a composite electric field, power, and signal line susceptibility system consisting of signal generators, amplifiers, and transducers for injection and radiation of electromagnetic energy.

The test frequency range is 30 Hz to 400 MHz for signal injection, and 10 kHz to 40 GHz for signal radiation.

All emissions test data are recorded in a swept spectrum analog format at specified receiver bandwidths. The data is then converted to a logarithmic amplitude versus frequency printout, including a specification limit when applicable, by an ISO9000-compliant software package.

The measurement and analysis system is used for both radiated and conducted emissions measurements.

All susceptibility data are acquired manually during the injection or radiation sweep.

During testing, if the experimenter notes frequencies at which the test item is susceptible, these frequencies and threshold levels are recorded manually on data log sheets.

Two auxiliary power systems are available which have the following capabilities. These DC systems are normally used to provide very low noise power to the test article to insure that any measured emissions are, in fact, generated by the test article and not the test equipment.

Low Power DC System - 13 amp maximum, 80 ± 0.1 VDC; digital power supply.

High Power DC System - 100 amp maximum, 600 amp-hour semi-portable battery system, 28 VDC, ± 4 VDC; also contains special connections for 24 to 36 VDC in 2-volt increments.