Military systems are susceptible to the destructive effects of High-altitude Electromagnetic Pulse (HEMP) events. To mitigate these risks, Mil-STD-188-125-1A provides guidelines for protecting electronic and communications systems of on the ground installations, as well as onboard aircraft and vessels.

The B-2 Spirit stealth bomber incorporates HEMP protection measures in its design, including shielding, grounding, and surge protection. Rigorous testing, including EMC and HPEM evaluations, is conducted to verify the aircraft’s resilience to HEMP events.

Similarly, the Aegis Combat System—used on various Navy ships—undergoes extensive HEMP protection testing to ensure its electronic systems can withstand HEMP-induced electromagnetic fields while maintaining mission-critical operations.

This article outlines the quality measures and testing requirements that ensure HEMP protection is effective in an emergency and safe during everyday operation. By adhering to these standards, Department of Defense (DoD) agencies can enhance system resilience and maintain operational capabilities in the face of electromagnetic threats.

The Metrics of Compliance

The major areas of concern in MIL-STD 188-125 can be summarized in the following categories:

Shielding Effectiveness: Proper electromagnetic shielding is essential for safeguarding electronic systems against HEMP. Effective shielding ensures that sensitive components are isolated from external electromagnetic fields. Quality measures involve evaluating the shielding materials, design, installation techniques, and verification of radio-frequency emission levels. For example, conductive gaskets, enclosures, and coatings can be tested to ensure their effectiveness in attenuating electromagnetic interference (EMI).

Grounding and Bonding: Robust grounding and bonding practices are critical for dissipating HEMP-induced currents and preventing damaging voltage differentials. Quality measures include verifying proper grounding of components, cables, and enclosures, as well as ensuring low-impedance pathways for current flow. Testing may involve measuring ground resistance, verifying proper bonding connections, and assessing the overall integrity of the grounding system.

Surge Protection: HEMP events can induce high-voltage surges that can cause permanent damage to electronic systems. Surge protection measures, such as surge arrestors and suppressors, help divert and dissipate excess energy. Quality measures involve evaluating the surge protection devices’ response time, clamping voltage levels, and overall reliability. Testing may include subjecting the devices to surge waveforms and assessing their ability to suppress surges effectively.

Installation of low-voltage and medium-voltage HEMP filters from TSS USA Manufacturing are a proven intervention for defense systems. The specialty filters attenuate the higher-end frequencies that represent the greatest threat to electronics during surges. Both types of HEMP filters are designed and tested to conform to this guidance and integrate into compliance military-grade systems.

Laboratory and On-Site Testing Requirements

Mil-STD-188-125-1A details the testing methods to ensure HEMP protection in critical systems. To gain approval for DoD use, new electronics products and systems undergo a battery of engineering tests. These physical tests may occur on site or in a laboratory setting that simulates the installation site and as well as various levels of electromagnetic radiation.

Electromagnetic Compatibility (EMC) Testing: EMC testing ensures that electronic systems can operate in the presence of electromagnetic interference, including HEMP. Quality measures involve subjecting systems to radiated and conducted emissions testing to assess their immunity to external electromagnetic fields. For example, conducted susceptibility testing evaluates the system’s ability to operate in the presence of conducted disturbances induced by HEMP.

High-Power Electromagnetic (HPEM) Testing: One of the main aspects of HEMP is the high-altitude burst, which emits an intense electromagnetic field. Mil-STD-188-125-1A specifies the characteristics of the HEMP waveforms—designated as designated as E1, E2, and E3—including its electric field strength, rise time, and pulse duration.

Quality measures include assessing the system’s ability to withstand HPEM without experiencing catastrophic failures or functional impairments. For instance, susceptibility testing exposes the system to controlled HEMP-like waveforms to assess its vulnerability.

System-Level Testing: Comprehensive system-level testing is essential to evaluate the effectiveness of HEMP protection measures in a realistic operational environment. Quality measures involve subjecting the entire system, including its components, interconnections, and external interfaces, to simulate HEMP events. This includes shielding, grounding, bonding, filtering, and surge protection considerations. This testing ensures that the protection measures are properly integrated, coordinated, and capable of withstanding the expected electromagnetic threats.

Mil-STD-188-125-1A also includes measures for system hardening, which involves modifying existing system components or adding protective measures to enhance their resistance to HEMP effects. This may include replacing vulnerable components, adding shielding, or incorporating surge protection devices.

Documentation and Submission

It is worth noting that the certification process for HEMP protection systems can be complex and may involve multiple stages of testing and evaluation.

Systems seeking certification must provide comprehensive documentation detailing the design, test results, and analysis of the system’s HEMP protection features. The system, along with the supporting documentation, needs to be submitted to the appropriate certification authority or testing laboratory for review and evaluation. The certification authority will assess the system’s compliance with Mil-STD-188-125-1A and issue the certification if the requirements are met.

Working with experts familiar with the standard and its requirements—along with the overall process of certification—is recommended to ensure a successful certification process. TSS USA Manufacturing has been assisting DoD clients with testing and compliance for decades. Discuss your organization’s specific compliance situation with a TSS HEMP specialist today.