Capabilities and limitations of HPM weaponisation
A number of technological and operational issues need to be addressed if HPMs were to move out of the confines of research and application laboratories to become serious contenders as operational weapons for defensive and offensive roles. These include issues of weapon systems’ compactness and efficiency to suit a range of military platforms, issues related to antenna aperture to get desired operational ranges and peak-versus-average powers. Target acquisition, tracking and beam-pointing technologies and lethality assessment are other important factors.
Key advantages of HPM based directed energy weapons include speed-of-light delivery, all-weather capability, effectiveness over large areas, scalable effects, deep magazines and minimised collateral damage.
HPMs are speed-of-light weapons with essentially no time-of-flight as compared to finite travel time of conventional kinetic energy weapons. A supersonic missile travelling at 6Mach speed would take a flight time of about 50 seconds to hit a target 300km away. On the other hand, an HPM weapon could hit the same target in a millisecond or so. This feature is particularly suitable for attacking fast-moving targets.
Unlike high-energy laser weapons (to be described later), which are clear-weather weapons, HPM weapons are not adversely affected by weather and atmospheric conditions. For all practical purposes, these are all-weather weapons.
HPM weapons are area weapons unlike high-energy laser weapons that are point weapons. The footprint depends on the weapon’s power output, distance from the target and beam divergence. These affect all vulnerable equipment that comes within their lethal footprint (Fig. 5).
HPM weapons are ideally suited for targeting in urban environment due to minimised collateral damage. Some collateral damage may occur if friendly or civilian electrical systems are also in the footprint. HPM weapons have a deep magazine. Unlike conventional kinetic energy weapons that are single-shot weapons, HPM weapons can operate any number of times as long as there is power source. This also implies reduced logistics cost and cost per shot.
HPM weapons’ effects are scalable. Depending upon the magnitude of energy deposited on the target, the effects may be non-lethal or lethal. Active Denial System of the USA is a non-lethal HPM system designed for area denial, perimeter security and crowd control. It operates by heating the target’s surface. In anti-personnel role, it is the skin of targeted human subjects. Also, HPM weapons have the potential of jamming the targeted system without any knowledge about the RF output of the system.
In the case of an HPM attack, targeted system recovery is extremely difficult as it may require component or sub-system-level troubleshooting.HPM weapons are highly effective against deeply-buried bunkers by targeting vulnerable electronic systems such as communications, power and air ventilation systems that support these bunkers.
Major limitations of HPM weapons include relatively shorter operational ranges, difficulty of damage assessment and likelihood of damage to friendly, unprotected systems.
HPM weapons are area weapons and therefore adversely affect all unprotected electronic systems within their lethal footprint. These could include civilian and friendly systems, which could be protected by using proper shielding. Proper planning before an HPM attack could prevent unintended damage to friendly assets.
In the case of an HPM weapon attack, target damage assessment is very difficult as there are no signs of any physical destruction. Just because a system has stopped operating or emitting does not mean it has been affected by an HPM attack. Both absence and presence of emission from the targeted system does not reliably establish the efficacy of attack. However, advanced techniques may be used to measure second- and third-order effects to corroborate the results and enhance attack assessment.
HPM weapons have relatively shorter ranges as compared to high-energy laser weapons. In case of an HPM weapon system, range is proportional to both power output and antenna size. However, at sufficiently high microwave power levels, atmosphere at the antenna aperture becomes plasma, a phenomenon called atmospheric breakdown.
Plasma density increases with time duration of HPM pulses, eventually reaching the point where plasma reflects and absorbs RF energy. This not only renders the beam ineffective but also creates a shielding problem for the delivery platform.
Once atmospheric breakdown occurs, operational range can be increased only by increasing the antenna aperture, which may not be possible for portable or airborne designs.
For applications where portability is not a requirement and size is not a limiting factor, one can increase the effective aperture size and power on the target by using phase-locking techniques and combining multiple transmitters.
Another approach may be adopting designs that integrate antennae into the skin of the system, which allows aperture to be as large as the delivery platform. One such application scenario is that of point defence where the target is travelling towards the weapon system rather than weapon travelling towards the target. Ranets-E and Vigilant Eagle HPM systems are examples of such systems.
In the next part we will learn about e-bombs and representative HPM weapon systems.
To be continued…
Dr Anil Kumar Maini is former director, Laser Science and Technology Centre, a premier laser and optoelectronics research and development laboratory of Defence Research and Development Organisation of Ministry of Defence