On-Board Power: The uncomfortable bottleneck of future Electronic Warfare

The relationship between onboard electrical generation and mission capability is quite obvious, although not discussed enough. Military fighter generations tend to be discussed in terms of aerodynamics, stealth, and maneuvering capabilities; however, a not-so-spoken factor about generations is on-board power generation, which keeps increasing and the trend is far from being over.
In terms of EW platforms, take the F-16CM Wild Weasel, the Air Force's classic platform for Suppression of Enemy Air Defenses, or SEAD. It runs on roughly 60 kVA from a single engine-driven main generator, with a 10 kVA backup, both designed in the 1970s–80s [1]. The AC is distributed at 115/200V, 400 Hz through a Constant Speed Drive gearbox, with passive TRUs feeding 28V DC avionics buses. The TRUs are a particularly unpleseant load, composed of rudimentary diode-bridge rectifiers drawing current in non-sinusoidal pulses, presenting an effective power factor of 0.6–0.7 at their input. Combined with the extensive use of inductive loads such as motor-driven hydraulic and fuel pumps, the composite power factor seen by the generator is roughly 0.75–0.78, yielding approximately 45–47 kW of usable power. That is all there is to run the radar, the HARM Targeting System, electronic warfare pods, datalinks, flight computers, and cockpit displays.

Comparatively, the F-35 represents a generational leap, also in power architecture. Unlike current-generation fighters, the F-35 relies on"more-electric" systems, including an electric starter, electrically driven flight-control surfaces, and all-electric auxiliary power and emergency power. Engine-mounted starter/generators produce approximately 160kVA of variable-frequency AC (no Constant Speed Drive, so the generator speed varies with engine RPM, eliminating the CSD's weight and maintenance burden) [2]. That AC is immediately converted to 270V DC through active front-end rectifiers that achieve power factors of 0.93–0.95, effectively eliminating reactive power loss at the generator. The 270V DC primary bus is a much higher voltage than legacy 28V DC systems, allowing the same power at far lower current and therefore lighter cabling, feeding mission systems through DC-DC converters. The F-35's electrical power system provides generation, distribution, load management, and protection across 270V DC, 28V DC, and 115VAC buses, with the 270V DC system powering high-demand loads like the electro-hydrostatic flight control actuators. Planned future electrical architecture reportedly targets 400 kVA (~345–360 kW usable) [3]. Pratt & Whitney describes the F135 engine as delivering substantially increased power and thermal management over 4th generation fighter engines, with the specific "more than a 300% increase in power and thermal management" cited in a 2020 modernization study announcement. The F-35 needs every single watt. Which should not be a surprise, considering the aircraft is practically a computer with wings: AN/APG-81 AESA radar, electro-optical targeting, electronic support measures, MADL and Link 16 datalinks, sensor fusion computers all draw power simultaneously. Every watt consumed eventually becomes heat that must be rejected from a stealth airframe with limited thermal sinks to avoid becoming "visible" to heat-seeking weapons.

In terms of dedicated EW and ISR platforms, the E-3 Sentry —a four-engine Boeing 707 derivative—carries multiple generators and requires the majority online simultaneously to power its klystron-based AN/APY-2 radar. Total generation capacity is estimated at approximately 320 kVA [4]. The E-3's architecture is legacy 400 Hz AC distribution, and its on-board power quality is challenging: the radar transmitter and its high-voltage electronics present a complex, highly reactive impedance, and the heavy loads (rotodome drive, cooling systems, hydraulic pumps) are highly inductive. With passive rectification on the avionics buses, the composite power factor is estimated at 0.75–0.78, yielding roughly 240–250 kW of usable power.

The RC-135 Rivet Joint, on the same four-engine C-135 airframe, has comparable generation capacity but a fundamentally different load profile. Its mission is primarily about receiving and digital processing, not high-power transmission. The banks of receivers and signal processors are fed through power supplies that, while not as modern as the F-35's 270V DC architecture, include more regulated conversion stages than the E-3's klystron transmitter chain. The composite efficiency is somewhat better, yielding an estimated 255–265 kW from a similar generation base [5].

The old EC-130H Compass Call draws from four turboprop-driven generators totaling an estimated 160 kVA [6]. Its high-power jamming transmitters present a similarly reactive load to the E-3's radar, and with legacy AC distribution, the usable power can be estimated at approximately 120–125 kW; every watt of which is needed to generate sufficient jamming energy to disrupt enemy command and control at operationally useful ranges.

Unmanned platforms such as the MQ-9 Reaper generate an estimated 10–15 kW. The RQ-4 Global Hawk generates approximately 30–40 kW [7]. At this scale, the loads are predominantly digital avionics and sensor payloads with modern switch-mode power supplies operating at high conversion efficiency. The architectures are basically all-DC downstream of the generator, and the power factor gap is smaller. These platforms can carry sensors and datalinks, although they cannot power the kind of high-energy radar, broadband SIGINT suite, or electronic attack systems that define the manned special-mission fleet.

The thermal problem

As the saying goes, there is no free lunch. Electrical power generation and thermal management are coupled engineering domains. The conversion losses described above all ultimately manifest as heat that must be handled and transferred awayfrom temperature-sensitive electronics into a thermal sink, which is typically the fuel (used as a coolant before combustion) and the airstream. However, the airframe's thermal management system has finite capacity.

When the F-35 was designed, engineers assumed the electronics would produce no more than 14 kW of waste heat. By the time Block 3F entered service, actual demand was 32 kW. Block4 capabilities are requiring more power and cooling than originally projected, and the power shortfall has forced the engine to work harder than contractors intended, reducing its life expectancy and adding an estimated $38 billion to the programme's lifecycle cost. It has been reported that the F-35's current Power and Thermal Management System is overtasked, requiring the engine to operate beyond its design parameters.
The aircraft is expected to remain in service into the 2070s. Every future sensor upgrade, every new, more powerful radar mode, every additional EW capability planned for the F-35 must fit within whatever power and cooling budget exists at the time. Of course, this challenge is not unique to the F-35. Every platform that carries electronically intensive mission systems will face the same constraints.

Shrinking platforms

EW platforms appearto be transitioning from legacy, large four-engine platforms to smaller airframes, which makes the power hunger only more acute.

The EA-37B Compass Call is moving the jamming mission from a four-engine C-130 to a twin-engine Gulfstream G550. The G550 is faster, flies higher, has greater range, and is more survivable. However, it has two engines' worth of generator shafts instead of four. The baseline G550 provides an estimated 80 kVA; with modern power conversion, the usable power is approximately 70–72 kW before augmentation [8]. Integrators had to redesign the power architecture to extract substantially more than this from two Rolls-Royce BR710 turbofans, while preserving enough shaft power and bleed air for flight. The planned fleet of 22 aircraft (vs. 14 EC-130Hs) partly compensates for any per-aircraft power reduction through greater numbers and operational flexibility.

NATO's replacement of the E-3 with the Saab GlobalEye follows the same pattern: moving from a four-engine 707 to a twin-engine Bombardier Global 6000. Here, AESA radar technology is the main driver, with solid-state transmit/receive modules right at the antenna which are comparatively more efficient at converting electrical power to radiated RF energy than the legacy klystron tubes and waveguide runs. The same detection performance can be achieved with meaningfully less electrical input. And because AESA T/R modules are solid-state devices powered through modern DC conversion stages rather than high-voltage AC modulator circuits, the power architecture is inherently more efficient than the reactive, harmonics-rich environment of a klystron-based system. But "less" is somewhat relative, and powering a capable AEW radar from two business-jet engines is still a demanding engineering quest. The trend indicates that operational imperatives (survivability, speed, altitude, efficiency) are driving platforms smaller, while the mission imperative (more powerful sensors, more computing, broader-band jamming, cognitive EW, directed energy) are driving power demand higher.

The directed energy horizon

Fast forward, and the power constraint becomes the single most critical limit on  airpower. The US Air Force has expressed interest in mounting 100+ kW class laser weapons on fighter aircraft for missile defence and SEAD. A 100 kW laser at 30–40% wall-plug efficiency requires 250–330 kW of electrical input, plus the cooling capacity to reject 150–230 kW of waste heat. The F-16 at ~46kW usable cannot even begin to approach this. The F-35 at ~143 kW is still insufficient. Even the 400 kVA future growth path (~350 kW) is barely adequate if other systems are simultaneously active.

Sixth-generation fighter programs are treating power generation and thermal management as main design drivers. The expectation is megawatt-class electrical generation: ten to fifteen times what the F-35 produces. This brings a different kind of engineering design challenge between the engine, the generator, and the thermal management system. The engine stops to be just a source of thrust with ancillary electrical generation to becomes a power plant in the most literal sense, with thrust as one of several energy outputs competing for shaft power.

Conclusion

The discourse around electronic warfare focuses almost entirely on the features: waveforms, algorithms, cognitive jamming, machine learning for signal classification. Which do matter. However, they are all downstream of a more fundamental problem: can the platform generate, sustain, and cool the electrical power that the mission demands?

A jammer that could defeat every threat in the electromagnetic spectrum is useless if the aircraft cannot power it at the time is needed because something else is running. A radar that could see every target is useless if the thermal management system cannot reject the waste heat or do it in a way its stealth capabilities would be compromised. A directed energy weapon that could defend against any missile is pointless if the engine cannot supply the electrical input needed.

Just like in data centers on the ground, power is the constrain in the air. It limits what electronic warfare can do, determines which platforms can perform which missions, and ultimately decides whether the next generation of airborne systems can deliver the capabilities that militaries are assuming. The countries and programs that solve the power-thermal-weight problem better will define the upper bound of what is possible in the electromagnetic domain. Those that do not will find that their most advanced software is running on hardware that cannot be powered on.

Photo: Jovian Kan on Unsplash

[1] Hamilton Sundstrand (now Collins Aerospace), F-16 Electric Power Systems — manufacturer product documentation specifying the40/60 kVA main generator and 10 kVA backup generator, including CSD and upgradekits.

[2] The 160 kVA figure for the F-35's starter/generator is widely cited in defence technical literature and corroborated by Pratt &Whitney's published "300% increase in power and thermal management"over 4th-generation engines (which produce 40–60 kVA).

[3] The 400 kVA growth target is referenced in defence trade press and technical forum discussions in the context of F135 modernization options. It is consistent with the GAO's reporting that Block 4 and future upgrades will require significantly more power than currently available, but the specific figure does not appear in publicly available GAO or JPO documents.

[4] E-3 Sentry electrical generation capacity estimated from the baseline Boeing 707-320B airframe specification (four engine-driven generators) and the known addition of mission-specific generators for theAN/APY-2 radar. The Boeing 707's standard electrical architecture uses 40 kVA integrated drive generators per engine; the E-3's mission modification adds additional generation capacity. The requirement for six of eight generators to be online for radar operations is reported in operational accounts. Precise figuresare held in Boeing/US Air Force technical orders.

[5] RC-135 generation capacity estimated from the sharedC-135/707 airframe baseline. The aircraft's mission modification for SIGINT collection involves extensive avionics additions but not the high-power radar transmitter of the E-3, resulting in a different load profile. Specific electrical system figures are not publicly available.

[6] EC-130H generation capacity estimated from the baselineC-130H Hercules specification. The C-130's four Allison T56-A-15 turbopropseach drive generators via power-takeoff arrangements. The Compass Call missionmodification adds power capacity for the electronic attack suite. Specificaugmented figures are not publicly available.

[7] MQ-9 and RQ-4 power generation estimates derived from published engine specifications and known payload power requirements. TheMQ-9's Honeywell TPE331-10 turboprop produces ~900 SHP, with electrical generation representing a fraction of shaft power. The RQ-4's Rolls-Royce AE3007H turbofan drives a higher-capacity generation system, with the Block40/RQ-4B upgrade specifically increasing electrical output. General Atomics and Northrop Grumman do not publish specific kW figures in unclassified product literature.

[8] G550 baseline generation capacity estimated from published Gulfstream specifications for the two Rolls-Royce BR710 turbofan engines and standard business-jet electrical architecture. The EA-37B's augmented power capacity is classified.