US Air Force's 80 kW cooling demand sparks speculation over secret F-35 radar attack modes.

The U.S. Air Force and the F-35 Joint Program Office confirmed to Congress that future Block 4 fighter modernization requires doubling the aircraft's thermal management capacity to support the upcoming AN/APG-85 active electronically scanned array radar. Testifying before the Senate Armed Services Committee, program officials disclosed that the new radar architecture demands a future cooling target of 62 to 80 kilowatts, a massive expansion that prominent defense analyst Bill Sweetman hypothesizes could allow the gallium nitride sensor to function as a high-power microwave directed-energy weapon. This significant increase from the current 30 to 32 kilowatt baseline is structurally necessary to sustain advanced electronic warfare, computing, and sensor-fusion modes that generate unprecedented internal heat within the stealth airframe.

The physical incompatibility of the new AN/APG-85 radar mounting system has forced the delivery of at least six Marine Corps F-35B aircraft with ballast weights instead of active fire control sensors due to near-term production delays. Long-term optimization of the sensor relies on a staggered modernization pathway that introduces a 2031 Engine Core Upgrade and a subsequent Power and Thermal Management System overhaul to achieve the necessary heat-rejection threshold required for these classified high-power capabilities.

Related topic: Lockheed Martin prepares first Block 4 software updates to increase the F-35's combat capabilities.

The U.S. Air Force and the F-35 Joint Program Office confirmed to Congress that future Block 4 fighter modernization requires doubling the aircraft's thermal management capacity to support the entire AN/APG-85 AESA radar capabilities. (Picture source: US Air Force)

On June 23, 2026, the F-35 Joint Program Office told the Senate Armed Services Committee Airland Subcommittee that the U.S. Air Force is seeking to upgrade the AN/APG-85 radar's current cooling power from 30-32 kW to 62-80 kW in the future. Lt. Gen. Gregory Masiello, Program Executive Officer for the F-35 JPO, confirmed that the AN/APG-85 will replace the AN/APG-81 under Block 4, as the hearing focused on how the new radar will be introduced into production beginning with Lot 17 aircraft, why it cannot simply replace the older radar on those aircraft, how the Technology Refresh 3 hardware and Block 4 modernization increase the aircraft's cooling requirements, and how the Engine Core Upgrade planned for 2031 and a future Power and Thermal Management System could provide the additional electrical power and cooling needed for later capability growth.

When Senator Mark Kelly asked whether the APG-85 capability would be reduced before the new thermal system arrives, Masiello declined to answer publicly, a point that has contributed to speculation that this large increase in available cooling could be linked to a highly-classified mode. For now, the near-term production problem comes from the physical design of the F-35's nose section. The AN/APG-85 does not fit into the same forward fuselage installation as the AN/APG-81, and Lot 17 aircraft are being manufactured with the new radar mounting rather than the older APG-81 interface. That means the program cannot install an APG-81 as a temporary substitute when APG-85 production slips, even if an older radar set is available.

Masiello confirmed that the U.S. Marine Corps has already accepted six F-35Bs with ballast installed instead of radar, a temporary measure that preserves weight and balance but leaves the aircraft without its primary fire control sensor. These aircraft can fly, train for limited purposes, and support some pilot or maintenance activity, but Masiello stated that they cannot be considered fully mission capable. U.S. Air Force and U.S. Navy deliveries in the same configuration are expected later in 2026, making the radar transition a near-term fleet management issue rather than only a procurement scheduling problem. The program's planned correction is a common radar interface beginning with Lot 20, which would reduce the risk of future F-35s being trapped between a new airframe configuration and delayed radar hardware.

The hearing separated the AN/APG-81 from the main readiness problems affecting the existing F-35 fleet. Kelly asked whether radar availability was contributing to low fully mission capable rates, and Masiello answered that the APG-81 installed on most F-35s "is up and operating fine." The main readiness degraders are instead low observable coating maintenance, canopy durability and time-on-wing, software implementation, sustainment system capacity, and spare parts shortages. The sustainment system was effectively sized for 700 to 800 F-35s, but the operational F-35 fleet already passed 1,300 aircraft worldwide. That mismatch, logically, creates a structural readiness problem because depot capacity, spares pipelines, component repair throughput, maintenance manpower, and software support have not scaled at the same rate as deliveries.

In this context, the APG-81 is not the bottleneck; the limiting factor is the capacity of the support system to keep a large, low observable, software-intensive aircraft fleet ready for operations. The thermal figures are the most important engineering data from the hearing. Current F-35 fighters provide 30-32 kW of cooling, and a complete Block 4 configuration consumes essentially the full available cooling budget. Masiello stated that operating with zero cooling margin is not desirable, because it leaves no practical reserve for higher electronic loads, extended high-power operation, new software functions, or additional mission systems. The future target of 62 to 80 kW is therefore not a minor reliability adjustment; it is an attempt to double the F-35's heat-rejection capacity.

This matters because AESA radar, electronic warfare equipment, mission computers, data links, and sensor-fusion processors all convert electrical power into heat inside a confined stealth airframe. If cooling is saturated, the F-35 may have to limit output power, duty cycle, simultaneous operating modes, or future growth options even if the hardware is installed. In that sense, the hearing positioned the cooling power as a structural limit on the F-35's modernization, because the fighter cannot fully exploit future electronics unless power generation and thermal management grow together. The modernization pathway is therefore staggered, because the APG-85 arrives before the full power and cooling solution. The radar is being introduced with Block 4 and Technology Refresh 3, but the Engine Core Upgrade is not planned until 2031.

That engine improvement is expected to provide only a marginal increase in electrical generation and cooling, so it will not by itself deliver the 62-80 kW objective. The larger Power and Thermal Management System is expected several years later and is intended to support capabilities beyond the current Block 4 baseline. The sequence is therefore radar installation first, engine core improvement second, aircraft thermal architecture third, and post-Block 4 capability growth afterward. This creates a phased fleet in which early APG-85 aircraft may carry the new radar before the F-35 has the full energy and cooling capacity needed to exploit later high-demand functions. The classified portion of the hearing became important, as when Kelly asked whether the AN/APG-85 would operate with reduced capability before the Power and Thermal Management System becomes available, Masiello refused to answer publicly.

It did confirm that the answer depends on classified radar-power relationships. The relevant variables are not only whether the radar is installed, but how much transmitter power it can use, how long it can sustain certain modes, how much heat those modes generate, and what other aircraft systems are operating at the same time. A radar can be functional while still being constrained in peak output, operating duration, simultaneous radar-electronic warfare functions, or future software-enabled modes. The public exchange did not identify which APG-85 functions require higher cooling capacity, but it confirmed that the answer is highly sensitive.

This is why the APG-85 cannot be assessed only as a replacement for the APG-81; its value depends on a larger energy generation system that must support radar operation, electronic warfare, computing, communications and sensor fusion without forcing trade-offs between them. The 62-80 kW cooling target has also driven a hypothesis that the APG-85 could eventually support functions beyond conventional radar operation. Bill Sweetman, former Jane's Defence Weekly editor, argues that moving from 30-32 kW to as much as 80 kW is difficult to explain solely through better detection range, resolution, reliability or processing.

His hypothesis is that gallium nitride AESA technology could allow the AN/APG-85 to generate substantially higher radio-frequency output, supporting both sensing and high-power microwave (HPM) effects. In that concept, the radar aperture could be used not only to detect and track targets, but also as a directed-energy attack weapon to disrupt radar receivers, communications systems, passive RF sensors and electronic infrastructure. Sweetman links the idea to earlier U.S. Air Force CHAMP work, which explored counter-electronics high-power microwave effects, and to British developments connected with the ECRS Mk2 radar and GCAP's ISANKE architecture.

No U.S. government official has confirmed that the APG-85 has such a function, and Masiello's classified-session response neither validates nor disproves the theory. The defensible conclusion is narrower: the radar's future capability is dependent on power and cooling, and the planned cooling increase is large enough to suggest functions beyond a routine sensor replacement may be under consideration. The hearing ultimately frames the AN/APG-85 as one component in a larger F-35 energy modernization effort. The radar transition is synchronized with Block 4 software releases, Technology Refresh 3 processors, the 2031 Engine Core Upgrade, the later Power and Thermal Management System, and long-term electrical growth.

Additional cooling is not being pursued only to make the new radar fit into the F-35; it is intended to create margin for future capabilities beyond the current Block 4 configuration. The program therefore distinguishes between delivering aircraft, making them fully mission capable, installing the APG-85 and later exploiting the full capability set that higher power and cooling could enable. In the near term, radar production is the immediate delivery issue, but electrical generation, cooling and sustainment capacity are the long-term pacing factors that will determine how much capability the F-35 can add after Block 4.

Written by Jérôme Brahy

Jérôme Brahy is a defense analyst and documentalist at Army Recognition. He specializes in naval modernization, aviation, drones, armored vehicles, and artillery, with a focus on strategic developments in the United States, China, Ukraine, Russia, Türkiye, and Belgium. His analyses go beyond the facts, providing context, identifying key actors, and explaining why defense news matters on a global scale.

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