Large UAV platforms–like Global Hawk, Predator, Fire Scout, Taranis and others–have a seemingly endless appetite for greater onboard compute density. The payloads aboard those systems are enabling ever greater autonomy for the UAV and its mission. The movement is toward more capable radar systems that fit into the same space, and in some cases more compact radar electronics to make room for other payload electronics.

Next-generation UAVs have shifted their internal architectures from a scheme of multiprocessing of big, power-hungry boards based on general-purpose processors to a strategy of relying on more integrated boards sporting powerful DSP-capable FPGAs. The original Global Hawk, for example, embedded around 40 processor boards. At least 30 of those boards were replaced by a couple of FPGA-based cards.

It isn’t just straight processing integration that the FPGAs provide. They’re most efficient at the DSP-kinds of functions done on board like radar processing and SIGINT. When the earlier version of Global Hawk used a multicomputer system made up of only general-purpose processors, it was inefficient when it came to many of the computing tasks. By instead letting FPGAs concentrate operations like repetitive convolutions–such as data reduction and manipulation–the general-purpose CPUs are off-loaded to focus on data-dependent control operations, which they’re good at.

Modular Radar System

An example of where this FPGA-based compute density is playing a role is the Multi-Platform Radar Technology Insertion Program (MP-RTIP). The MP-RTIP is a modular, active electronically scanned array radar system designed to be scaled in size so that it can be carried on board different platforms. Mezzanine form factors like PMCs and XMCs are well represented in the MP-RTIP program.

Earlier this month Northrop Grumman got approval to begin a portion of MP-RTIP Radar System Level Performance Verification (RSLPV) flight testing. The approval comes following a successful test readiness review for the MP-RTIP sensor’s Synthetic Aperture Radar imaging mode. This radar is slated for the RQ-4 Block 40 Global Hawk currently in production. The goal of the RSLPV test program is to verify that the radar meets operational requirements established by the Air Force, including Synthetic Aperture Radar (SAR) Spot image capabilities, SAR Swath imaging wide area capability, and Ground Moving Target Indicator (GMTI) capability to detect and track moving vehicles on the ground.

For RSLPV, the sensor is being flown on Northrop Grumman’s Proteus aircraft (Figure 1) as a surrogate for the first Block 40 Global Hawk. By verifying sensor performance on Proteus, the sensor testing has progressed without impact to production, significantly lowering the risk with regard to the Global Hawk’s operational capability. The first Block 40 Global Hawk, AF-18, has been built at Palmdale, CA, and is undergoing testing in preparation for its first flight later this year.

Cooling Enables Use of Faster Processing

Another method of boosting compute-density aboard large UAVs is the concept of using advanced cooling solutions that enable integrators to use boards that are less environmentally rugged in and of themselves. The problem can be addressed by using sealed, air-conditioned or pressurized compartments. These include both the U-2 Dragon Lady (ASIP program–Air Force Signals Intelligence Payload) and RQ-4 Global Hawk UAV. In both cases, alternative cooling solutions were needed to accommodate the upgrades. Meanwhile, other UAV platforms such as the MQ-1 Predator and MQ-9 Reaper don’t have any conditioned space, yet they had similar requirements for improved sensor capabilities and their designers likewise wished to leverage existing air-cooled board sets. The article “UAVs Embrace the Benefits of Direct Spray Cooling” in this section discusses how direct spray cooling enclosures help solve those problems.

Last summer Northrop Grumman’s ISR Systems Division awarded SprayCool a contract to provide its liquid-cooled enclosures for the ASIP-1C program. The SprayCool enclosures will house SIGINT electronics for the Air Force’s SIGINT-equipped MQ-1B Predator UAV (Figure 2) in support of Predator’s tactical warfighting role, sometimes described as a hunter/killer/scout mission. Under this contract, the SprayCool Multi-Platform Enclosure (MPE) was selected as a component in the ASIP-1C sensor payload for SIGINT-equipped Predator aircraft.