The U.S. Navy and contractor Northrop Grumman are building an engineering development model of a sense-and-avoid (SAA) radar subsystem for the MQ-4C Triton unmanned aircraft that they plan to complete by December. The Navy then expects to field a working system on the Triton by late 2019.
Fitting an SAA radar on the Triton, which in November had entered into an operational assessment at Naval Air Station Patuxent River, Md., will resolve a nagging challenge that could limit the operational flexibility of Global Hawk maritime derivative. The Triton needs a collision-avoidance capability to help it comply with an International Civil Aviation Organization requirement that military aircraft fly with “due regard” for the safety of other aircraft when operating over international waters. It will also be fitted with the traffic alert collision avoidance system (Tcas) and signal its position by automatic dependent surveillance-broadcast (ADS-B), but those two systems alone are not considered adequate for an unmanned aircraft.
In 2013, the Navy instructed Northrop Grumman to stop work on the SAA radar after subcontractor Exelis ran into problems in sizing the system to the space available in the Triton’s nose. The service restarted the effort a year later with Northrop Grumman leading the subsystem development and providing the radar’s front-end antenna array.
Last June, the Naval Air Systems Command (Navair) awarded Northrop Grumman a $39 million contract modification “for the correction of deficiencies to the current air-to-air radar subsystem design and to demonstrate that radar technology, performance and manufacturing risks have been effectively mitigated.” In response to a query from AIN, Navair said those deficiencies “were related to the producibility of the system’s radar antenna. Technical challenges associated with this included issues in the design and producing a system that could meet technical requirements within the available size, weight, power and cooling parameters for the Triton UAS.”
The contract calls for redesigning thin-tile arrays in the antenna assembly for integration into an SAA engineering development model (EDM), said Sean Burke, Navair’s Triton program manager. Through thin-tile technology, the transmit/receive modules of an electronically scanned radar are packaged on a substrate parallel to the array plane in a “tile” architecture, enabling a thin profile. Exelis had promoted its proprietary thin-tile array technology as “the key to smaller packaging, minimized cost and exceptional reliability” of an SAA radar, resulting “in one of the thinnest active electronically scanned arrays currently available.”
Under the contract, work on the EDM is scheduled for completion by December and should provide the production specifications for a working system. The Navy “intends to field a viable SAA solution that includes an air-to-air radar for Triton by Fiscal Year 2020,” which begins in October 2019, according to Burke.
The Navy and the Air Force are also cooperating on the latter service’s Common Airborne Sense and Avoid (C-ABSAA) program, an effort the Navy earlier joined but stopped funding in 2012. After initially focusing on an SAA system for the Global Hawk, the Air Force broadened the effort in 2013 to cover other unmanned aircraft platforms. In its current-year budget, the Air Force transferred the C-ABSAA effort to the Airborne Reconnaissance Systems project. “This transfer will provide greater visibility into this capability and prepares for expanded applications by making the capability program and platform agnostic,” the service stated in budget documents.
Asked if the Navy is formally participating in the C-ABSAA program, the Air Force Research Laboratory (AFRL) said the services are “informally collaborating (informing one another of our activities and sharing ideas and lessons learned) but our activities remain separate.” Navair’s Burke replied: “The Navy and the USAF will continue to review common solutions for airspace integration.”
Northrop Grumman, manufacturer of both the Global Hawk and its Triton derivative, suggested even closer collaboration by the services. During a press trip to the company’s facilities in California last month, Mick Jaggers, Global Hawk program manager, said the Air Force’s research also covers Triton. “We all have the same problem, how to put (an SAA system) on an autonomous vehicle, when the last line of defense for aviation is the human eyeball,” he said. “It is possible you will have unique variants associated with whatever the platform is,” added Tom Vice, Northrop Grumman Aerospace Systems president. “A common system, with probably a variant for the Navy and a variant for the Air Force—I could see that as a potential outcome.”
Separately, Northrop Grumman has participated with the AFRL in the multiple-intruder autonomous avoidance (MIAA) project to develop an SAA system, initially using a manned aircraft as an unmanned surrogate. That effort is due to continue using the Firebird optionally piloted aircraft built by Northrop Grumman’s Scaled Composites subsidiary in Mojave, Calif. However, plans to begin flight-testing this month have been delayed, according to the AFRL. “We're currently reevaluating the objectives and determining the next likely window to schedule it,” the laboratory said.
