Ultra-endurance drone missions, boosted by air-to-air refueling, could enhance America’s surveillance war.
RQ-4 Global Hawk. Image: Northrop Grumman
While America's most expensive surveillance drone, the Northrop Grumman RQ-4 Global Hawk, can stay aloft for 32 hours, the Pentagon is looking for a drone that can fly nonstop for a week or more at a time, if two recently submitted solicitations are to go by.
In a solicitation published last November, the Department of Defense (DoD) is calling on contractors to submit designs for a low cost, ultra-long endurance UAV that can perform intelligence, surveillance, and reconnaissance (ISR) missions for seven days or more. Specifically, the DoD wants to eliminate the need for launching new waves of drones to replace the ones that have run out of fuel and have to return to base.
"The objective of this topic is to develop a low cost UAV with very long endurance, of at least seven days, that would enable the ISR mission to be accomplished with reduced manpower and system resources (esp. number of vehicles) to maintain near continuous coverage," writes the DoD.
"Notionally the UAV will transit from its launch point to the area of interest nominally several hundred miles away, and loiter in that region for the mission duration, although the ability to move quickly between nearby areas of interest is also desired."
The ability to maintain secrecy is a necessity with this proposed drone, and the DoD requires submitted proposals to have an acoustic and visual signature that is "virtually undetectable" by unaided ground troops. The solicitation is offering a sum of less than $1 million for this project, and application proposals are due by February 8, 2017.
How does the Pentagon think such a drone would be powered? "A number of possible technologies can be considered to meet this requirement, but it is anticipated that the most likely candidates include hybrid power systems, solar power, and possibly power harvesting," the agency writes.
Solar technology for drones is a tested but yet to be proven method for prolonged flight. Facebook's Aquila solar-powered drone, a key aspect of the social network's 'internet for everyone' initiative, is still in an intensive testing phase. Airbus's Zephyr solar-powered drone is also being trialed by the British military for surveillance purposes. Still, the DoD mentions conventional and logistically available fuels for powering the drones too, such as diesel and jet fuel.
In January, a DARPA-sponsored small aviation manufacturer flew a small, diesel-powered drone for 56 hours, but had to be brought down ahead of schedule because of bad weather. The VA001, built by Vanilla Aircraft, started its flight on the morning of November 30, 2016 at New Mexico State University's Unmanned Air Systems Flight Test Center near Las Cruces International Airport. For two days and two nights, the drone flew at an altitude between 6,500 feet and 7,500 feet above sea level, averaging 57 knots before landing on the afternoon of December 2.
Simultaneously, another drone solicitation from the Department of Defense, first reported by The National Interest, calls for contractors to build a capability to conduct air-to-air refueling of UAVs to "radically increase" mission length. "Unfortunately, returning to base of operations to obtain additional fuel creates a deployment and logistics challenge," writes the DoD.
A standard air-to-air refueling (AAR) operation for the US Air Force involves a KC-135 tanker aircraft dragging along a refueling boom or hose to allow an aircraft to come up behind the KC-135, dock a refueling probe with the fuel house, and fill up on fuel. The problem for the Air Force is that KC-135s and other tankers are large, loud, and need humans to fly them. As America's surveillance UAVs tend to fly over hostile territory, flying in a crewed tanker would be problematic, and also alert the enemy to the presence of drones. "Because of this, an unmanned, automated tanker could a potential solution," writes the DoD.
The US Navy's X-47B drone has already completed successful air-to-air refueling tests in conjunction with a K-707 tanker, proving that drones can easily perform the precise manoeuvres needed for AAR, but delivering heavy fuel from another drone is something yet to be seen. The refueling procedure would require the UAV to operate in close proximity of the tanker drone. Ergo, one of the aircraft would need to know its own location relative to the other. Because of latency issues or the possibly of signal disruption interrupting delicate drone operations, "one or both the tanker and UAV must respond quickly if an unsafe refueling condition occurs," writes the DoD, therefore it can be inferred that autonomous technologies may be required in any future drone AAR operations.
While the solicitations may not bear any fruits for some years to come, the requests from the Department of Defense clearly demonstrate the future direction of America's UAV surveillance program that's as much about intelligence gathering as it is about psychological warfare. Possessing the ability to keep a drone in the air for weeks at a time is a significant boon for both of those tactics.