An Airbus' Zephyr S solar-powered, very-high-altitude unmanned aircraft is in the midst of a long-duration test flight and has already been aloft for 17 days so far. The drone, sometimes described as a pseudo-satellite in terms of potential capabilities, took off from the U.S. Army's Yuma Proving Ground in Arizona last month for what the service says is a test of its highly efficient long-endurance flight characteristics as part of broader work to demonstrate its ability to serve as a persistent sensor platform.
The Zephyr S in question, a design originally known as the Zephyr 8, was first spotted on online flight tracking software taking off from an airstrip at Yuma Proving Ground (YPG) on June 15. For the next ten days, the unmanned aircraft, which has been using the callsign Zulu 82, flew various patterns over the adjacent Yuma Test Range and Kofa National Wildlife Refuge. This isn't an uncommon sight as Zephyr has been undergoing testing high above YPG for some time now. What it did next, on the other hand, was uncommon.
On June 23, the Zephyr S's flight activity began to include runs to the southeast roughly parallel to Arizona's border with Mexico, but the drone continue to spend most of its time in the air around YPG. Two days later, it departed the Yuma area, following a route along the southwestern border of the United States toward the Gulf of Mexico.
It arrived over the Gulf of Mexico on June 27. It subsequently flew further south into the Caribbean Sea and then into the airspace over the Central American country of Belize.
Online flight tracking software shows that the drone left Belizean airspace yesterday and it now appears to be heading back to the United States. Flight tracking data from today appears to show it flying patterns over the Gulf of Mexico.
"The Assured Positioning, Navigation and Timing/Space (APNT/Space) Cross-Functional Team (CFT) is experimenting with [the Zephyr S] solar powered fixed-wing aircraft to demonstrate military utility of long-duration assessments of various types of sensors," a spokesperson for the APNT/Space CFT office, which is part of Army Futures Command, told The War Zone in a statement. "This experiment is intended to test the UAV's energy storage capacity, battery longevity, solar panel efficiency, and station-keeping abilities."
The War Zone has also reached out to Airbus for more information.
The Zephyr S's design is optimized for highly efficient hight altitude flight. It has an 82-foot (25-meter) wingspan, but a small central fuselage containing its avionics and datalinks. Its total weight is just 165 pounds, light enough to be literally hand-launched by a small team of people holding it over their heads while running it down the runway. It can fly up to 76,100 feet (23,200 meters). How fast it can fly is unclear, but its immediate predecessor, the smaller Zephyr 7, has a stated cruising speed of around 30 knots.
It's unclear how long Zulu 82's current flight may ultimately last. When the Zephyr S first flew in 2018, the drone remained airborne for nearly 26 days. This stands to this day as the world record for the longest duration flight by an unmanned aircraft of any kind. That flight was enabled in part by improvements to the design that ensured that it could remain at very high altitudes the entire time. Older Zephyrs had to dip down to lower altitudes during multi-day flights.
"Unlike previous flights when the aircraft had to come down to between 25,000 and 35,000 feet at night, [but] this time we were able to stay above the weather," Lori Slaughter, a test officer at YPG, explained in 2019. "Our lowest altitude during the flight itself was 55,000 feet."
This capability also means that the drone can evade pretty much all bad weather, further improving its mission performance and ability to stay on scene for very long periods.
The Zephyr 7 was the previous record holder, having flown continuously for more than 14 days back in 2010. For comparison, the longest flight, at least that we know about, ever completed by a Northrop Grumman RQ-4 Global Hawk unmanned aircraft, the U.S. Air Force's current premier high-altitude, lasted just over 34 hours. The RQ-4 has a service ceiling of 60,000 feet, thousands of feet below that of the Zephyr S.
Zephyr was originally developed by U.K. defense contractor QinetiQ, which then sold the design to Airbus in 2013. The U.S. military, including both the Army and the Navy, have been experimenting with various Zephyr models since the late 2000s.
The connection to the United Kingdom, which had three Zephyr S drones on order as of 2016, may help explain the flight from YPG to Belize. The British Army maintains a contingent in that country, currently known as the British Army Training and Support Unit Belize (BATSUB), which is primarily charged with conducting jungle training courses and related exercises within a designated area spanning some 5,000 square miles.
It is also equally possible that Belize was chosen for some other reason. The possibility of utilizing Zephyr-series drones for persistent surveillance or networking support over open-ocean and littoral areas has long been one particular area of interest for the U.S. military.
A briefing that QinetiQ presented at a science and technology conference hosted by U.S. European Command (EUCOM) and U.S. Africa Command (AFRICOM) in 2009 specifically outlined how a "constellation" of these drones might be used to provide persistent sensor coverage along the coast of Somalia with a "low cost and [with a] low manpower footprint." That presentation came after a U.S. Navy-led Joint Capability Technology Demonstration (JCTD) had been conducted the year before using an earlier Zephyr model on loan from the British government.
In the role of sensor platform, Zephyr-series drones have the benefit of being more flexible compared to traditional spy satellites, but with much higher degrees of persistence than other existing high-altitude, long-endurance drones. Zephyrs can be forward deployed relatively rapidly, in addition to just being able to fly long distances to an area of interest, and then can be quickly retasked in flight in response to evolving operational demands.
There are various other potential uses of Zephyr beyond carrying sensors, too. The performance capabilities of these drones would be equally useful when acting as nodes supporting navigation and communications and data-sharing networks.
In terms of communication and data-sharing, a distributed 'mesh' network made up of multiple examples of these drones could also provide a beyond-line-of-sight-like signal relay capability.
When it comes to navigation, these drones could be particularly useful for feeding into so-called Assured Positioning, Navigation, and Timing (Assured PNT) networks. Elements of such a system might leverage alternative signal sources to guide aircraft, ships, vehicles, and munitions in the event things like the GPS constellation are jammed, spoofed, or otherwise damaged or destroyed. You can read more about the growing need for these kinds of capabilities here. With this in mind, it's worth remembering that the Army's APNT/Space CFT office is the one currently managing this latest Zephyr S test flight.
So, in this broader context, the Zephyr series presents an alternative to space-based assets of various kinds that could readily swing to action should certain satellites get knocked out or otherwise disabled. As The War Zone regularly highlights, the U.S. military faces serious threats to critical capabilities in space now and the anti-satellite capabilities of potential adversaries are only likely to keep growing. High-altitude balloons and various rapid space launch capabilities are also being explored as ways to mitigate these issues.
The ability of Zephyr drones to augment or even replace satellite-based systems as necessary could be valuable in post-disaster scenarios, especially where traditional cellular or internet networks are rendered inoperable, as well.
With any luck, when the Zephyr S finally lands back at YPG, or wherever it might fly to in the end, hopefully we'll learn more about what this experiment accomplished, whether it turns out to be a new record-setting flight duration-wise or not.
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