Lots of news lately with high altitude spy balloons, unidentified “objects”, and air-to-air “kills” (does it count as a kill if it isn’t crewed?)   What is being revealed is something that is not well known to the public – there’s more up there than you think.

The truth is, it isn’t very expensive or hard to launch a stratospheric balloon.   Just search for “stratospheric balloon” on YouTube and you’ll find all sorts of STEM projects at the high school and University level, some hobbyists who want some good GoPro shots, and yes – plenty of professional and “official” use cases as well.

Post-the Chinese Spy Balloon “incident”, NORAD changed their RADAR settings to no longer ignore slow moving objects like these and well….we are living the result.

The question is – what, if anything are we going to do about it?  It turns out that regulators like the FAA and the air traffic management industry have indeed been thinking about this for a while.   This is really a spin off of all of the drone-related activity – because when you get down to it – if the FAA want to classify a 251g consumer drone as an uncrewed aircraft – these things are as well – just operating at the opposite end of our atmosphere. Even worse – if these are left free to drift as the winds take them….they are technically in a lost link scenario – completely uncontrolled – a huge NO-NO from a UAS perpective!

Historically, aside from military operations, FL600 (60,000 feet) is generally the limit when it comes to the vast majority of aircraft and where the FAA generally just stops controlling (caring about?) what goes on up there.   Up there the air is increasingly so thin that traditional technology – engines, aircraft structures, wing shapes and sizes – simply and literally do not fly.  For that matter – why go there at all?  At one time, the need was primarily for satisfying military or intelligence objectives. Flying high and fast offered immunity to an enemy’s air defenses. 

FL600 is also the upper boundary of Class A airspace – the controlled “transit” airspace whose lower boundary is generally 18,000 MSL – where pretty much all commercial air traffic flies. If you look on many explanatory airspace charts – Class A is depicted at the very top, with not so much as a mention of what lies above. But something IS above Class A, and it’s called “Upper Class E”. Due to advances in technology, we now have a number of aircraft types that fly there.

Who and Why? – the Aircraft

There are a couple of broad “mission” categories best performed in Upper Class E. The first is High Altitude Long Endurance (HALE).  Usually unmanned, HALE missions include surveillance, research, and providing connectivity to disenfranchised portions of the globe.  In most cases the mission is regional; they aren’t transiting to or from anywhere. Their job is to loiter in a region – possibly for months at a time – to fulfill their mission.  HALE aircraft are sometimes solar-electric balloons with little or no ability to control direction of flight.  Loon is perhaps the best known example of this (and unfortunately ill-fated, given Alphabet’s decision to close up shop), but several other companies are conducting similar balloon-based missions such as World View, Near Space Corporation, and Raven Aerostar.  Alternatively, some HALE aircraft are gigantic solar-electric powered wings.  The Airbus Zephyr and AeroVironment High Altitude Pseudo-Satellite (HAPS) are prominent examples.  These aircraft are optimized to maintain lift at slow speed in thin atmosphere at the expense of maneuverability.  They are so aerodynamically stable that their max turn rate is limited to a couple of degrees per minute.

The second category is almost the polar opposite of the first category. Enabling it is new class of supersonic and hypersonic aircraft in development.  These successors to the Concorde are optimized for lift in the upper atmosphere at extremely high speeds.  At first these are likely to be piloted and most probably will transit passengers from one continent to another in a matter of hours.  A couple of these are in development, one if which is Boom.

What does this mean? – Air Traffic Management (ATM)

In May 2020, the U.S. FAA, and NASA – with input from industry partners – published a Concept of Operations (CONOPS) v1.0 of Upper Class E Traffic Management (ETM).  The CONOPS begins by acknowledging that the National Airspace System (NAS) is ill-equipped to serve the future needs of commercial operations in Upper Class E, and “the future of Upper-Class E airspace operations presents opportunities for alternative traffic management approach.”  This calls to mind early discussions of Unmanned Traffic Management (UTM) CONOPS and for good reason – many concepts from UTM are also present in ETM. 

But there is one significant operational difference which separates the ETM and UTM concepts.  In low-altitude (under 400’ AGL generally) UTM operational airspace, Uncrewed Aircraft Systems (UAS) are largely segregated from other traffic and controlled airspace simply by virtue of the low operating altitude.  In the case of Upper Class E operations, however, many of these aircraft are launching from traditional airports in Class B, C, or D airspace, and ALL of them have to transit through Class A airspace on their way to – and from – their target operating altitudes.  While operating above FL600 they may fall under an ETM regime, but when flying below that floor, they need to play nice with the conventional ATM infrastructure.  This is indeed the path that CONOPS v.1.0 takes.

The CONOPS identifies two methods for maintaining separation of these aircraft.  The first is straightforward “ATC Separation Services” –the same infrastructure and technology (e.g., transponders and ADS-B) as used today. It will be leveraged during ascent from launch to transit through Class A, and during descent through recovery.  While nothing is novel from a technology standpoint, new challenges need to be overcome. Flight paths and maneuverability of HALE and supersonics vary significantly from “traditional” aircraft managed today, so disruption to normal traffic routing is expected.

The second method of maintaining separation is described as “Cooperative Separation.”  Cooperative Separation is reminiscent of UTM in that it is dependent upon “community-based separation,” where the Operators are responsible for the coordination, execution, and management of operations – with “rules of the road” established by the FAA.

Like UTM, ETM cooperative operations above FL600 are organized, coordinated, and managed by a federated set of participants.  The Operators use a complementary set of services which can either be self-provisioned or provided by third parties. These services likely will be qualified by the FAA to ensure interoperability and safety.  Operators share their intent with each other and coordinate to de-conflict.  Also similar to UTM, conformance monitoring is used to identify when actual behavior deviates from communicated intent, with an alert to whoever is appropriate.  Details on technologies applicable to vehicle deconfliction are only lightly touched on in the CONOPS. Supporting technologies may need to be created.

Accommodation to the peculiarities of Upper Class E airspace is going to be interesting to watch unfold.  Separation technologies need to be adapted to this use case.  For HALE balloons or slow-moving fixed wing aircraft, the Detect and Avoid (DAA) mantra may need modification to “Detect and Alert” simply because avoidance maneuvers are impossible.  A slow mover may need to continue to broadcast its position via ADS-B so an inbound supersonic flight can detect it at a great enough distance so deconfliction can be achieved with gentle maneuvering. For example, a supersonic traveling at Mach 1 would want to detect a HALE balloon about 130 miles out in order to have a 10-minute warning.  The concerns of HALE aircraft, though, are not limited to physical collisions. Shockwaves and wake turbulence from a supersonic aircraft can destroy a lightweight HALE structure if passing by too closely.

While ground-based surveillance infrastructure will perform as expected within their coverage volumes, space-based ADS-B networks like the one provided by Aireon will be especially helpful, providing global coverage in areas where ground-based systems do not, or cannot – like over the ocean or in remote locations far from existing infrastructure.  uAvionix’s solutions are particularly well suited for HALE applications which require low-SWaP (Size, Weight, and Power) avionics in order maximize the aircraft’s flight time and/or payload while providing outstanding performance as related to space-based surveillance.  In particular, the dipole antenna design, mounting location, and power outputs of the ping200X, ping200XR and tailBeaconX solutions were specifically optimized for high update rates when tracked by Aireon.

Cooperative solutions like the ones offered by uAvionix take the “unidentified” of these high-altitude operations. It removes the mystery and may just save these operations from a visit from the USAF.

I’m interested to see where this goes….has the FAA ever taken a stance on STEM projects?  I’m not sure, but I’m betting some pressure is coming to figure this out quickly.

Christian Ramsey, President uAvionix