To start off 2023, the Chief of Staff of the French Air Force organized a colloquium on Very High Altitude Operations, meaning operations between conventional airplane altitudes, under 20km, and “orbital space” above 100km. It featured Air Force officials, but also the companies and research institutes involved in developing platforms able to fly at these altitudes.
The first roundtable was focused on the various projects in development by French companies. The first speaker to take the floor was the CEO of Thales Alenia Space, which is developping the Stratobus high-altitude maneuvrable balloon. Stratobus is a 115m-long dirigible able to fly in the stratosphere, where the winds are relatively moderate compared to lower altitudes. To keep on station, it is covered in solar cells that power electric motors. I covered it in detail in this previous article:
The CEO gave a quick overview of the performances: the balloon can carry a 250kg payload to 19km altitude, and can provide it with 5kW of electrical power. It can stay on station for a year. While initially Thales thought it would meet commercial interest, especially as a kind of stationary quasi-satellites for much cheaper than a traditional communication satellite in geostationary orbit, as years progressed they realized that military applications are much more promising. So the focus is now on using it for surveillance, with optical, radar or signal intelligence payloads, or for communications.
Due to the low commercial interest the program has progressed more slowly than anticipated, but is on track to fly a first half-scale demonstrator in 2025. A Spanish company will provide a LIDAR and communication intelligence payload. German and Italian company will also provide payloads. [Commentary: A 50% scale demonstrator would have around 12% of the payload if it has the same form factor, so around 30kg]
Thales underlined that Stratobus is not directly competing with their offering of geostationary communication satellites, as Stratobus only covers a region with a diameter of 1000km while a satellite covers a third of the globe. It also needs to ask for overfly permissions from the countries, while a satellite does not. Finally, Stratobus is more vulnerable in the case of a high-intensity conflict, as technical-operational studies run by the French armaments agency have demonstrated that jammers and directed energy weapons have more impact on high-altitude platforms and even low Earth orbit satellites than on geostationary satellites.
Another balloon concept was presented by Hemeria, the company also manufacturing the Stratobus envelope. It is done in cooperation with the French space agency CNES, which has a long history with high altitude balloon, to the point the Google asked them for advice on their now defunct loon project. The concept is called BALMAN, for maneuvrable balloon, and does not look like a dirigible, so it probably stays on station by changing altitude to catch winds blowing in the right direction, like loon did. BALMAN is to fly in 2025 as well. Airbus is also part of the BALMAN project.
The third company to pitch on the topic was Stratolia, which plans to deploy maneuvrable balloons with optical observation payloads for between 6 month and a year on station. [Optical payloads are the worst observation payloads to put on a balloon: they are sensitive to clouds and fog, visible bands are useless at night, they have a narrow field of view and do not work well at long distances. Radar is much better if you have the mass and power for it]
Airbus presented is Zephyr solar-powered plane. It is developed in the UK, and has already flown. It stayed on station for 64 days during a test in the USA. It is also targeted towards communications and observation applications, although with a much smaller payload of only 25kg. During the test it carried a video payload with 18cm resolution, which is very high. Airbus stated that making the platform able to penetrate non-permissive airspaces was a goal, so they designed it with a reduced signature in mind. The representative from the French weapons procurement agency DGA explained why they have funded Stratobus and not Zephyr: balloons have much larger payloads and can stay on station for longer, and that is needed by the military users. Airbus stressed the need to interconnect the platforms between them and with satellites, for which optical communications is very interesting.
Dassault Aviation, the famous business jet and fighter jet manufacturer, was also invited and talked about space planes. Dassault has a small space business, they manufacture a bit of hardware for launchers, and also their aerodynamics department has expertise in hypersonic flight and atmospheric reentry. For instance, they contributed to the aerodynamic studies of the European IXV experimental reentry glider. They previously worked on the Hermes and S3 spaceplane projects but those never got into real development. So based on that, they are looking into space planes and are designing a family of them called Smart Astrée. However, the talk was not very clear on what that means. It seems they are considering reusable platforms with lifting bodies, but they were very light on why this has advantages compared to a reusable launcher like Starship. The Dassault representative claimed that the expertise of the company in conventional airplanes, applied to a space plane, would result in more reliability, but without any solid argument. He also mentionned they would use hydrogen engines, while every newly designed launcher (Starship, Themis, Vulcan, …) is moving away from hydrogen to methane for good reasons. Finally, he said that such spaceplanes would be required to carry humans to maintain a space solar power infrastructure, which is an extremely far-fetched application when the near-term applications of space are communications and observation.
The only technical details he would provide is that they are looking into variable-geometry concepts, because the aerodynamic regimes between reentry and landing on an airfield are very different. For instance, the successor to IXV, the Space Rider, which Dassault is working on along with Thales Alenia Space, uses a parachute to glide to landing after the reentry.
Hypersonic cruise missiles
Hypersonic cruise missiles were not touched on in the first panel but in a later one involving the head of military applications at ONERA, the French state aerospace lab. ONERA has long been working on high-altitude platforms, albeit in a very camera-shy way. They contributed to the design of the current air-launched nuclear missile, the ASMP-A, which is only supersonic and uses a ramjet, and are developing its successor, the ASN4G, which will use a scramjet and be hypersonic. The ONERA stressed that high altitude is either the domain of very low speeds, with balloons and solar planes, or very high speeds with hypersonics cruise missiles and gliders. They are experts in combustion chambers, which is especially challenging in scramjets as the air within the chambers flows faster than the speed of sound. For hypersonic vehicles, thermal protection is also a challenge, because the compression shockwave in front of the vehicle can make it reach a skin temperature of over a thousand degrees Celcius. To help in designing protection materials, they have digital simulation tools as well as hypersonic wind tunnels.
Hypersonic glide vehicles
Not much was said on hypersonic glider developments, even though the spaceplane projects from Dassault are in some way hypersonic gliders. The French ministry of armed forces does have one in development, with ArianeGroup (and maybe Dassault) as contractors. It was supposed to fly in 2022 but there has been no recent news on the topic. As a reminder, hypersonic gliders have no engine: they are launched on a rocket to gain speed, and then bounce/fly in the upper atmosphere using aerodynamic lift. So they lose energy and speed over time, especially if they turn a lot during flight.
Views within the ministry of armed forces
Four high-ranking generals (3 or 4 stars) were involved in the discussion: the second in command of the Air Force, the head of state aeronautics safety (in a panel on regulation that I did not watch), the head of space command (CDE, Commandement de l’Espace) and the head of operational air combat command (CDAOA, Commandement de la Défense Aérienne et des Opérations Aériennes). Also involved was a civilian representative from DGRIS, the high-level strategy directorate within the ministry.
They debated a variety of topics, whuch I am going to try to summarize:
One was the defensive side of high-altitude operations: how do you know what is out there, react in time and act in this domain. They identified two threats.
The first is low-speed persistent platforms like balloons and solar planes. They are great intelligence collection assets, and so they do not want than an hostile country places one next to or within the French airspace. The issue is that it is not so easy to detect them, and it is even more complicated to know what they are doing, who is operating them and what is their intent. Indeed, they can have a quite long range and so if they take off from within a foreign country, spend a few month to get on station and stay there, they are hard to track. As such, operations in this domain somewhat mirror operations in space or in the deep sea: it is hard to classify objects and attribute them, and that creates ambiguity. An answer could be to have a global detection network to track them during all their flight. They used the Ukraine war as an example of a situation were such platforms could be useful, and said that other countries would reach the same conclusion. For instance, China could use them with a lot of impact in the Pacific, and if they have a fleet of them operating in the mid 2030s then a response has to be developped starting now. One open question is for isntance how to neutralize a small high-altitude balloon from far away, and for a reasonable cost, as shooting a million-dollar missile at it will be an issue.
The second family of threats is high-speed, maneuvrable objects, meaning hypersonic cruise missiles and gliders. High-speed hypersonic missiles are nothing new: intercontinental ballistic missiles reach Mach 25 on reentry. However, they are on a ballistic trajectory, meaning that on the rocket has finished burning in the early stage of the flight, the trajectory is completely determined. This makes it easy to determine the target, and to plan an intercept trajectory. Furthermore, ballistic trajectories reach a quite high altitude, making them visible to radar from very far away. Thus, for the hypersonic gliders and scramjet-powered cruise missiles, early warning is a challenge, and interception even more so [Taht is why France is developing the ASN4G]. The generals were considering using satellites to detect these objects, as early warning satellites aimed at detecting ballistic missiles could also pull double-duty for this. More on this and the challenges of detecting hypersonics in this previous article, and the US approach here.
The representative from ONERA however proposed a different approach, which is to use skywave over-the-horizon (OTH) radars. OTH radars bounce radio waves againt the ionosphere, and thus can see targets thousands of kilometers away, even if they are at low altitude. The ionosphere being at around 100km, they can detect things flying below that, and gliders and missiles fly below. As a benefit, OTH radars use the doppler effect and thus are especially sensitive to high-speed objects, and their wavelength is around one meter, so objects of that size create an even bigger echo. It turns out that is roughly the scale of the gliders and missiles. ONERA already operates the NOSTRADAMUS OTH radar and thus has expertise in the subject.
There was discussion on whether developing missiles to intercept hypersonics was really worth the cost. [Since the Russians have put in service the Zircon hypersonic anti-ship cruise missile, it would have been a definite yes if an admiral had been on the panel. Although the Navy has had a hard time taking foreign hypersonic development seriously in the past. Still, it’s very surprising not to have a Navy point on view in this colloquium]
Overall, regarding the defensive side, the DGRIS representative stressed that France can no longer assume it has a technical lead in these areas. Knowledge is much more easily shared these days than during the cold war, and so even regional powers could develop threats that are more advanced that what is in the French arsenal or laboratories. [This is why France is developing the VMAX hypersonic glider: to not get left far behind, and learn how to use it or defend against it]
On the offensive side, the officials were less talkative. VMAX and ANS4G are extremely classified, and their application for nuclear weapon delivery makes it a politically sensitive topic. They were more open regarding persistent platforms, stating they do not care much if it is a balloon or a solar plane, what they want is payload and persistence. Surveillance applications, especially radar surveillance, were mentionned, as well as electronic warfare.
Since the head of Air Command and the head of Space Commande were there, there were a lot of questions on how to split responsibilities between the two, starting with whether the commands need to be separate in the first place. The answer was that space and high altitude follow different physical laws, so it does make sense. Indeed, in space objects are in orbit, so they stay there and they stay in motion in a predictable way. In the air, objects either rely on lift and thus consume energy to stay airborne, so they cannot stay there [except solar-powered planes] or they use buyancy for balloons, which consumes no energy. In any case, they do not have high speeds for long, but can maneuver much more easily than in space.
The question of detection assets was raised. Space command has satellites looking towards the ground that could contribute to detecting airplanes or high altitude objects [for instance signal intelligence satellites can detect communications or radars], and has upwards-looking sensors like radars, They will be reinforced within the ARES space control program, which might also contribute. Air command has other radars, optimized for a different range of altitude and speed that could also be useful.
Overall, both commanders stressed the need to agree on an altitude to split responsibilities (which seems to be 100km, space command dealing with what is above), to think about emerging problems together, define procedures, and do exercises to train on the procedures in order to be able to take decisions very quickly when the day comes. Thinking about what you can do for the other side of the interface, or what the other side can do for you, was also emphasized.
The conclusion of the colloquium was delivered by the chair of the Defense committee of the National Assembly and by the Chief of Staff of the Air Force. The member of parliament stressed that the world is moving towards more troubled times with autocratic powers trying to challenge the status quo, and that conflicts would expand to all possible domains, as they always do. As such, an all-encompassing thinking and startegy are needed, and well as communicating the situation to the voters.
The Chief of Staff congratulated the speakers and said that a first strategy for the high-altitude domain was to be delivered to his boss the Joint Chief by summer, and likened the efforts to define it to what happened for the recently created deep sea strategy.
My personal conclusion is that the domain seems ripe with opportunities, especially for persistent surveillance on the cheap compared to satellites, but also threats as the only public program of record to defend against hypersonic threats, the TWISTER interceptor, is only in the very early stages and will not enter service before 2035-2040, whereas the Russians and the Chinese have maneuvrable hypersonic gliders or missiles in service.