By Lt Gen P R Shankar (Retd)
The advent and proliferation of Unmanned Aerial Vehicles(UAV) enabled commanders to “Look Over the Hill” and kindled “Precision” in firepower delivery. UAVs with their ability to carry out surveillance, acquire targets and direct/deliver firepower accurately heralded a new trend of “One Warhead One Target”. From this trend, the“Hunter Killer” UAV concept came into being. However, the efficacy of sub-stratospheric UAVs is bound by their footprint; which in turn is dictated by the height and speed at which they fly. The higher they fly, the larger the footprint. The faster they fly, the footprint morphs accordingly enabling greater area coverage. The longer they endure the better the stability of operations. However, all in all, UAVs which operate at high altitudes (HALE variety) have posed problems related to area coverage, endurance, sensor accuracy, energy, persistence, detectability, vulnerability, utility over wide areas et al. A combination of technical and tactical problems has limited the ability of UAVs to “Stay and Stare” on a persistent basis. This has led to thinking about exploiting Near Space as the new horizon to explore.
What is Near Space?
This new frontier needs some understanding. Near Space is that region of Earth's atmosphere that extends from 20 to 100 km above sea level. It encompasses the stratosphere, mesosphere, and the lower thermosphere. It extends roughly from the Armstrong limit (above which humans need a pressure suit to survive) up to the Kármán line where Earth’s atmosphere ends and gravity is near zero. After that astrodynamics prevails over aerodynamics in order to achieve flight. In simpler and understandable terms, near space is above heights where commercial airliners fly but below orbiting satellites. In technical terms, near space begins above the internationally accepted ceiling of controlled airspace. The air becomes too thin above this for most air-breathing aircraft. Its upper limit ends where air friction becomes too strong for low Earth satellites to maintain an orbit. Near space is also referred to as the Death Zone. It is the least explored and resultantly the least exploited zone of the Atmosphere.
Why Near Space?
Potentially, near-space vehicles could stay and stare for weeks or months as opposed to tropospheric and lower stratospheric UAVs, whose missions can last up to 24–40 hours. The USA has estimated that the swathe of a system in Near Space can cover entire Afghanistan in one look. In our context, it would be entire Pakistan or Tibet in one look. Such persistence and coverage can be achieved in space only by a well-designed low orbit constellation or very distant geostationary orbits. Both are costly and have issues related to them. In effect, near space offers, better operational benefit at relatively lower cost. Near space, systems could be treated as surrogate to space-based satellite. Hence, they bear comparison with them. They offer shorter transmission distances and shorter ranges for surveillance sensors.
Additionally, deployment time and responsiveness of a near-space system is expected to be much better. Satellites can take months for system calibration and checkout after settling into their orbit, whereas a near-space vehicle requires only hours to arrive at the desired altitude and can be positioned on station in a week or so. Proponents of near space also feel that these vehicles could give image footprints like those of satellites in low earth orbit. Payloads can be lighter because they need not configured to ward off effects of the ionosphere. Thus, near space offers unique opportunities for communications, reconnaissance and surveillance.
Approaches to Near Space UAVs
It is mentioned at the outset that the appetite for near space has been low due to the challenges involved and the alternatives available. However, two distinct approaches have emerged when near-space vehicles are considered. The first approach is to have a steerable helium-filled balloon in near space. The second is to have a solar-powered UAV loiter in near space. Both approaches will be discussed.
The USA has made significant headway in the field of helium-filled balloons, airships and aerostats. At the low end, these could be simple helium-filled free-floating balloons which can stay at about 30000-40000’ above mean sea level (MSL) and provide some persistence. At the higher end, these could be steerable airships designed to operate at heights above 60000’ to become the theatre commanders’ eye in the sky. However, there are many issues. The structure poses a challenge. UV radiations degrade hull fabric.
Metallized and reactive coating of the fabric increases hull strength but it also increases the radar cross-section and makes the craft vulnerable to air defences. Helium leakage is an issue and will constrain endurance. Payload capacity is also a restraining factor. Controllability of the craft is another signiﬁcant concern. The airship must ascend through lower atmosphere and persist at near space with enough manoeuvrability. The design requirements in these atmospheric layers are opposing and pose significant challenges for military use. A major issue in the Indian context is the heavy import dependence on Helium. Helium reserves are geographically based in the North American continent and hence controlled by Canada and USA.
Solar Powered UAVs
Low air densities and rarefied atmosphere degrades the efficiency of air dependent engines severely. The major problem faced by a UAV based on air-breathing technology is energy to sustain itself over long periods of time in near space. In addition, energy is needed to power sensors. Hence there is no other option but to depend on solar energy. That approach comes with its own problems. The other major issue is aerodynamics. The air densities and air speeds at near space altitudes are such that they are not enough to generate lift but are high enough to generate drag which the UAV must overcome to sustain flight.
New technologies related to graphene are being delved to make airframes and innovative energy solutions are being explored to tap and store solar energy. The Solar powered UAV as a military tool is still some distance away. In any case, it will be a large structure flying at low speeds and hence vulnerable to enemy air defences. In 2017, China made news by launching a solar-powered UAV. It was an experimental flight at a height of 20000’ above MSL. Typical to China a lot of hype has been created around this launch. It is pointed out that the height attained was only 20000’ much lesser than the normal operating altitude of a HALE UAV.
Near space is not a panacea for all difficulties faced in UAV development and operations. Near space may only complicate current problems. All in all, development of Near Space UAVs is in nascent stages. As of now the scope for civil applications hold more promise. The ceiling for civil jets to cruise maxes out around 40000’. Hence UAVs with traditional technologies suitably hybridized can be flown up to 40000’ with some innovation. They will immediately find huge military and civil applications; especially in communications and georeferencing. In my opinion, the 40000’ area has the best potential with current technologies even if they are projected over the next 15-20 years. From there one can go higher in times to come.
Low Orbit Micro-Satellites
Low orbit satellites continue to offer viable alternatives in persistent surveillance from high altitude. Especially in our context where we have been able to master technologies related to launch and building of satellites. The low orbit microsatellite constellation approach must be explored. As of now, it offers the best solution to surveillance problems, notwithstanding the cost implications. This is an avenue which the military must exploit straight away since technologies and capabilities are indigenous and available immediately.
The Way Forward
The way forward must be a combination of many pathways. First and foremost a concentrated effort must be put in to explore near space and develop suitable technologies. Dependence on foreign technologies will only put us behind in time and space; not to mention the import costs involved. Whether to go in for Solar UAVs or Helium based balloons is a matter of which technology matures fast in the indigenous context. However, one thing is clear, it must be an inter-ministerial national effort. No single Service, Department of Ministry will be able to do it on its own. Secondly, there must be a national approach to surveillance and related activities. The entire sandwich of surveillance platforms needs to be exploited and integrated. These include low-level drones, long-range UAVs, near space vehicles, low orbit satellites and geostationary satellites. The technologies related to each platform, sensors and energy sources need to be mastered. We have the potential to do so. Unfortunately, we have not had the national vision to do so. Our shortsightedness in harnessing tomorrow’s technologies in a segregated manner will get us nowhere as has been proved till now.
As I visualize it, surveillance and associated platforms and technologies have far greater relevance to humanity than to only uses related to the military. In our context, I visualize that disaster management; saving lives and monitoring own resources have far more relevance than mere destructive military usage. We need to put our foot forward. We must dare to take the big jump into tomorrow.