Come May, India will see its first high-altitude platform (HAP) take off. The prototype device will hover about 3 km above ground while its designer-manufacturer, National Aerospace Laboratories (NAL), tests and validates the onboard equipment.

The HAP is much like a drone, except that it can fly at much higher altitudes — 18-20 km above the earth. They are not satellites, which reach much greater altitudes and revolve around the earth only with the help of gravity. They are also not balloons of the Chinese kind that the Americans shot down recently (though some classify balloons as HAPs). Balloons are held in place by the lift provided by a light gas (helium) and they typically cannot move laterally; HAPs are fully powered propulsion systems like any other aircraft.

Dr Abhay A Pashilkar, Director, NAL, told  Quantum that the prototype is roughly one-third the size of a regular HAP. While the fully operational HAP would be stationed at an altitude of around 20 km, the prototype would remain at 3 km.

The full-fledged HAP would be ready in 2-3 years. Once India is HAP-ready, there are plenty of uses in waiting. Potential applications include guarding against external threats (border surveillance), piracy, smuggling, irregular migration, and pollution; search and rescue operations; wireless access; emergency communications; and rural communications.

Complex machines

HAPs are complex machines. They have to be lightweight because the air at 20 km altitude is very thin — one-16th the density at sea level — so the HAP must be designed for much less ‘lift’; it is the under-wings force that keeps the aircraft in flight.

An HAP would typically be stationed in the upper atmosphere for several months; since it can’t carry its own fuel, the energy must come from solar power. The solar panels must be flexible enough to adhere to the wings. They must also be high-efficiency — around 30 per cent — to be able to generate enough power to not only run equipment such as control systems and the payload, but also store enough for night-time. This would require carrying onboard an ultra-high-energy dense battery, which comprises high-end lithium-ion batteries with silicon nanowire electrodes.

Amprius, a US-based manufacturer, says these batteries have energy densities of 450 Whr/kg of lithium. Because the batteries are heavy, it can skew the load of the airframe. “All the areas of aerodynamics pose challenges,” Pashilkar said.

The prototype has been entirely designed by NAL, which is one of the public-funded laboratories under the Council for Scientific and Industrial Research (CSIR).

Early days

HAP is still a lab-baby, but industry is getting ready for business. The public sector Hindustan Aeronautics Ltd is collaborating with a start-up, NewSpace Research and Technologies, for HAPs. In February 2022, HAL said it had allocated ₹42 crore for developing an HAP prototype. In October 2022, a spokesman of NewSpace Research and Technologies told the  Janes publication that the company had test-flown a scaled version of its HAP for five minutes, without solar panels.

Jayant Patil, member of the executive committee of management, L&T, told  Quantum recently that HAPs were still in the “concept stage” but, when perfected, it would be a much cheaper way of providing many of the services that satellites provide today.

L&T has signed an MoU with a start-up for developing advanced HAP, Patil said, but declined to give more details because it was still too early. He, however, said that if L&T did get into the business, it would produce only advanced HAPs.

Airbus has an HAP, which it calls Zephyr; in October 2021, the company announced that Zephyr had achieved 36 days of stratospheric flight, at an altitude of 76,100 ft (23 km) — a world record.

In March 2022, Saudi Arabia said it had successfully tested providing 5G services from an HAP.