HAPS IN DEFENCE: THE NEW STRATOSPHERIC DOMAIN FOR ISR & COMMUNICATIONS

Part 1 in the Bridge Connect series: “The Rise of Stratospheric Infrastructure: HAPS, Defence Readiness, and the Future of Connectivity”

High-Altitude Platform Systems (HAPS) have quietly moved from experimental aerospace concepts to one of the most strategically significant developments in modern defence and national security. Over the last decade, military organisations across the UK, US, Europe and the Asia-Pacific have come to the same conclusion: there is an operational and strategic gap between satellites and traditional unmanned aircraft, and the stratosphere — that largely unutilised band above 60,000 feet — is becoming the next domain of competitive advantage.

The growing interest in HAPS is not a passing fascination with aerospace novelty. It reflects deep structural forces shaping defence: rising geopolitical instability, the erosion of uncontested airspace, the growing vulnerability of satellites, and the need for persistent surveillance in theatres where political or logistical limits restrict the use of conventional assets. Defence leaders now view the stratosphere as the place where persistence, sovereignty and tactical flexibility come together in a way that neither UAVs nor satellites can deliver.

HAPS platforms, whether solar-powered fixed-wing aircraft or high-endurance aerostats, offer something distinct: the ability to loiter for weeks or months over a specific region, carrying advanced ISR, communications and electronic intelligence payloads, without the prohibitive cost or vulnerability of space assets. This combination of endurance, altitude and operational responsiveness is driving ministries of defence to rethink their force structures as they confront a world in which multi-domain integration is no longer optional.

“The stratosphere is quickly becoming defence’s new real estate.”

Filling the Capability Gap Between UAVs and Satellites

Traditional defence doctrine has long depended on the twin pillars of satellites and high-altitude aircraft. Satellites provide global reach and highly capable sensing, but their movement is dictated by orbital mechanics, their availability is episodic rather than continuous, and they are rapidly becoming prime targets for adversary counter-space capabilities. At the other end of the altitude spectrum, UAVs have transformed tactical ISR but face endurance constraints, airspace restrictions, and increasing exposure to air-defence systems.

Between these layers sits an operational vacuum. HAPS fill this vacuum with a combination of persistence and proximity. A platform operating at 65,000 feet is high enough to avoid weather, aviation traffic and most surface-to-air threats, yet close enough to the Earth to deliver high-resolution imaging, precise RF intelligence, and stable, low-latency communications. Unlike satellites, they can be repositioned rapidly. Unlike UAVs, they do not need to rotate crews or land every few hours. And unlike both, they can be deployed without triggering geopolitical concerns associated with orbital surveillance.

It is this interplay — persistence, flexibility and sovereignty — that has caught the attention of defence chiefs. In many ways, HAPS represent a new category of infrastructure: a stratospheric layer that can be deployed tactically like aircraft, operated persistently like satellites, and owned directly by governments without reliance on commercial constellations.

Why Defence Forces Are Moving Toward the Stratosphere

The strategic drivers behind HAPS adoption are consistent across regions. Defence ministries need persistent ISR in locations where aviation rights are constrained, where basing is politically sensitive, or where long-term monitoring is essential. For countries with extensive maritime borders — the UK, Japan, Korea, Australia — stratospheric surveillance is particularly attractive. A single HAPS platform can monitor hundreds of kilometres of ocean, identify movements across sensitive choke points, and detect early signs of grey-zone activity.

In land environments, HAPS provide enduring coverage of borders, remote deserts, mountain passes, or conflict theatres where traditional aircraft face political or kinetic risk. Defence leaders emphasise that the ability to maintain continuous eyes and ears in these regions without rotating aircraft or relying on third-party satellite operators is a fundamental shift in capability planning.

Communications resilience is another powerful catalyst. Modern militaries increasingly depend on data — compressed video, sensor fusion, targeting information, command-and-control traffic. HAPS can act as dedicated, sovereign relay nodes that operate independently of terrestrial networks. They can also provide assured connectivity when fixed infrastructure is denied, degraded or destroyed. This has enormous implications for operations in contested regions and for national resilience during crises.

Finally, cost is an unavoidable factor. The escalating price of space launches, the vulnerability of satellites, and the time required to deploy replacements have pushed defence ministries to consider hybrid architectures. HAPS introduce a way to augment satellite fleets without incurring billion-dollar programmes or committing to multi-decade orbital investments.

They provide flexibility and adaptability at a time when threats evolve too fast for 15-year procurement cycles.

Global Defence Programmes Show the Momentum Is Real

Nowhere is the momentum more evident than in the UK, where the Ministry of Defence and Royal Air Force have been pursuing Project AETHER — one of the world’s most advanced stratospheric ISR initiatives. Built around a long-endurance platform and modular payload system, AETHER aims to give the UK a sovereign capability for persistent surveillance, deployed rapidly from small teams and lightweight infrastructure. The programme demonstrates how the UK sees HAPS not as an experimental adjunct to ISR, but as a central pillar of its future force design.

In the United States, the Department of Defense has revived and expanded its high-altitude experimentation, catalysed in part by geopolitical instability and the need for persistent tracking of strategic assets. DARPA, AFRL and multiple service branches have accelerated both fixed-wing and balloon-based programmes, often using commercial suppliers for rapid deployment cycles. The US interest is not merely technical — it reflects a strategic assessment that access to the stratosphere will be as important as access to space in the decades ahead.

Asian defence actors are similarly active. Japan is positioning HAPS as part of its maritime security architecture, seeking persistent monitoring of contested waters around its southwest islands. South Korea is exploring HAPS for border ISR and as a communications layer during crises where infrastructure could be compromised. These efforts reflect a broader regional pattern: nations are developing HAPS as an insurance layer, one that provides situational awareness and communications continuity even in high-risk scenarios.

NATO’s emerging doctrine also treats the stratosphere as a domain that enhances multi-domain operations. HAPS are conceptualised as assets that can integrate satellite data, link aircraft and maritime platforms, and provide real-time information to land forces — effectively acting as glue between vertical layers of the forces. This vertical integration is central to NATO’s future C4ISR framework, and HAPS are positioned as enabling nodes within it.

Strategic Missions: The Defence Use Cases Driving Adoption

For defence leadership teams evaluating the strategic value of HAPS, the mission set typically falls into several interlocking categories.

The first is persistent ISR. This remains the cornerstone use case and the one with the clearest economic justification. The ability to station a platform over a region for weeks transforms how militaries think about border security, maritime monitoring, and crisis-response overwatch. Instead of cycling aircraft, relying on episodic satellite passes, or losing visibility entirely during deteriorating weather, a HAPS platform provides stability and continuity.

The second major use case is secure communications. Modern forces depend on connectivity across domains, but this connectivity is increasingly vulnerable. Terrestrial networks are exposed to cyberattack; satellites face jamming, dazzling and kinetic threats; UAV relays are subject to short endurance and high-risk flight profiles. A HAPS-based relay architecture offers a sovereign, elevated and enduring alternative that can serve as a national fallback layer or even as the primary tactical communications backbone in specific theatres.

Electronic intelligence forms the third cluster. From 65,000 feet, a platform can intercept, locate and characterise signals across a vast footprint. In regions where adversaries employ mobile radar units, shifting communication patterns or grey-zone electromagnetic activity, the ability to map, track and analyse these signatures persistently gives defence forces a significant advantage.

The final use case is humanitarian and civil contingency support. Although not a core military mission, dual-use capability is an increasingly important factor in defence procurement. Governments under fiscal pressure seek assets that contribute to both national security and civilian resilience — wildfire detection, post-disaster communications, and flood monitoring among them. HAPS offer this crossover capability at a time when climate-related disruptions are becoming more frequent and more severe.

The Technological Foundations Are Now Mature Enough

HAPS are gaining traction now because several enabling technologies have matured simultaneously. Improvements in solar cell efficiency, battery energy density, and ultra-light composite materials have altered the endurance profile of high-altitude aircraft. Payload miniaturisation — especially in EO/IR sensors, RF detection systems and steerable communications arrays — has made it possible to conduct sophisticated missions without the weight penalties traditionally associated with airborne ISR. Meanwhile, advances in AI-driven autopilot systems and high-altitude flight control have reduced operational risk and increased reliability.

What once required a satellite bus can now be carried by a platform weighing a few hundred kilograms. What once demanded a network of ground stations can now be managed from compact, mobile control units. In many respects, HAPS represent the convergence of aerospace innovation, mobile communications, and semiconductor efficiency.

Challenges Defence Forces Must Address

Despite the growing interest, HAPS adoption still comes with challenges that defence ministries must confront early in programme planning.

The first is survivability. While operating above most threats, HAPS platforms are not invulnerable. State actors could theoretically target them with specialised anti-air capabilities; cyber vulnerabilities must be managed with rigour; jamming and spoofing must be countered with robust GNSS authentication and alternative PNT solutions. For platforms intended to provide ISR in contested theatres, these risks must be designed out, not managed reactively.

The second challenge involves integration with aviation regulation — a topic explored in more depth in Part 2.

Operating in higher airspace requires coordination between defence forces and civil aviation authorities, especially in countries pursuing mixed-use airspace strategies. Issues such as detect-and-avoid systems, deconfliction with space-launch paths, and certification of high-altitude envelopes need coherent policy frameworks.

A third challenge is procurement and industrial partnering. Few nations currently possess indigenous HAPS programmes at scale. Defence ministries must decide whether to develop sovereign platforms, rely on international suppliers, or adopt hybrid procurement structures. These decisions have long-term implications for sovereignty, interoperability and economic value.

Finally, there is the question of fleet integration. A single HAPS platform provides compelling capability; a fleet of them transforms national surveillance and communications posture. Defence planning must consider ground infrastructure, data pipelines, maintenance cycles, and the orchestration of combined HAPS–satellite–UAV architectures.

“HAPS fill the capability gap satellites cannot reach — persistence, responsiveness, and sovereignty.”

Conclusion: Defence Forces Are Entering the Stratospheric Decade

The 2020s represent a pivotal decade in which defence organisations will operationalise the stratosphere as a core domain. HAPS are emerging not as replacements for satellites or UAVs but as a complementary layer — a persistent, responsive, and sovereign capability that strengthens resilience, enhances situational awareness, and expands the options available to political and military decision-makers.

For governments confronting increasingly complex security environments — from maritime grey-zone pressure, to contested borders, to hybrid warfare — the ability to maintain continuous eyes, ears and communications over critical areas is becoming non-negotiable. HAPS provide this capability at a cost point and operational flexibility that aligns with the economic and geopolitical realities of the next decade.

Defence ministries, air forces and joint commands that understand the potential of the stratosphere will shape the next generation of ISR and communications doctrine. Those that delay may find themselves dependent on commercial orbital networks or constrained by adversaries with superior persistent sensing.

The stratosphere is becoming the new strategic high ground. The defence organisations that move early will define how it is used.