The Hybrid High Altitude Airship (HHAA) developed by the Italian Aerospace Research Center. Not long ago, the Italian Aviation Research Center conducted flight tests on its hybrid high-altitude airship (hereinafter referred to as HHAA). This move means that this high-altitude platform system is one step closer to being put into use. For decades, countries have been competing to develop high-altitude platform systems, and some countries have achieved certain results, with HHAA being one of them. The high-altitude platform system refers to a system that uses a platform located at an altitude of 20 to 50 kilometers from the ground as a vehicle to provide intelligence, surveillance, reconnaissance, communication, and other services. A typical high-altitude platform system typically consists of satellite communication transfer stations, high-altitude platforms, and fixed/mobile user terminals. Among them, high-altitude platforms generally refer to aircraft that can stay in the stratosphere for a long time, such as new high-altitude balloons, stratospheric airships, etc. From a military application perspective, it can be equipped with various sensors and communication devices to carry out diverse tasks. Compared with traditional satellite detection, high-altitude platform systems have higher detection accuracy, more flexible deployment, and lower costs; Compared with traditional drones deeply embedded in the battlefield, high-altitude platform systems have stronger endurance and wider detection range. In actual combat, if the high-altitude platform system is networked with low orbit satellites, an integrated reconnaissance system of air, space, and earth can be constructed, transforming into a "stratospheric sentinel"; If equipped with an electronic jamming module, it can disable the enemy's communication link. Compared with conventional high-altitude airships, HHAA has certain innovations in lift generation mechanism and energy supply mechanism. At the beginning of its takeoff, the head begins to inflate first. The buoyancy generated by helium will drive other parts of the hull to rise and slowly unfold during this process. At a distance of 10 to 12 kilometers from the ground, it reaches a fully inflated state and transitions to a horizontal flight attitude. Then, driven by an electric motor, the propeller climbs to the target altitude with the help of its lifting body configuration. The entire process takes about 4 hours to complete. The energy required for HHAA electric motors comes from flexible thin-film solar cells covering the surface above the body. During the day, the batteries convert light energy into electrical energy to drive the propulsion system and charge the onboard lithium battery pack. At night, it is independently powered by batteries, and the stored electricity can support the boat's operation for 15 hours. This "day charging night use" cycle mode, as well as its flight altitude, eliminates the need for it to return to land to replenish energy, thus avoiding the danger of being intercepted and attacked by enemies during this process. Although high-altitude platform systems have shown considerable potential to serve as "stratospheric sentinels," the harsh environment in suborbital space still poses significant challenges for HHAA: continuous power support is required for stratospheric flight, which may lead to structural fatigue of the aircraft; Extremely low temperatures may affect battery efficiency. Simply developing a monitoring system for operational status is far from enough to solve these problems. Moreover, on the battlefield, once locked by the enemy, the weak maneuverability of the airship will make it difficult for it to escape surveillance and strike. Overall, as a high-altitude platform still under development, HHAA's related technology is still not mature enough. However, once key technological challenges are overcome, there may be another type of "stratospheric sentinel" on the battlefield in the future. (New Society)