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Stratoplanes: Aircraft That Will Fly at the Edge of Space

The stratosphere has long been a challenging environment for aviation, but new developments may usher in a golden age of stratospheric flight. It's June 2022, and an aircraft resembling something between a prehistoric beast and a spaceship is about to take off. Named Zephyr S, it has long, slender wings resembling those of a commercial airliner. Along with its small, slender body and head, it bears a resemblance to a pterosaur. Its shiny solar panels, akin to foil, and lightweight skeletal frame are more reminiscent of a spacecraft designed for space travel.

To lift the "Zephyr," it takes five or six people. When it's ready for launch, they run along the runway, holding the aircraft above them. Two small propellers on the device spin frantically before the aircraft begins its slow ascent into the cloudless sky, reaching altitudes of 60,000 feet (18,300 meters) or 70,000 feet (21,300 meters) — a steady climb into the stratosphere that can take up to 10 days.

Its purpose for the US military remains a secret, but its manufacturer clearly has aspirations to break a few records, notably for the longest duration flight of any aircraft, potentially lasting 63 years. In 1959, two men flew in a four-seat light aircraft, a Cessna, for 64 days, 22 hours, and 19 minutes, refueling in flight from a truck.

British aviation pioneer Chris Kelleher designed the first Zephyr in 2002. His vision was an unmanned aircraft capable of "eternal flight" in the stratosphere. He foresaw that solar power and lightweight materials would lead to aircraft capable of staying in the air for months or even years. Zephyr S is the first production model.

The stratosphere is the Earth's second atmospheric layer, starting at an altitude of about 33,000 feet (10,000 meters) and ending at about 160,000 feet (48,800 meters). If an aircraft can fly above 50,000 feet (15,150 meters), it can stay above the turbulent weather experienced closer to the Earth's surface in the troposphere. The challenge at this altitude is the very thin air, which makes flying and breathing difficult.

For a long time, there was only one option for exploring the stratosphere — the use of balloons. Balloons could reach the ceiling of the world, where there's too little oxygen for wings or jet engines. The problem then was surviving at such altitudes, and many balloonists didn't make it.

In 1931, humanity finally reached the stratosphere when a balloonist ascended to an altitude of 52,000 feet (15,800 meters) in a sealed gondola attached to a hydrogen-filled balloon. Two years later, Jeanette Piccard became the first woman to reach the stratosphere, rising to 57,600 feet (17,600 meters).

From the 1950s onwards, there came a succession of expensive, government-funded, and highly classified reconnaissance aircraft, such as the U-2, SR-71, and more recently, the RQ-170 drone. Now, the stratosphere is also home to weather balloons, high-altitude amateur balloonists, Chinese spy balloons, and marketing stunts. A group of schoolchildren in Cornwall used a weather balloon to send a Cornish pasty to the incredible height of 116,410 feet (35,500 meters). It returned frozen.

However, the era of exploration is not over. The airtight glider Windward Performance Perlan 2 set a new altitude record of 73,800 feet (23,500 meters) in September 2018. It soared higher than any glider had ever flown, even surpassing the maximum altitude record of the U-2 spy plane using mountain waves to ascend into the stratosphere.

The challenge for their designers is to find the sweet spot: having an aircraft that is light and sturdy enough to stay at such altitudes for extended periods, carry enough payload to be useful to paying customers, and survive the ascent and descent through the troposphere. According to Robert "Bob" Kraus, dean of the John D. Odegard School of Aerospace Sciences at the University of North Dakota, "The task of their designers is to find the golden mean in creating an aircraft that is light and sturdy enough to stay afloat at these altitudes for a long time, can carry enough payload to be useful to paying customers, and can survive the ascent and descent through the troposphere."

Even in low Earth orbit, microsatellites orbit about 340 miles (547 kilometers) higher than an aircraft like the "Zephyr." This means there's still a small delay – communication lag – that can hinder high-speed broadband communication. There are also some fundamental limitations in using satellites for remote sensing in terms of resolution, speed, and flexibility, further underscoring the need for High-Altitude Pseudo-Satellites (Haps).

These autonomous, ultra-light aircraft, known as Haps (High-Altitude Pseudo-Satellites), range from solar-powered gliders to solar-powered silver airships. Their duties include providing 4G or 5G phone and internet services after a natural disaster, detecting forest fires, and tracking enemy troop movements during wartime. They can do it better, cheaper, faster, and more flexibly than satellites.

Technological advancements, particularly in lightweight materials, solar panels, and battery technologies, are making the "long-duration" project a reality.

The "Zephyr" may take up to 10 days to reach its operational altitude (Photo: Zephyr)

"The task for their designers," says Robert "Bob" Kraus, dean of the John D. Odegard School of Aerospace Sciences at the University of North Dakota, "is to find the golden mean in creating an aircraft that is light and sturdy enough to stay afloat at these altitudes for a long time, can carry enough payload to be useful to paying customers, and can survive the ascent and descent through the troposphere."

Even in low Earth orbit, microsatellites orbit about 340 miles (547 kilometers) higher than an aircraft like the "Zephyr." This means there's still a small delay – communication lag – that can hinder high-speed broadband communication. There are also some fundamental limitations in using satellites for remote sensing in terms of resolution, speed, and flexibility, further underscoring the need for High-Altitude Pseudo-Satellites (Haps).

These autonomous, ultra-light aircraft, known as Haps (High-Altitude Pseudo-Satellites), range from solar-powered gliders to solar-powered silver airships. Their duties include providing 4G or 5G phone and internet services after a natural disaster, detecting forest fires, and tracking enemy troop movements during wartime. They can do it better, cheaper, faster, and more flexibly than satellites.

Technological advancements, particularly in lightweight materials, solar panels, and battery technologies, are making the "long-duration" project a reality.