The spy drone lurking above our heads: British-built solar-powered planes can fly silently through the stratosphere for months

It looks like a cross between a toy plane and a drone, but this British solar-powered plane could be the future of aerial surveillance.

PHASA-35, built by the British company BAE Systems, is a 150 kg solar-electric aircraft that can fly silently through the stratosphere for months.

The unmanned aerial vehicle (UAV), named for its 115-foot wingspan, travels at a maximum altitude of 70,000 feet, at a leisurely speed of 55 mph.

It is designed as a cheaper and lighter alternative to satellites and can be used for Earth observation and surveillance, border control, communications and disaster relief.

Now BAE Systems reveals that PHASA-35 has just completed a second round of test flights into the stratosphere – the second layer of Earth’s atmosphere.

Launched from Spaceport America in New Mexico, it flew for 24 hours, climbing to over 70,000 feet before making a smooth landing.

PHASA-35 will be able to fly non-stop in the stratosphere for up to twenty months in 2026, offering a ‘sustainable and affordable alternative’ to satellites.

It uses the sun’s energy to stay aloft, charging a battery of small batteries during the day to keep it flying at night.

BAE Systems said the PHASA-35 completed two stratospheric test flights from Spaceport America in October, the first since its maiden flight in June 2023.

Both times it made a successful landing at Spaceport America in a usable condition, meaning it was ready to fly again just two days later.

This is a major advantage over satellites: it can be brought back down to Earth and the payload can be switched or added and sent back up quickly.

“These latest flight tests are a significant step forward in proving the PHASA-35’s capabilities for operations and a real moment of pride for our entire team,” said Bob Davidson, CEO of BAE Systems’ Prismatic subsidiary.

“We are committed to continuing to develop PHASA-35 at a pace to make it available for operational activities as early as 2026.”

In addition, this time for the first time, the PHASA-35 flew with an operational payload: a software-defined radio developed by BAE Systems.

‘This is actually a very powerful sensor that enables Earth observation and can be adjusted remotely using software,’ a company spokesperson told MailOnline.

It weighed 10 kg – a payload twice as heavy as the first stratospheric test flight in 2023 – but the PHASA-35 can carry a payload of up to 15 kg if necessary.

These recent flights are part of a series of tests intended to confirm the aircraft’s performance before it can be purchased by defense and commercial customers.

The company does not want to say who exactly these are, but is in discussions with ‘a number of customers’ about further financing of additional flight tests.

BAE Systems has invested tens of millions of pounds in PHASA-35, which, like conventional aircraft, builds up speed on a runway but releases the wheels shortly after take-off.

He glides to a soft landing on his stomach and any damaged propellers or components are replaced.

Because it glides gently and looks more like a paper airplane, the risk of a hard landing causing significant damage is low.

Because it operates in the stratosphere, regardless of any weather conditions such as wind and rain, it can provide stable observations of a specific area over long periods of time.

According to Prismatic – the Hampshire-based subsidiary of BAE Systems that designed and manufactured the aircraft – the PHASA-35 can deliver services at a ‘fraction of the cost of satellites’ and can be deployed anywhere.

Prismatic says: ‘Further important advantages include simplicity of construction and ease of transport, due to the relatively low number of structures composing the aircraft.’

The PHASA-35’s maximum payload of 15 kg could include cameras, sensors and communications equipment that would allow troops to talk to each other or provide internet access to rural locations during a natural disaster or emergency.

Engineers see a number of core applications for the drone in areas typically covered by low-Earth orbit satellites, such as environmental surveillance, disaster relief, border protection, maritime and military surveillance, and mobile Internet communications.

One example is the ability to add a sensor, fly over a vulnerable forest for months at a time and continuously monitor the moisture levels in the trees – predicting with weeks’ advance warning when a fire is likely to break out.

It also has the potential to be used in the provision of communications networks, including 4G and 5G, for example for regions that currently have poor coverage.

Construction of the UAV began in 2018, along with the release of concept images, following the successful launch of a quarter-scale model called PHASE-8 in 2017.

The full-size version of PHASA-35 made its maiden flight in February 2020, flying from the Woomera Test Range in South Australia, followed by the first full-size stratospheric test in June 2023.