Zephyr 3

In 2003, QinetiQ, a commercial offshoot of the UK Ministry of Defence, was planning to fly its Zephyr 3 up to 40 km at 70 m/s (250 km/h; 140 kn), after being released from a high-altitude balloon at 9 km, besting the NASA Helios which had reached 29 km.^[3] It was envisionned as an alternative to space satellites, stationed permanently in the stratosphere for environmental monitoring, mobile phone coverage or military applications.^[3] The QinetiQ 1 balloon altitude record attempt failed in 2003.^[4]

In February 2005, Qinetiq was preparing a demonstration above 30,000 ft for the UK Ministry of Defence at the Woomera Test Range in Australia, for reconnaissance or as a communications relay.^[4]

Zephyr 6

Between 28 and 31 July 2008, in a demonstration for the US military at its Yuma Proving Ground in Arizona, the Zephyr 6 flew for 82 hours and 37 minutes, an unofficial record as the FAI wasn't involved.^[5]

Zephyr 7

On 23 July 2010, the Zephyr 7 took the FAI-sanctioned duration record after a 336 hours (14 days), 22 min and 8 s flight,^[6] reaching 21,562 m (70,741 ft).^[7] It exceeded the nine days (216 hours) of the 1986 round-the-world flight of the Rutan Voyager.^[8]

In March 2013, the project was sold to EADS Astrium (now Airbus Defence and Space).^[9]

In 2014 it flew for 11 days in the short days of winter whilst carrying a small payload for the British Ministry of Defence,^[10] and later near civilian airspace.^[11]

Zephyr 8/S

In February 2016, the UK Ministry of Defence purchased two Zephyr 8 planes.^[12] In August 2016, a third was purchased.^[13]

In 2016, a twin-tailed Zephyr T variant, providing a maritime surveillance and communications capability, was scheduled for flight testing in 2018.^[14]

In summer 2018, for its maiden flight from Arizona, the Zephyr S remained aloft for 25 days 23 hours 57 minutes, nearly twice as long as the previous record flight of 14 days set by its predecessor.^[15] By October 2021, it had flown 2,435 hours.^[16]

On 15 June 2022, the Zephyr S took off in Arizona, venturing for the first time into international airspace and over water.^[17] On 19 August, the plane was lost over the Arizona desert after a flight time of 64 days.^[18] It covered 56,000 km over the southern United States, the Gulf of Mexico, and South America.^[19]

The aircraft was lost when one engine component (redesigned since) failed in an unusual high-altitude storm turbulence at 17 km.^[2] By early 2023, Airbus planned to launch operations from the end of 2024 with around 18 aircraft.^[2] By 2034, a 1,000 aircraft constellation could cover 2.9 billion people, and would provide emergency 4G/5G following natural disasters.^[2] The larger Zephyr variant, with twice the payload capacity, is expected for 2026.^[2]

Zephyr 3

The 12 m (39 ft) wide aircraft had a carbon composite frame to weigh 12 kg (26 lb), and 1 kW of solar cells powering five motors.^[3]

Zephyr 6

The carbon fiber Zephyr 6 has a 18 m (59 ft) span and weighs 30-34 kg (70 lb) for a 2 kg (4.5 lb) payload.^[5] Amorphous silicon solar cells from Unisolar recharge lithium-sulphur batteries from Sion Corporation with twice the energy density of the best alternative, lithium polymer batteries.^[5] Launched by hand, it can reach 18 km (60,000 ft).^[5] The first version had a battery capacity of 3 kW·h, driving two propellers.^[20]

Zephyr 7

Zephyr 7 was larger, at 53 kg,^[21] and capable of a maximum altitude between 20 and 21 km,^[22] it required five ground crew to launch, as opposed to three previously for the Zephyr 6.^[23]

Zephyr 8/S

Designed to fly at 20 km (65,000 ft) for more than a month, the 25 m (82 ft) wide Zephyr 8 is 30% lighter and can lift 50% more batteries than the Zephyr 7.^[24] It weighs 60 kg, 40% of which are batteries (24kg), and the 5 kg payload can transmit video with a 50 cm resolution from above 20 km.^[12] They should be able to operate year-round between 40 degrees North and South, while winter operation gets more difficult at higher latitudes.^[12]

It used Amprius lithium-ion batteries with silicon nanowire anodes for a 435 Wh/kg specific energy up from 300–320 Wh/kg.^[25] Solar cells are high-efficiency, lightweight, and flexible inverted metamorphic multi-junction epitaxial lift-off GaAs sheets manufactured by MicroLink Devices, with specific power exceeding 1,500 W/kg and areal powers greater than 350 W/m².^[26]

One Zephyr can replace 250 cell phone towers.^[27] It can be used to perform intelligence, surveillance and reconnaissance (ISR) with a wide visual payload coverage of 20×30 km (12.4×18.6 mi) and can be equipped with radar, LIDAR and infrared technologies.^[17]

Endurance is targeted for up to 200-300 days.^[2] An 8 kg (17.6 lb) mobile connectivity payload can serve up to 100,000 people on the ground.^[2] A 5 kg Airbus-developed Opaz optical sensor can deliver 18 cm-resolution imagery.^[2]