Solar Drones Are Filling the Skies, But There's Still No Clear Winner

The promising contenders and past failures of our attempt to create solar-powered flight.

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NASA

These are exciting times for the solar aircraft industry. Airbus and Boeing have carried out high-profile launches, as have technology giants Facebook and Google – but not all still in the race. So who is in, who is out, and who is on top? And what are they competing for?

When Sunrise 1, the world’s first solar-powered aircraft, took off in 1974 it was a demonstrator with no practical use. As solar cells and batteries become more efficient, flights became ever longer, raising the possibility of an eternal aircraft that could stay aloft indefinitely.

Circling solar drones could provide high-speed communications or survey the ground below cheaper than satellites. That’s a prize worth competing for. Building one that works has proven challenging though. Solar power needs the wingspan of an airliner but provides the power of a motor scooter. The resulting huge, lightweight aircraft are apt to disintegrate when they hit turbulence or land hard. One such accident ended NASA’s Helios program in 2003.

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Google / Titan Aerospace
Google / Titan Aerospace: Solara 50

Wingspan: 165 feet Weight: 200 pounds First Flight: 2015

Google likes to think in terms of global projects, and universal high-speed internet access is an obvious goal. In 2014 they acquired Titan Aerospace, a New Mexico company developing a solar-powered aircraft, for a reputed $60 million.

At the same time, Google built a large radio facility in New Mexico, reportedly part of their Project Skybender which employs millimeter waves to beam data at gigabits per second to provide 5G internet coverage.

Titan built the Solara 50 test aircraft, a forerunner of the larger Solar 60 production version. However, the Solara 50 crashed just four minutes into its maiden flight, due to structural failure – basically, it fell apart. In 2017 Google canceled the drone program altogether.

It looks like Google has decided to go with another platform for global internet: their Project Loon solar-powered stratospheric balloons, which will compete with solar drones.

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New Mexico State University / Boeing
Boeing / DARPA: SolarEagle

Wingspan: 400 feet Weight: Over 2,000 pounds First Flight: N/A

In 2010, Boeing won an $89m contract to build a plane for DARPA’s VULTURE II demonstration program. VULTURE was a spy drone intended to circle indefinitely over a target—supposedly “Very-high altitude, Ultra-endurance, Loitering Theater Unmanned Reconnaissance Element.”

Boeing’s solution was SolarEagle.

"SolarEagle is a uniquely configured, large unmanned aircraft designed to eventually remain on station at stratospheric altitudes for at least five years," said Pat O'Neil, program manager at Boeing’s Phantom Works program.

SolarEagle’s first flight was scheduled for 2014, but the program ran into difficulties and DARPA canceled it in 2012. Instead, the agency backed off from building an aircraft and focused on better solar cell and energy storage technology for future long-endurance programs.

This was not quite the end for Boeing. In 2017 it acquired Aurora Flight Sciences, which built structural components of SolarEagle, and had special expertise in this area.

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Aurora Flight Sciences
Aurora Flight Sciences: Odysseus

Wingspan: 243 feet Weight: around 2,500 lbs. First Flight: Scheduled “Spring 2019”

In November 2018, Aurora—now part of Boeing—rolled out Odysseus, described as a High-Altitude Pseudo-satellite. Aurora say it has the biggest payload capacity available in solar aviation “55 pounds or more,” along with the capacity to supply 250 watts power to the payload.

The power available indicates how effective arrays of lightweight solar cells have become. Being able to gather up every scrap of sunlight means that it can operate in more extreme latitudes, where winter days are shorter, than previous aircraft.

John Langford, CEO of Aurora, says they have been working on the concept for “thirty years or so.” The makers suggest that as well as providing communications for underserved areas, Odysseus would be useful for disaster response, monitoring wildfires, flooring or earthquake damage in real time. It might also be applied to weather research.

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BAE Systems
BAE Systems : PHASA-35

Wingspan: 115 feet Weight: 330 pounds First Flight: Scheduled 2019

In May 2018, British multinational BAE Systems announced that they were collaborating with a small company called Prismatic to develop a high-altitude solar drone called PHASA-35. It is another case of a big company with money working with a smaller partner with specialist skills, Prismatic having previous history in this field.

Prismatic successfully flew a quarter-scale version, PHASA-8 in 2017. PHASA-35 is powered by two propellers and carries a 30-pound payload, enough for a communications or surveillance package. It is intended to stay airborne for up to a year at a time.

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People Daily Online
Chinese Academy of Aerospace Aerodynamics (CAAA): Caihong (“Rainbow) T-4

Wingspan: 130 feet Weight: 880 pounds First Flight: 2017

It is no surprise that China takes an active interest in this area, especially given its obvious military applications. They have decades of catching up to do, but they have already made significant progress.

The T-4 flew in 2017 and immediately set a new national altitude record for unmanned flight in China of over 65,000 feet—though still well short of the 96,000 feet achieved by NASA’s solar-powered Helios in 2001.

For the time being, the CAAA’s goals are less ambitious than their Western counterparts. The T-4’s initial flight lasted only a few hours, and the design goal is for it to fly for ‘several months’ at a time rather than years. The Chinese look to be on course to compete in the solar aircraft arena, so long as they can avoid the crashes that have terminated other programs.

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AeroVironment
AeroVironment Inc: HAWK30

Wingspan: 260 feet Weight: Not disclosed First Flight: Scheduled 2019

Californian company AeroVironment Inc are the heirs to NASA’s solar aircraft program, having built much of the NASA hardware, including the giant Helios solar demonstrator drone. There were plans to turn Helios into a flying cell tower

in the early 2000’s, and tests were carried out for the Japanese Ministry of Telecommunications. That fell through when Helios broke up mid-air, but now AeroVironment are back with a new aircraft.

On April 24th, the company rolled out HAWK30 in Tokyo, as a joint venture with Japanese investors SoftBank. This is clearly a descendant of Helios, and is powered by ten propellers spaced evenly along its wings.

Flight testing is due to begin ‘soon’ at NASA’s Armstrong Flight Research Center. Though not the biggest company in the race, AeroVironment’s long pedigree in this area makes them one of the most experienced players and a force to be reckoned with.

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Facebook
Facebook / Ascenta: Aquila

Wingspan: 140 feet Weight: 880 pounds First Flight: 2016

In 2014, Facebook acquired UK drone maker Ascenta for a modest $20 million. Rumors suggest that they originally attempted to acquire Titan which Google later snapped up. Ascenta were put to work on a project called Aquila which combined drones with high-bandwidth laser communications.

“Aquila is a solar powered unmanned plane that beams down internet connectivity from the sky,” wrote Mark Zuckerberg wrote on Facebook. “Using aircraft to connect communities using lasers might seem like science fiction. But science fiction is often just science before its time.”

The first flight ended in a “structural failure,” although technically it was claimed as a success. There was a second flight a year later, but Facebook later announced it was stepping back from drone development to look at the underlying technology needed for high-altitude communications—and an alliance with Airbus.

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Airbus
Airbus: Zephyr-S

Wingspan: 81 feet Weight: 160 pounds First Flight: 2003

The Zephyr was originally developed in 2003 by British defense firm QinetiQ. Since then the design has gone through a number of versions and its latest incarnation is the Zephyr-S built by Airbus. This is one of the smallest solar aircraft and can only carry eleven pounds of sensors or communications gear. A larger version able to carry a bigger payload, known as Zephyr-T, is under development.

The Zephyr-S holds the world record for flight duration for an unrefueled, unmanned aircraft of just under 26 days, achieved in Arizona last year.

The Zephyr-S is currently undergoing flight testing by the UK’s Ministry of Defense in Australia. In early April reports emerged of a ‘mysterious aviation incident’ in the outback in which air traffic was diverted from one area. Airbus confirmed that one of its Zephyr aircraft was involved and had been forced to land early due to bad weather. They would not say whether there had been a crash.

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