Hey, HN! We're James and Cyriel, co-founders of Radical. We're making an autonomous solar-powered aircraft designed for continuous flight in the stratosphere. Our 20 ft. prototype recently flew nonstop for over 24 hours, which you can see in this video: https://youtu.be/E6oDxQYEksc (edit—warning, there are rapidly flashing lights starting just after 1m, in case you're sensitive to that). Our website is at https://www.radicalaero.com/, but it's pretty bare. If you use LinkedIn, we have a few more posts at https://www.linkedin.com/company/radicalaero.

Our aircraft is designed to fly over specific areas for months, carrying various payloads for tasks like imagery, sensing, and telecommunications. What we’re building behaves like a drone in some ways, and like a satellite in other ways. Much like satellites, we’re able to provide service for long periods of time, but we’re also much closer to users (we fly at around 20 km altitude) and able to maneuver or remain over an area of interest. This makes what we’re building really well suited to applications that require continuous coverage or high-resolution/bandwidth data.

Examples of this include continuous real-time monitoring (such as in wildfire management or illegal fishing), high-resolution mapping and imagery (we’re able to collect sub-10 cm resolution imagery), and high-speed direct-to-device internet. The ability to permanently host sensors and devices in the sky in this way opens the door to lots of new opportunities. In truth, we still don’t know all the new applications that will arise from this (we’re really interested to hear your thoughts on potential applications!).

As for the technical details: Our aircraft is battery electric and driven by propellers. It has a large wing for high aerodynamic efficiency and to generate the necessary lift required to fly in the thin air of the stratosphere. The wing is covered in solar cells, during the day, these power the aircraft and charge its batteries. Through the night, battery energy is deployed to continue flight. We repeat this process daily, enabling us to fly for up to a year without needing to land. Ultimately, battery cycle life is what limits our aircraft’s flight endurance - and we can land, carry out simple maintenance tasks and then re-launch to continue flying. Our aircraft has multiple tails which help to stabilize the ultra-lightweight structure (our 20 ft. prototype weighs just 13 lbs.). We also use these tails to control the aircraft, they provide roll control by twisting the main wing of the aircraft, increasing or decreasing lift as needed.

The aircraft is fully autonomous; it has a full autopilot system onboard and various sensors for position, airspeed, and other key data streams (much like a typical drone or UAS). The aircraft flies at high altitudes of around 70,000 ft. (20 km) avoiding cloud cover, civil air traffic, and the turbulent winds of the troposphere.

Long endurance flight has been the goal of many past projects. NASA’s Helios and the DARPA Vulture program tried to develop long endurance aircraft. Helios’s crash led to an overhaul of aircraft structural analysis codes, and DARPA Vulture led to advancements in battery and solar tech. More recently, both Facebook’s Aquila and Google’s Loon were discontinued. Recent advancements in battery and solar tech, and miniaturization of electronics mean long endurance flight is now feasible - but we are aware we need to do things differently to succeed. Unlike those before us, we’re not tying ourselves to a single application and are focused on bringing a cost-effective solution to market. That means avoiding research-grade components and moving quickly. Additionally, we firmly believe that iterat...