The US Navy’s Skydweller completed a 73-hour uninterrupted solar flight as part of a 220-hour test, paving the way for extended maritime surveillance.
On August 5, 2025, the US Navy achieved a major milestone in long-endurance aerial surveillance with the successful completion of a 73-hour uninterrupted flight of the Skydweller solar-powered drone. The flight was part of a larger 220-hour cumulative test campaign conducted from Stennis Air and Space Station in Mississippi. The program aims to validate the Skydweller’s flight endurance capabilities under operational conditions, without refueling and with full day-night cycles powered solely by solar energy. This type of drone, designed for maritime surveillance missions, represents a strategic solution for militaries seeking to reduce operating costs while maintaining a constant presence over large areas. The US Navy is counting on this platform to enhance its maritime ISR (Intelligence, Surveillance, Reconnaissance) capabilities, particularly in remote areas or areas without land bases.
The 220-hour test campaign and its operational challenges
The Skydweller’s 73-hour flight was part of an experimental program conducted by the Naval Air Warfare Center Aircraft Division (NAWCAD). Weather conditions forced the teams to split the tests into several segments, but the August 5 mission demonstrated full autonomous flight capability, day and night, powered exclusively by solar energy. The drone managed to maintain sufficient battery recharge to operate without interruption for three consecutive days, without critical altitude loss or return to ground.
The engineers responsible for the project have confirmed that, from a technical standpoint, there are currently no limitations to extending the flight beyond 220 hours. This endurance is based on a rigorous energy balance between daytime solar production and nighttime consumption, thanks to onboard energy management algorithms.
This program is part of COLDSTAR, a Department of Defense initiative to enhance ISR capabilities at sea, particularly to support missions assigned by the US Southern Command in the fight against drug traffickers, the monitoring of maritime migration flows, and the securing of strategic sea lanes.
Unlike satellites or piloted aircraft, the Skydweller can maintain a stationary position over a defined area for several days, at an altitude sufficient to remain out of reach of tactical threats while providing continuous observation.
Technical characteristics and flight performance of the Skydweller
The Skydweller is derived from the experimental Solar Impulse 2 aircraft. It has a wingspan of 72 meters, the same as a Boeing 747, and a maximum takeoff weight of 2,540 kg. It is built around a carbon fiber structure, combining lightness and rigidity, with a payload capacity of 360 kg. Its wing surface is covered with more than 17,000 photovoltaic cells spread over an area of 270 m².
These cells can generate up to 100 kilowatts in optimal sunlight conditions. The energy produced powers the electric motors during the day, while recharging a lithium-ion battery pack weighing approximately 635 kg, which provides the energy needed during the night.
The drone is capable of reaching a cruising altitude of between 7,500 and 10,000 meters. During the day, it can climb to 13,500 meters to maximize sunlight, then descend at night to around 2,000 to 3,000 meters to limit energy consumption. This altitude variation is automatically controlled by the on-board computer based on energy forecasts.
The payload can include various sensors: EO/IR cameras, lightweight synthetic aperture radar, AIS receiver for identifying ships at sea, and communication relay equipment. All these elements can operate simultaneously, depending on the mission requirements. The entire system is managed by a redundant avionics suite with four secure automatic piloting systems designed to ensure flight continuity even in the event of component failure.
Strategic interest for long-term maritime surveillance
One of the Skydweller’s major advantages is its ability to temporarily replace satellites or manned aircraft on long-endurance missions. In vast and poorly monitored maritime areas, particularly in the South Atlantic, the Pacific, or around sensitive straits, this drone can be deployed from a land base, climb to altitude, and cover an area of several thousand square kilometers for several days.
For the US Navy, this means a significant reduction in flight hour costs. The absence of fuel, frequent maintenance, on-board personnel, and in-flight support logistics reduces operational expenses.
The drone can also act as a communications relay for isolated ships or special forces deployed at a distance, ensuring continuity of transmission without going through geostationary satellites. In addition, in crisis situations, it can play a persistent surveillance role over a sensitive area, with enhanced observation capabilities thanks to its stability and endurance.
In the medium term, several joint uses are envisaged: coupling with tactical drones operating at lower altitudes, ISR coverage of an air and sea group, or permanent maritime control in areas of tension (Gulf of Guinea, South China Sea).
Current limitations and avenues for technical development
Despite its performance, the Skydweller is not without its limitations. Its dependence on sunlight makes it difficult to use at high latitudes, in winter, or in persistent cloudy weather. In addition, its low speed (approximately 90 km/h at cruising speed) and range limited to areas defined by energy efficiency make it unsuitable for dynamic reconnaissance or interception missions.
To enhance its versatility, Skydweller Aero and its partners are considering several improvements. Higher-efficiency solar cells, optimized battery thermal management, and advanced automation solutions would increase endurance to 90 days or more under certain conditions.
Finally, a modular version could allow the drone to be configured for specialized missions such as electronic warfare, anti-piracy surveillance, monitoring of ship emissions, or support for humanitarian operations with dedicated sensors.
This type of platform will not replace existing systems, but it is set to become an effective strategic complement, particularly in terms of passive deterrence and discreet but permanent presence.