SOUNDER STRATOSPHERIC AIRSHIP

The SOUNDER system was a stratospheric station-keeping platform designed to transport a 10 kg payload capable to maintain station for several weeks and that could be launched, operated and recovered with a minimum of ground support. The project was developed by the Southwest Research Institute and Aerostar International and sponsored by the U.S. Joint Command and Control Warfare Center

In the image above we can see a basic scheme of the vehicle. It featured a torpedo-shaped hull with a hemispherical nose, cylindrical midsection, and an overall length of 37.8 meters. The hull was constructed from a single layer of 25-micron-thick biaxially oriented Nylon-6 in eighteen longitudinal gores, with a total volume of 1371 cubic meters. Its superpressure design eliminated the need for ballonets, while a liquid ballast system adjusted the angle of attack.

The propulsion system used a lightweight, tail-mounted, electric motor-driven propeller made of carbon fiber composite. A brushless electric motor drove a 3-meter-diameter propeller via a transmission, monitored by the control system for speed, voltage, and temperature. Power was provided by an internally mounted solar array on a two-axis gimbal, allowing it to track the sun independently of the airship's orientation. This system powered the electronics and propulsion during the day and charged lithium-ion batteries for nighttime operation.

The tail structure comprised three fins made of biaxially oriented nylon, attached to the hull with lightweight composite struts and guy lines. These fins, supported by self-erecting masts, provided longitudinal and roll stability. The payload pod was attached using a unique suspension system that supported its weight both above and below the hull.

The control system was a microprocessor-based flight controller communicating with a ground station via redundant radio modems. It managed propulsion, communication, and power systems and offered three control modes: full remote control, semi-automatic, and fully autonomous navigation. It utilized data from GPS, an electronic compass, and solar positioning for its operations.

Ground station functionality included data presentation and airship control using personal computers. Commands sent to the airship were verified and executed, and telemetry provided near real-time updates on system status and location.

Balloon launched on: 4/27/1999 at 11:00 local
Launch site: Hondo Airport, New Mexico, US  
Balloon launched by: Joint Command and Control Warfare Center, Kelly AFB, Texas / Southwest Research Institute
Balloon manufacturer/size/composition: Stratospheric Airship 1500 m3
End of flight (L for landing time, W for last contact, otherwise termination time): 4/27/1999 at 17:15 local
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): ~ 6 h
Landing site: S of Jourdanton, Texas, U.S.

• Autonomous stratospheric airship description of the Sounder system in the U.S. patent registry
• Development of a small stratospheric Station Keeping Balloon system Proceedings, 22nd ISTS, Morioka, Japan (2000)
• Spokesman On Line July 1999 (via Archive.Org)