Design and test of autonomous scientific payloads for sounding balloons

Sounding balloons are a fast and cost-effective transport system to lift up scientific payloads to stratospheric altitudes around 30 km, where equipment can be tested in low pressure environments and extreme temperature conditions to simulate space operation or conduct investigations of atmospheric parameters. Furthermore, ascent and descent phases offer fast changing dynamic conditions which can be used to evaluate instrument sensitivity to variation of environmental parameters and to test operation of optical systems on different target areas on ground. Images acquired with changing spatial and time resolution can be correlated with mission altitude and trajectory providing information for the validation of detection algorithms and scene mosaic reconstruction methods. This paper describes two autonomous payloads for stratospheric sounding balloon designed, assembled and tested at University of Padova, one devoted to measurement of light pollution, the other to tracking and automatic identification of targets on ground. They both rely on commercial cameras and comprise all electronic boards for sensor conditioning, data acquisition, compression and storage. Acquired images, position and attitude information are saved into on board non-volatile memory and may be partially transmitted on ground through telemetry depending on available transmission capacity. Energy for at least 4-hour continuous operation is provided by rechargeable lithium battery packs, powering all subsystems through a dedicated distribution unit. Both units have been enclosed in a light weight Styrofoam insulated structure and present a final mass lower than 3 kg, staying into the limits of a light balloon according to International Civil Aviation Organization regulations. The payloads have been selected by HEMERA Peer Review Group for a flight in 2019 from CNES base in Aire sur l'Adour but operations have been postponed to 2020 for bad weather conditions in both available launch windows. To speed up the operative testing of the units a joint effort has been started with university of Pisa that will hopefully lead to a first launch from Italy in January 2020. Design, calibration activities, functional and thermomechanical tests conducted in the University lab are presented along with a rationale of the expected scientific goals when operating in the stratospheric mission.