BEXUS 37 (Balloon EXperiments for University Students)

BEXUS which stands for Balloon Experiments for University Students is a project part of the REXUS/BEXUs initiative that allows students from universities and higher education colleges across Europe and more recently also Canada to carry out scientific and technological experiments on stratospheric research balloons. The basic idea behind BEXUS is to provide an experimental space platform for students in different areas of interest such as atmospheric research, fluid physics, magnetic field, materials science, radiations physics, astrophysics, biology and also to serve as a platform for new technology demonstrations.

Each year, two balloons are launched from the European Space Range (ESRANGE) base near Kiruna, Sweden each carrying several experiments assembled on a medium-sized gondola (1.16 m x 1.16 m x 0.84 m). The total lifted-mass is approximately 300kg on each flight. With each payload weighing between 30 and 112 kg that means that 4 student experiments can be accomodated per gondola.

The first five flights of the program were carried out under sponsorship of the Swedish Space Corporation that offered available space on yearly technological flights carried out at ESRANGE. Since 2008, BEXUS is realised under a bilateral Agency Agreement between the German Aerospace Center (DLR) and the Swedish National Space Agency (SNSA). The Swedish share of the payload is made available to students from other European countries through a collaboration with the European Space Agency (ESA). EuroLaunch, a cooperation between ESRANGE and the Mobile Rocket Base (MORABA) of DLR, is the organism responsible for the campaign management and operations of the launch vehicles.

On each cycle of the initiative, experts from DLR, SSC, ZARM (Center of Applied Space Technology and Microgravity, University of Bremen) and ESA provide technical support to the student teams throughout the project. It begins with a Call for Proposals, followed by a condensed space project lifecycle, including typical design phases and reviews, culminating in the launch of the experiments and publication of the final reports.

Balloon launched on: 10/8/2025 at 19:23 CEST
Launch site: European Space Range, Kiruna, Sweden  
Balloon launched by: Swedish Space Corporation (SSC)
Balloon manufacturer/size/composition: Zero Pressure Balloon  
End of flight (L for landing time, W for last contact, otherwise termination time): 10/9/2025
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): F 4 h 47 m
Landing site: In Finland

BEXUS 37 was launched from ESRANGE on 8 October 2025 at 19:23 CEST, marking the first night-time flight of the programme in many years. Benefiting from exceptionally calm winds, the balloon remained almost stationary, reaching an altitude of 27 km and maintaining a float time of 4 hours and 47 minutes, a new duration record for the campaign. The flight provided ideal conditions for experiments requiring darkness, such as optical imaging and infrared calibration. Landing occurred in Finland.

The BEXUS 37 mission, carried four experiments investigating radiation detection, thermal imaging and communications, and the observation of space objects from the stratosphere.

OSTRICH (Observation System Tracking Radiation Incidence through Correlation Heuristics), developed by Eindhoven University of Technology and Radboud University Nijmegen, investigated methods for measuring and characterizing radiation at high altitude. The experiment used radiation sensors to record particle events and applied correlation techniques to identify relationships between detected events and environmental or flight parameters. The measurements were intended to improve understanding of the radiation environment encountered by balloon-borne systems and to investigate techniques that could eventually support radiation monitoring and particle detection in space.

RATATOSK (Radiometric Analysis for Thermal Animal Tracking with Optimized Streaming utilizing K-band technology), from the University of Southern Denmark, demonstrated a communications and data-transmission system based on K-band technology. The experiment was designed to transmit thermal-imaging data from the balloon platform to a ground station. Its application concept involved the remote observation and tracking of animals using thermal signatures, requiring the transmission of relatively large quantities of imaging data. The BEXUS flight provided an opportunity to test the K-band communication link and evaluate its performance under stratospheric conditions, including the transmission of data from the airborne platform to the ground.

SETH (Scintillation Event Triggering Hodoscope), developed by Kiel University, investigated the detection and characterization of energetic particles using scintillation detectors. When charged particles pass through scintillating material, they produce short flashes of light that can be detected and converted into electrical signals. SETH used multiple detector elements to register these events and determine information about the incoming particles. The experiment focused on particle detection in the stratospheric radiation environment and on evaluating the performance of the detector system during flight. The collected measurements can contribute to the characterization of cosmic-ray and other radiation events at high altitude.

SOBER (Space Object Brightness Evaluation and Reference), developed by the University of Waterloo, investigated the photometric observation of objects in space. The experiment used an optical system to observe the brightness of satellites and other space objects and to record changes in their reflected light. Such measurements can provide information about an object's apparent brightness and its variation as viewing geometry changes. The BEXUS flight provided a high-altitude platform from which to conduct observations above much of the atmosphere, reducing atmospheric effects compared with observations made from the ground. The experiment therefore demonstrated techniques for optical space-object observation and brightness characterization from a balloon platform.

• BEXUS 36/37: A stratospheric student experience ESA press release
• Europe’s Students Take Off in BEXUS 36-37 Swedish Space Corporation press release