The BEXUS 24 research balloon was launched from the Esrange Space Center in Sweden at 13:39 Central European Summer Time on Wednesday 18 October 2017. The balloon reached its maximum altitude of 24.6 kilometres at 15:25 at which point the gondola separated from the balloon (in a procedure called 'cut down'). The gondola landed back on Earth at 17:22 local time. On board the joint mission by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) and the Swedish National Space Board (SNSB) were four science experiments designed by student teams from Spain, Italy and Sweden.
The BEXUS 25 balloon followed its predecessor on Friday 20 October with four more experiments on board, the focus here being on solar radiation, micrometeorites and other scientific topics. Two student teams from Germany and one team each from Sweden and Great Britain took part in this campaign. Michael Becker, head of the BEXUS programme at the DLR Space Administration, adds: "All the experiments were planned, put together, built and tested by the students themselves. In this way, the REXUS/BEXUS programme offers students a unique opportunity to carry out their own spaceflight project under real conditions."
BEXUS 24: On the hunt for cosmic radiation
The Spanish CADMUS (Cloud chamber for high Altitude Detection of Muons Under Special relativity effect) team from the Polytechnic University of Catalonia aimed to measure elementary particles (muons) that travel at almost the speed of light in the atmosphere. Muons are a major component of secondary cosmic radiation. Using a cloud chamber, they pick up muon traces and calculate, during the balloon’s ascent, the quantity of these particles detected at each altitude range. These data will be used to obtain the mean lifetime of a muon, which will then be compared to the value predicted by Albert Einstein’s special theory of relativity.. By making the decay visible, the half-life of elementary particles can be determined and information on the products of cosmic radiation and their composition at high altitudes can be acquired.
The NEMESYS (Neutron Effects on MEmory SYStems) team from the University of Rome Tor Vergata is looking into the effects of cosmic radiation on electronic storage systems. This experiment was designed to study how particle impacts affect a memory card – in other words, how the radiation environment influences the storage error rate (bit flips). The experiment included measurements of the altitude, position, temperature and the detection of impacts. Electronic storage systems are critical components in satellites, for example.
The Italian DREX (Deployable Reflector Experiment) team from the University of Padua tested the stability of a spring-based reflector antenna in the stratosphere. The advantage of the antenna is its very low weight and its ability to unfold a reflector in the lower layers of the atmosphere. Such an antenna could be used for future satellites and suborbital missions.
The students from EXIST (Examination of Infrasound in the Stratosphere and Troposphere), the team from the University of Luleå, studied infrasound in the stratosphere and troposphere in the Arctic region. The frequency of infrasound is between 16 to 20 Hertz and lies below the human hearing threshold. Infrasound occurs everywhere in nature, but is also generated artificially, for example through mining or by wind turbines. The EXIST team used special instruments on BEXUS 24 to record infrasound and analyse the infrasound spectrum in the arctic region, to subsequently determine the origin of the signals. Measuring infrasound can, for example, help in the prediction of extreme weather conditions and earthquakes.
BEXUS 25: Collecting micrometeorites in the stratosphere
The aim of the HAMBURG (High Altitude Meteoroids-dust-catching Balloon constrUcted by a Revolutionary Generation) student team from the Technical University of Hamburg-Harburg was the automated collection of micrometeorites that contain iron and nickel.
Micrometeorites are extraterrestrial particles with a size of less than 100 micrometres that can be scattered into the atmosphere by the wind. Micrometeorites that contain iron and nickel are ferromagnetic and so could be captured using strong magnets. During the BEXUS 25 flight these micrometeorites were captured at altitudes of five to 20 kilometres and 20 to 30 kilometres to determine their density distribution in the stratosphere. "In addition, we are analysing the composition of the micrometeorites in the laboratory. This information is used not only to determine the age, but also the origin of the micrometeorites, and enable a better understanding of the particles in the atmosphere. The biggest challenge here was to prevent contamination by Earth particles," explains team leader Ihsan Kaplan.
The LOTUS_XD (Light power and Optical Transmission experiment of University Students – eXtra Data) team from the Technical University of Dresden tested solar cells under space conditions. During the flight with the stratospheric balloon, they investigated how solar cells that are suitable for laser-based energy transfer from a satellite in orbit to an exploration vehicle on the surface of, for instance, the Moon or Mars behave as the temperature fluctuates. They did so by exposing the solar cells and associated electronics to temperatures as low as minus 60 degrees Celsius. "The experiment is expected to show that it is possible to use the energy from solar cells to freeze the electronics of an exploration vehicle or a satellite in space when it is not needed, and reactivate it again as necessary," explains team leader Jan Walter. "At the same time, the solar cells are expected to be available for transferring scientific data."
Team IRIS (Infra-Red albedo measurements In Stratosphere) focused on climate research. The Swedish team from the Technical University of Luleå used its experiment on board BEXUS 25 to study the behaviour of Earth's incident and reflected solar radiation, i.e. the level of Earth's reflectivity. The data gained will enable better error analysis of measurements by satellites, as the BEXUS measurements were carried out directly in the thin atmospheric layers. The results also support studies on the extent of ice melting in the polar regions, and hence the question of whether reduced reflection of solar radiation is contributing to global warming.
Also participating on board BEXUS 25 was a team from Great Britain. The SUNBYTE team from the University of Sheffield built an especially stable telescope to track the Sun automatically and then photograph the structure of the outermost layer of the Sun in the H-alpha spectral line. The experiment delivered images to the ground station during the flight itself.
BEXUS: a programme for junior researchers
The German-Swedish BEXUS programme (Balloon Experiments for University Students) allows students to gain practical experience in the preparation and implementation of space projects. The Calls for Proposals for the BEXUS 26/27 programme, which will be launched in the autumn of 2018, and the rocket equivalent, REXUS 25/26, foreseen for March 2018, are already open. Both programmes will again be organised by the DLR Space Administration in Bonn, the European Space Agency (ESA) and the Swedish National Space Board (SNSB).
Half of the balloon payload is being made available for experiments undertaken by students from German universities and higher education facilities. The Swedish National Space Board (SNSB) has also opened up their programmes to students from other ESA Member States. The German team of students receive technical and logistical support from the Centre of Applied Space Technology and Microgravity (ZARM) in Bremen. The flights will be carried out by EuroLaunch, a joint venture between DLR's Mobile Rocket Base (MoRaBa) and the Esrange Space Center of the Swedish Space Corporation (SSC).