How can space debris be captured? How can students reduce the rotation of research rockets in microgravity? The REXUS 22 research rocket was launched from the Esrange Space Center near Kiruna in northern Sweden, at 14:00 Central European Time (CET) on 16 March 2017. On board were student experiments to try and answer these and other questions. REXUS 21 was successfully launched just one day earlier, on 15 March 2017. Around 50 students from Germany, Sweden, Poland and Italy took part in the joint mission by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) and the Swedish National Space Board (SNSB). The flights of the six-metre-long, single-stage rockets lasted approximately 10 minutes, from take-off to the landing of the payload.
Effectively tracking down and collecting space debris
Five German experiments took part in the dual campaign. In their UB-SPACE experiment (University of Bremen - Image Processing for Determination of relative Satellite Motion), students from the University of Bremen and Bremen University of Applied Sciences tested software that is intended to detect the relative motion of a satellite using images. To simulate this scenario, a cube-shaped microsatellite was ejected from the REXUS 22 rocket and filmed by multiple cameras attached inside the rocket. Autonomous satellites might subsequently be fitted with this technology to autonomously collect space debris. Capturing space debris is also the focus of the GRAB team (Gecko-Related Adhesive testBundles). Students at the Technical University of Braunschweig are aiming to use their experiment to make it easier to dock with a target object such as a defective satellite. To do so they tested adhesive material, called 'Gecko material', in microgravity, on surfaces typical for spaceflight. Because of their structure of fine hairs, these materials exhibit good adhesion on smooth surfaces.
Reducing the rotation of rockets with RaCos
Because space is predominantly a vacuum, releasing gas leads to a recoil. A rocket can be decelerated in this way, for example, and its angular momentum reduced. To stabilise the flight path of the REXUS rocket, the rocket rotates around its own axis while rising using a special setting for the fins attached to the rocket engine. However, some experiments require microgravity, so the rotation must be reduced to a minimum. With RaCoS (Rate Control System Experiment), the rotation of the REXUS 22 rocket should be reduced and controlled using a cold gas thruster. For this, students at the University of Würzburg have drawn up a control algorithm to calculate the opening times of the valves that control the gas flow. This system could be used for the attitude control of satellites.
Using unfolding antennas in satellite communication
Unfolding structures are of particular interest in space research, as they take up little room and are light due to their low mass materials made of thin films and gastight textiles. With DIANE (Dipole Inflatable Antenna Experiment), the team from the Technical University of Dresden tested a seven-metre-long, dipole antenna that was due to unfold in microgravity during the REXUS 21 flight. The antenna was stowed away with its equipment, unfolding mechanism, gas generation system, transmitter and control board, in a cube-shaped microsatellite. During the deployment, the dynamic flight behaviour and antenna's signal transfer were investigated and monitored with a camera.
AtmoHIT – an Earth observation experiment
The AtmoHIT (Atmospheric Heterodyne Interferometer Test) experiment is aimed at testing the AtmoCube 1 Earth observation instrument under space conditions. It was designed to measure temperatures in the middle atmosphere during the REXUS 22 flight, using a special spectrometer. The instrument is distinguished by its high light sensitivity and small size, making it ideal for scientific remote sensing measurements using a cube-shaped microsatellite (CubeSat). The experiment was developed under an initiative for microsatellites for climate research via tomography, developed by students at the University of Wuppertal in cooperation with the Jülich Research Centre (Forschungszentrum Jülich).
Other European teams' experiments on REXUS 21/22
Investigation of salt samples typical of Mars was the focus for students from Luleå University of Technology, Sweden. The SALACIA (Saline Liquids And Conductivity In the Atmosphere) experiment could support a subsequent Mars mission, as similar environmental conditions to those on Mars exist at some of the flight altitudes of the REXUS 21 rocket. During the rocket flight, the team investigated the absorption properties – the absorption of water and the reaction of salts with water – by measuring the conductivity. The composition, moisture and temperature of the salt sample changed depending on the altitude.
In their U-Phos (Upgraded Pulsating heat pipe Only for Space) experiment, the team from the University of Pisa investigated how a liquid changes depending on temperature in microgravity. To do so, the students developed a passive temperature control system consisting of capillary tubes filled with fluid. The aim was to find out to what extent a temperature management system functions and can be used under space conditions.
DREAM (DRilling Experiment for Asteroid Mining) was the name of the experiment from the team at the Technical University of Wroclaw, Poland. It is used to prepare for asteroid mining, meaning the extraction processes of raw materials and mining in space. During the REXUS 21 rocket flight, the students tested the distribution and behaviour of bore chips in microgravity.
REXUS and BEXUS – a programme for scientific young talent
The German-Swedish REXUS/BEXUS programme (Rocket/Balloon Experiments for University Students) enables students to gain practical experience in the preparation and implementation of space projects. Their experiment proposals can be submitted annually each October. This year's call will be published in June 2017. Half of the rocket and balloon experiments are available to students at German universities and colleges. Swedish space agency SNSB has opened up the Swedish proportion to students of the other European Space Agency (ESA) member states.
On the German side, project leadership and support for the experiments is run by the Center of Applied Space Technology and Microgravity (Zentrum für angewandte Raumfahrttechnik; ZARM) in Bremen. The flight campaigns are carried out by EuroLaunch, a joint venture by DLR's mobile rocket base (MORABA), which is responsible for providing the rocket systems, and Esrange Space Center run by the Swedish Space Corporation (SSC), which provides the launch infrastructure. The programme is coordinated by the DLR Space Administration in Bonn.