For collecting space debris

Task: "Collecting" space debris
How to "collect" and dispose of these parts is already being discussed in space research. But first you have to know how the parts move in space in the first place.

This question is the focus of the UB-Space project, which was founded by six students from different disciplines at the University of Bremen. team leader Maren Hülsmann: "So far, two modules have been able to dock when they communicate with each other. However, space debris are so-called 'uncooperative objects' that a spacecraft has to recognise, approach and grab."

This requires complex mathematical calculations - Maren Hülsmann and her team colleague Amina Zaghdane are studying technomathematics - but you also need to collect reference values and test data. And that is precisely the task of UB-Space.

Into space with the sounding rocket
The fact that six students are conducting a very real and complex space experiment is thanks to the German-Swedish REXUS/BEXUS programme. The abbreviation stands for "Rocket Experiments for University Students" or "Balloon Experiments for University Students". Student teams can submit research tasks to the programme. A jury examines the proposals and in each project round, four teams receive - in simple terms - a section of a rocket in which to place their research setup. The four modules are housed in a sounding rocket that is launched into space once a year from the Kiruna space centre in northern Sweden.
 
The idea behind UB-Space: the rocket module releases a test body into the thermosphere and uses sensors and several cameras to record the position and movement of this "free-falling unit". Maren Hülsmann: "We receive image and position data from the real movement of the FFU in space. Until now, there have only been simulations of the movement of components in space."

Complex calculations are again required when analysing the experiment, as each rocket constantly rotates around its own axis to compensate for imbalances.

Designing for special environmental conditions
In the twelve months before the rocket launch, the project teams are very busy. At UB-Space, this is particularly true for Oliver Dorn, who is studying marine engineering and designing the module's mechanics. Space-specific restrictions apply: "Energy consumption is limited by the system, as are weight and installation space, and air friction generates temperatures of up to 200 °C." Under these conditions, how do you design the drive that transports the test body out of the rocket? It quickly became clear that a flap in the rocket would be blown off first. Then a unit containing the "Free Falling Unit" is extended. Lars Flemnitz, electrical engineering student and proximity switch of the UB-Space project: "We tested several propulsion systems. Two screw drives used in parallel worked best here."

Drive and bracket from the igus® programme
The spindle drives come from the drylin® programme from igus®. The stainless steel spindles cover an extension path of 150 millimetres. They are driven by a NEMA 11 stepper motor, which operates at a high torque and low speed of 3 cm/s. The holder in which the FFU is located is attached to a lead screw nut, which was printed from the tribo-filament iglidur® J260. This is one of a total of six different filaments for 3D printing that igus® offers. What they all have in common is that they are optimised for friction and wear and that special parts for prototypes or small series can be produced quickly and cost-effectively, even with complicated geometries. UB-Space also sourced other components for the bracket from igus®.
 
A barely visible component also comes from the igus® construction kit, which is of crucial importance here. Oliver Dorn: "The test body (FFU) rests in a holder that is fixed with Tribo-Tape.

is lined." This sliding film made of iglidur® with very low coefficients of friction is relatively new in the igus® programme. It ensures that the unit slips out of the holder and moves away from the rocket after the flap has opened and the drive extends.

Complex tests before launch

Each of the REXUS experiments has to undergo the same complex test and approval procedures that are customary in commercial and scientific space travel in accordance with ESA standards. For example, the rocket module from UB-Space has just completed vibration and acceleration tests with 12 g on three axes.
 
The effort involved is understandable, as there are no test flights or prototypes in space travel: The experiment has to succeed on the first and only flight. However, the UB-Space team is optimistic and is encouraged by the professional test engineers who are continuously supporting the project.

It goes without saying that the REXUS rocket with the UB-Space experiment will not become space debris. After a parabolic flight with an apex at an altitude of 90 kilometres, which takes it beyond the three layers of the atmosphere and into the thermosphere, the rocket lands back in northern Sweden. The data collected by UB-Space en route will then be analysed.

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