From drone flight to sounding rocket

Suspended on a five-metre rope under a mighty drone, a 50 cm long plastic tube swings in a soft breeze above ESTEC’s football field. It’s a scorching hot day, and the test team seek refuge in the shade of a parasol, keeping all equipment close to prevent it from overheating.

ESA engineer Giovanni Serafini brings the drone 120 metres into the air, then drops it in a fast descent, stopping when the suspended payload hangs only three metres above the field. More manoeuvres take the drone from the air above one side of the field to the other.

Why? To test a clever invention made by a student team from Ruhr University Bochum in Germany.

Students in the lead

“We are here to test a radar retroreflector, which we developed for a competition organised by the Institute of Electrical and Electronics Engineers (IEEE),” explains Daria Tsukanova from the university team. 

“A retroreflector is a passive structure, in this case a 28 cm long metal tube covered with cavities, designed to reflect signals back towards their source. This makes an object easier to detect and track without requiring active electronics or transmitters onboard.”

Such devices can help improve the radar visibility of small airborne vehicles like drones or sounding rockets, which launch experiments to the edge of space before falling back to Earth. For the purpose of this test, the students attached their reflector to a longer plastic tube simulating a rocket.

Radars currently rely on the fact that rockets are made out of metal, and so are relatively reflective by nature. However, even those rockets become no longer detectable at certain viewing angles. The advantage of the student team’s reflector is that it can extend these limits, keeping rockets or other objects visible to the radar for much longer.

Cheap and effective

“What’s unique about this technology is that it’s very cheap. The reflector itself is passive, made by 3D printing and laser cutting,” adds Stephan Hauptmeier from the university team.

“Another advantage is that to detect it, we can use a radar technology well-established in the automotive industry – the same one that is part of driver assistance systems and will, for example, cause a car to break automatically if an obstacle is detected. This means no special ‘space-grade’ radar is needed.”

“This has been a unique opportunity to leverage hardware previously developed within ESA’s Technology Development Element programme for planetary and in-orbit missions, based on automotive radar technology,” says Václav Valenta, ESA’s microwave engineer. “By making one of these prototypes available to students, we enable them to gain practical experience with real radar technology and explore how such systems can be configured and optimised for specific applications.”

From competition to an ESA-backed launch

In one afternoon, the team successfully verified the retroreflector’s functionality ahead of the next step – launch aboard a sounding rocket up to one kilometre above a field in Brno, Czech Republic, scheduled for later this summer.

“This project is a great example of how student initiatives can evolve beyond the competition environment,” comments Karol Masztalerz, ESA Graduate Trainee.

“What began as a university-led challenge has grown into an international collaboration between ESA, two European universities – the Ruhr University Bochum in Germany and Imperial College London in the UK – industry partners and the Czech Rocket Society, who are providing their new Sherpa rocket for the next round of testing.”

Statement on collaboration

This project was selected as the winner of an International Microwave Symposium (IMS) competition, organised by the Institute of Electrical and Electronics Engineers (IEEE). It is managed in collaboration between Václav Valenta (ESA) and Markus Gardill (Brandenburg University of Technology Cottbus-Senftenberg), who organised the competition as co-chair and chair of IEEE’s Microware Theory and Techniques Society’s technical committee for Microwave Aerospace Systems (TC-29).

The radar unit used for the testing was initially sent to Imperial College London, where engineer Václav Pavlíček modified both the system configuration and operating parameters to accommodate the new terrestrial use cases.