W-band on the run

A trio of ESA engineers took to the roof of the Agency’s technical heart to link up with a satellite the size of a shoebox as it sped overhead.

The team deployed a portable, self-made ground station to acquire W-band microwave signals from ESA’s W-Cube mission, as part of an effort to better understand how this portion of the electromagnetic spectrum interacts with the atmosphere, encouraging its use for satellite communications.

Put in place within half an hour, the ground station was improvised from various outcomes of past ESA projects, combined with a computerised telescope mount usually employed for amateur astronomy. But at the first try the station succeeded in tracking and gathering signal data from W-Cube as it performed a ten minute pass over the ESTEC technical centre in Noordwijk, the Netherlands.

ESA Young Graduate Trainee Hugo Debergé, the microwave engineer responsible for building the station, commented: “Of all the thousands of satellites in space, we are currently pointing at the very first 75 GHz beacon in flight, and receiving signals from it – it’s amazing!”

W-Cube, launched in 2021, was developed through ESA’s Advanced Research in Telecommunications, ARTES, programme, to explore the use of W-band for future satellite missions. This particular millimetre-band – used on Earth for various commercial applications such as automotive radar and point-to-point wireless links – is being adopted for use in space, offering very high data throughput across a largely untrafficked span of the electromagnetic spectrum.

But the International Telecommunications Union, which assigns frequencies for use, has only limited modelling and prediction models to show how W-band signals propagate through Earth’s atmosphere and weather conditions. W-Cube was flown to help shrink this blind spot and prove the feasibility of future space missions operating using W-band.

A single fixed ground station was put in place to track W-Cube, at the premises of mission prime contractor Joanneum Research at Graz in Austria, with another one in preparation by VTT Research in Finland.

The nanosatellite itself – a ‘three-unit’ CubeSat, meaning it has been built up from three standardised 10-cm boxes – was constructed by Kuva Space in Finland (previously Reaktor Space Lab) with the W-band payload coming from VTT.

“W-Cube itself is working well, and only a few days ago another satellite carrying an experimental W-band payload was put in orbit from the University of Stuttgart,” explained ESA microwave engineer Vaclav Valenta. “So we decided to build our own station based on available hardware and chips from past projects in our lab, then assigned the challenging job of building it to Hugo through ESA’s Young Graduate Trainee programme. The satellite is switched on for acquisitions from Austria but as we found we can still track it from the Netherlands. 

“We’re excited by today’s success on our first try, and our next plan to fine-tune our station design to make it truly portable. Also, our intention is to set up a permanent W-band station here at ESTEC. This design, combined with the tracking techniques we’re deploying, will certainly become the basis for other mobile W-band stations.”

Digital payload engineer Marek Peca equipped the portable ground station with motion control software and geodetic calculations: “We began by homing in on the Sun, and its output of radio white noise, serving as a reference point so the ground station knew where to look for W-Cube as it passed over our heads – a pinhole camera taped to the side of the antenna gave us a coarse visual confirmation of being centred on the Sun; we’ll improve on this with building-mounted radio beacons in the future. But it all worked well: today’s success makes this only the second ground station in the world to acquire W-band signals from orbit!”

Michael Schmidt of Joanneum Research is Principal Investigator for the W-Cube mission: “I congratulate the ESTEC team in achieving this goal. I know from experience it is no easy task to receive the satellite’s very weak signal. Their work is providing important additional measurements in different climate zones from Graz and Helsinki, and the mobile nature of their ground station means it can be located in other locations as well, helping to improve our W-band propagation models and learning more the use of low-orbiting satellites for propagation experiments.”

Marek processed some 32GB of captured radio-frequency data to confirm that the first full pass of the satellite signal had been correctly tracked, representing six and a half minutes of the full pass. See plots from the W-Cube pass here and here. Read about the open source element of the project to use telescope mounts to track satellites and celestial objects here.