A team of researchers at the Institute of Information and Communication Technologies, Electronics and Applied Mathematics (ICTEAM) has just completed a project on behalf of the European Space Agency (ESA) whose goal is somewhat puzzling: locating objects lost in space. Known for its sense of humour, ESA named the project LOST.
With 40 professors and approximately 200 researchers, ICTEAM conducts diverse research: signal processing, image processing, digital communications, antenna design, video compression, medical imaging, etc. When ESA launched a tender for its LOST project (Localization of Objects in Space through RF Tags), ICTEAM was well equipped to respond and did so through its ‘antennae’ team (Professor Christophe Craeye) and ‘digital communications’ team (Professor Luc Vandendorpe) in collaboration with the University of Bologna.
But why did ESA decide to finance such research? The problem it addresses is more serious than those uninitiated to space conditions can imagine. For example, over the years the International Space Station (ISS) has received many crews and, as a result, there are many lost objects floating around inside it whose original purposes are no longer very well known. Localisation of a long-abandoned object can also be useful in an external environment, such as the moon, to which there’s talk of a return. Another potential application of localisation is to align satellites that work in tandem, or several of their parts that must remain within a few meters of each other but never touch. Such alignment is currently performed by optical systems that prove faulty when an obstacle gets in the way. Radio waves eliminate this problem.
Tags, transmitters and antennae
‘The constraint,’ Professor Christophe Craeye explains, ‘is that these objects must obviously not be carrying power sources, that is, fuel cells or batteries. It’s hard to imagine attaching a battery to a toothbrush! In any case, such a battery would quickly wear out. Hence the use of RFID (Radio Frequency Identification) tags.’
The technique has existed for some time now, especially in commerce where it has replaced barcodes. It consists on the one hand of a tag that contains a chip and an antenna for exchanging information and is placed on the object (or the animal), and on the other hand of an always active radio transmitter-receiver whose frequencies activate tags that pass within its range and identify themselves to the transmitter-receiver.
As part of the LOST project, it was necessary to significantly increase the system’s precision (to within one centimetre on a 10x10 m surface area) by using a system without an active – and thus sustainable – transmitter that consumes practically no energy.
What is the apparatus developed by UCL and Bologna researchers to overcome these constraints? Ultra High Frequency (UHF) transmitters are arranged around the room to be monitored, for example inside the ISS. They emit power in waves. Passive tags placed on the objects to be localised (for example, an astronaut’s toothbrush) collect the energy emitted by the UHF, transforming it into very short pulses that they send to receiving antennae arranged on the periphery of the monitored area (see videos). These antennae relay the received signals to a processing unit that calculates the difference between the arrival times at each of the antennae, which makes it possible to localise the misplaced object.
Make way for miniaturisation
While the demonstration in Noordwijk’s ESA facilities was successful and the contract with ESA has ended (the final report remains to be written), Thomas Feuillen, a PhD student who was one of the main instigators of the research, doesn’t hide the fact that improvements still need to be made. ‘There will probably be a miniaturisation step to go through’, he says. ‘Today, our tags are around 6x6 cm. That's too large to attach to tools. Some objects can also absorb some of the energy sent to the tag they support. So we had to isolate the components. Here, too, there’s still work. But what interested ESA was to see that the system’s elements could work together. The applications it has in mind aren’t for tomorrow but for ten years from now.’
Henri Dupuis
The two videos presented here show the device created by UCL and University of Bologna researchers in two particular cases: in the laboratory; in conditions a little closer to reality (a lunar or Martian environment) where the tag to be localised was placed on the Martian rover developed by ESA and the ETH robotics laboratory in Zurich.
UHF transmitters are clearly visible in the middle of the walls, receiving antennae in the corners and the system (the ‘toothbrush’) that the researcher sets in motion and needs to be localised. The computer processes the information and translates it into a location: the tag, the object is spotted. The experiment was filmed in different ways, in particular with and without certain types of obstacles placed between the object and the receiving antennae.
A glance at Christophe Craeye's bio
1994 Electrical Engineer, UCL
1998 PhD, Applied Sciences, UCL
1994-99 Research Assistant, UCL
1999-2001 Postdoctorate, Eindhoven University of Technology (Netherlands) and University of Massachusetts
Since 2002 Professor, Louvain School of Engineering, UCL; antenna research
A glance at Thomas Feuillen's bio
2015 Master’s Degree in Electromechanical Engineering, Louvain School of Engineering, UCL
Since 2015 Research Assistant and PhD student focusing on radio signal processing, UCL
Since 2016 Master’s Degree in Management, Louvain School of Management, UCL