ESA’s Juventas is a tiny spacecraft assigned a very big goal. Small enough to fit in an aircraft carry-on bag, this nanosatellite would be carried to deep space by ESA’s proposed Hera mission, before diving down to perform the very first radar probe into the depths of an asteroid. A specialist Luxembourg-based company is developing the radar electronics to make this happen.
The Agency’s Hera mission for planetary defence is being presented to Europe’s space ministers for approval at Space19+ next week. The first mission to a binary asteroid system, Hera will carry two 6-unit ‘CubeSats’ – small spacecraft built up from standardised 10 cm boxes, making maximum use of the latest commercial technology.
APEX will survey the target asteroid’s surface, working like a mineral prospector, while Juventas will fly just 3 km away, operating a low-frequency radar to see deep into the body’s core – the first ever direct look into the mysterious interior of a space rock.
Only 30x20x10 cm in size, Juventas is nevertheless as sophisticated as a full-size spacecraft, and is being planned by a Europe-wide team. Its design is being overseen for ESA by the GomSpace company in Luxembourg and Denmark with GMV in Romania.
Juventas’s radar instrument has been designed by France’s Institut de Planétologie et d'Astrophysique de Grenoble (IPAG) at the Université Grenoble Alpes with Astronika in Poland, working on its deployable quartet of 1.5-m long radar antennas, larger in scale than the entire CubeSat.
That leaves EmTroniX in Luxembourg, working on the radar electronics and eventually their integration and testing. The 18-strong company was founded by two engineers in 2001, initially focused on automobile systems, going on to expand into other sectors including aircraft avionics and space.
“We’ve been active in the space sector for more than 10 years now,” explains co-founder Cedric Lorant, “including working with LuxSpace to pioneer Automatic Identification System (AIS) vessel tracking with the Pathfinder 2, VesselSat 1 and 2 missions.”
The internationally mandated AIS system enables port authorities and coast guards to track seagoing traffic. But the onboard transponders have a horizontal range of only around 74 km. This is sufficient for coastal tracking or ship-to-ship monitoring but means that traffic on the open ocean disappears into vast blind spots.
However AIS signals do reach much further in the vertical direction – all the way up to space. This fact is enabling a new industry of satellite-based ship tracking. The challenge is to disentangle overlapping AIS messages from highly-trafficked regions, and take account of the Doppler shifting due to satellites’ rapid motion. Achieving this has required high-performance systems and clever processing, expanding EmTroniX’s capabilities in the process.
Mr Lorant adds: “For ESA we have developed and implemented algorithms for an autonomous software-defined radio transceiver digital signal processor – this was for the Proximity-1 UHF link, a communication standard optimised for Mars missions. We also collaborated with Thales Alenia Space on a high sensitivity ADS-B receiver for another Agency project.”
ADS-B, short for ‘Automatic Dependent Surveillance—Broadcast’, is the aircraft equivalent of AIS, requiring similarly sophisticated processing techniques to achieve accurate positioning from Earth orbit.
“All these projects have contributed to increasing our competences,” notes the co-founder. “For example we started with our first project in the VHF frequency bands and are now working on projects in the X and soon Ka frequency bands.”
Juventas presents a new challenge, to set up a working radar system on such a small platform, in the demanding environment of deep space rather than Earth orbit.
“We have worked on several missions based on microsatellites, and currently CubeSat avionics. All the same Juventas will be one of the smallest platforms we will work on,” adds Mr Lorant. “It will not be our first mission beyond Earth orbit however, but our second. In 2015 we collaborated on the 4M Manfred Moon Memorial Mission, commemorating the founder of OHB, which flew over the Moon.”
Operating beyond the protection of Earth’s magnetic field involves designing for a higher level of radiation, Mr Lorant explains: “Hopefully the payload will sleep during its travel time, helping tackle the radiation challenges. Its electronics will be well shielded, with redundancies used wherever possible, according to the size, weight and power consumption.
“We’re making a lot of use of commercial off the shelf components, which give performance advantages, based on our previous mission experience. Our philosophy is always to improve our electronics quality by careful component selection and proper protection, using ‘derating’ – meaning operating below maximum power levels – to create a robust design.
“For the instrument itself, the big challenge is that the electronics should not perturb the operating modes of the radar in any way. There are a lot of specific requirements, for instance that we must generate an extremely low noise with stable clocks, and while working within the limits of our power and size.”
Juventas’s radar is tiny compared to the large-scale radar instruments used in planetary missions like Mars Express. But the instrument can boost its overall signal-to-noise ratio by taking advantage of its relatively slow orbit around the asteroid – around a few metres a second – to send the same signal multiple times, carefully coded to support subsequent disentangling of the reflected signals.
“This is a really exciting and challenging mission for us,” says Mr Lorant. “And our hope it goes further than simply the Hera mission and Juventas. This radar could become an extremely useful tool for many future asteroid missions, such as ESA’s follow-up M-Argo nanosatellite, and other space resources endeavours.”