Photonics tech brings in the big guns for next-gen satellite speeds
Image credit: Airbus
Next-generation terabit speed satellites will never happen without photonic technologies. We find out how close industry is to extreme communications.
Just last year, France-based Thales Alenia Space revealed that its cutting-edge communications payload for satellite flight would use high-speed serial links with fibre-optic interconnects instead of coaxial cables. The development may not have stirred, let alone shaken, the world, but out in space, the ramifications are set to be huge and exciting.
“This is the first time fibre-optical interconnects will be employed on a massive scale in a commercial satellite,” says Nikos Karafolas, technical officer at the European Space Agency. “Once these are introduced the technology will be here to stay.”
Why are such photonics technologies so crucial to future telecommunications satellites? In short: size, weight and power.
Today’s high-throughput communications satellites (comsats) generate narrow beams to transmit data, exploiting frequency re-use schemes and raising overall satellite capacity and data rates to some 100Gbit/s. Yet come the early 2020s, the 100Gbit/s capacity will need to shift upwards by an order of magnitude to a mighty 1Tbit/s to meet operators’ rising bandwidth demands.
Even if today’s microwave and radio-frequency technologies could hit the terabit data-rate target for a next-generation satellite, components and systems would struggle to meet the power consumption, size and weight limits of space flight.
Enter photonics. Already the norm in telecommunications, the race has been on since the turn of the century to transfer lightweight, compact, high-performance technologies from the ground to satellite payloads and space.
In 2005, France-based navigation and positioning device pioneer IXBlue qualified its Fibre Optic Gyroscope for flight on the Planck scientific satellite. The gyroscope uses optical waves propagating in a fibre-optic coil to accurately measure a rotation rate and, crucially, is resilient to temperature changes, magnetic perturbations, extreme shock and vibrations.
In 2009, two ESA satellites – Soil Moisture Ocean Salinity (SMOS) and PRoject OnBoard Autonomy (Proba-2) – were launched aboard a Russian Rockot launch vehicle. Karafolas says: “SMOS was critically dependent on tens of fibre-optic communications links and was the first operational use of fibre-optics communications in an institutional satellite.”
Proba-2 also contained a fibre sensor-system to monitor temperature and tank pressure within the satellite propulsion system, marking the first full fibre-optic sensor network in space. “We had demonstrated we could use fibre optics with confidence and nine years later the systems are still working fine... a defining moment for photonics in space,” says Karafolas.
Since this time, worldwide space agencies and partners have also been working on the use of fibre-optic cables, instead of coaxial cables, within comsat payloads.
ESA has delivered its SpaceWire and SpaceFibre standards for high-speed communications, with VTT Technical Research Centre of Finland, France-based Radiall and Reflex Photonics from Canada also developing high-frequency, fibre-optic transceiver modules. Meanwhile, Norway-based T&G Elektro has been devising a flexible routing assembly that will one day route hundreds, even thousands, of optical fibres.
Then, of course, came Thales Alenia Space’s ‘digital transparent processor’, dubbed SpaceFlex. Karafolas says: “What we have been developing for years could fly in 2019... and the [payload] mass is going to be massively reduced.”
However, fibre-optic digital interconnections is just the beginning for photonics in satellite communications. Aerospace companies have also been developing systems that can perform microwave functions in analogue satcom payloads. And again, results are edging closer to commercial exploitation.
In a key ESA collaboration, Thales Alenia Space demonstrated a lightweight satcom repeater based on microwave photonic technologies to frequency-convert and cross-connect the growing number of channels in future satellites. Key partners on this development were DAS Photonics of Spain, Sercalo, Switzerland, and France-based Vectrawave.
In parallel, Airbus Defence and Space has been collaborating with DAS Photonics, Cordon Electronics, IMEC, UK firm Polatis and France-based Sodern on a project called OPTIMA, which will deliver a test photonic payload demonstrator for communications satellites.
According to Airbus project manager Javad Anzalchi, the demonstrator is the first step towards maturing this technology for space applications. What’s more, the project has been focusing efforts of European photonics and space players, from both industry and academia, on proving the validity of the photonic payload concept.
“Key challenges include the low interest of large companies to qualify a small number of recurrent items for space... while some photonic devices and technologies for terrestrial applications are not capable of sustaining flight [or withstanding] a space environment,” he says.
Importantly, Anzalchi reckons the photonic equipment Airbus has developed for OPTIMA and other projects will reduce payload mass by at least 25 per cent compared to conventional payload technology. “Most of this comes from replacing coaxial cables with fibre-optic cables,” he says. “We also use wavelength division multiplexing in our payload architecture which, in most cases, reduces the equipment required.”
Anzalchi reckons Airbus will perform an in-orbit technology demonstration after 2021, with ESA’s Karafolas also expecting systems from Thales and Airbus to be offered to satellite operators within five years. Yet as years of dogged research reaches fruition, perhaps the most ambitious developments are yet to come.
ESA has also spent over a decade working on microphotonics – miniaturised photonics components on a chip – for use in satellites. Collaborating with the likes of DAS Photonics, Lionix from the Netherlands, Antwerp Space, the University of Ghent and IMEC from Belgium, EPFL and CSEM from Switzerland, the organisation has already demonstrated how the comsat payload microwave functions of frequency generation, frequency conversion, beam-forming and RF filtering can be performed by microphotonic circuits.
ESA and partners will spend the next five to ten years looking at developing and maturing microphotonics for photonic payloads. Karafolas says: “This is going to be a real challenge. Ten years in space is a very short time, and once you put your spacecraft into a rocket you cannot access it for its entire lifetime, which is up to 20 years. This means we really have to take extra care with all developments and qualification.”