A study backed by the European Space Agency (ESA)’s Advanced Research in Telecommunications Systems (ARTES) Core Competitiveness programme has successfully demonstrated the viability of using optical wireless communications in satellites, in a move that could help reduce mass and costs by removing the need for cabled connections.
Accommodating bundles of wires is a key challenge in telecom satellites. The harness and wiring can account for a significant proportion of a spacecraft’s weight – up to 8% – and incur additional penalties in terms of size, power consumption and cost. To address these issues, the Transmission of Optical Wireless Signals for telecom satellites (TOWS) study, led by Scuola Superiore Sant’Anna (Pisa, Italy), explored the viability of replacing cables with optical wireless solutions, with the potential added benefit of increasing development speed by using commercial off-the-shelf (COTS) devices.
Optical wireless communications (OWC) solutions have previously been considered for space applications but it is only recently that the components and systems have matured sufficiently to be a practical and viable option. Unlike radio frequency (RF) wireless technologies, there are no electromagnetic interference effects with OWC. A wider benefit of optical communications is that they also provide significantly enhanced resistance to hacking and jamming, in turn increasing the security and reliability of communications.
The TOWS study looked at using optical wireless in three scenarios related to satellite applications: inside and outside the spacecraft, and during the assembly, integration and test (AIT) phase. The target was to prove OWC as a viable alternative to wired onboard communications like 1553 buses, with solutions that had small volume, very low mass and very limited power consumption.
The challenges in each scenario vary. Within a telecom satellite, for example, the design of the OWC links benefits from the environment being fundamentally dark but there will be shadowing effects, whereas external applications have to work with a strong background light, high temperature variations and cosmic radiation. The OWC solutions therefore had to be tailored, optimised and tested for each use case.
The Scuola Superiore Sant’Anna team, supported by Thales Alenia Space Italy, designed and tested a unique, compact, lightweight transceiver board that would work in all three scenarios, with very minor tuning of the devices. The OWC systems were successfully demonstrated to technology readiness level 5 (TRL5) in mock-ups of a real satellite and an AIT room in Rome, Italy.
Ernesto Ciaramella from Scuola Superiore Sant’Anna said “dealing with wiring is a headache in many industrial applications, but particularly in space where it is vitally important to minimise size, weight and power consumption. OWC, which is becoming a mature technology, will help. We called upon our long-term expertise in OWC demonstration for terrestrial environments and proved that optical wireless solutions can replace traditional cables and wiring harnesses in spacecraft. This is a great achievement, which we wouldn’t have been able to carry out without the support provided by ESA and the Italian Space Agency (ASI) through the ARTES programme.”
Xavier Geneste, Space Segment Engineer at ESA, said “the consortium has achieved a significant milestone in the development of satellites. Being able to replace wiring with optical wireless solutions will have multiple benefits, including speed of development, testing and build. Reducing the weight of satellites is also beneficial from an environmental and cost perspective as lighter satellites require less fuel for launch. The fact that the TOWS study focused on using COTS components is also significant, as this could have additional cost-cutting benefits. This is not the end of the story as, thanks to ASI support, the consortium will carry out further demonstrations to foster the interest of communication satellite prime manufacturers.”
Giancarlo Varacalli, Head of the Telecommunication and Navigation Unit at the Italian Space Agency said: “The TOWS project is part of a broader Italian roadmap in the field of the space optical technologies and confirms the remarkable national competence in the sector. Thanks to the effective management of ESA, the project is also the exemplary result of a synergic partnership between a top-notch research centre - Scuola Superiore Sant’Anna - and a leading space industry - Thales Alenia Space Italy - and represents a crucial step for designing and developing cheaper, more compact, efficient and reliable satellites.”