Safeguarding Europe’s role in Solar System Internet: First Stop, the Moon

The future of space communication is being imagined now. The European Space Agency (ESA), together with international partners, is leading the way towards the Solar System Internet, an advanced communication network stretching from Earth to the outer planets, providing radio frequency and optical communication, as well as Positioning, Navigation, and Timing (PNT) services.

Building upon ESA’s Moonlight programme, ESA is proposing the ASSIGN (Advancing Solar System Internet and GrouNd) programme at the ESA Council Meeting at Ministerial level (CM25) in November.

ASSIGN will aim at federating existing and planned networks into a secure and resilient interoperable network of networks - the Solar System Internet – for ESA’s missions as well as institutional and commercial ones, and fostering European industry competitiveness for its realisation and future exploitation.

Introducing the Solar System Internet Node-1

As with other ambitious space programmes, the Moon is an excellent stepping stone before venturing further to Mars and across the Solar System. ESA’s SSI Node-1 is a central element of ASSIGN. This proposed mission that will lay the groundwork for future optical communication links, resilient and secure space internetworking and autonomous deep-space navigation.

The aim of the mission will be to demonstrate reliable routine operations of an optical trunk link from Moon’s orbit, as well as providing a testing ground for the three key technologies identified by ESA for the realisation of the SSI:

• Optical communication
• Resilient and secure disruption-tolerant networking
• Deep-space positioning, navigation, and timing

The initial mission design was completed early this year at ESA’s Concurrent Design Facility at ESTEC, defining a clear path forward for payload development.

“We are ready to move to the next phase of development,” says Felix Flentge, ESA SSI lead in international standardisation bodies and the SSI-Node-1 Study Manager. “Either the payload - or parts of it – could fly as hosted payloads on other missions or as part of a dedicated SmallSat mission”.

SSI-Node 1 concept is fully aligned and coordinated with the vision of the ESA Moonlight Programme. It builds on the concepts, devised under Moonlight and demonstrates their evolution into a larger vision behind the Moon in the Solar System.

A world-first optical relay in lunar orbit

“Deep-space optical communication is key as it promises data throughput 10 to 100 times greater than current radiofrequency solutions”, explains Clemens Heese, ESA Head of Optical Technologies. “Combining this technology with the ones we have for radiofrequency communications is essential to transmit the ever-increasing data output of the missions exploring the universe”.

The design foresees a 13.5 cm Laser Communication Terminal, capable of transmitting data at up to 5 Gbps. This high-speed relay could link to an optical ground station on Earth or a geostationary node extending the HydRON network, another ESA initiative building optical infrastructure across Earth’s orbits.

A test bench for resilient and secure, disruption-tolerance networking

In current space missions, communications rely on rigid, pre-planned point-to-point connections between spacecraft and ground stations. A link is established between a control centre, a particular antenna and a spacecraft, the data gets sent back and forth and then the link is actively disconnected. While this approach has been suitable for many years, we are now heading into a period of increased data volumes resulting in congestion which can only be solved by implementing a more dynamic and resilient approach.

“The Solar System Internet requires a paradigm shift,” says Mehran Sarkarati, ESA Head of Ground Stations Engineering Division and Programme Manager for ASSIGN Programme. “We need communications that are secure, flexible, autonomous, and above all, resilient against disruptions, delays, and high latencies”.

To achieve this, ESA and its partners are exploring disruption tolerant networking (DTN) using the Bundle Protocol, enabling space assets to exchange data in a secure and resilient way, much like the internet on Earth but without requiring simultaneous end-to-end connectivity. The SSI Node-1 would be the first ESA mission to put these DTN technologies into practice.

A technology integrator for deep-space PNT and lunar timekeeping

The SSI will not only enable secure and resilient communication across the solar system, it will also incorporate provisioning of positioning, navigation, and timing services in its system architecture from the outset, as these functions are deeply interconnected and costly to deploy separately in space.

PNT and communication are interdependent: spacecraft need precise timing to coordinate communications and calculate contact windows, while PNT systems require communication links for time synchronisation and share location data. Merging these functions enhances efficiency, reduces deployment costs, and improves mission resilience.

The SSI Node-1 will carry a comprehensive navigation payload. Additionally, the mission will help to improve the accuracy of lunar timekeeping and their alignment with Earth-based systems.

Towards a resilient, secure and interconnected future of space communications

Given the current geo-political landscape, network security and resilience are a strategic concern for ESA and our Member States. ASSIGN will pave the way for maturating the concept and system design of a resilient and secure Solar System Internet, to be ready to start its gradual implementation in CM28.

“The ambition behind the Solar System Internet aligns with ESA’s Strategy 2040,” says Mehran Sarkarati. “Resilient and secure space communication is a strategic objective for ESA and Member States”.

Beyond increasing mission data return, the envisaged SSI will ultimately reduce mission costs, enable more onboard autonomy and optimise utilisation of communication resources across providers. It is essential for ESA and Europe to remain a key player in this international endeavour and safeguard the interests of European industry in its utilisation, hence the economic benefits for Member States.

The ASSIGN Programme is an ESA Multi-Directorate Activity, led by the directorate of Operations (OPS) and devised together with the directorates of Connectivity and Secure Communications (CSC), and Navigation (NAV).