At the start of the project, the team focused on gathering and analyzing the current state of service interfaces (SOTA). The consortium created a benchmarking table to compare the features of existing interfaces, including SIROM, iSSI, and Hotdock, alongside other external solutions. This allowed for a comparative evaluation based on key factors such as mechanical durability, data and power transfer capabilities, and space qualifications.
The project introduced the first version of the Space USB specification interface, aiming to establish a generic and standardized approach. This specification defined a set of common requirements and categories, based on the partners’ expertise and findings from the SOTA analysis. The specification was designed to remain open for updates throughout the project, allowing for the inclusion of results from workshops and technical feedback. After the project’s conclusion, the specification is available as a public version.
Key technical areas addressed in the specification included mechanical load tolerances, electrical power levels per orbit, environmental resistance, and connector/data standards. An applicability matrix was also developed to clarify which requirements applied to each interface category.
To ensure cross-validation, a compliance matrix was created, with each partner aligning their internal designs to the standards. Workshops were held to test bilateral interoperability, laying the foundation for future integration, interoperability, and standardization.
The project followed a methodology based on technical workshops organized between partner pairs. Each session focused on evaluating mechanical and electrical compatibility through simplified design iterations and mutual adjustments. Every partner confirmed their willingness to adapt their interface architecture to achieve convergence, while keeping core functionalities intact. Intermediate models were developed to serve both validation and learning purposes.
After successful outcomes from the pairwise workshops, the consortium decided to merge efforts into a single Common Passive Interface (CPI), replacing the three separate 2-in-1 configurations. The goal was to move toward a unified 3-in-1 interface. This significant decision was agreed upon by all partners, setting the new direction for the project.
The CPI combines the mechanical and electrical features from the three partner interfaces. A 3D-printed prototype was created to demonstrate the integration of the joint design. Partners then began finalizing their “delta designs” to ensure CPI compliance, while also maintaining compatibility with existing systems.
A test plan for validating the CPI was established using the ROBY test bench, operated by Thales Alenia Space. Each partner was responsible for delivering one CPI-compatible active interface and one passive unit. Two full CPI sets were produced for testing both single and Orbital Replacement Unit (ORU) configurations. The ROBY system operates in a position-controlled environment, later enabling more precise and generic validation scenarios, focusing on the SI capabilities unaffected by external robotic systems. Thales Alenia Space coordinated the integration, testing, and logistics.
While misalignment stress tests were excluded for risk management reasons, the planned testing campaign ensured thorough verification of the core interface functionalities. All tests, including direct interconnections and ORU configurations, were successfully conducted as planned and the results were documented in a test report. A complete analysis of the test results, including development plans and future activities for SI and interoperability improvements, is available in the report.
