Vision of an autonomous robotic service satellite approaching a completely modular iBOSS satellite.
Photo: iBOSS GmbH

Like Lego bricks

Coupling Kit for Modular Satellites

The Institute of Structural Mechanics and Lightweight Design (SLA) at RWTH has developed a connector which will soon be deployed on the ISS in an inorbit test. This marks a breakthrough on the path to a more sustainable aerospace future.

Like Lego bricks, the satellites of the future should be capable of assembled, dismantled, reconfigured, and reassembled over and over again. There is a general consensus about this vision in international spaceflight because because it is the only way of tackling the problem of space debris and the hazards it presents to spacecraft. Such a new generation of modular satellites would be capable of being repaired in space. The Institute of Structural Mechanics and Lightweight Design at RWTH performed pioneering research for the next generation of modular satellites within the iBOSS project (Intelligent building blocks for on-orbit satellite servicing and assembly). In addition to the primary structure of the satellite modules, the interface that links these together was researched in particular. Put simply, the Aachen researchers developed a suitable connector system, called iSSI (Intelligent Space System Interface) – a sort of USB system for space.

RWTH filed for a patent in 2014, and the idea was brought to market in Europe, the USA, and other spacefaring countries through the formation of a spinoff company, iBOSS GmbH. The system is now being tested in space for the first time. On February 19, the iSSI modules were launched on a U.S. space mission to the International Space Station (ISS). There, in the Japanese section of the ISS, they were connected together and disconnected for the first time in an experimental setup outside of the space station. When connected, data and power can be transmitted via the interface of the connector system in addition to the mechanical loads.

‘Our approach is revolutionary; our system has the potential to set a standard like that of the USB connector.’

A Pioneering Approach

For SLA director Kai-Uwe Schröder and his team, this is a milestone: Satellite modules can be reconfigured anywhere, including in space, any number of times thanks to the simple handling that the concept provides. ‘Our approach is revolutionary; our system has the potential to set a standard like that of the USB connector. A successful demonstration in space, under vacuum and cosmic radiation conditions, would be the great breakthrough,’ says Schröder. ‘We have the chance to finally make space travel more sustainable.’

Flight model of the compact iSSI satellite interface.
Photo: iBOSS GmbH

In the future, defective components could be replaced to significantly increase the service life and functionality of a satellite. For example, satellites use what are known as reaction wheels to control their position in space. If the swirl wheels stop working, the satellite can no longer be properly aligned – and is therefore only available to a limited extent or not at all. Reaction wheels integrated in a modular component can be replaced if they become defective. Finally, satellites can even be expanded to include further components and functionality thanks to this possibility of on-orbit servicing.

Since 2010, the RWTH-based Institute has been involved in a research project on modular satellites conducted by the German aerospace agency DLR. Twelve years later, the idea of creating the building blocks of satellites on Earth and assembling them in space is becoming a reality. The RWTH spinoff iBOSS recently received the Innovation in Space award for its iSSI concept.

The Aachen research team has already successfully deployed the iSSI system on the ground. The connector is already being used in the upBUS project, for example – a hybrid mobility concept in which a vehicle switches between operating as an aerial tramway and an autonomous bus. The changeover requires coupling and decoupling the vehicle and the aerial tramway system.

Successful tests

According to Thomas A. Schervan, director of iBOSS GmbH, the iSSI interface has now been operational on the Japanese Kibo experiment platform since mid-March 2022. So far the data and power transfer functions have been successfully tested. These tests were conducted in an endurance test designed to show that the technology is capable of maintaining the desired data connection and power over an extended time, in this case several weeks at a time. In the future, the system is intended to couple satellite modules together, and in such situations will have to be capable of functioning reliably in space for ten years at a time or more. Testing of the mechanical decoupling and recoupling function of the interface, mirroring the releasing and recoupling of a satellite module, will begin soon. If these tests are successful, the main milestones of the in-orbit demonstration (IOD) will have been successfully tested – data transmission, power transmission, and mechanical coupling. Further tests will follow to evaluate the robustness and load capacity of the iSSI system.

The next stage of the ISS mission will soon begin. Meanwhile RWTH is also involved in the AMS project, with its alumnus Matthias Maurer until recently an astronaut on the station. The vision is for an extraterrestrial application, such as for the installation of stations on distant planets.

– Thorsten Karbach