EuroSMG - European Stepper Motor Gearbox qualification

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The primary project objective of this contract is to qualify the design for space use, using one Qualification Model (QM), against a user specification and applicable ECSS requirements.

This builds upon previous developments by Reliance where an Engineering Model (EM), representative of the QM, was subjected to a full test campaign and strip-down to give confidence regarding the qualification test campaign.

The output from this contract is a Qualification Model (QM).


The SMG assembly is required to work as part of an existing SADM product. It therefore has to maintain the same electrical interfaces from the control system and also the same mechanical interfaces between SMG assembly and SADM, as is currently in place.

The SMG assembly performance data, when fitted to a SADM, should be within the historic SADM family test data (or better).

The key challenge is achieving the above (including mass, size and cost) while meeting ECSS requirements.

Secondly, Reliance is to ensure that the EuroSMG product is ITAR free as well as the overall supply chain.

Finally, Reliance’s design approach is for a completely new SMG without use of 3rd party, space approved sub-assemblies (e.g. motor), so a full concept to qualification programme. 


The overall benefit of the EuroSMG is that it is designed and manufactured in Europe and ITAR free, supporting ESA’s strategic objective of independence in the supply chain for the European telecom satellite industry and cost competitiveness.

There are currently a very limited number of stepper motor gearboxes available in the market which suit this current and future telecom satellite mechanism applications.

Achieving a product fully qualified for space application means that the EuroSMG not only is a product qualified to suit the intended primary end-user requirements but, based on system modelling understanding and test performance to-date, together with EM & QM test campaign data, the EuroSMG can also be adapted to suit other space mechanism applications with minimal risk and development.

The EuroSMG has already been adapted, its gearbox used as a common building block for an additional SMG with a different design of motor to suit an alternative control requirement.


The Stepper Motor Gearbox (SMG) assembly is the means of providing a rotary motion to the Solar Array Drive Mechanism (SADM), the SADM itself providing the means of aligning the solar panels to the sun.

The SMG assembly is a single integrated unit that packages together both a pair of motors (prime/ redundant) and gearbox. The motor and gearbox are being developed at the same time in order to reduce risk of designs not meeting the overall specification when combined.

The gearbox design is considered unique to space, with less components than an epicyclic while being stiffer and more efficient than a harmonic drive.

System Architecture

The system architecture can be broken into the two motors and a gearbox.


The qualification programme includes the following project activities:

Critical Design Review - review of conclusions from all EM testing (inclusive of a full test campaign representative of the Qualification campaign, strip-down and inspection) and test data (correlated with the analytical substantiation).

Combined MRR/MPCB0 - a QM baseline MPCB immediately prior to build activities commencing.

Build - build of a number of units.

QTRR - following all build activities (inclusive of lead coating and painting).

Testing - according to that agreed at QTRR.

Final Review - to close the activity.

Current status

Development successfully completed. Product ready for commercial supply, subject to specific customer application requirements.

Prime Contractor