Development of a Sealed Brush Gear Motor for deployment mechanism

The activity aims to develop an EM of a Sealed Brush Gear Motor (SBGM) to fulfil an appendage deployment function, based on the Sealed Brush DC motor background and heritage obtained in the frame of the METOP contract 16278 “Development of a sealed Brush DC motor”.

For an efficient development, the potential end user Thales Alenia Space has issued, at the beginning of the project, a specification for application on its Spacebus platform.

From this specification, the development covers the following phases:

• The design phase (through a PDR and a Design Review),
• The MAIT phase: Motor supplied by Soterem and Gear supplied by RUAG,
• The components tests (Motor TRR and TRB, Gear TRR and TRB),
• The assembled SBGM tests.

The main issue was relative to the mechanism efficiency and the compliance to the ECSS motorization margin at cold temperature (-65°C). RUAG developed 2 gears: one with wet lubrication and one with dry lubrication. After the Gear tests, the wet lubrication configuration has been selected for further proceeding.

Another issue was linked to the hysteresis torque coupler, which transmits the motor torque without any passing through the sealed housing. The device has been characterized: in addition, it offers a capability to limit the transmitted torque, which may bring interesting trade-off solutions between the contradictory minimum and maximum torque requirements.

The project ended with the successful development of the SBGM which will continue with aqualification and a flight phase.

The activity objective is to develop an EM of a brush gear motor to fulfil an appendage deployment function in the following context.

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Brush Gear motors are often used to motorise and regulate the speed of large solar arrays for telecommunication applications. Today, most of actuators are coming from US with the associated ITAR regulation constraints. One of the major concerns of this technology is the very poor electro-mechanical behaviour of the brushes under high vacuum that has lead in the past to many on ground and in orbit failures.

In the frame of a previous ESA contract, SOTEREM has successfully developed a breadboard of a sealed brush DC motor. This particular configuration offers the benefit of avoiding all electro-tribological issues relating to the operation of brushes under vacuum (wear and contact resistance issues).

This motor has been identified as a solution to fulfil an appendage deployment function. For that purpose the existing motor design has to be slightly adapted and a gearbox must be developed to reach the targeted speed and torque. The first application foreseen is the deployment motorisation and speed regulation of a high power solar array from Alcatel Space (F) for Spacebus spacecraft family.