How 'absolutely critical' bearings ensure operators make the most of satellites

Increasing numbers of smaller, more cost-effective telecommunications satellites are being launched into the Earth’s orbit, which has led to a growing need for high precision, high reliability bearings to support onboard sub-systems such as reaction wheels and other critical mechanisms, says Gary Hughes, product engineering manager at The Barden Corporation.

In the past, building and launching a civil telecommunications satellite into space required a multi-million pound investment. More recently, however, the size and cost of satellites have reduced. An increasing number of satellites are now being launched into space from Europe, USA, China, Turkey, India and the Far East.

For bearing suppliers like us, high requirements are now being placed on bearings that support satellite sub-systems such as reaction wheels and other onboard precision mechanisms.

A reaction wheel is a type of flywheel used primarily by spacecraft and satellites for attitude control – alignment with the Sun and stars – without using fuel for rockets or other reaction devices. A satellite typically uses three reaction wheels – for the x, y and z axes – which are particularly useful when the spacecraft must be rotated by very small degrees. They can also help reduce the on-board fuel mass. This is accomplished by equipping the satellite with an electric motor attached to a flywheel which, when its rotation speed is changed, causes the satellite to begin to counter-rotate proportionately, through conservation of angular momentum.

The failure of one or more reaction wheels can cause a satellite to lose its ability to maintain position and potentially cause a mission failure. The reliability of reaction wheel bearings is therefore absolutely critical. The bearings must satisfy demanding requirements, continuing to reliably spin for 10-15 years in the vacuum of space, using only a small amount of lubricating oils on the bearing surfaces. At the same time, the bearings must minimise any vibration, so as not to negatively affect the observational performance of the satellite. The bearings must also withstand the vibration and loads at launch, as well as endure the temperature variations while in orbit.

At Barden UK, reaction wheel bearings are typically custom-engineered angular contact ball bearings, manufactured with high surface finish requirements and visual appearance of the raceways. The bearings typically comprise 440C stainless steel rings and balls with phenolic cages. Two bearings are required per reaction wheel.

The bearings are assembled in clean room conditions using special handling techniques. Every part of the rolling contact surface of the bearing is inspected by the company and any slight defect is captured and documented.

The procedures provide full traceability, controlled lubrication and complete retention of records, giving full traceability. Torque test traces and functional tests can be performed on the bearings, as well as complete inspection of bearing raceway surfaces. They are typically shipped as a kit, ready for further examination and screening by the customer prior to assembly. If the customer requires, documentation and measurement reports can be provided on every bearing, in every batch.