Gearbox is crucial to satellite success

The recent successful launch and subsequent solar array deployment of the Eur 2 billion (GBP 1.2 billion) Envisat satellite depended on a 4in-diameter gearbox, created by David Brown Engineering. The gearbox controlled the deployment of the satellite's crucial power-generating solar array. The Envisat environmental monitoring satellite is the largest satellite yet launched by ESA (the European Space Agency).

It boosts Europe's capacity to take part in the study of the Earth and its environment by supporting critical research programmes on global warming and climate change issues.

The satellite depends for power on a giant solar array capable of generating up to 8kW of electricity.

The solar array design was termed 'flatpack', because it was folded away during the launch.

Once the satellite was stationed in orbit the Flatpack was deployed using a battery operated electric motor in combination with a cable pulley system, with power routed through the David Brown Engineering gearbox.

Control is effected by an epicyclic gear train of a two stage sun and triple planet wheel arrangement giving an overall ratio of 38:1.

Fokker Space, the contractor for the solar array has a 100% record of successful solar array deployments and chose David Brown as a partner in the confidence that the gear specialist would help maintain this record.

Phil Dalton, Technical Sales Manager for David Brown Engineering said: "The small gearbox only had to operate once but it had to work with absolute certainty in a harsh environment and following the stresses imposed by a rocket launch.

In space, on a satellite orbiting at this distance above the earth, there are, of course, no opportunities for repair and servicing!".

Every component on the satellite is critical in terms of its weight and size.

An extra gram of weight on a mechanical component means one less gram for the satellite's monitoring equipment, likewise components and equipment must be balanced millimetre for millimetre.

The gearbox therefore had to produce the maximum power to weight ratio with the lowest possible space envelope.

David Brown engineered a gearbox which can be held in the palm of a hand, and yet was entirely capable of deploying the 70m2 solar array from its position folded within the body of the satellite to full deployment and 'snap-locked' into position.

On behalf of Fokker Space, Wim den Haak, Product Assurance Manager said: "I congratulate David Brown on the successful deployment of the solar array which was possible thanks to the co-operation between our companies during the development and manufacturing of this complicated solar array".

Phil Dalton of David Brown Engineering said: "This contract is a major success for David Brown, showing, as it does, the capability the company possesses to manufacture bespoke gearboxes capable of producing maximum torque in the most challenging environment and with absolute reliability.

It also demonstrates the underlying strength of the David Brown portfolio, encompassing gearboxes used in everything from military vehicles and ships, to power plants and industrial machinery".

The gearbox was originally designed by Alvis Transmissions, a company which David Brown purchased in 1998.

Development continued during the handover period.

David Brown is supplying similar gearboxes to another European Space Agency project, this being the METOP series of weather and climate monitoring satellites, the first of which is scheduled for launch in 2005.