A key activity at TWI is the selection of the most appropriate assembly method for all kinds of systems, including sensors and transducers. TWI has been involved in these types of projects since the 1960s. In fact an early example was the development of novel arc welding processes for the manufacture of a pressure transducer.
In addition, a series of thermal properties sensors were manufactured by TWI for the European Space Agency, and were installed along with many other experiment systems on board the Huygens module on the Cassini space probe.
The sensors were designed by The Space Sciences Group at The University of Kent, to measure the thermal properties of gas and liquids which the Huygens module may experience whilst landing on the surface of Titan – a particularly interesting moon of Saturn.
The sensor consists of a 10 or 25um diameter platinum wire element attached between 1mm diameter Pt pins within a titanium cage. The specification for the wire demanded a precise length between the attachment points and a high degree of accuracy in placing the wire on the pins for attachment. In order to accurately cut the wires to length a pulsed Nd:YAG laser was used. The added benefit of the technique was to produce a ball on either end of the wire, enabling micro-resistance welding of the wires without reducing the wire cross-section – another key requirement for accurate operation of the sensor element.
The team at TWI developed the welding processes and tooling to enable reliable, accurate assembly of the sensor capsules.
Following calibration of a number of assemblies, four were selected and installed on the module.
The Cassini orbiter was successfully launched on 15 October 1997 and, travelling at a speed of 30,000 kph, successfully reached its Saturn orbit position in July 2004. At the last system “health check”, the sensors were still working.
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