In January 2003, the European Space Agency (ESA) is launching its ROSETTA probe into space for the purpose of studying the comet Wirtanen. The University of Bern participates in this mission with the ROSINA module, which consists of three sensors designed to analyse the cometary gases. The Applied Technology and Development Group (GVE) has in recent years developed and produced various ion optical components for these three sensors. One of the instruments is a time-of-flight mass spectrometer, which, as for all space applications, has to be of small physical dimensions and low weight. For this reason, the reflectron type (RTOF) was chosen, whereby the reflection of the ions inside the vacuum enclosure multiplies the measurement (flight) path length, allowing the realisation of a high resoluting but at the same time very compact instrument. The resulting RTOF mass spectrometer has an overall length of about 1 m but is capable of analysing and separating light to moderately heavy molecules in the range of 1–300 amu (atomic mass unit): it is possible to clearly resolve nitrogen (N₂) and carbon monoxide (CO), despite a difference in the mass of the two molecules of only approx. ¹/₃₀₀₀.
The instrument uses two grid-free reflectors, both realized by GVE. One of the two reflectors, the so called "Integrated Reflectron", is welded on at one end of the instrument. In Fig. 1 the complete RTOF can be seen, while Fig. 2 and 3 show the Integrated Reflectron ready for integration.
In order to comply with the strict weight requirements, the Integrated Reflectron had to fulfill both structural and functional tasks: it is part of the spectrometer vacuum enclosure, while its internal surface generates the electric fields used to decelerate the incoming ion beam and reaccelerate it in the opposite direction. This type of construction implied that a challenging combination of requirements had to be achieved.

Contact:  Hans Rudolf Elsener