Development of an ultra-high vacuum system for space application

The aim of this paper is to present the development of a very specific ultra-high vacuum system for the space application PHARAO. In order to reach the specified pressure (2.6×10⁻⁸ Pa) during 3 years in a self-contained system, specific solutions have been developed. A calculation of partial pressures of different chemical species (typically hydrogen, rare gases and cesium) in the different areas of the vacuum tube has been computed. Experiments have been also performed in order to verify the possibility of using different kind of materials (outgassing rates of bulk and porous titanium, silicon carbide reinforced aluminum, graphite, etc.) and pumping systems such as getters and a specially developed ion pump.