The role of purged bakeout method in achieving the required cleanliness for the polarimetric and helioseismic imager on the Solar Orbiter mission

We have selected a number of materials used in construction of space instruments and spacecraft that require a bakeout to reduce outgassing under vacuum in view of the environment of the Solar Orbiter mission. Most of the materials were used in the PHI instrument on board Solar Orbiter. We subjected the samples to the bakeout process using a quartz crystal microbalance (TQCM) monitor and, for a similar duration, using a much simpler setup with a vacuum oven, equipped with a rough vacuum pump, called “purged bakeout process”. We compared the residual outgassing of those samples after the bakeout process and compared the efficiencies of the two methods. We find that the bakeout in a vacuum oven with clean gas purging is equally efficient as the high-vacuum bakeout with TQCM monitor for those samples with simple geometry of the material such that purging is efficiently accessing all surfaces, whereas complex structures like honeycomb panels will not be well enough purged under rough vacuum conditions