Satellites operating on LEO and GEO trajectories are subject to the effect of ionizing space radiations, mostly electrons, that are concentrated in the Van Allen belts. These ionizing radiations are responsible for accelerated ageing (especially compaction, i.e. local material density variation), which is thought to be detrimental for the optical figure of the embedded optical devices. The studies made on this topic during the last four decades, are proposing very different phenomenological power laws description of this effect. However, the simulated deformations derived from these laws are in partial disagreement with the observations made at the laboratory, moreover they do not account for the absence of problems reported during the space missions embedding ZERODUR material. In order to elucidate these mismatches, we defined a new experimental approach suited for the description of the compaction phenomenon for doses corresponding to typical astrospace missions. An overview of the preparatory simulation work for the design of the irradiation environment, for the design of the build-up shielding material as well as of the design of the target samples will be presented. This study will also give a short description of the experimental irradiations sequence as well as the high precision metrological approaches used in order to determine the changes induced in the ZERODUR.
ZERODUR has been and is still being successfully used as mirror substrates for a large number of space missions. Improvements in CNC machining at SCHOTT allow to achieve extremely light weighted substrates incorporating very thin ribs and face sheets. This paper is reviewing data published on the interaction of space radiation with ZERODUR. Additionally, this paper reports on considerations and experiments which are needed to confidently apply an updated model on ZERODUR behavior under space radiation for extremely light weighted ZERODUR substrates.
In a continuous effort since 2007 a considerable amount of new data and information has been gathered on the bending
strength of the extremely low thermal expansion glass ceramic ZERODUR®.
By fitting a three parameter Weibull distribution to the data it could be shown that for homogenously ground surfaces
minimum breakage stresses exist lying much higher than the previously applied design limits.
In order to achieve even higher allowable stress values diamond grain ground surfaces have been acid etched, a
procedure widely accepted as strength increasing measure.
If surfaces are etched taking off layers with thickness which are comparable to the maximum micro crack depth of the
preceding grinding process they also show statistical distributions compatible with a three parameter Weibull
distribution. SCHOTT has performed additional measurement series with etch solutions with variable composition
testing the applicability of this distribution and the possibility to achieve further increase of the minimum breakage
For long term loading applications strength change with time and environmental media are important. The parameter
needed for prediction calculations which is combining these influences is the stress corrosion constant. Results from the
past differ significantly from each other. On the basis of new investigations better information will be provided for
choosing the best value for the given application conditions.