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ISS instrument characterized at BESSY

On the International Space Station ISS, at the end of this year, quantitative measurements of solar radiation with as yet unattained accuracy – above all, in the wavelength range from 17 nm to 220 nm – are to begin. The measuring instrument developed for this purpose has been characterized by the PTB in its radiometry laboratory at the Berlin electron storage ring BESSY II.

Installation of SolACES in the vacuum chamber of the EUV reflectometer system of the PTB at BESSY II

The solar observation instrument SolACES (Solar Auto-Calibrating EUV/UV Spectrophotometers) for the short-wave spectral range is a component of the scientific instrument package SOLAR for the ISS. SolACES was developed under the auspices of the Fraunhofer-Institut für Physikalische Messtechnik (IPM) in Freiburg and is composed of two double spectrophotometers for the spectrally resolved detection of the incident EUV/UV radiation as well as two ionisation chambers with whose aid auto-calibrations are to be conducted regularly during the flight in order to reliably detect the unavoidable changes in sensitivity of the spectrophotometers. Thus – as the scientific priority objective of SolACES – the measurement of the spectral EUV/UV radiant flux of the sun which constitutes the main energy source of the Earth‘s upper atmosphere, is to be achieved with an as yet unattained low uncertainty of below 10 %. So far, the uncertainties have been at best between 20 % and more than 400 %. The more accurate measurement results are to also particularly enable the improved prediction of the influence of the so-called space weather on the paths of satellites and space debris as well as on satellite-supported telecommunication and navigation.

By means of the measurements in the PTB laboratory at BESSY II, which took place at two different beamlines within the scope of a research cooperation with the IPM, the radiometric basis for the aimed at measurement uncertainties was created. For this purpose, correction factors were determined for both of the ionisation chambers. Moreover, the transmission of the – all in all – 43 different thin-film metal and crystal filters and the spectrophotometer sensitivities were measured.

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