Experimental Astronomy https://doi.org/10.1007/s10686-018-09618-4 ORIGINAL ARTICLE The soft X-ray spectrometer polarimeter SolpeX J. Sylwester 1 · M. Ste ¸´ slicki 1 · J. Ba ¸ kała 1 · S. Płocieniak 1 · ˙ Z. Szaforz 1 · M. Kowali ´ nski 1 · D. ´ Scisłowski 1 · P. Podg ´ orski 1 · T. Mrozek 1 · J. Barylak 1 · A. Makowski 1 · M. Siarkowski 1 · Z. Kordylewski 1 · B. Sylwester 1 · S. Kuzin 2 · A. Kirichenko 2 · A. Pertsov 2 · S. Bogachev 2 Received: 29 August 2018 / Accepted: 21 December 2018 / © The Author(s) 2019 Abstract We present a novel X-ray assembly of functionally related instrument blocks intended to measure solar flare and active region (AR) spectra from within the Russian instru- ment complex KORTES, to be mounted aboard the International Space Station (ISS). SolpeX consists of three blocks: fast-rotating multiple flat crystal Bragg spectrom- eter, pin-hole X-ray spectral imager and Bragg polarimeter. This combination of measuring blocks will offer an opportunity to detect/measure possible X-ray polar- ization in soft X-ray emission lines/continuum and record spectra of solar flares, in particular during their impulsive phases. Polarized Bremsstrahlung and line emission may arise from presence of directed particle beams colliding with denser regions of flares. As a result of evaporation, the X-ray spectral-components are expected to be Doppler shifted, which will also be measured. In this paper, we present details of the construction of three SolpeX blocks and discuss their functionality. Delivery of KORTES with SolpeX to ISS is expected in 2020/2021. Keywords Solar flares · Soft X-rays · Polarimetry · Spectroscopy · ISS  ˙ Z. Szaforz zs@cbk.pan.wroc.pl J. Sylwester js@cbk.pan.wroc.pl S. Kuzin kuzin@lebedev.ru 1 Space Research Centre, Polish Academy of Sciences, Bartycka 18A, 00-716 Warsaw, Poland 2 P.N. Lebedev Physical Institute, Russian Academy of Sciences, Leninsky Prospekt 53, Moscow 119991, Russia