  Measuring the Cosmic X-ray Background (CXB) is a key to understand the Active
Galactic Nuclei population, their absorption distribution and their average
spectra. However, hard X-ray instruments suffer from time-dependent backgrounds
and cross-calibration issues. The uncertainty of the CXB normalization remain
of the order of 20%. To obtain a more accurate measurement, the Monitor Vsego
Neba (MVN) instrument was built in Russia but not yet launched to the ISS
(arXiv:1410.3284). We follow the same ideas to develop a CXB detector made of
four collimated spectrometers with a rotating obturator on top. The collimators
block off-axis photons below 100 keV and the obturator modulates on-axis
photons allowing to separate the CXB from the instrumental background. Our
spectrometers are made of 20 mm thick CeBr$_{3}$ crystals on top of a SiPM
array. One tube features a $\sim$20 cm$^2$ effective area and more energy
coverage than MVN, leading to a CXB count rate improved by a factor of $\sim$10
and a statistical uncertainty $\sim$0.5% on the CXB flux. A prototype is being
built and we are seeking for a launch opportunity.
