  The beta decay of the free neutron provides several probes to test the
Standard Model of particle physics as well as to search for extensions thereof.
Hence, multiple experiments investigating the decay have already been
performed, are under way or are being prepared. These measure the mean
lifetime, angular correlation coefficients or various spectra of the charged
decay products (proton and electron). NoMoS, the Neutron decay prOducts
MOmentum Spectrometer, presents a novel method of momentum spectroscopy: it
utilizes the $R \times B$ drift effect to disperse charged particles dependent
on their momentum in an uniformly curved magnetic field. This spectrometer is
designed to precisely measure momentum spectra and angular correlation
coefficients in free neutron beta decay to test the Standard Model and to
search for new physics beyond. With NoMoS, we aim to measure inter alia the
electron-antineutrino correlation coefficient $a$ and the Fierz interference
term $b$ with an ultimate precision of $\Delta a/a < 0.3\%$ and $\Delta b <
10^{-3}$ respectively. In this paper, we present the measurement principles,
discuss measurement uncertainties and systematics, and give a status update.
