  A good understanding of the ionization rates of neutral species in the
heliosphere is important for studies of the heliosphere and planetary
atmospheres. So far, the intensities of the ionization reactions have been
studied based on observations of the contributing phenomena, such as the solar
spectral flux in the EUV band and the flux of the solar wind protons, alpha
particles, and electrons. The results strongly depend on absolute calibration
of these measurements, which, especially for the EUV measurements, is
challenging. Here, we propose a novel method of determining the ionization rate
of neutral species based on direct sampling of interstellar neutral gas from
two locations in space distant to each other. In particular, we suggest
performing observations from the vicinity of Earth's orbit and using ratios of
fluxes of ISN He for the direct and indirect orbits of interstellar atoms. We
identify the most favorable conditions and observations geometries, suitable
for implementation on the forthcoming NASA mission Interstellar Mapping and
Acceleration Probe.
