  Hard X-/soft gamma-ray astronomy is a crucial field for transient, nuclear
and multimessenger astrophysics. However, the spatial localization, imaging
capabilities and sensitivity of the measurements are strongly limited for the
energy range > 70 keV. To overcome these limitations, we have proposed a
mission concept, ASTENA, submitted to ESA for its program Voyage 2050. We will
report on a pathfinder of ASTENA, that we intend to propose to ASI as an
Italian mission with international participation. It will be based on one of
the two instruments aboard ASTENA: a Laue lens with 20 m focal length, able to
focus hard X-rays in the 50-700 keV passband into a 3-d position sensitive
focal plane spectrometer. The combination of the focussing properties of the
lens and of the localization properties of the detector will provide
unparalleled imaging and spectroscopic capabilities, thus enabling studies of
phenomena such as gamma-ray bursts afterglows, supernova explosions, positron
annihilation lines and many more.
