  GRIPS is one example of next generation telescopes proposed for astronomy the
energy range between hard X-ray mirror instruments such as NuStar and the Fermi
telescope. The Compton telescope principle is an advantageous concept in view
of background suppression, imaging sensitivity within a large field of view and
energy range, and capability to measure polarization. The diversity of
astrophysical sources at high energies (diffuse emission from cosmic-ray
interactions, nuclear lines from point-like and diffuse sources, accreting
binaries, cosmic-ray acceleration sites, novae and supernovae, GRBs) presents a
challenge, and in particular emphasizes the need for large fields of view and
surveys. We discuss the astrophysical challenges which are expected to remain
after the extended INTEGRAL mission, and how such a next-generation survey at
low-energy gamma-rays would impact on these. We argue that qualitatively new
and more direct insights could be obtained on cosmic high-energy phenomena and
their underlying physical processes.
