  This paper describes the architecture and demonstrates the capabilities of a
newly developed, physically-based imaging simulator environment called SISPO,
developed for small solar system body fly-by and terrestrial planet surface
mission simulations. The image simulator utilises the open-source 3D
visualisation system Blender and its Cycles rendering engine, which supports
physically based rendering capabilities and procedural micropolygon
displacement texture generation. The simulator concentrates on realistic
surface rendering and has supplementary models to produce realistic dust- and
gas-environment optical models for comets and active asteroids. The framework
also includes tools to simulate the most common image aberrations, such as
tangential and sagittal astigmatism, internal and external comatic aberration,
and simple geometric distortions. The model framework's primary objective is to
support small-body space mission design by allowing better simulations for
characterisation of imaging instrument performance, assisting mission planning,
and developing computer-vision algorithms. SISPO allows the simulation of
trajectories, light parameters and camera's intrinsic parameters.
