  We present the design of a point-and-shoot non-imaging full-Stokes
spectropolarimeter dedicated to detecting life on Earth from an orbiting
platform like the ISS. We specifically aim to map circular polarization in the
spectral features of chlorophyll and other biopigments for our planet as a
whole. These non-zero circular polarization signatures are caused by
homochirality of the molecular and supramolecular configurations of organic
matter, and are considered the most unambiguous biomarker. To achieve a fully
solid-state snapshot design, we implement a novel spatial modulation that
completely separates the circular and linear polarization channels. The
polarization modulator consists of a patterned liquid-crystal quarter-wave
plate inside the spectrograph slit, which also constitutes the first optical
element of the instrument. This configuration eliminates cross-talk between
linear and circular polarization, which is crucial because linear polarization
signals are generally much stronger than the circular polarization signals.
This leads to a quite unorthodox optical concept for the spectrograph, in which
the object and the pupil are switched. We discuss the general design
requirements and trade-offs of LSDpol (Life Signature Detection polarimeter), a
prototype instrument that is currently under development.
