  We describe a new implementation of a broad-band soft X-ray polarimeter,
substantially based on a previous design. This implementation, the Pioneer Soft
X-ray Polarimeter (PiSoX) is a SmallSat, designed for NASA's call for
Astrophysics Pioneers, small missions that could be CubeSats, balloon
experiments, or SmallSats. As in the REDSoX Polarimeter, the grating
arrangement is designed optimally for the purpose of polarimetry with
broad-band focussing optics by matching the dispersion of the spectrometer
channels to laterally graded multilayers (LGMLs). The system can achieve
polarization modulation factors over 90%. For PiSoX, the optics are lightweight
Si mirrors in a one-bounce parabolic configuration. High efficiency, blazed
gratings from opposite sectors are oriented to disperse to a LGML forming a
channel covering the wavelength range from 35 to 75 Angstroms (165 - 350 eV).
Upon satellite rotation, the intensities of the dispersed spectra, after
reflection and polarizing by the LGMLs, give the three Stokes parameters needed
to determine a source's linear polarization fraction and orientation. The
design can be extended to higher energies as LGMLs are developed further. We
describe examples of the potential scientific return from instruments based on
this design.
