The Imaging X-ray Polarimetry Explorer (IXPE) will add polarization to the properties (time, energy, and position) observed in x-ray astronomy. A NASA Astrophysics Small Explorer (SMEX) in partnership with the Italian Space Agency (ASI), IXPE will measure the 2–8-keV polarization of a few dozen sources during the first 2 years following its 2021 launch. The IXPE Observatory includes three identical x-ray telescopes, each comprising a 4-m-focal-length (grazingincidence) mirror module assembly (MMA) and a polarization-sensitive (imaging) detector unit (DU), separated by a deployable optical bench. The Observatory’s Spacecraft provides typical subsystems (mechanical, structural, thermal, power, electrical, telecommunications, etc.), an attitude determination and control subsystem for 3-axis stabilized pointing, and a command and data handling subsystem communicating with the science instrument and the Spacecraft subsystems.
Ball Aerospace has developed CIRiS (Compact Infrared Radiometer in Space), a versatile multispectral, infraredimaging radiometer with on-orbit calibration capability. CIRiS generates images in three spectral bands between 7.5 um and 13.5 um. On-board calibration employs views to two flat-panel, high-emissivity carbon nanotube calibration sources and a third view to deep space. Image processing capabilities of the single electronics board include frame shifting and co-adding, binning and windowing, all with parameters selectable on orbit. An uncooled microbolometer focal plane enables CIRiS to operate without a cryocooler, thereby eliminating the associated power draw, complexity, and mission-life limitation. Total instrument power consumption measured in vacuum is < 10 Watts, including instrument heater power. A modular architecture that permits independent changes to CIRiS subsystems facilitates customization for Earth and planetary science missions. Constellations of 8 to 12 spacecraft carrying CIRiS instruments achieve global coverage from Low Earth Orbit (LEO) with daily revisit times, and varying spatial resolution. Among the potential Earth Science applications are measurements of evapotranspiration, plant health, volcano activity, sea surface and inland water body temperature, and vertical atmospheric profile of temperature and trace gas concentration. Lunar CIRiS, or “L-CIRiS” is a modified implementation for lunar surface mineralogy and thermophysical measurements from a lander or rover on the Moon’s surface. The present CIRiS flight model has completed all testing in preparation for an upcoming demonstration mission in LEO on a 6U CubeSat.
The Imaging X-ray Polarimetry Explorer (IXPE) will expand the information space for study of cosmic sources, by adding polarization to the properties (time, energy, and position) observed in x-ray astronomy. Selected in 2017 January as a NASA Astrophysics Small Explorer (SMEX) mission, IXPE will be launched into an equatorial orbit in 2021. The IXPE observatory includes three identical x-ray telescopes, each comprising a 4-m-focal-length (grazing-incidence) mirror module assembly (MMA) and a polarization-sensitive (imaging) detector unit (DU). The optical bench separating the MMAs from the DUs is a deployable boom with a tip/tilt/rotation stage for DU-to-MMA (gang) alignment, similar to the configuration used for the NuSTAR observatory. The IXPE mission will provide scientifically meaningful measurements of the x-ray polarization of a few dozen sources in the 2-8 keV band, over the first two years of the mission. For several bright, extended x-ray sources (pulsar wind nebulae, supernova remnants, and an active-galaxy jet), IXPE observations will produce polarization maps indicating the magnetic structure of the synchrotron emitting regions. For many bright pulsating x-ray sources (isolated pulsars, accreting x-ray pulsars, and magnetars), IXPE observations will produce phase-resolved profiles of the polarization degree and position angle.