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Scheduled to launch in late 2021 the Imaging X-ray Polarimetry Explorer (IXPE) is a Small Explorer Mission designed to open up a new window of investigation -- X-ray polarimetry. The IXPE observatory features 3 identical telescope each consisting of a mirror module assembly with a polarization-sensitive imaging x-ray detector at its focus. An extending beam, deployed on orbit provides the necessary 4 m focal length. The payload sits atop a 3-axis stabilized spacecraft which among other things provides power, attitude determination and control, commanding, and telemetry to the ground. During its 2-year baseline mission, IXPE will conduct precise polarimetry for samples of multiple categories of x-ray sources, with follow-on observations of selected targets. IXPE is a partnership between NASA and the Italian Space Agency (ASI).

IXPE, an international collaboration, will conduct x-ray imaging polarimetry for multiple categories of cosmic x-ray sources such as neutron stars, stellar-mass black holes, supernova remnants and active galactic nuclei. The Observatory uses a single science operational mode capturing the x-ray data from the targets. This paper summarizes the IXPE Mission System: Observatory, Launch Segment and Ground System. The IXPE Observatory consists of spacecraft and payload modules built up in parallel to form the Observatory during system integration and test. The payload includes three x-ray telescopes each consisting of a polarization-sensitive, gas pixel x-ray detector, paired with its corresponding grazing incidence mirror module assembly (MMA), x-ray optics set. A deployable boom provides the correct separation (focal length) between the detector units (DU) and MMAs. These payload elements are supported by the IXPE spacecraft which is derived from the BCP-small spacecraft architecture. IXPE is launched to a circular LEO orbit at an altitude of 600 km and an inclination of -0.2 degrees by a Falcon 9 launch vehicle. The ground system consists of three major elements: the ground stations for data receipt and command upload to the Observatory; the Mission Operations Center (MOC) at University of Colorado Laboratory for Atmospheric and Space Physics (CU/LASP); and Science Operations Center (SOC) at NASA Marshall Space Flight Center (MSFC). This paper summarizes the IXPE mission science objectives, updates the Observatory implementation concept including the payload and spacecraft elements, covers the launch segment, ground system and summarizes the mission status since last year's conference including COVID impacts.

The goal of the Imaging X-Ray Polarimetry Explorer (IXPE) Mission, a NASA Small Explorer (SMEX), is to expand understanding of high-energy astrophysical processes and sources, in support of NASA's first science objective in Astrophysics: “Discover how the universe works.” Polarization uniquely probes astrophysical anisotropies—ordered magnetic fields, aspheric matter distributions, or general relativistic coupling to black-hole spin—that are not otherwise measurable. Imaging enables the specific properties of extended X-ray sources to be differentiated. IXPE will conduct X-ray imaging polarimetry for multiple categories of cosmic X-ray sources such as neutron stars, stellar-mass black holes, supernova remnants and active galactic nuclei. The Observatory uses a single science operational mode capturing the X-ray data from the targets. The IXPE Observatory consists of spacecraft and payload modules built up in parallel to form the Observatory during system integration and test. The payload includes three X-ray telescopes each consisting of a polarization-sensitive, gas pixel X-ray detector, paired with its corresponding grazing incidence mirror module assembly (MMA). A deployable boom provides the correct separation (focal length) between the detector units (DU) and MMAs. These payload elements are supported by the IXPE spacecraft which is derived from the BCP-small spacecraft architecture. This paper summarizes the IXPE mission science objectives, describes the Observatory implementation concept including the payload and spacecraft elements and summarizes the mission status.

Silicon quantum dots with indirect bandgap photoluminescence are promising luminophores for large-area luminescent solar concentrators (LSCs). However, if commercially viable devices are to be achi...

Silicon quantum dots (Si QDs) are attractive, nontoxic luminophores for luminescent solar concentrators (LSCs). Here, we produced Si QD/poly(methyl methacrylate) (PMMA) films on glass by doctor-blading polymer solutions and achieved films with low light scattering at an order of magnitude higher Si QD weight fraction than has been achieved previously in the bulk. We suggest that the fast solidification rate of films as compared to slow bulk polymerization is an enabling factor in avoiding large agglomerates within the nanocomposites. Scanning electron microscopy confirmed that ∼100 nm or larger QD agglomerates exist in light-scattering films, and photoluminescence intensity measurements show that light scattering, if present, significantly reduces waveguiding efficiencies for LSCs. Nonscattering films fabricated in this work exhibit high ultraviolet absorption (>80%) paired with high visible transmission (>87%) and minimal visible haze (∼1%), making them well suited for semitransparent coatings for LSCs realized as solar harvesting windows.

The goal of the Imaging X-Ray Polarimetry Explorer (IXPE) Mission is to expand understanding of high-energy astrophysical processes and sources, in support of NASA's first science objective in Astrophysics: “Discover how the universe works.” Polarization uniquely probes astrophysical anisotropies — ordered magnetic fields, aspheric matter distributions, or general relativistic coupling to black-hole spin — that are not otherwise measurable. IXPE will conduct X-ray polarimetry for multiple categories of cosmic X-ray sources that are likely to be polarized such as neutron stars, stellar-mass black holes, supernova remnants and active galactic nuclei. The IXPE Observatory consists of Spacecraft and Payload modules built up in parallel to form the Observatory during system integration and test. The Payload includes three polarization-sensitive, X-ray detectors, each paired with its corresponding grazing incidence mirror module assembly (MMA). A deployable boom provides the correct separation (focal length) between the detector units (DU) and MMAs. These Payload elements are supported by the IXPE Spacecraft which is derived from the BCP-100 small Spacecraft architecture. This paper summarizes the IXPE mission science objectives, describes the Observatory implementation concept including the payload and spacecraft elements and summarizes the expected concept of operations.

Thin film luminescent solar concentrators are promising components of distributed power generation systems for building integrated photovoltaic applications. However, thin film geometries require high luminophore loading fractions to achieve sufficient absorption of sunlight, which, in the case of nanocrystal luminophores, can lead to aggregation and light scattering. In this work, we integrate CdSe/CdS nanocrystals into thin films of poly(cyclohexylethylene) at a range of loading fractions and characterize the composites with a combination of spectroscopic and simulation tools. We find that increased incident sunlight scattering is observed for the increasing luminophore loading fraction, but that the scattering is mostly limited to higher energy sunlight such that visible transmittance and haze of the samples are all greater than 89.7% and less than 8.3%, respectively. We then analyze the refractive index of the composite and show that the increase in loading fraction also affects the propagation of photoluminescence in the film, especially if the refractive index of the film is greater than that of the substrate. These studies show the importance of understanding the optical transport within thin films and provide design criteria to fabricate thin films for future implementation into building integrated photovoltaic applications.

SPIE grants to authors (and their employers) of papers, posters, and presentation recordings published in SPIE Proceedings or SPIE Journals on the SPIE Digital Library (hereinafter "publications") the right to post an author-prepared version or an official version (preferred version) of the publication on an internal or external server controlled exclusively by the author/employer or the entity funding the research, provided that (a) such posting is noncommercial in nature and the publication is made available to users without charge; (b) an appropriate copyright notice and citation appear with the publication; and (c) a link to SPIE's official online version of the publication is provided using the item's DOI. This authorization does not extend to third-party web sites not owned and maintained by the author/employer such as ResearchGate, Academia.edu, YouTube, etc. 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.