Launched in 2021, the Imaging X-ray Polarimetry Explorer (IXPE) program now approaches an extended scientific mission. The measurements to date of X-ray polarization of astronomical bodies have been groundbreaking with over 21 discovery papers published to date from data produced by IXPE’s three imaging polarimeters. In an effort to continue to collect this data for as long as possible, the IXPE mission is proactively examining ways to enhance the lifetime of its spacecraft. The IXPE spacecraft is a single-string platform designed for a 2-year life that supports the science payload by providing pointing, power, data storage and downlink, and thermal control. One limiting factor to spacecraft life is the wet chemistry of IXPE’s lithium ion battery, which degrades over time as a function of its temperature, the number of charge and discharge cycles, and the level of charge and discharge. The resultant degradation reduces stored energy and the end of discharge voltage, an important parameter for the space vehicle electrical loads and fault protection monitoring system. This paper reports how the factors affecting battery life can be modified while maintaining the current level of instrument performance. Heater setpoint adjustments are described as well as modifications to the on-orbit concept of operations.

In its first year of on-orbit operations, the Imaging X-ray Polarimetry Explorer (IXPE) has made numerous polarimetric observations of astronomical X-ray sources, providing a new dimension of data with which to understand our universe. IXPE measures the linear polarization angle of each incoming X-ray photon in an imaged scene, allowing study of both point and extended source phenomenon. Each of IXPE's three X-ray telescopes consists of a grazing incidence angle X-ray mirror module and an imaging gas pixel detector at a 4-meter focal length. During the design phase, thermal modeling revealed that simple thermostatic heater control would be insufficient to achieve low gradients across the concentric shells of IXPE's mirror modules and the structural elements that ensure telescope alignment. Although traditional instrument electronics with proportional-integral-derivative (PID) controllers were considered, the project selected an alternative solution to achieve the requisite temperature control while avoiding the cost and complexity of additional payload electronics. IXPE implemented a proportional heater controller with a pulse-width-modulated (PWM) output using the spacecraft bus flight software and standard power switches. Pre-flight demonstrations during the observatory thermal vacuum test exhibited excellent payload thermal performance but created challenges for spacecraft bus voltage regulation. These challenges were overcome through frequency separation between the charge control algorithm and the heater controller. This paper examines the benefits, challenges, and lessons learned for this implementation, as well as provides recommendations for future implementations of this cost saving strategy.

The Imaging X-Ray Polarimetry Explorer (IXPE) is designed 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 measurements and imaging are key capabilities of the IXPE observatory. IXPE, an international collaboration between NASA and the Italian Space Agency (ASI), is a NASA Small Explorer designed as a 2-year mission. It launches to a circular LEO orbit at an altitude of 600 km and an inclination of ~0 degrees on a Falcon 9 launch vehicle. The payload uses a single science operational mode to capture the X-ray data from the science targets. The mission design follows a simple observing paradigm: pointed viewing of known X-ray sources (with known locations in the sky) over multiple orbits (not necessarily consecutive orbits) until the observation is complete. IXPE's payload is a set of three identical, imaging, X-ray polarimetry telescopes mounted on a common optical bench and co-aligned with the pointing axis of the spacecraft. The BCP-Small spacecraft provides the necessary resources to support and operate the payload elements and enable continuous science data collection. The Observatory communicates with ground stations via S-band link. The ground system consists of three major elements: the ground stations for data receipt and command upload to the Observatory; the Mission Operation Center (MOC); and Science Operations Center (SOC). Launch occurred on 9 December 2021. The IXPE Observatory has been collecting science data from cosmic X-ray sources since 11 January 2022. These include extreme astronomical objects, such as stellar-mass and supermassive black holes, magnetars, Blazars, neutron stars, and pulsars. This paper summarizes the IXPE mission, describes the Observatory, ground system, and commissioning and overviews recent science results.

Scheduled to launch in late 2021, the Imaging X-ray Polarimetry Explorer (IXPE) is a NASA Small Explorer Mission in collaboration with the Italian Space Agency (ASI). The mission will open a new window of investigation - imaging X-ray polarimetry. The observatory features 3 identical telescopes each consisting of a mirror module assembly with a polarization-sensitive imaging X-ray detector at the focus. A coilable boom, deployed on orbit, provides the necessary 4-m focal length. The observatory utilizes a 3-axis-stabilized spacecraft which provides services such as 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.

The Imaging X-Ray Polarimetry Explorer (IXPE) is designed 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 measurements and imaging are key capabilities of the IXPE observatory. IXPE, an international collaboration between NASA and the Italian Space Agency (ASI), is a NASA Small Explorer designed as a 2-year mission which launches to a circular LEO orbit at an altitude of 600 km and an inclination of ~0 degrees on a Falcon 9 launch vehicle. The payload uses a single science operational mode to capture the x-ray data from the science targets. The mission design follows a simple observing paradigm: pointed viewing of known x-ray sources (with known locations in the sky) over multiple orbits (not necessarily consecutive orbits) until the observation is complete. IXPE's payload is a set of three identical, imaging, x-ray polarimetry telescopes mounted on a common optical bench and co-aligned with the pointing axis of the spacecraft. The payload is accommodated on the spacecraft top deck. The BCP-Small spacecraft provides the necessary resources to support and operate the payload elements and enable continuous science data collection. The Observatory communicates with ground stations via S-band link. The ground system consists of three major elements: the ground stations for data receipt and command upload to the Observatory; the Mission Operation Center (MOC); and Science Operations Center (SOC). The primary ground station, contributed to the IXPE mission as part of an international collaboration with ASI is at Malindi, Kenya. The back-up ground station is in Singapore through the NEN. TDRSS is used for early operations and contingencies. The MOC is located at CU/LASP using their existing multi-mission MOC. The SOC is located at MSFC and the data archive at the GSFC HEASARC. The IXPE Project completed its Phase A activities in July 2016; Project start occurred in February 2017. Currently, the Project is finishing up Phase D activities, having completed all Observatory environmental testing and launch with final commissioning activities ongoing. Launch occurred on 9 December 2021. This paper summarizes the IXPE mission, describes the Observatory, launch segment, ground system, discusses launch and commissioning and reviews lessons-learned.

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 Imaging X-ray Polarimeter Explorer (IXPE) focuses on high energy astrophysics in the 2—8 keV x-ray band. IXPE is designed to explore general relativistic and quantum physics effects of gravity, energy, electric and magnetic fields at extreme limits. IXPE, a NASA Small Explorer (SMEX) Mission, will add new dimensions to onorbit x-ray science: polarization degree, polarization angle and extended object polarization imaging. Polarization uniquely probes physical anisotropies that are not otherwise measurable—ordered magnetic fields, aspheric matter distributions, or general relativistic coupling to black-hole spin. Detailed imaging enables the specific properties of extended x-ray sources to be differentiated. 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 polarizationsensitive, x-ray detector arrays paired with three x-ray mirror module assemblies (MMA). A deployable boom provides the correct separation (focal length) between the detector units and MMAs. Currently, the boom has been delivered, all four detectors units (DU) are complete, the detectors service unit (DSU) is complete, instrument system testing has been completed (DSU with 3 DUs), three of four MMAs is built and all spacecraft components except the solar array have been delivered along with the spacecraft and payload structures. Payload and spacecraft integration and test (I&T) started in March 2020. This paper overviews the flight segment (the Observatory, payload, and spacecraft implementation concepts) with emphasis on the build status and summarizes the launch segment. Launch is planned to occur on a Falcon 9 launch vehicle during Summer 2021. The paper summarizes the impacts of switching from the ‘design-to baseline’ of Pegasus XL to the selected launch vehicle for flight, Falcon 9. COVID-19 impacts to the Project are also summarized. The paper will close with a summary of the mission development status. The Project is firmly into the build phase for both the spacecraft and payload and rapidly approaching Observatory I&T.

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.

The Imaging X-ray Polarimetry Explorer (IXPE) is a NASA Small Explorer X-ray astrophysics mission being implemented by a geographically dispersed team. The IXPE collaboration and Observatory complexity provide both unique challenges and advantages for Project V&V. A rigorous and iterative V&V process is essential to ensuring the successful realization of reliable and cost effective IXPE Mission System. The IXPE verification, validation and characterization (V&V) process starts at the component/unit level and rolls up to appropriate higher levels. V&V compliance is assured by collaborative development by the V&V Team which spans all project organizations. The V&V process provides a framework, with appropriate confidence, to show that all needs and expectations are met by the as-built system. Proof is in the form of traceable detailed evidence of compliance at every level rolling up to and including the overall system and architecture levels. The detailed verification approach for IXPE components/units/subassemblies/subsystems is the responsibility of the applicable subsystem RE supported by systems and the I&T team. All verification processes, analyses and steps are documented. IXPE is using a V&V threads process which is ideal for use in showing compliance when a requirements set is dependent on a complex set of actions/processes. It's a system engineering graphics method to ensure all 'contributors' and 'influencers' are included. When applicable, verification threads are provided to support the verification compliance/selloff process. This paper summarizes the IXPE mission and describes the verification, validation and characterization activities planned for the IXPE mission including the use of V&V threads.

Ball Aerospace has been conducting detailed studies on the feasibility of accommodating chemical (including green) propulsion and solar electric propulsion (SEP) on small Ball Configurable Platform (BCP), ESPA-class spacecraft. The BCP-Small spacecraft bus is used as the baseline to leverage its flight heritage (STPSat-2, STPSat-3, GPIM (in storage, awaiting launch) and IXPE (under development). The study approach is focused on aligning the BCP-Small design with multiple ongoing and upcoming small sat pursuits. Work is focusing on Demonstration-Class and Operational-Class spacecraft product development with reduced recurring engineering, volume production capability and equivalent or improved capabilities. Propulsion module options are considered for both BCP-Small products. Chemical systems providing up to 100's of m/s AV and SEP providing up to 1000's of m/s AV are being assessed. Chemical systems being assessed include hydrazine-based systems and green propellant systems based on the propellants AF-M315E and LMP-1035. SEP systems include several different plasma thruster systems including Hall and ion. This work is making use of the improved mass qualification limits for ESPA, the newly defined ESPA-Heavy and ESPA-Grande. Mission applications in various Earth orbits are the current focus for propulsion-enabled, BCP-Small spacecraft. The results of the ongoing work show BCP-Small spacecraft can be modified to accommodate meaningful chemical propulsion or SEP capability while meeting the mass and volume constraints for ESPA and/or ESPA-Grande. Mission options starting in both GTO and LEO are included in the assessments. This paper further summarizes the BCP-Small spacecraft design and capabilities, status of the heritage flight and in-development programs and describes how the BCP-Small is adapted to include chemical or SEP along with on-orbit control.

When the Imaging X-ray Polarimetry Explorer (IXPE) launches in 2021, the world will have a new orbiting Xray observatory capable of examining previously unexplored celestial phenomena. For the first time, an earth-orbiting observatory will be able to resolve the polarization angle of each incoming X-ray photon in an imaged scene, and provide polarization measurements of each source within the instrument's field of view. The two top-level project requirements that drive the mission design and observatory capability are the execution, in a one year period, of a Design Reference Mission (DRM) containing 48 representative targets, and the ability to observe any location on the celestial sphere for 30 days every six months. IXPE exceeds these driving requirements with a straightforward observatory design concept that allows a large instrument field of regard with a fixed solar array. IXPE completed its preliminary design review in June 2018 with a baseline power and thermal design that accommodates all observatory attitudes that maintain a +/- 25 degree angle between the body-fixed solar array and the plane normal to the sun vector. This paper examines how observatory attitude affects power consumption, how the DRM targets drive the observatory power and thermal design, and potential system design trades.

The Imaging X-ray Polarimetry Explorer (IXPE) is a space-based observatory that will have the capability to measure the polarization of X-rays from astrophysical sources. IXPE will improve sensitivity over OSO-8, the only previous X-ray polarimeter, by two orders of magnitude in required exposure time. IXPE will yield insight into our understanding of X-ray production in objects such as neutron stars as well as stellar and supermassive black holes. IXPE measurements will provide new dimensions for probing a wide range of cosmic X-ray sources - including active galactic nuclei (AGN) and microquasars, pulsars and pulsar wind nebulae, magnetars, accreting X-ray binaries, supernova remnants, and the Galactic center. Addressing NASA's Science Mission Directorate's science goal “to probe the origin and destiny of our universe, including the nature of black holes, dark energy, dark matter, and gravity.” IXPE will introduce the capability for X-ray polarimetric imaging, uniquely enabling the measurement of X-ray polarization with scientifically meaningful spatial, spectral, and temporal resolution. These polarization measurements will help answer fundamental questions regarding 1) the geometries of the flows, emission regions, and magnetic fields, 2) the physical process that lead to particle acceleration and X-ray emission, and 3) the physical effects of gravitational, electric, and magnetic fields at their extreme limits. This scientific mission, IXPE, is being developed by the NASA Marshall Space Flight Center (MSFC), Ball Aerospace, the Italian Space Agency (ASI), the Institute for Space Astrophysics and Planetology (IAPS)/ National Institute of Astrophysics (INAF), the National Institute for Nuclear Physics (INFN), the University of Colorado Laboratory for Atmospheric and Space Physics (LASP), Stanford University, McGill University, and the Massachusetts Institute of Technology. The IXPE partners each provide unique capabilities and experience which are utilized to design, build and launch the IXPE observatory resulting in the collection of on-orbit scientific data measurements which are transmitted to ground stations and analyzed. The established systems engineering (SE) methods and teaming approach to achieve the IXPE mission goals will be discussed. For this paper, the focus is the IXPE observatory and the collaboration of NASA MSFC, Ball Aerospace and IAPS/INAF. Our current focus is on requirements development and analysis along with definition of the interface control documents (ICD). Of particular note are requirements and ICDs between major flight elements and between organizations. This paper will describe the SE philosophy being used to ensure complete inter-organizational understanding and agreement as the Project moves towards SRR in September 2017 and PDR in June 2018. Current status and future milestones will be discussed.

The Imaging X-ray Polarimetry Explorer (IXPE) project is an international collaboration to build and fly a polarization sensitive X-ray observatory. The IXPE Observatory consists of the spacecraft and payload. The payload is composed of three X-ray telescopes, each consisting of a mirror module optical assembly and a polarization-sensitive X-ray detector assembly; a deployable boom maintains the focal length between the optical assemblies and the detectors. The goal of the IXPE Mission is to provide new information about the origins of cosmic X-rays and their interactions with matter and gravity as they travel through space. IXPE will do this by exploiting its unique capability to measure the polarization of X-rays emitted by cosmic sources. The collaboration for IXPE involves national and international partners during design, fabrication, assembly, integration, test, and operations. The full collaboration includes NASA Marshall Space Flight Center (MSFC), Ball Aerospace, the Italian Space Agency (ASI), the Italian Institute of Astrophysics and Space Planetology (IAPS)/Italian National Institute of Astrophysics (INAF), the Italian National Institute for Nuclear Physics (INFN), the University of Colorado (CU) Laboratory for Atmospheric and Space Physics (LASP), Stanford University, McGill University, and the Massachusetts Institute of Technology. The goal of this paper is to discuss risk management as it applies to the IXPE project. The full IXPE Team participates in risk management providing both unique challenges and advantages for project risk management. Risk management is being employed in all phases of the IXPE Project, but is particularly important during planning and initial execution - the current phase of the IXPE Project. The discussion will address IXPE risk strategies and responsibilities, along with the IXPE management process which includes risk identification, risk assessment, risk response, and risk monitoring, control, and reporting.

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 polarizationsensitive, 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.

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." X-ray polarimetry is the focus of the IXPE science mission. Polarimetry uniquely probes physical anisotropies-ordered magnetic fields, aspheric matter distributions, or general relativistic coupling to black-hole spin that are not otherwise measurable. The IXPE Observatory consists of Spacecraft and Payload modules. The Payload includes three polarization sensitive, X-ray detector units (DU), each paired with its corresponding grazing incidence mirror module assemblies (MMA). A deployable boom provides the correct separation (focal length) between the DUs and MMAs. These Payload elements are supported by the IXPE Spacecraft. A star tracker is mounted directly with the deployed Payload to minimize alignment errors between the star tracker line of sight (LoS) and Payload LoS. Stringent pointing requirements coupled with a flexible structure and a non-collocated attitude sensor-actuator configuration requires a thorough analysis of control-structure interactions. A non-minimum phase notch filter supports robust control loop stability margins. This paper summarizes the IXPE mission science objectives and Observatory concepts, and then it describes IXPE attitude determination and control implementation. IXPE LoS pointing accuracy, control loop stability, and angular momentum management are discussed.