Solar X-ray Irradiance Variations: Instrument Design, CubeSat Mission Design, and Science Analysis of Solar Observations from Sounding Rocket and CubeSats

Satellites obtain scientific data needed to answer some of the fundamental questions about our world and the universe in which we reside. The first Miniature X-ray Solar Spectrometer (MinXSS-1) CubeSat and its successors try to answer "can we better understand the evolution of the solar corona?" and "which heating mechanisms are dominant in making the solar corona more than 100 times hotter than the photosphere?". A scientific mission involves careful planning and rigorous testing. Improved testing methods, such as the Battery Automation Test System (BATS) described here, create more accurate and efficient battery performance testing techniques for the flight battery pack that was used in INSPIRESat-1 SmallSat and can benefit future missions. The MinXSS and INSPIRESat-1 missions capture solar spectra from orbit and observe the Sun on two key time scales important for the coronal evolution. The first is seconds to hours for solar flares and the second is days to years for active region evolution as related to the 27-day solar rotation and 11-year solar cycle. Three flares from the MinXSS-1 mission were analyzed using CHIANTI spectral models to fit the temperatures, emission measures, and relative elemental abundances of the solar corona plasma. It was found that the relative abundances of elements with a low First Ionization Potential (FIP) decrease during the beginning of the flare's gradual phase before relaxing following the flare peak, which supports the magnetic reconnection heating mechanism for the solar corona. The Dual Aperture X-ray Solar Spectrometer (DAXSS) instrument, which launched on a NASA sounding rocket in 2018, obtained the highest resolution to date for solar soft X-ray (SXR) spectra over a broad energy range. The novel design of the dual aperture and the instrument characterization techniques are discussed. Additionally, the quiescent solar spectra are analyzed and abundances of Mg, Si, and S were found to agree within 2% of the expected values, but the abundance of Fe was found to be 35 percent higher than expected in the quiescent sun's corona. This is an unexpected result that is discussed herein. DAXSS was put on orbit in the INSPIRESat-1 CubeSat on 2022 February 14, and its SXR spectral data will, going forward, provide further insight into the sources of coronal heating through modeling the changes of relative elemental abundances during developments of active regions and solar flaring events

Appendix_A.1 and Appendix_A.2 to Schwab2021 LASP BATS Paper

CubeSat missions are flying a variety of battery technologies and range of battery capacities. As the CubeSat form factors continue to grow in size, the battery capacities will need to grow too. Thus maximizing battery capacity and the efficiency of battery packs are increasingly more important. To address this need for our university-built CubeSats, a new automated system used for flight testing battery cells was developed to optimize the capacity and long-term performance of a battery pack. The important steps of creating a low-cost, highly-efficient battery pack are described in detail, along with an overview of the safety acceptance testing for CubeSats deployed from the International Space Station (ISS), a location with some of the most demanding acceptance criteria, and often used as a launch platform for CubeSats. These steps include selecting the battery pack materials, developing the testing hardware and related automation software, and selecting matched battery cells for the flight battery packs. Our automation software is publicly available. The task of matching the maximum voltages and capacities of individual battery cells is an important but often time consuming process if not automated. Our battery test system autonomously charges and discharges multiple cells independently and at the same time tracks the current, voltage, and elapsed time of each cycle for capacity calculations. From these results we can combine cells to maximize the capacity for a flight battery pack. This battery test system also provides automated battery pack charge / discharge cycling to identify the battery packs with the higher efficiencies to be selected for flight. The measured state of charge curves for a battery pack, and the trending of those curves, is important for mission planning and operations. Our battery test system is low cost, and the build and test processes are easy to replicate, making it highly desirable for small spacecraft.</p

Modeling the Daily Variations of the Coronal X-ray Spectral Irradiance with Two Temperatures and Two Emission Measures

The Miniature X-ray Solar Spectrometer (MinXSS-1) CubeSat observed solar X-rays between 0.5 and 10 keV. A two-temperature, two-emission measure model is fit to each daily averaged spectrum. These daily average temperatures and emission measures are plotted against the corresponding daily solar 10.7 cm radio flux (F10.7) value and a linear correlation is found between each that we call the Schwab Woods Mason (SWM) model. The linear trends show that one can estimate the solar spectrum between 0.5 keV and 10 keV based on the F10.7 measurement alone. The cooler temperature component of this model represents the quiescent sun contribution to the spectra and is essentially independent of solar activity, meaning the daily average quiescent sun is accurately described by a single temperature (1.70 MK) regardless of solar intensity and only the emission measure corresponding to this temperature needs to be adjusted for higher or lower solar intensity. The warmer temperature component is shown to represent active region contributions to the spectra and varies between 5 MK to 6 MK. GOES XRS-B data between 1-8 Angstroms is used to validate this model and it is found that the ratio between the SWM model irradiance and the GOES XRS-B irradiance is close to unity on average. MinXSS-1 spectra during quiescent solar conditions have very low counts beyond around 3 keV. The SWM model can generate MinXSS-1 or DAXSS spectra at very high spectral resolution and with extended energy ranges to fill in gaps between measurements and extend predictions back to 1947

Design and Development of a PS4-OP Payload for Solar Spectral Irradiance Measurements and Technology Demonstration of Small-Satellite Subsystems

This article describes the design and development of INSPIRE-0, a payload on the spent stage of the ISROs PSLV. Recently, the Indian Space Research Organisation (ISRO) released an announcement of opportunity inviting proposals to develop payloads that can be tested on the PS4-Orbital Platform (PS4-OP). This platform is a novel idea formulated by ISRO to use the spent fourth/final stage of the Polar Satellite Launch Vehicle (PSLV), called the PS4, to conduct in-orbit scientific experiments and technology demonstration of small-satellite subsystems. INSPIRE-0 is a PS4-OP payload, jointly developed by the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado Boulder, the Indian Institute of Space Science and Technology (IIST), and the Nanyang Technological University (NTU) in Singapore. This payload has two main objectives. Firstly, the scientific objective is to characterize the solar spectrum using a novel sensor, developed by NTU, that has a wide frequency range from visible to near the infra-red region. The specific objective of the INSPIRE-0 payload is to demonstrate that accurate Solar Spectral Irradiance (SSI) continuous measurements are possible using new compact and robust disruptive technologies. A successful demonstration will pave the way for a future constellation of CubeSats that will provide a very cost-effective way to monitor the Total Solar Irradiance and SSI of the sun in the various spectral bands. Secondly, the INSPIRE-0 payload aims to flight qualify the in-house developed subsystems for the INSPIRESat-1 small satellite mission, namely, the Command and Data Handling (C&DH) Subsystem and the Electrical Power Subsystem (EPS). The article first describes the systems architecture of the payload which has a size of 15cm x 10cm x 7.5 cm, a mass of 1kg, and power consumption of 1.75 W. This is followed by the details of the science instrument and an overview of the different subsystems, namely the C&DH, the EPS, and the PS4-OP interface board. The article concludes with the details of the testing, including comprehensive performance tests and environmental tests, performed to prepare the payload for a planned launch on the PS4-OP in the third quarter of 2021

INSPIRESat-1: A Year of On-Orbit Operations

INSPIRESat-1 (IS-1) was the first mission under the INternational Satellite Program In Research and Education (INSPIRE) program, a consortium of universities coming together to space science missions. IS-1 launched on February 14, 2022 at 00:30 UTC to a sun synchronous dawn-dusk orbit onboard the Indian Space Research Organization\u27s PSLV C52 mission. The IS-1 spacecraft was primarily developed at the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado with significant contributions from the Indian Institute of Space Science and Technology (IIST), NCU of Taiwan and Nanyang Technological University (NTU) in Singapore. The IS-1 carries two scientific instruments: The Compact Ionospheric Probe (CIP) developed at National Central University (NCU) for studying Earth\u27s dynamic ionosphere and the NASA funded Dual-zone Aperture X-ray Solar Spectrometer (DAXSS) developed at LASP for studying the highly-variable solar X-ray radiation. DAXSS is a follow on from the highly successful MinXSS 1 &2 missions. First contact was established with the spacecraft 45 minutes after launch. The first science instruments were turned on by February 27th. DAXSS has now observed multiple solar flares in the current increasing phase of solar cycle 25 for a period of 16 months. In this paper we will present details on spacecraft performance in a unique dawn dusk orbit which presents thermal challenges not encountered frequently by nano-satellite platforms. We also present preliminary science results from CIP and DAXSS instruments from a year of on-orbit operations. Operations of the Spacecraft has also been unique with multiple universities commanding and downlinking science data

A Methodology for Successful University Graduate CubeSat Programs

The University of Colorado Smead Department of Aerospace Engineering has over a decade of success in designing, building, and operating student led CubeSat missions. The experience and lessons learned from building and operating the CSSWE, MinXSS-1, MinXSS-2, and QB50-Challenger missions have helped grow a knowledge base on the most effective and efficient ways to manage some of the “tall poles” when it comes to student run CubeSat missions. Among these “tall poles” we have seen student turnover, software, and documentation become some of the hardest to knock-down and we present our strategies for doing so. We use the MAXWELL mission (expected to launch in 2021) as a road-map to detail the methodology we have built over the last decade to ensure the greatest chance of mission success

First Results for Solar Soft X-ray Irradiance Measurements from the Third Generation Miniature X-Ray Solar Spectrometer

Three generations of the Miniature X-ray Solar Spectrometer (MinXSS) have flown on small satellites with the goal "to explore the energy distribution of soft X-ray (SXR) emissions from the quiescent Sun, active regions, and during solar flares, and to model the impact on Earth's ionosphere and thermosphere". The primary science instrument is the Amptek X123 X-ray spectrometer that has improved with each generation of the MinXSS experiment. This third generation MinXSS-3 has higher energy resolution and larger effective area than its predecessors and is also known as the Dual-zone Aperture X-ray Solar Spectrometer (DAXSS). It was launched on the INSPIRESat-1 satellite on 2022 February 14, and INSPIRESat-1 has successfully completed its 6-month prime mission. The INSPIRESat-1 is in a dawn-dusk, Sun-Synchronous Orbit (SSO) and therefore has 24-hour coverage of the Sun during most of its mission so far. The rise of Solar Cycle 25 (SC-25) has been observed by DAXSS. This paper introduces the INSPIRESat-1 DAXSS solar SXR observations, and we focus the science results here on a solar occultation experiment and multiple flares on 2022 April 24. One key flare result is that the reduction of elemental abundances is greatest during the flare impulsive phase and thus highlighting the important role of chromospheric evaporation during flares to inject warmer plasma into the coronal loops. Furthermore, these results are suggestive that the amount of chromospheric evaporation is related to flare temperature and intensity.Comment: 43 pages including 19-page Appendix A, 8 figures, 7 table

INSPIRESat-1: An Ionosphere and Solar X-ray Observing MicroSat

The International Satellite Program in Research and Education’s (INSPIRE) first satellite is an Ionosphere and Solar X-ray observing microsat slated for launch in November of 2019 onboard an ISRO Polar Satellite Launch Vehicle. The microsat has a mission specific structure fitting on a PSLV ring deployer. There are two payloads aboard with two different science objectives. The Compact Ionosphere Probe (CIP) will take in-situ measurements of ion density, composition, temperature, velocity, and electron temperature. The CIP is a smaller version of the Advanced Ionosphere Probe (AIP, both developed in Taiwan) currently operating onboard the FORMOSat-5. This instrument is capable of sampling the ionosphere at 1 and 8 Hz. The second payload is the Dual Aperture X-ray Solar spectrometer (DAXSS). DAXSS is a modified Amptek X123 that will observe Solar X-rays, specifically soft X-rays. Hot plasma in the sun’s corona is best measured in the soft X-rays. Many emission lines for important elements (Fe, Si, Mg, S, etc) are in the soft X-ray range. Soft X-rays are always present in the sun but 100 times brighter during flares, these observations will also lend to understanding the temperature difference between the sun’s corona and photosphere. The solar soft x-rays are also important for the Earth’s Ionosphere, adding to the ionosphere observations made by CIP. The DAXSS instrument has heritage from a NASA calibration rocket experiment and two cubesats, MINXSS 1 and 2. The newer model Amptek X123 has much improved energy resolution for the X-ray spectrum. The primary science objectives of the INSPIRESat-1 are twofold. First, enabling the characterization of the temporal and spatial distributions of small-scale plasma irregularities like plasma bubbles and the Midnight Temperature Maximum (MTM) in season, location, and time by CIP. Second, giving a greater understanding of why the Sun’s corona is orders of magnitude hotter than the photosphere, why there is an abundance of elements change during different solar events, and how these events (observed with greater soft x-ray fidelity) effect the earth’s ionosphere. In this paper, we present science expectations for the INSPIRESat-1 and a concept for coordinated Ionospheric measurements covering several altitudes and local times using three satellite platforms carrying the same CIP instrument (INSPIRESat-1, IDEASat/INSPIRESat-2, INSPIRESat-4, FORMOSat-5). We describe the development of DAXSS and how the dual aperture prevents the need for two X123 to get the similar data. We also highlight the unique development of the INSPIRESat-1 microsat being developed by international collaboration across three different universities

Neonatal severe bacterial infection impairment estimates in South Asia, sub-Saharan Africa, and Latin America for 2010.

BACKGROUND: Survivors of neonatal infections are at risk of neurodevelopmental impairment (NDI), a burden not previously systematically quantified and yet important for program priority setting. Systematic reviews and meta-analyses were undertaken and applied in a three-step compartmental model to estimate NDI cases after severe neonatal bacterial infection in South Asia, sub-Saharan Africa, and Latin America in neonates of >32 wk gestation (or >1,500 g). METHODS: We estimated cases of sepsis, meningitis, pneumonia, or no severe bacterial infection from among estimated cases of possible severe bacterial infection ((pSBI) step 1). We applied respective case fatality risks ((CFRs) step 2) and the NDI risk among survivors (step 3). For neonatal tetanus, incidence estimates were based on the estimated deaths, CFRs, and risk of subsequent NDI. RESULTS: For 2010, we estimated 1.7 million (uncertainty range: 1.1-2.4 million) cases of neonatal sepsis, 200,000 (21,000-350,000) cases of meningitis, 510,000 cases (150,000-930,000) of pneumonia, and 79,000 cases (70,000-930,000) of tetanus in neonates >32 wk gestation (or >1,500 g). Among the survivors, we estimated moderate to severe NDI after neonatal meningitis in 23% (95% confidence interval: 19-26%) of survivors, 18,000 (2,700-35,000) cases, and after neonatal tetanus in 16% (6-27%), 4,700 cases (1,700-8,900). CONCLUSION: Data are lacking for impairment after neonatal sepsis and pneumonia, especially among those of >32 wk gestation. Improved recognition and treatment of pSBI will reduce neonatal mortality. Lack of follow-up data for survivors of severe bacterial infections, particularly sepsis, was striking. Given the high incidence of sepsis, even minor NDI would be of major public health importance. Prevention of neonatal infection, improved case management, and support for children with NDI are all important strategies, currently receiving limited policy attention