cometadata/datacite-titles-descriptions-related-identifiers huggingface dataset:
DOI: 10.48577/jpl.i2rxkt
title: Demonstration of 100 kg Xenon Propellant Throughput by a Low-Power Magnetically Shielded Hall Thruster

description: The Hall thruster component of the Ascendant Sub-kW Transcelestial Electric Propulsion System (ASTRAEUS) successfully demonstrated a propellant throughput of over 100 kg of xenon and demonstrated a total of 1.55 MN-s of impulse in a long-duration wear test. The thruster was operated for a total of 7205, with the test broken into five segments each with a different discharge power between 200 and 1350 W: 3291 h at 300 V – 1000 W, 1739 h at 500 V – 1000 W, and 416 h at 400 V – 600 W, 388 h at 200 V – 200 W, and 1371 h at 300 V – 1350 W. Telemetry and temperature measurements periodically recorded throughout the test revealed constant performance across each test segment and over the full test duration. Each segment was sufficiently long to obtain erosion rate data on the thruster by an optical profilometer. Sub-nominal magnetic field strengths were inadvertently applied to the thruster during the first 5 kh of the test due to an electrical ground-support equipment issue, which caused a downstream shift of the discharge plasma and higher erosion of the thruster’s pole covers than originally expected. This issue was corrected for the latter three test segments; however, the thruster performance and operational behavior at all reference operating conditions remained unaffected. The long-duration wear test was voluntarily terminated after the thruster processed 100.3 kg of xenon.
DOI: 10.48577/jpl.ut0u0t
title: Export of ice sheet meltwater from Upernavik Fjord,West Greenland

description: Meltwater from Greenland is an important freshwater source for the North Atlantic Ocean, released into the ocean at the head of fjords in the formof runoff, submarine melt and icebergs. The meltwater release gives rise to complex in-fjord transformations that result in its dilution through mixing with other water masses. The transformed waters, which contain the meltwater, are exported from thefjords as a new water mass “Glacially Modified Water” (GMW). Here we use summer hydrographic data collected from 2013 to 2019 in Upernavik, a major glacial fjord in northwest Greenland, to describe the water masses that flow into the fjord from the shelf and the exported GMWs. Using an Optimum Multi-Parameter technique across multiple years we then show that GMW is composed of 57.8 8.1% Atlantic Water, 41.0 8.3% Polar Water, 1.0 0.1% subglacial discharge and 0.2 0.2% submarine meltwater. We show that the GMW fractional composition cannot be described by buoyant plume theory alone since it includes lateral mixing within the upper layers of the fjord not accounted for by buoyant plume dynamics. Consistent with its composition, we find that changes in GMW properties reflect changes in the AW and PW source waters. Using the obtained dilution ratios, this study suggests that the exchange across the fjord mouth during summer is on the order of 50 mSv (compared to a freshwater input of 0.5 mSv). This study provides a first order parameterization for the exchange at the mouth of glacial fjords for large-scale ocean models.
DOI: 10.48577/jpl.ae97jw
title: Geotechnical assessment of terrain strength properties on Mars using the Perseverance rover's abrading bit

description: To date, instruments for measuring geotechnical properties have been absent from Mars exploration missions. This paper examines the use the Mars 2020 Perseverance rover’s abrading bit tool to perform regolith strength measurements. The Perseverance rover’s abrading bit has a similar form factor to a Bevameter, a tool commonly used to collect engineering geotechnical data to assess terrain traversability. To demonstrate the use of the abrading bit to characterize soil strength, a portable testbed that mimics the flight system has been designed and built using commercial off-the-shelf components. The testbed comprises an 80/20 housing, avionics box, and drill feed mechanism. Additionally, a data-processing pipeline was developed to convert raw measurements to soil strength. Tests were performed on three characterized simulants with different mechanical properties. The results show that the abrading bit is capable of making shear and bearing strength measurements and demonstrate, for the first time, the ability to perform controlled geotechnical analysis using a standard science instrument.
DOI: 10.48577/jpl.hinaae
title: National CO2 budgets (2015–2020) inferred from atmospheric CO2 observations in support of the Global Stocktake

description: Accurate accounting of carbon stock changes is critical for the planning and verification of emission reduction targets in support of the Paris Agreement. Here, we present a pilot dataset of country-specific net carbon exchange (NCE; fossil plus terrestrial ecosystem fluxes) and terrestrial carbon stock changes aimed at informing countries’ carbon budgets. These estimates are based on “top-down” NCE outputs from the v10 Orbiting Carbon Observatory (OCO-2) modeling intercomparison project (MIP), wherein an ensemble of inverse modeling groups conducted standardized experiments assimilating OCO-2 column-averaged dry-air mole fraction (XCO2) retrievals, in situ CO2 measurements, or combinations of these data. The OCO-2 MIP NCE estimates are combined with “bottom-up” estimates of fossil fuel emissions and lateral carbon fluxes to estimate changes in terrestrial carbon stocks, which are impacted by anthropogenic and natural drivers. These flux and stock change estimates are reported annually (2015-2020) as both a global 1ox1o gridded dataset and as a country-level dataset. Across the OCO-2 MIP experiments, we obtain increases in the ensemble median terrestrial carbon stocks of 3.29-4.58 Pg CO2 yr-1 (0.90-1.25 Pg C yr-1). This is a result of broad increases in terrestrial carbon stocks across the northern extratropics, while the tropics generally have stock losses but with considerable regional variability and differences between OCO-2 MIP experiments. We discuss the state of the science for tracking changes in terrestrial carbon stocks using top-down methods, including current limitations and future developments towards top-down monitoring and verification systems.
DOI: 10.48577/jpl.8is6xr
title: Property-based Brittleness Analysis of Temporal Networks, with application to Planetary Rovers and Bio-Manufacturing

description: We propose a new framework to analyze the brittleness of task networks with respect to an arbitrary set P = {P1, ..., Pk} of user-specified properties, such as dynamic controllability or minimum battery state of charge of a rover. The proposed algorithms allow the detection and enumeration of activities that, with modest task execution duration variation, make the success of execution no longer guaranteed in terms of the given set of properties. We introduce a metric for measuring an activity's brittleness, defined as the degree of acceptable deviation from its nominal duration that preserve the desired user-specified properties, and describe how that measurement is mapped to task network structure. Complementary to existing work on temporal robustness analysis which informs how likely a task network is to succeed or not under temporal controllability constraints, these new analysis and metric not only generalize robustness analysis to a set of user-defined properties (as opposed to strong or dynamic controllability for instance), but it also goes deeper to pinpoint the sources of potential brittleness. We develop an analyzer that helps human designers and/or automated task network generators focus on and address sources of undesirable brittleness. We apply the approach to a set of task networks in development for NASA's Perseverance rover and present common patterns that are sources of brittleness. The proposed technique and tools are currently under evaluation for potential use supporting operations of the rover.
DOI: 10.48577/jpl.dpkx4n
title: Flight Photon Counting EMCCD Development for the Roman Space Telescope Coronagraph Instrument

description: We describe the development of flight EMCCDs (electron multiplying charge coupled devices) for the photon counting camera system of the JPL Coronagraph Instrument (CGI) to be flown on the 2.4~m Nancy Grace Roman Space Telescope. Roman is a NASA flagship mission that will study dark energy and dark matter, and search for exoplanets with a planned launch in the mid-2020s. The CGI is intended to demonstrate technologies required for high contrast imaging and spectroscopy of exoplanets such as high speed wavefront sensing and pointing control, adaptive optics with deformable mirrors, and ultra-low noise signal detection with photon counting, visible-sensitive (350-950 nm) detectors. The camera system is at the heart of these demonstrations and is required to sense both faint and bright targets ($10^{-4}$ - $10^7$~counts-s$^{-1}$) adaptively at up to 1000 frames-s$^{-1}$ in order to provide the necessary feedback to the instrument control loops. The system includes two identical cameras, one to demonstrate faint light scientific capability, and the other to provide high speed real-time sensing of instrument pointing disturbances. Our program has evaluated the low signal performance of radiation damaged commercial EMCCD sensors and used those measurements as a basis for targeted radiation hardening modifications developed in partnership with the Open University (Milton Keynes, UK) and Teledyne-e2v (Chelmsford, UK). A pair of EMCCDs with test features was then developed and their low signal performance is reported here. The program has resulted in the development of a flight version of the EMCCD with low signal performance improved by a factor of 3.8 over the commercial one after exposure to $2.6\times 10^{9}$ protons-cm$^{-2}$ (10 MeV equivalent). The flight EMCCD sensors are contributed by ESA through a contract with Teledyne-e2v (Chelmsford, UK). In this paper, we will describe the program requirements, sensor design, test results and metrics used to evaluate photon counting performance.
DOI: 10.48577/jpl.npwiml
title: Results of Radiation-Induced Conductivity Testing of Europa Clipper Dielectric Materials

description: No abstract available.
DOI: 10.48577/jpl.aw5qzy
title: A new algorithm to generate a priori trace gas profiles for the GGG2020 retrieval algorithm

description: Optimal estimation retrievals of trace gas total columns require prior vertical profiles of the gases retrieved to drive the forward model and ensure the retrieval problem is mathematically well-posed. For well-mixed gases, it is possible to derive accurate prior profiles using an algorithm that accounts for general patterns of atmospheric transport coupled with measured time series of the gases in questions. Here we describe the algorithm used to generate the prior profiles for GGG2020, a new version of the GGG retrieval that is used to analyze spectra from solar-viewing Fourier transform spectrometers, including the Total Carbon Column Observing Network (TCCON). A particular focus of this work is improving the description of CO2, CH4, N2O, HF, and CO in the stratosphere. We show that the revised priors agree well with independent in situ and space-based measurements and improve the total column retrievals.
DOI: 10.48577/jpl.ebxk1w
title: Optical Atomic Clock aboard an Earth-orbiting Space Station (OACESS): Enhancing searches for physics beyond the standard model in space

description: We present a concept for a high-precision optical atomic clock (OAC) operating on an Earth-orbiting space station. This pathfinder science mission will compare the space-based OAC with one or more ultra-stable terrestrial OACs to search for space-time-dependent signatures of dark scalar fields that manifest as anomalies in the relative frequencies of station-based and ground-based clocks. This opens the possibility of probing models of new physics that are inaccessible to purely groundbased OAC experiments where a dark scalar field may potentially be strongly screened near Earth’s surface. This unique enhancement of sensitivity to potential dark matter candidates harnesses the potential of space-based OACs.
DOI: 10.48577/jpl.najl6l
title: Avoiding the “Great Filter”: Extraterrestrial Life and Humanity’s Future in the Universe

description: Our Universe is a vast, tantalizing enigma - a mystery that has aroused humankind’s innate curiosity for ages. Begging answers to questions on alien lifeforms have been thus far unfruitful, even with bounding technological advancements of recent years. Coupled with logical assumptions and calculations such as those made by Dr. Frank Drake starting in the early 1960s, evidence of life should arguably exist in abundance in our galaxy alone, yet in practice we’ve produced no clear affirmation beyond our own planet. So, where is everybody? The silence of the Universe beyond Earth reveals a pattern of both human limitation and steadfast curiosity. Even as ambitious programs such as SETI take aim at the technological challenges involved, the results have thus far turned up empty for any signs of life. We postulate an existential disaster may lay in wait as civilizations advance exponentially towards space exploration, acting as the Great Filter: a phenomenon that wipes out civilizations before they can encounter each other, explaining the cosmic silence. We propose several possible scenarios for the Great Filter, including anthropogenic and natural hazards, both of which can be prevented with reforms in individual, institutional and intrinsic behaviors. Multiple calamity candidates are considered: nuclear warfare, pathogens and pandemics, artificial intelligence, meteor impacts, and climate change. The Great Filter has the potential to eradicate life on Earth, especially as our rate of progress correlates directly to the severity of our fall. A necessary period of introspection, followed by appropriate refinements to more effectively approach our predicament, is required to mitigate risk to humankind and the nearly 9 million other species on Earth.
DOI: 10.48577/jpl.qeoiah
title: Low-Thrust Trajectory Optimizatoin for the Solar System Pony Express

description: We present a method for designing and optimizing Earth-Mars cycler orbits forthe Solar System Pony Express (SSPE) mission concept. The SSPE is aimedat augmenting the capabilities of the Deep Space Network (DSN) by enablinghigh latency and high bandwidth communications through the use of interplanetarydata mules. The SSPE will leverage a network of smallsats, outfitted withoptical laser communications, and by exploiting cycler orbits it will perform flybysof Mars at least once a year, retrieving 1-3 petabits of data per flyby frommissions already operating at the planet. This data will then be downlinkedto Earth during the next Earth flyby, also occurring about once a year. TheSSPE satellites are launched as a rideshare payload with another Mars-boundmission. Each data mule flying in the SSPE network is equipped with a lowthrustpropulsion system that is used for cycler orbit injection and for targetingflybys of Earth and Mars. Cycler orbits are first computed using a patchedconic approximation and impulsive thrust. These candidate solutions are thentransitioned into a higher-fidelity ephemeris model, and using an indirect optimizationmethod, fuel-optimal low-thrust transfers are computed between eachpair of flybys. We present three high-fidelity candidate solutions where a 500kg data mule is inserted into an Earth-Mars cycler orbit using the NASA Evolutionary Xenon Thruster (NEXT). In all three cases, the results show that thefuel consumption is feasible from a mission design perspective and that solutions obtained in the patched conics model can be successfully transitioned tothe ephemeris model using low-thrust propulsion.
DOI: 10.48577/jpl.4jbeis
title: Optimizing the isoprene emission model MEGAN with satellite and ground-based observational constraints

description: Isoprene is a hydrocarbon emitted in large quantities by terrestrial vegetation. It is a precursor to several air quality and climate pollutants including ozone. Emission rates vary with plant species and environmental conditions. This variability can be modelled using the Model of Emissions of Gases and Aerosols from Nature (MEGAN). MEGAN parameterizes isoprene emission rates as a vegetation-specific standard rate which is modulated by scaling factors that depend on meteorological and environmental driving variables. Recent experiments have identified large uncertainties in the MEGAN temperature response parameterization, while the emission rates under standard conditions are poorly constrained in some regions due to a lack of representative measurements and uncertainties in landcover. In this study, we use Bayesian model-data fusion to optimize the MEGAN temperature response and standard emission rates using satellite- and ground-based observational constraints. Optimization of the standard emission rate with satellite constraints reduced model biases but was highly sensitive to model input errors and drought stress and was found to be inconsistent with ground-based constraints at an Amazonian field site, reflecting large uncertainties in the satellite-based emissions. Optimization of the temperature response with ground-based constraints increased the temperature sensitivity of the model by a factor of five at an Amazonian field site but had no impact at a UK field site, demonstrating significant ecosystem-dependent variability of the isoprene emission temperature sensitivity. Ground-based measurements of isoprene across a wide range of ecosystems will be key for obtaining an accurate representation of isoprene emission temperature sensitivity in global biogeochemical models.
DOI: 10.48577/jpl.gn9ngn
title: Metagenomic Methods for Meeting NASA's Planetary Protection Policy Requirements on Future Missions – a Workshop Report

description: Molecular biology methods and technologies have advanced substantially over the past decade. These new molecular methods should be incorporated among the standard tools of planetary protection and could be validated for incorporation by 2026. To address the feasibility of applying modern molecular techniques to such an application, NASA conducted a technology workshop with private industry partners, academics, government agency stakeholders, along with NASA staff and contractors. The technical discussions and presentations of the Multi-Mission Metagenomics Technology Development Workshop focused on modernizing and supplementing the current planetary protection assays. The goals of the workshop were to assess the state of metagenomics and other advanced molecular techniques in the context of providing a validated framework to supplement the bacterial endospore-based NASA standard assay and to identify knowledge and technology gaps. In particular, workshop participants were tasked with discussing metagenomics as a stand-alone technology to provide rapid and comprehensive analysis of total nucleic acids and viable microorganisms on spacecraft surfaces, thereby allowing for the development of tailored and cost-effective microbial reduction plans for each hardware item on a spacecraft. Workshop participants recommended metagenomics approaches as the only data source that can adequately feed into quantitative microbial risk assessment models for evaluating the risk of forward (exploring extraterrestrial planet) and back (Earth harmful biological) contamination. Participants were unanimous that a metagenomics workflow, in tandem with rapid targeted quantitative (digital) PCR, represents a revolutionary advance over existing methods for the assessment of microbial bioburden on spacecraft surfaces. The workshop highlighted low biomass sampling, reagent contamination, and inconsistent bioinformatics data analysis as key areas for technology development. Finally, it was concluded that implementing metagenomics as an additional workflow for addressing concerns of NASA’s robotic mission will represent a dramatic improvement in technology advancement for planetary protection and will benefit future missions where mission success is affected by backward and forward contamination.
DOI: 10.48577/jpl.iywbbl
title: Science opportunities with solar sailing smallsats

description: Recently, we witnessed how the synergy of small satellite technology and solar sailing propulsion enables new missions. Together, small satellites with lightweight instruments and solar sails offer affordable access to deep regions of the solar system, also making it possible to realize hard-to-reach trajectories that are not constrained to the ecliptic plane. Combining these two technologies can drastically reduce travel times within the solar system, while delivering robust science. With solar sailing propulsion capable of reaching the velocities of ~5--10~AU/year, missions using a rideshare launch may reach the Jovian system in two years, Saturn in three. The same technologies could allow reaching solar polar orbits in two years. Fast, low-cost, and maneuverable sailcraft that may travel outside the plane of the ecliptic open new opportunities for affordable solar system exploration, with great promise for heliophysics, planetary science and astrophysics. Such missions could be modularized to reach different destinations with different sets of instruments. Benefiting from this progress, we present the ``Sundiver'' concept, offering novel possibilities for the science community. We discuss some of the key technologies, including the current design of the Sundiver sailcraft vehicle and innovative instruments, along with unique science opportunities that these technologies enable, especially as this exploration paradigm evolves. We formulate policy recommendations to allow national space agencies, industry, and other stakeholders to establish a strong scientific, programmatic and commercial focus, enrich and deepen the space enterprise and broaden its advocacy base by including the Sundiver paradigm as a part of broader space exploration efforts.
DOI: 10.48577/jpl.jghroe
title: Modest dust settling in the IRAS04302+2247 Class I protoplanetary disk

description: We present new VLA observations, between 6.8mm and 66mm, of the edge-on Class I disk IRAS04302+2247. Observations at 6.8mm and 9.2mm lead to the detection of thermal emission from the disk, while shallow observations at the other wavelengths are used to correct for emission from other processes. The disk radial brightness profile transitions from broadly extended in previous ALMA 0.9mm and 2.1mm observations to much more centrally brightened at 6.8mm and 9.2mm, which can be explained by optical depth effects. The radiative transfer modeling of the 0.9mm, 2.1mm, and 9.2mm data suggests that the grains are smaller than 1cm in the outer regions of the disk and allows us to obtain the first lower limit for the scale height of grains emitting at millimeter wavelengths in a protoplanetary disk. We find that the millimeter dust scale height is between 1au and 6au at a radius 100au from the central star, while the gas scale height is estimated to be about 7au, indicating a modest level of settling. The estimated dust height is intermediate between less evolved Class 0 sources, that are found to be vertically thick, and more evolved Class II sources, which show a significant level of settling. This suggests that we are witnessing an intermediate stage of dust settling.