cometadata/datacite-titles-descriptions-related-identifiers huggingface dataset:
DOI: 10.48577/jpl.yjnwh4
title: For the 71st IAC System Engineering a Solar Thermal Propulsion Mission Concept for Rapid Interstellar Medium Access

description: The interstellar medium (ISM) represents the next frontier in space exploration, with many new discoveries to be made. The challenge, being so far away from Earth, the ISM requires many decades to reach. To advance our knowledge of what exists beyond our Solar System, new approaches for rapid access are required. One such approach is solar thermal propulsion (STP). The approach uses several Venus and Earth gravity assists to fly to Jupiter and use its gravity well to dive towards the Sun. Approaching within 3 solar radii a perihelion burn would be performed, maximizing the spacecraft’s ΔV to achieve high Solar System escape velocities. A unique aspect of the STP mission concept is that the Sun is not only used as a gravity well for an Oberth manoeuvre, but also to heat the fuel to ultra-high-temperatures (&gt;3000 K), enabling a monopropellant burn with high specific impulse (Isp). Prior preliminary studies indicated escape velocities of over 20 astronomical unit (AU)/yr would be possible. An in-depth modelling exercise was undertaken to determine how such a system would perform. The model in this paper showed the current STP design is capable of providing just under 9±1 AU/yr, but there are many technology developments that could increase escape velocity. The technologies vary from items that could be implemented in the near term, like turbo-pumps driven by the hydrogen, to items requiring more extensive development programs like thin coatings which do not erode in superheated hydrogen. After reviewing the STP approach, and comparing it to a solid rocket motor (SRM), it was found that with currently available technology, SRM outperforms STP with an escape velocity of approximately 10-12 AU/yr. However, future advances in heat exchanger lining materials, turbo pumps, and advanced heat exchanger geometries may enable solar thermal propulsion to provide higher escape velocities, providing one of the fastest ways to exit the solar system. Ultimately, if all technology paths could be implemented with minimal side effects, the performance in a best-case scenario could reach up to 16 AU/yr.
DOI: 10.48577/jpl.knuw9c
title: UAVSAR observations of InSAR polarimetric phase diversity: implications for NISAR ionospheric phase estimation

description: The NASA-ISRO Synthetic Aperture Radar (NISAR) is a repeat-pass radar mission that will 15 acquire fully-polarimetric SAR data in an innovative acquisition mode known as quasi-quad 16 pol (QQP). It consists of simultaneously operating a HH/HV and a VH/VV dual-pol modes 17 in the lowest and upper parts of the transmitted frequency spectrum. Compared to more 18 traditional acquisition modes, the ionospheric phase estimation algorithms for QQP repeat19 pass data will likely exploit the dierence of two sub-band SAR interferograms acquired 20 not only at distinct center frequencies but also at dierent polarizations (e.g HH/VV), 21 making the ionospheric phase estimation vulnerable to possible bias caused by polarimetric 22 interferometric scattering phase components. 23 Using UAVSAR airborne data, we show that temporal variations of the interferometric 24 scattering phase may introduce spurious polarimetric-dependent phase terms which may 25 bias QQP ionospheric phase estimates. The magnitude of this bias depends on the type 26 of observed land cover. For bare soil and forested areas, we detect HH-VV interferometric 27 phase discrepancies up to 30 degrees over 12 days, corresponding to a 10 cm bias at L28 band. Over comparable time intervals, changes in vegetation vitality introduce HH-VV 29 interferometric phase inconsistencies beyond 90 degrees for vertically-oriented agricultural 30 elds. We simulate the QQP ionospheric phase screen over the San Andreas Fault, USA, a 31 region characterized by a mixture of vegetated and bare soil surfaces. Based on the results 32 from the UAVSAR data analysis, we recommend using the same polarization on the main 33 and side-bands of the NISAR operational science modes (e.g. single-pol or dual-pol) to 34 avoid potential biases in the ionospheric phase estimates.
DOI: 10.48577/jpl.pn0x8l
title: Earth as a Proxy Exoplanet: Deconstructing and Reconstructing Spectrophotometric Light Curves

description: Point source, spectrophotometric light curves of Earth-like planets contain a surprising amount of information about the spatial features of those worlds. Spatially resolving these light curves is critical for assessing time-varying surface features and the existence of a climate system, which in turn is critical to life on Earth and significant for determining habitability on exoplanets. Given that Earth is the only celestial body confirmed to harbor life, treating it as a proxy exoplanet by analyzing its time-resolved spectral images provides a benchmark in the search for habitable exoplanets. The Earth Polychromatic Imaging Camera (EPIC) on the Deep Space Climate Observatory (DSCOVR) provides such an opportunity, with observations of ~5000 full-disk sunlit Earth images each year at ten wavelengths with high temporal frequency. By integrating over the Earth’s disk to create a single point source and then deconstructing and reconstructing these spectral images, different spatial features on Earth are successfully separated and compared with known ground truth data. Our analysis reveals that the first and fourth principal components of single-point light curves derived from DSCOVR measurements, contributing ~83.23% of the light curve variability, contain information about low and high clouds, respectively. Surface information relevant to the contrast between land and ocean reflectance is contained in the second principal component, while individual land sub-types are not easily distinguishable (&lt;0.1% total light curve variation). The Earth model with real clouds and reconstructed spectra can serve as a baseline for analyzing light curves of Earth-like exoplanets and guide wavelength selection and sampling strategies for future observations.
DOI: 10.48577/jpl.z2zjep
title: Environmental controls on tropical mesoscale convective system precipitation intensity

description: Using multiple independent satellite and reanalysis datasets, we compare relationships between mesoscale convective system (MCS) precipitation intensity (Pmax), environmental moisture, large-scale vertical velocity, and system radius among tropical continental and oceanic regions. A sharp, nonlinear relationship between column water vapor (CWV) and Pmax emerges, consistent with nonlinear increases in estimated plume buoyancy. MCS Pmax increases sharply with increasing boundary layer and lower free tropospheric (LFT) moisture, with the highest Pmax values originating from MCS environments exhibiting a peak in LFT moisture near 750 mb. MCS Pmax exhibits strikingly similar behavior as a function of water vapor among tropical land and ocean regions. Yet while the moisture-Pmax relationship depends strongly on mean tropospheric temperature, it does not depend on sea surface temperature (SST) over ocean or surface air temperature (SAT) over land. Other Pmax dependent factors include system radius, the number of convective cores, and the large-scale vertical velocity. Larger systems typically contain wider convective cores and higher Pmax, consistent with increased protection from dilution due to dry air entrainment and reduced re-evaporation of precipitation. Additionally, stronger large-scale ascent generally supports greater precipitation production. Lastly, temporal lead-lag analysis suggests that anomalous moisture in the lower-middle troposphere favors convective organization over most regions. Overall, these statistics provide a physical basis for understanding environmental factors controlling heavy precipitation events, providing metrics for model diagnosis and guiding physical intuition regarding expected changes to precipitation extremes with anthropogenic warming.
DOI: 10.48577/jpl.std6rz
title: Enabling Limited Resource-Bounded Disjunction in Scheduling

description: We describe three approaches to enabling aseverelycomputationally limited embeddedscheduler to consider a small number of alternative activities based on resource availability.We consider the case where the scheduler is so computationally limited that it cannot backtracksearch. The first two approaches precompile resource checks (called guards) that only enableselection of a preferred alternative activity if sufficient resources are estimated to be availableto schedule the remaining activities. The third approach mimics backtracking by invokingthe scheduler multiple times with the alternative activities. We present an evaluation of thesetechniques on Mars mission scenarios (called sol types) from NASA’s next planetary roverwhere these techniques have been evaluated for inclusion in an onboard scheduler.
DOI: 10.48577/jpl.xziq6e
title: Radiometric Autonomous Navigation Fused with Optical for Deep Space Exploration

description: With the advent of the Deep Space Atomic Clock, operationally accurate and re-liable one-way radiometric data sent from a radio beacon (i.e., a DSN antenna or other spacecraft) and collected using a spacecraft’s radio receiver enables the de-velopment and use of autonomous radio navigation. This work examines the fu-sion of radiometric data with optical data (i.e. OpNav) to yield robust and accu-rate trajectory solutions that include selected model reductions and computation-ally efficient navigation algorithms that can be readily adopted for onboard, au-tonomous navigation. The methodology is characterized using a representative high-fidelity simulation of deep space cruise, approach, and delivery to Mars. The results show that the combination of the two data types yields solutions that are almost an order of magnitude more accurate than those obtained using each data type by itself. Furthermore, the combined data solutions readily met representative entry navigation requirements (in this case at Mars).
DOI: 10.48577/jpl.acmzup
title: Thermophysical Properties and Surface Heterogeneity of Landing Sites on MarsFrom Overlapping Thermal Emission Imaging System (THEMIS) Observations

description: Orbitally derived thermal inertia (TI) values of surfaces allow for remote interpretation ofrock and sediment physical characteristics. The evolving local times of the Mars OdysseyThermal Emission Imaging System (THEMIS) mission have enabled surface temperature datacollection over multiple seasons and local times over ∼9 Mars years (MY). We utilize thishigher temporal resolution data set to separate TI values of individual materials withinTHEMIS pixels (100 m sampling). In this study, we focus on geologic units within Gusev, Gale,and Jezero crater landing sites to determine their respective TI and ground-truth ourmethods. We use the KRC model to predict temperatures for a range of homogeneous andtwo-component thermophysical mixing scenarios (laterally and vertically heterogeneous),and compare those to THEMIS brightness temperatures. The Gusev and Gale crater resultsare consistent with rover-based evaluations, indurated or clast-covered sands. The best-fi tscenarios along the Jezero crater volcanic fl oor unit show low to moderate TI valuesrepresentative of coarse sediment, volcaniclastic, or pyroclastic rocks. The light toned unitand western fan deposits both indicate sands and a moderate TI component; we interpretthis as heavy fracturing within the rock. Diffi culties in modeling some THEMIS temperaturesare attributed to daily weather eff ects, local atmospheric dust variability, and real surfacechanges over time (e.g., dust deposition and removal); we also observe that sometemperature observations lead to non-unique modeled physical solutions. Nevertheless,these methods can still rule out a signifi cant range of material properties and providemeaningful geologic information about Mars’ surface.
DOI: 10.48577/jpl.mvfqvv
title: The Impacts of Climate and Wildfire on Gross Primary Productivity in Alaska

description: The increase in wildfire occurrence and severity seen over the past decades in the boreal and Arctic biomes is expected to continue in the future in response to rapid climate change in this region. Recent studies documented positive trends in gross primary productivity (GPP) for Arctic boreal biomes driven by warming, but it is unclear how GPP trends are affected by wildfires. Here, we used satellite vegetation observations and environmental data with a diagnostic GPP model to analyze recovery from large fires in Alaska over the period 2000-2019. We confirmed earlier findings that warmer-than-average years provide favorable climate conditions for vegetation growth, leading to a GPP increase of 1 Tg C yr-1, contributed mainly from enhanced productivity in the early growing season. However, higher temperatures increase the risk of wildfire occurrence leading to direct carbon loss over a period of 1-3 years. While mortality related to severe wildfires reduce ecosystem productivity, post-fire productivity in moderately burned areas shows a significant positive trend. The rapid GPP recovery following fires reported here might be favorable for maintaining the region’s net carbon sink, but wildfires can indirectly promote the release of long-term stored carbon in the permafrost. With the projected increase in severity and frequency of wildfires in the future, we expect a reduction of GPP and therefore amplification of climate warming in this region.
DOI: 10.48577/jpl.rjrogw
title: THE IMPACT OF IN-SITU PROBE ORIENTATION ON SMAP VALIDATION STATISTICS

description: Ongoing evaluation of the Soil Moisture Active Passive (SMAP) soil moisture products have utilized validation networks distributed in several regions around the world. The in-situ reference used for validation of the soil moisture retrieval algorithm is associated with measurements from soil moisture probes typically located at 5cm beneath the soil surface, however some networks also consider a vertically oriented probe that measures from 0-5cm. In this study we compare the correlation and ubRMSE (unbiased Root Mean Square Error) from the SMAP L2 radiometer soil moisture product when compared to in-situ measurements taken at 5cm (approximately 3.5-6.5cm) below the surface and measurements taken as an integrated measure from 0-5.7cm. The data was obtained from two SMAP validation networks in Canada the: Kenaston network in Saskatchewan and Carman network situated in Manitoba. At both sites, correlations between the in-situ and the SMAP L2 product were consistently higher with vertically oriented probes following rain events. With respect to the ubRMSE the vertically oriented probes at the Carman site had lower ubRMSE with the SMAP product than the horizontal probes that are currently used for validation activities. In some cases, vertical probe information should be considered in validation approaches when this data is available and could be considered in the design of in-situ calibration/validation networks. These results may be useful in design considerations of networks for upcoming soil moisture product validation.
DOI: 10.48577/jpl.gcyk9n
title: Faster Exo-Earth yield for HabEx and LUVOIR via extreme precision radial velocity prior knowledge

description: The HabEx and LUVOIR mission concepts reported science yields for mission scenarios in which the instruments must search for potentially habitable planets, determine their orbits, and, if worthwhile, invest the integration time for a spectral characterization. We evaluate the impact of prior knowledge on yield for starshade only, coronagraph only, and hybrid architectures. We use perfect prior knowledge to establish an upper bound on yield and use partial prior knowledge from a potential future Extreme Precision Radial Velocity instrument with 3 cm/s sensitivity. We detail a modeling framework that performs dynamically responsive observation scheduling with realistic mission constraints. We evaluate exo-earth yields against three metrics of spectral characterization for four mission architectures and three levels of prior knowledge (none, partial and perfect). The EPRV provided prior knowledge increases yields by $\sim$30\% and accelerates by a factor of 3 - 6 the time to achieve half of the yield of the mission. Prior knowledge makes all the mission architectures more nimble and powerful, and most especially starshade-based architectures. With prior knowledge, a small telescope with a starshade can achieve comparable yield to a larger telescope with a coronagraph.
DOI: 10.48577/jpl.t8boxh
title: Comparison of Deep Space Navigation using Optical Imaging, Pulsar Time-of-Arrival Tracking, and/or Radiometric Tracking

description: Recent advances with space navigation technologies developed by NASA in space-based atomic clocks andpulsar X-ray navigation combined with past successes in autonomous navigation using optical imaging, brings tothe forefront the need to compare space navigation using optical, radiometric, and pulsar-based measurementsusing a common set of assumptions and techniques. This review article examines these navigation data types in twodifferent ways. First, a simplified deep space orbit determination problem is posed that captures key features of thedynamics and geometry, and then each data type is characterized for its ability to solve for the orbit. The data typesare compared and contrasted using a semi-analytical approach with geometric dilution of precision techniques. Theresults provide useful parametric insights into the strengths of each data type. In the second part of the paper, ahigh-fidelity, Monte Carlo simulation of a Mars cruise, approach, and entry navigation problem is studied. Theresults found complement the semi-analytic results in the first part, and illustrate specific issues such as each datatype’s quantitative impact on solution accuracy and their ability to support autonomous delivery to a planet.
DOI: 10.48577/jpl.awsinq
title: Gravitational Wave Detection with Photometric Surveys

description: Gravitational wave (GW) detections have considerably enriched our understanding of the universe. To date, however, all events were observed via direct detection. In this paper, we study a GW detection technique based on astrometric observation and demonstrate that it offers a highly flexible frequency range that can uniquely complement existing detection methods. Using repeated astrometric measurements, periodic GW-induced deflections can be extracted and wave parameters inferred. We illustrate how Roman Space Telescope's high-cadence observations of the galactic bulge during its Exoplanet MicroLensing (EML) survey have the potential to turn it into a potent GW probe with complementary frequency range to \textit{Gaia}, pulsar timing arrays (PTAs), and the Laser Interferometer Space Antenna (LISA). We calculate that the Roman EML survey is sensitive to GWs with frequencies ranging from $7.7\times10^{-8}~{\rm{Hz}}$ to $5.6\times10^{-4}~\rm{Hz}$, which opens up a unique GW observing window for supermassive black hole binaries and their waveform evolution. While the detection threshold assuming the currently expected performance proves too high for detecting individual GWs from realistic supermassive black hole binaries, we show that binaries with chirp mass $\mchirp&gt;10^{7.6}~M_\odot$ out to 10 Mpc can be detected if the telescope is able to achieve an astrometric accuracy of 0.11 mas. To confidently detect binaries with $\mchirp&gt;10^{7}~M_\odot$ out to 50 Mpc, a factor of 100 sensitivity improvement is required. We propose several improvement strategies, including recovering the mean astrometric deflection and increasing astrometric accuracy, number of observed stars, field-of-view size, and observational cadence. We also discuss how other existing and planned surveys could contribute to detecting GWs via astrometry.
DOI: 10.48577/jpl.j8y5lf
title: Inferring the Subsurface Geometry, Stress, and Strength of Slow-moving Landslides using 3D Velocity Measurements from the NASA/JPL UAVSAR

description: The hazardous impact and erosive potential of slow-moving landslides depends on landslide properties including velocity, size, and frequency of occurrence. However, constraints on size, in particular, subsurface geometry, are lacking because these types of landslides rarely fully evacuate material to create measurable hillslope scars. Here we use pixel offset tracking with data from the NASA/JPL Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) to measure the three-dimensional surface deformation of 134 slow-moving landslides in the northern California Coast Ranges. We apply volume conservation to infer the actively deforming thickness, volume, geometric scaling, and frictional strength of each landslide. These landslides move at average rates between ~0.1–3 m/yr and have areas of ~6.1 x 103–2.35 x 106 m2, inferred mean thicknesses of ~1.1–25 m, and volumes of ~7.01 x 103–9.75 x 106 m3. The best-fit volume-area geometric scaling exponent is γ ~ 1.2–1.5, indicating that these landslides fall between typical soil and bedrock landslide scaling. A rollover in the scaling relationship suggests that the largest landslide complexes in our dataset become large primarily by increasing in area rather than thickness. In addition, the slow-moving landslides display scale-dependent frictional strength, such that large landslide tend to be weaker than small landslides. This decrease in frictional strength with landslide size is likely because larger landslides are composed of higher proportions of weak material. Our work shows how state-of-the-art remote sensing techniques can be used to better understand landslide processes and quantify their contribution to landscape evolution and hazards to human safety.
DOI: 10.48577/jpl.gnat74
title: The NANOGrav 12.5-year Data Set: Search For An Isotropic Stochastic Gravitational-Wave Background

description: We search for an isotropic stochastic gravitational-wave background (GWB) in the 12.5-year pulsar timing data set collected by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). Our analysis finds strong evidence of a stochastic process, modeled as a power-law, with common amplitude and spectral slope across pulsars. The Bayesian posterior of the amplitude for a f^{−2/3} power-law spectrum, expressed as characteristic GW strain, has median 1.92E−15 and 5%–95% quantiles of 1.37–2.67E−15 at a reference frequency of fyr = 1 yr^{−1}. The Bayes factor in favor of the common-spectrum process versus independent red-noise processes in each pulsar exceeds 10, 000. However, we find no statistically significant evidence that this process has quadrupolar spatial correlations, which we would consider necessary to claim a GWB detection consistent with General Relativity. We find that the process has neither monopolar nor dipolar correlations, which may arise from, for example, reference clock or solar-system ephemeris systematics, respectively. The amplitude posterior has significant support above previously reported upper limits; we explain this in terms of the Bayesian priors assumed for intrinsic pulsar red noise. We examine potential implications for the supermassive black hole binary population under the hypothesis that the signal is indeed astrophysical in nature.