The "Oxygen from Regolith (O2fR) Collaborative Systems Interface Study" explores strategies for managing interactions at system interfaces of lunar in-situ resource utilization (ISRU) technologies. Last year, the Lunar Surface Innovation Consortium (LSIC) ISRU Capability Area (CA) introduced the O2fR Collaborative Systems Interface Workbook, including a Design Structure Matrix (DSM) and Interface Worksheets. The workbook provides a framework to help the ISRU community identify quantitative mismatches between upstream and downstream system parameters as well as map dependencies such as energy, mass, and information flows across ISRU functions. On September 18, 2024 the LSIC ISRU CA held the Collaborative Systems Interface Workshop, where the participants explored how concepts in the workbook can influence their interface design and encourage smooth system integration to support NASA's lunar sustainability goals. Insights from the workshop and feedback from the community have influenced the LSIC ISRU CA's planned activities in the year ahead. The path forward for the O2fR Study includes maintaining a database of interface parameters on Confluence and providing opportunities to facilitate application of the workbook to the ISRU systems.

Molten Regolith Electrolysis, as an in situ resource utilization (ISRU) technology, has the potential to enable the production of oxygen and metallic alloys on the Lunar surface; opening new doors in Cis-Lunar, and eventually Martian space exploration. This research studies the fundamental physics which govern the formation, growth, detachment, and rise of electrolytic bubbles. To this end, computational fluid dynamic (CFD) models were developed and run, to simulate water electrolysis, molten salt electrolysis (MSE), and molten Lunar regolith (MRE) electrolysis across multiple reduced gravity levels. The results demonstrate that reduced gravity, electrode surface roughness (possibly due to surface degradation), fluid properties, and electrode orientation can all affect electrolytic efficiency and possibly even stall electrolysis by delaying bubble detachment. The findings of this research must be considered when designing and operating electrolysis systems at reduced gravity levels.

This research, which builds upon research presented at ASCEND 2023, explores the efficacy and efficiency of electrolysis systems in reduced gravity environments, such as those found on the Lunar and Martian surfaces. Electrolysis systems have the potential to be a viable in-situ resource utilization (ISRU) technology. With the potential of producing economically viable amounts of oxygen and metallic alloys on the Lunar surface, molten regolith electrolysis could possibly power and construct the next generation of Cis-Lunar space exploration. Computational fluid dynamic (CFD) models have been developed to model water electrolysis, molten salt electrolysis (MSE) and molten regolith electrolysis (MRE) across various gravity levels. The results provide significant insights, which should be considered when designing and operating electrolytic systems, expected to operate in a reducedgravity environment. The reduced gravity, possible surface degradation of the electrodes, and unique properties of molten regolith have the potential to delay bubble detachment and thus, decrease electrolytic efficiency.

Water at the poles of the Moon represents a compelling resource for supporting a sustained human presence. The location, abundance, composition, and physical state of this water needs to be characterized to determine the extent to which this in-situ resource could serve as a reserve to support a sustained presence. The general concept and need for a multiphase campaign to obtain this information has been previously established, and here we discuss the attributes, feasibility, and challenges of one specific implementation consisting of three components: 1. An orbital reconnaissance to refine knowledge of near surface water reserves to a 5-10km scale, 2. A multiple small rover campaign to locate the reserve in the most accessible 25-100km2 region of high water content, and 3. Concluding with a detailed assessment of the then located reserve. There is no technological hurdle to conducting first phase; the second and third phases would rely upon mature and/or currently funded technology developments with some additional development required to enable extended operations in cryogenic shadowed regions.

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This research explores the use and efficiency of Molten Regolith Electrolysis (MRE) as an in-situ resource utilization (ISRU) technology, which has the potential to produce economically viable and useful amounts of oxygen and metallic alloys on the Lunar surface; possibly powering and constructing the next generation of Cis-Lunar space exploration. To this end, computational fluid dynamic (CFD) models were developed to model water electrolysis and MRE across various gravity levels. The results provide significant insights, which should be considered when designing MRE systems, expected to operate in a Lunar environment. The reduced gravity of the Moon, possible surface degradation of the electrodes, and unique properties of molten Lunar regolith have the potential to delay bubble detachment and thus, decrease electrolytic efficiency.

Production of food in space via photosynthetic crops similar to the ones we use on Earth requires profligate use of resources that will be in short supply in early long duration space missions. We demonstrate that production of bulk calories via chemotrophic single-cell organisms is 2-3 orders of magnitude less expensive in terms of energy, volume, and water usage than via photosynthetic crops. In addition, we survey the history and current state of the art in production of food from nonphotosynthetic single-cell organisms.

Neutron spectroscopy observations from very low-altitude orbits over the Moon’s south pole could improve the spatial resolution maps for water ice reserves. We explore these low-altitude orbits to identify minimum achievable altitudes and evaluate stability. Additionally, we analyzed maneuver sequences to mitigate impact threat and to quantify the propulsion costs associated with placing and maintaining a spacecraft in such an orbit. Our sample observation and cruise trajectories demonstrate feasibility.

Lunar In-Situ Resource Utilization, defined here as the use of O2 and/or H2O derived from the surface of the Moon, can potentially be enabling to the development of a sustained human lunar presence. Rocket propellant will be needed to enable humans to return to Earth from the Moon. As demonstrated by the rocket equation, launching this propellant from the Earth is extremely inefficient for multiple reasons (large Earth mass, Earth atmosphere, significant (non-zero) lunar mass, etc.). Not launching this mass from Earth and instead making it on the Moon, especially the oxidizer O2 that is 80%????? of the mass of a liquid oxygen/hydrogen system), saves incredible costs and reduces the technical challenges of launching so much mass. The challenge is though, that one needs to know HOW MUCH O2 is going to be required well before the demand is actually there. And not knowing the demand, it’s challenging to design the technology that will be required for extracting and storing this re-source. This supply and demand conundrum is essentially a chicken-and-the-egg analogy for which we worked with the community and NASA to put an initial stake in the ground.

The Stokes reflectometer concept presented here takes a novel approach to microwave remote sensing of soils. It relies on a constellation of low-power, low-mass, continuous wave, ultrahighfrequency transmitters and receivers. The systems are arranged in a forward scattering configuration over a range of angles of incidence and scattering set to cross the Brewster angle to retrieve soil properties. Proof of concept is provided by a series of COMSOL Multiphysics finite element runs to model Stokes parameters (SP) of forward-scattered RF signals through layers of varying compositions, dielectric constants, and surface roughness, assuming no sources of contamination during transmission. Significant variations for all four SP were demonstrated. At frequencies around 430 MHz, contamination during transmission is due to Faraday rotation (FR) in the ionosphere. A hybrid-polarimetric configuration minimized ionospheric contamination and provided for simplified expressions to retrieve FR angles and scattering coefficients from the received polarimetric power. With these, SP can be correctly calculated to soil moisture retrievals.

A simple approach to the detection and estimation of target motion based on phase measurements from a single-aperture synthetic-aperture radar (SAR) is presented. In this analysis the SAR is treated as a pure range-measuring device. Each stationary object in a scene produces a unique range-time history in the radar. Thus, ideal SAR processing is reduced to finding the response to the set of matched filters associated with stationary targets. For this purely geometrical model, it is shown that there exists a class of moving targets that are absolutely indistinguishable from a stationary target. These are targets that move in such a way that the range to the SAR is always identical to the range from the SAR to some stationary target. Moreover it turns out that most moving targets are also indistinguishable from some other moving targets. The idealized SAR is only sensitive to a single velocity component of the target, and thus most solutions are degenerate. Theoretical limits of the detection of motion are established that are dependent on SAR parameters and observation time. Fast-moving (e.g. spaceborne) SARs can detect along-track motions with less ambiguity than a slow-moving SAR. It is shown that most moving targets do produce apparent motion in sequences of multilook SAR imagery. These apparent motions can be used to estimate the measurable component of target velocity.

Compact polarimetry is a technique that allows construction of pseudo quad-pol information from dual-polarization synthetic aperture radar (SAR) systems. Compact polarimetry showed promise of being able to reduce the complexity, cost, mass, and data rate of a SAR system while attempting to maintain many capabilities of a fully polarimetric system. In this paper, we study different transmit/receive configurations to determine which polarimetric configurations allow for superior reconstruction of the fully polarimetric data. We discuss modifications of the original reconstruction algorithm proposed by Souyris et al., which show potential to better reconstruct fully polarimetric data.

Recent interest in dual-pol SAR systems has lead to a novel approach to dual-pol SAR, the so-called compact polarimetric imaging mode. The original idea, presented by Souyris et al. [1], employed a SAR system transmitting a linearly polarized wave rotated by 45° with respect to the orientation of the vertical (V) and horizontal (H) receive antennas. One then constructed pseudo quad-pol data from the dual-pol data assuming reflection symmetry and a model relationship between the |HV| return and the HH-VV correlation coefficient. Recently Stacy and Preiss [2], and Nord et al. [3], presented extensions of the original dual-pol compact polarimetry ideas and, independently, Raney [4] has analyzed the Stokes parameters for dual-pol SAR systems. Here we briefly present the extensions of the original compact polarimetry ideas following the development in [3]. We then discuss the dual-pol signature plot and show that it provides a simple, visual means to assess the polarimetric content for any dual-pol SAR system that transmits a polarized wave of arbitrary ellipticity / orientation, and coherently receives any two orthogonal polarizations. Lastly, we consider the default dual-pol mode of ALOS PALSAR: H-transmit with coherent (V, H) receive. We provide an interpretation of the α-entropy plot for this (HH, HV) dual-pol data.

An error was made in the application of the astrometric correction when converting data files into table values, resulting in a 400 positional offset in the published right ascension values in Table 2. Here we publish the table with the correct right ascension values. The work is otherwise unaffected. We thank Christina Johnson, a student at Sweet Briar College, for assistance in discovering and quantifying the error. Online material: machine-readable table

At low radio frequencies (ν ≲ 100 MHz), classical H II regions may become optically thick (optical depth τ ≥ 1) and can be observed as discrete absorption regions against the Galactic nonthermal background emission created by Galactic cosmic-ray electrons spiraling around magnetic fields. However, the historically poor angular resolution (>30′) of previous low-frequency surveys has limited such observations to the largest and nearest H II regions. The significantly enhanced resolution and surface brightness sensitivity of the 74 MHz system on the Very Large Array now allow for the detection of absorption regions on scale sizes of just a few arcminutes that can be readily identified with many more H II regions previously cataloged in emission at higher frequencies. These absorption measurements directly constrain the brightness temperature of the cosmic-ray synchrotron emission emanating from behind the H II regions based on reasonable physical assumptions. Many such observations could be used to map out the three-dimensional cosmic-ray emissivity in the Galaxy without resorting to a priori assumptions about Galactic structure. This measurement is unique to low-frequency radio astronomy. In this work we present 74 MHz observations in the region 26° > l > -15°, -5° < b < 5°; report the detection of 92 absorption features associated with known H II regions; and derive the brightness temperature of the Galactic cosmic-ray electron synchrotron emission emanating from the column behind these regions. For the 42 H II regions with known distances, the average emissivity of the column behind the H II region is derived. The 74 MHz emissivity values range between 0.3 and 1.0 K pc-1 for a model assuming uniform distribution of emissivity. Methods for using this type of data to model the three-dimensional distribution of cosmic-ray emissivity and the possibility of using this method to break the H II region kinematic distance degeneracy are discussed.

Recent interest in dual-pol SAR systems has lead to a novel approach to dual-pol SAR, the so-called compact polarimetric imaging mode. The original idea, presented by Souyris et al. (1), employed a SAR system transmitting a linearly polarized wave rotated by 45 with respect to the orientation of the vertical (V) and horizontal (H) receive antennas. They then constructed pseudo quad-pol data from the dual-pol data assuming both reflection symmetry and a model relationship between the HV return and the HH-VV correlation coefficient. Recently Stacy and Preiss (2), and Nord et al. (3), extended the original dual-pol compact polarimetry ideas and, independently. Here we assess the polarimetric content for a general dual-pol SAR system that transmits a polarized wave of arbitrary ellipticity / orientation, and receives any two orthogonal polarizations. Starting from quad-pol imagery we extract the polarimetric dual-pol data for each specific dual-pol mode. Comparison of classification results using the dual-pol imagery and the original quad-pol imagery provides a direct assessment of the polarimetric content of these dual-pol modes. Employing idealized targets with specific scattering mechanisms, e.g. dihedral, surface, volume, helix, dipole, etc., we illustrate the capabilities of the various dual-pol modes studied. We also determine the applicability of the original compact polarimetric models to these new dual-pol imaging modes. To do so, we first construct the pseudo quad-pol data using the compact polarimetric model and then compare polarimetric entropies and angles to those derived from the full quad-pol data. As a result of these comparisons we proposed new variant on the original compact polarimetric model. Unlike quad-pol SAR systems that transmit two orthogonal polarizations, dual-pol SAR systems only transmit a single polarization and therefore will not detect polarized targets that do not reflect the transmitted polarization. Therefore the choice of transmitted polarization directly affects the capability of the dual-pol SAR system to detect specific targets and more generally to determine geophysical properties of the imaged terrain. We will present several examples employing L-, C- and X-band SAR imagery. References: