Future Exploration Missions Research Articles

Development of Progressively Earth-Independent Medical Operations to Enable NASA Exploration Missions.

Introduction -The National Aeronautics and Space Administration's (NASA's) transition from operations in low-Earth orbit to long-duration missions to the Moon and Mars necessitates the development of progressively Earth-independent medical operations (EIMO) to support crews and reduce overall mission risk. Previous work has defined and laid the foundation for EIMO, but further development of the concept is required to prepare for future exploration missions. Methods -NASA's Exploration Medical Capability element organized a series of 5 technical interchange meetings from 2023 to 2024, which included internal (NASA) and external subject-matter experts in human spaceflight, health technology, and austere medicine to create a framework for developing the technologies and procedures necessary to maintain human health and performance in a progressively Earth-independent fashion. Results -The EIMO technical interchange meetings provided a forum for a field of experts and stakeholders to better understand gaps between current approaches to medical care in low-Earth orbit and the innovations needed to maintain the health and performance of astronauts on long-duration deep-space missions. These discussions were recorded, analyzed, and collated into reports that can inform the maturation of EIMO concepts. Conclusions -Multidisciplinary input from experts with experience in human spaceflight, health technology, and austere medicine is critical when planning for long-duration exploration missions. Innovations such as probabilistic risk assessment tools, extended reality devices, and advanced clinical artificial intelligence capabilities have been identified as high-value targets that can enhance inflight medical autonomy while maintaining appropriate workload balance and crew safety. By further developing the EIMO paradigm, NASA aims to identify areas of future work, research, and collaboration to reduce overall risk on future human spaceflight missions into deep space.

Electrostatic Transport Characteristics of Olivine Particles under Electron Irradiation in Vacuum

Abstract Electrostatic dust transport on airless planetary bodies, such as the Moon, plays a crucial role in shaping their surface environment and influencing the evolution of surface materials. To investigate the effects of electron irradiation on the transport characteristics of micron-sized dust particles under simulated lunar conditions, we measured the diameters and velocities of moving olivine particles using a laser Doppler system. Experiments were conducted under electron irradiation with energies up to 500 eV and currents ranging from 1 to 500 μA. The results demonstrate a strong dependence of electrostatic dust migration on the incident electrons’ energy and current, with more pronounced effects observed at higher energies. This offers insights into the mechanisms behind localized dust migration during magnetic tail crossings and in the lunar terminal/polar plasma wakes, where electrostatic charging likely plays a key role. However, further observations are necessary to verify these phenomena fully. Olivine particles exhibited significantly higher transport rates than anorthite particles under the same conditions, confirming the distinct transport characteristics of various dust components. Furthermore, based on the patched charge model, we examined the driving force and initial vertical velocity distribution to better understand the mechanisms behind dust lofting. These findings provide valuable insights into dust transport mechanisms on airless planetary surfaces, with implications for future space exploration missions and environmental modeling.

Gas-Liquid Separation of Liquid Hydrogen in Microgravity: Optimization of Structural Parameters, Angles, Rotational Speeds, and Gas-Liquid Ratios

Abstract Liquid hydrogen (LH2) is a high-efficiency cryogenic propellant extensively used in the aerospace industry due to its superior specific impulse and energy density. Despite its advantages, managing LH2 in orbit presents significant challenges, particularly in microgravity, where fluid transport and gas-liquid interface stability are adversely affected. This study addresses these challenges by investigating the effects of different structural parameters, angles, rotational speeds, and gas-liquid ratios on LH2 gas-liquid separation through comprehensive numerical simulations validations. We analyze the impacts of various pore diameters and axial spacings, as well as the evolution of gas-liquid configurations at different angles and rotational speeds. Additionally, we explore the effects of different gas-liquid ratios on separation performance. Our findings identify optimal parameter combinations and elucidate key mechanisms influencing gas-liquid separation efficiency. The study employs high-precision models and microgravity simulation experiments to validate the numerical results, providing a robust foundation for optimizing LH2 management devices. This research contributes valuable insights into the management of liquid hydrogen (LH2) in microgravity environments and provides foundational knowledge that may benefit future deep-space exploration missions.

Comparison of Line-Focused and Point-Focused Raman Mineral Analysis in Planetary Exploration

Raman spectroscopy plays a critical role in planetary exploration by providing detailed analysis of mineralogical and chemical compositions. However, the conventional point-focused Raman systems, while precise, are limited by their time-consuming nature, which hampers efficiency in space missions. This study compares a line-focused Raman spectroscopy system equipped with a cylindrical mirror array to a traditional point-focused system by testing various lunar-analogue minerals. The results demonstrate that the line-focused mode significantly reduces mineral detection time while covering larger sample surface areas, albeit with a slightly higher detection limit compared to the point-focused mode. Both modes exhibit similar capabilities in mineral identification and compositional analysis, with the line-focused system offering a more practical solution for rapid, high-throughput analysis in large-scale planetary geological surveys. These findings suggest that the line-focused Raman system could be a valuable tool in accelerating geochemical data collection during future deep space exploration missions.

Shape-from-Shading Derived DEMs from ShadowCam Images in Permanently Shadowed Regions at the Lunar South Pole: A First Look

Abstract. The lunar south pole, particularly its permanently shadowed regions (PSRs), has been the focus of future lunar exploration. The solar altitude angle at the lunar south pole is less than ∼ 2°, resulting in the PSRs not being directly illuminated and the possible existence of water ice in the PSRs due to the low temperatures. High-resolution digital elevation models (DEMs) in PSRs are crucial for future exploration missions and scientific research. However, existing image datasets (e.g., LROC NAC images) cannot penetrate the PSRs. Laser altimetry (e.g., LOLA) can measure the PSRs, but the DEMs derived from LOLA suffer from noises and interpolation defects. ShadowCam is a newly deployed camera onboard the Korea Pathfinder Lunar Orbiter, with a high imaging sensitivity. ShadowCam can capture the faint secondary illumination within PSRs, revealing previously indistinguishable topographic features in persistent darkness. Based on our existing Shape-from-Shading (SfS) pipeline for generating high-resolution DEMs from monocular images, we introduce a novel SfS approach that utilizes secondary illumination and reflectance to reconstruct pixel-wise high-resolution DEMs from ShadowCam images in PSRs. The approach consists of three steps: (1) modeling the secondary illumination on the target surfaces in PSRs based on the view factor; (2) optimizing a low-resolution LOLA DEM using the secondary illumination model; (3) refining the DEM to pixel-wise resolution based on SfS using the ShadowCam images. A test area (approximately 1 km × 1 km) within the PSR in the Shackleton crater near the lunar south pole is used for experimental evaluation. The results show that the DEM generated by the proposed approach is highly consistent with the direct LOLA measurements, particularly in small-scale topographic features such as crater floors and rims that are absent from the LOLA DEM. A first look at the results indicates that the proposed approach has great potential for generating high-resolution DEMs from ShadowCam images in PSRs, which can aid future exploration missions targeting the PSRs at the lunar south pole and support related scientific research on the water ice in the PSRs.

Comparative Analysis of Next-Generation Space Computing Applications on AMD-Xilinx Versal Architecture

Space computing has unique considerations that limit the achievable performance capabilities of onboard processing. Due to these limiting factors, current state-of-the-art devices for space computing are unable to meet the performance and energy-efficiency requirements for next-generation communication, navigation, and artificial-intelligence applications planned for future science and exploration missions. Space designers are transitioning to domain-specific architectures with specialized acceleration hardware, such as the AMD-Xilinx Versal Adaptive System-on-Chip, to address these issues. This heterogeneous platform provides developers with several processing subsystems that allow for mission-specific customization, including scalar processing units, programmable logic, and AI engine technology enabled by vector processing units. In this paper, performance, power-consumption, energy-efficiency, and resource-utilization tradeoffs for each Versal processing subsystem are evaluated by benchmarking a suite of representative next-generation artificial-intelligence and communication applications for space. This evaluation yields a design tradespace that mission designers can use to determine the Pareto-optimal solution for an artificial-intelligence or communication application based on performance requirements and power constraints. Additionally, this evaluation demonstrates that the performance and energy-efficiency benefits of the AI engines for space computing are significant; however, they are curtailed by considerably more power consumption than the scalar processors and programmable logic.

Mercury’s Meteorite Mysteries: A Directional Statistical Guide to Mercury’s North Pole, Hidden Hazards and Roadmap to Safe Landing Havens Based on Solar Elevation, Ice Stability, Temperature

Studying meteoroid impact patterns on planetary surfaces is critical for understanding surface dynamics and selecting safe landing sites. Mercury, one of the least explored rocky planets, presents unique challenges due to its extreme temperatures and the angular nature of its surface data. Traditional linear statistical methods are often inadequate for analyzing such directional data. This study introduces a novel approach using directional data analysis techniques to interpret the cyclical nature of meteoroid impact locations on Mercury. We employed Watson’s test, Bayesian Information Criterion scores, and a mixture of von Mises–Fisher distributions to model the distribution of impact craters and solar elevations on Mercury’s surface. Our findings indicate that while location parameters adhere to the von Mises distribution, solar elevations do not exhibit directional distribution characteristics. Additionally, by filtering datasets based on temperature thresholds and crater diameters, we pinpointed areas with a high probability of providing suitable landing surfaces. These insights enhance our understanding of the surface conditions on Mercury and provide valuable groundwork for future exploration missions.

Perspective View of Hydrology on the Martian Surface

The discovery of water ice within craters at the Martian North Pole has provided unprecedented insights into the planet's hydrology and climatic history. High-resolution images from the Mars Reconnaissance Orbiter (MRO) have revealed extensive ice deposits in these craters, some spanning several kilometers, offering a detailed perspective of Mars' frozen reservoirs. These ice layers, preserved under a thin dust cover, present a unique opportunity to study ancient climatic conditions and the planet's potential to support life. This paper examines the morphology and distribution of these polar ice deposits, their implications for understanding Martian hydrology, and their significance for future exploration missions. The stability and purity of the ice suggest it has been preserved for millions of years, potentially holding valuable records of past climate variations. Furthermore, the presence of accessible water ice is crucial for human exploration, providing essential resources for sustained missions. The study of these ice-filled craters not only enhances our knowledge of Mars' geologic and climatic history but also paves the way for future endeavors aimed at exploring and possibly colonizing the Red Planet.

An Operational Assessment of Team Cognition for Long-Distance Space Missions

Long-duration and long-distance space missions create a complicated context for collaboration. The combination of environmental and psychosocial factors will negatively impact individual and team cognition, potentially jeopardizing mission success. To provide a richer understanding of the issues surrounding team cognition for future space exploration missions, this paper describes an operational assessment to identify the key team cognition factors most likely to affect problem solving. Semi-structured interviews were conducted to elicit team cognitive and associated factors relevant to long-duration spaceflight missions. Ten NASA employees (e.g., astronauts, mission controllers) were interviewed to provide a more complete and accurate representation of individual and team cognitive demands. Our goal was to explicate critical cognitive processes associated with team effectiveness in space missions and provide guidance on technology and training collaborative problem solving for space missions.

Extrusion-based additive manufacturing of zirconium carbide for nuclear fuel cell structures

Nuclear thermal propulsion relies on heating hydrogen propellant using nuclear fuel to generate thrust for spacecraft propulsion. Ceramic fuel elements like zirconium carbide (ZrC) offer advantages over metals due to their high melting points and high temperature stability. The primary function of ZrC in this context is to provide structural integrity and stability to the nuclear fuel, especially under high-temperature and high-radiation conditions. Vanadium carbide (VC), with similar properties, is being used as a sintering additive for ZrC to enhance densification and mechanical properties. Traditional ZrC fabrication methods struggle with intricate geometries, but additive manufacturing (AM), specifically extrusion-based methods, revolutionizes ceramic fabrication by offering material flexibility, multi-material printing, minimal waste, and rapid prototyping. This study explores extrusion-based AM for the fabrication of ZrC nuclear fuel cell structures. Experimental findings highlight the impact of Nano Crystalline Cellulose (NCC) and VC additives on 3D-printed ZrC ceramics: higher NCC concentrations improves ink recovery and reduces deformation during the printing process, but excessive NCC increases the porosity after sintering process; VC additives mitigate decreased mechanical properties caused by higher NCC content, emphasizing the crucial role of ink composition and additive selection in achieving desired material properties for broader applications. These insights pave the way for innovative approaches in AM structures for nuclear propulsion and other high-performance applications. The integration of AM technologies with advanced materials like ZrC and tailored additives represents a significant step towards efficient and sustainable propulsion systems for future space exploration missions.

Lunar Exploration Based on Ground-Based Radar: Current Research Progress and Future Prospects

Lunar exploration is of significant importance in the development and utilization of in situ lunar resources, water ice exploration, and astronomical science. In recent years, ground-based radar (GBR) has gained increasing attention in the field of lunar exploration due to its flexibility, low cost, and penetrating capabilities. This paper reviews the scientific research on lunar exploration using GBR, outlining the basic principles of GBR and the progress made in lunar exploration studies. Our paper introduces the fundamental principles of lunar imaging using GBR and systematically reviews studies on lunar surface/subsurface detection, the dielectric properties inversion of the lunar regolith, and polar water ice detection using GBR. In particular, the paper summarizes the current development status of the Chinese GBR and forecasts future development trends in China. This review will enhance the understanding of lunar exploration results using GBR radar, systematically demonstrate the main applications and scientific achievements of GBR in lunar exploration, and provide a reference for GBR radar in future lunar exploration missions.

Partial gravity flammability of cast PMMA rods in concurrent axial stagnation flow

Testing was performed in a partial gravity centrifuge drop vehicle in the Zero Gravity Research Facility with cast PMMA rods in concurrent axial buoyant stagnation flow to determine flammability limits as a function of partial gravity level. The partial gravity levels studied varied from 0.04 g to a simulated 1g for ambient oxygen concentrations from 13.2 % to 15.2 % O2 by volume at an average 57.6 kPa (8.4 PSIA) ambient pressure, which is very close to the anticipated Lunar habitat pressure. The PMMA flammability boundary as a function of oxygen concentration and gravity level has been determined at five gravity levels. Coriolis effects appear to be minimal in the stagnation region where the flame is stabilized while the tips of the flame do show some bending at the higher gravity levels. Lunar gravity levels are near the minimum in the oxygen - gravity level flammability boundary. This suggests that fire is a significant safety risk for future exploration missions to the Moon since materials are screened in normal gravity to evaluate their safe use in space. If normal gravity screening is not conservative, a material derating method will need to be applied to ensure the material is not flammable on the Moon. Since the blowoff boundary appears to be linear with forced flow velocity, it may be possible to conduct elevated forced flow blowoff testing that could then be extrapolated down to effective Lunar gravity levels to provide an oxygen delta between 1g and Lunar flammability limits to derate the material.

Space radiation measurements during the Artemis I lunar mission

Space radiation is a notable hazard for long-duration human spaceflight1. Associated risks include cancer, cataracts, degenerative diseases2 and tissue reactions from large, acute exposures3. Space radiation originates from diverse sources, including galactic cosmic rays4, trapped-particle (Van Allen) belts5 and solar-particle events6. Previous radiation data are from the International Space Station and the Space Shuttle in low-Earth orbit protected by heavy shielding and Earth’s magnetic field7,8 and lightly shielded interplanetary robotic probes such as Mars Science Laboratory and Lunar Reconnaissance Orbiter9,10. Limited data from the Apollo missions11–13 and ground measurements with substantial caveats are also available14. Here we report radiation measurements from the heavily shielded Orion spacecraft on the uncrewed Artemis I lunar mission. At differing shielding locations inside the vehicle, a fourfold difference in dose rates was observed during proton-belt passes that are similar to large, reference solar-particle events. Interplanetary cosmic-ray dose equivalent rates in Orion were as much as 60% lower than previous observations9. Furthermore, a change in orientation of the spacecraft during the proton-belt transit resulted in a reduction of radiation dose rates of around 50%. These measurements validate the Orion for future crewed exploration and inform future human spaceflight mission design.

Sintering trials and microstructural changes mechanism of analogues of americium oxides for radioisotope power systems

Radioisotope thermoelectric generators (RTGs) are deal energy supply devices for deep space and deep-sea exploration, and it is also the energy core of the operation of the working equipment. Except for 238Pu (Plutonium), 241Am (Americium) was also used as a nuclide in the radioactive energy system for future space exploration missions. In this work, neodymium oxide (Nd2O3) was used as analogues for Am2O3. Cold-press-and-sinter methods was used. Different particle parameters (morphology, size, and crystal structure) and synthesized parameters of Nd2O3 were investigated. The synthesized powders contained lath-shaped particles, and batches with different particle sizes and microscopic topography were made and sintered. The results show that the optimal precipitation temperature of Nd2O3 is 25 °C. The optimal thermal decomposition temperature range is 900 °C to 1100 °C, and the optimal thermal decomposition heating rate is 10 °C min−1. The samples of Nd2O3 pellets without cracking is obtained with relative density of 85%–90 %. The Vickers hardness of Nd2O3 pellets was also studied. This paper provides an important scientific guiding significance for the cold-press-and-sinter of radioisotope 241Am batteries in the future.

(Invited) Advances in Wide Bandgap Thermal Resonant Infrared Detectors

Exploring the surface of distant planets, notably Venus, requires robust technologies capable of withstanding extreme environmental conditions while providing valuable scientific insights. This paper delves into the advancements made in designing an instrument tailored for capturing infrared (IR) images in the harsh Venusian environment, where temperatures soar to 500°C. The presented IR detector harnesses the power of a sparse array of resonant-based micromechanical devices, strategically addressing the limitations of existing technologies that can only withstand extreme conditions for limited durations.At the core of this technology lies the utilization of high-temperature-tolerant InAlN/GaN as the primary resonating element. GaN's resilience and high temperature tolerance make it a crucial player in challenging space environments. Its wide bandgap and chemical stability are advantageous for enduring harsh conditions during space missions. In tandem with GaN's intrinsic properties, high-temperature-tolerant meta-absorbers strategically positioned on the surface of each pixel play a pivotal role in the functionality of the IR detector. These meta-absorbers exhibit a remarkable capacity to absorb incoming infrared (IR) radiation, promptly transforming it into heat. The resonant frequency of these devices exhibits a linear shift with temperature variations, and a high-temperature-tolerant read-out electronic adeptly senses this frequency shift, enabling the seamless transfer of imaging data. Extraction of IR source power occurs through the resonance frequency shift in the exposed GaN resonator, compared to a reference resonator. The reference resonator, lacking the IR-absorbing layer, establishes a baseline for minimal resonant shifts.The sparse array configuration strategically reduces imaging elements to optimize power consumption and cost-effectiveness. Inspired by techniques employed in medical imaging instruments, this approach allows the construction of images from a low-power 2D array, striking a balance between imaging capabilities and processing efficiency. This sparse array configuration serves a dual purpose, streamlining signal routing for integrated read-out electronics and simplifying the overall integration and packaging of the IR imaging instrument. Monolithic integration of the read-out electronic with the sensor platform on the same chip overcomes challenges related to electrical and mechanical stability at high temperatures.The resonant effect delivers a remarkable enhancement in the signal-to-noise ratio, surpassing existing thermal detector technologies by a factor of 70×. Furthermore, the strategic implementation of sparse arraying results in approximately a 4× reduction in power consumption, presenting an efficient and resilient solution for imaging in extreme environments. Diverging from traditional IR detectors limited in performance at high temperatures, these detectors rely on the temperature coefficient of elasticity (TCE), offering a wide dynamic range of operational temperatures.Finally, this paper includes recent results measured at 500°C, demonstrating the instrument's capability to operate effectively in Venus's challenging conditions. These advancements pave the way for future planetary exploration missions, promising a deeper understanding of Venus's geological and atmospheric processes.

Efficient adversarial attacks detection for deep reinforcement learning-based autonomous planetary landing GNC

Given the constraints of remote communication and the unpredictability of the environment, autonomous planetary landing mechanisms are expected to achieve the high criteria of autonomy and provide optimal trajectory in future space exploration missions. As the results, applying Deep Reinforcement Learning (DRL) techniques into autonomous landing has produced encouraging findings. Due to the black-box nature of deep learning algorithms, one of the main concerns regarding the robustness of DRL is its vulnerability to adversarial attacks. This constraint prevents the transfer of DRL-based autonomous landing schemes from simulation to real-world applications. In this article, we explore how the DRL-based autonomous landing will be impacted by adversarial attacks and how to protect the system effectively and efficiently. To achieve this, a Long Short Term Memory (LSTM) based adversarial attack detector is been proposed. The proposed method adopts the explainability measurement of the target DRL scheme and flag the detection of adversarial attacks when acting. The proposed method is built and tested on 3D digital terrain model of Candidate Landing Site for 2020 Mission in Jezero Crater to simulate the landing scenario on the Mars. The experimental results demonstrate the proposed methodology can effectively detect adversarial attacks when acting on DRL agent with a high confidence in detection accuracy.

Joint analysis of JUICE and Europa Clipper tracking data to study the Jovian system ephemerides and dissipative parameters

Context. Jupiter and its moons form a complex dynamical system that includes several coupling dynamics at different frequencies. In particular the Laplace resonance is fundamental to maintaining the energy dissipation that sustain Io’s volcanic activity and Europa’s subsurface ocean; studying its stability is thus crucial for characterizing the potential habitability of these moons. The origin and evolution of the Laplace resonance is driven by the strong tidal interactions between Jupiter and its Galilean moons, and the future planetary exploration missions JUICE and Europa Clipper could bring new light to this unsolved mechanism. During the Jupiter tours of both missions and JUICE’s Ganymede orbital phase, two-way radiometric range and Doppler data will be acquired between Earth ground stations and the spacecraft, which will be processed to recover the static and time-varying gravity field of the moons. Moreover, range and Doppler data will improve the orbit accuracy of the moons, providing precise measurements of Jupiter’s tidal parameters. Aims. This work presents a covariance analysis of the joint orbit determination of JUICE and Europa Clipper, aimed at quantifying the expected uncertainties on the main parameters that characterize the dynamics of the Jupiter system. Methods. We simulated radio science data from JUICE and Clipper missions under conservative noise assumptions, using a multi-arc approach to estimate the ephemerides and dissipation in the system. Results. Even though JUICE and Europa Clipper will not perform flybys of Io, the strong coupling with Europa and Ganymede will allow an improvement of our knowledge of the Jupiter-Io dissipation parameters thanks to JUICE and Europa Clipper radiometric data. Moreover, the expected uncertainty in Jupiter’s dissipation at the frequency of Callisto could unveil a potential resonance locking mechanism between Jupiter and Callisto.

Asteroid-NeRF: A deep-learning method for 3D surface reconstruction of asteroids

Context. Asteroids preserve important information about the origin and evolution of the Solar System. Three-dimensional (3D) surface models of asteroids are essential for exploration missions and scientific research. Regular methods for 3D surface reconstruction of asteroids, such as stereo-photogrammetry (SPG), usually struggle to reconstruct textureless areas and can only generate sparse surface models. Stereo-photoclinometry (SPC) can reconstruct pixel-wise topographic details but its performance depends on the availability of images obtained under different illumination conditions and suffers from uncertainties related to surface reflectance and albedo. Aims. This paper presents Asteroid-NeRF, a novel deep-learning method for 3D surface reconstruction of asteroids that is based on the state-of-the-art neural radiance field (NeRF) method. Methods. Asteroid-NeRF uses a signed distance field (SDF) to reconstruct a 3D surface model from multi-view posed images of an asteroid. In addition, Asteroid-NeRF incorporates appearance embedding to adapt to different illumination conditions and to maintain the geometric consistency of a reconstructed surface, allowing it to deal with the different solar angles and exposure conditions commonly seen in asteroid images. Moreover, Asteroid-NeRF incorporates multi-view photometric consistency to constrain the SDF, enabling optimised reconstruction. Results. Experimental evaluations using actual images of asteroids Itokawa and Bennu demonstrate the promising performance of Asteroid-NeRF, complementing traditional methods such as SPG and SPC. Furthermore, due to the global consistency and pixel-wise training of Asteroid-NeRF, it produces highly detailed surface reconstructions. Asteroid-NeRF offers a new and effective solution for high-resolution 3D surface reconstruction of asteroids that will aid future exploratory missions and scientific research on asteroids.

Polymer transfer film formation from cryogenic to elevated temperatures

This study reports on the tribological performance of aromatic thermosetting co-polyester (ATSP) and polyether ether ketone (PEEK)-based polymer composite coatings mixed with PTFE filler. The coatings were tested across a wide temperature range from −180 to 110 °C to simulate the environmental temperatures on Titan, Moon, and Mars, which are of particular interest for NASA’s future exploratory missions. An experimental setup was developed to conduct the pin-on-disk experiments under dry sliding conditions and extreme temperature and contact pressure. Transfer film formation and its characteristics were found to play significant roles in the tribological performance, and the characteristics of the film were temperature-dependent. The XPS and SEM analysis indicated the increase of the PTFE content in the transfer film as the temperature decreased to cryogenic conditions. The coefficient of friction did not follow a linear trend with temperature and was minimum at 110 °C and maximum at −180 °C. ATSP coating showed superior performance with lower friction and unmeasurable wear at all temperatures, whereas PEEK coating exhibited maximum wear at 25 °C followed by −180, and 110 °C.

Optimality principles in spacecraft neural guidance and control.

This Review discusses the main results obtained in training end-to-end neural architectures for guidance and control of interplanetary transfers, planetary landings, and close-proximity operations, highlighting the successful learning of optimality principles by the underlying neural models. Spacecraft and drones aimed at exploring our solar system are designed to operate in conditions where the smart use of onboard resources is vital to the success or failure of the mission. Sensorimotor actions are thus often derived from high-level, quantifiable, optimality principles assigned to each task, using consolidated tools in optimal control theory. The planned actions are derived on the ground and transferred on board, where controllers have the task of tracking the uploaded guidance profile. Here, we review recent trends based on the use of end-to-end networks, called guidance and control networks (G&CNets), which allow spacecraft to depart from such an architecture and to embrace the onboard computation of optimal actions. In this way, the sensor information is transformed in real time into optimal plans, thus increasing mission autonomy and robustness. We then analyze drone racing as an ideal gym environment to test these architectures on real robotic platforms and thus increase confidence in their use in future space exploration missions. Drone racing not only shares with spacecraft missions both limited onboard computational capabilities and similar control structures induced from the optimality principle sought but also entails different levels of uncertainties and unmodeled effects and a very different dynamical timescale.