Deep Space Gateway Research Articles

Meta-Reinforcement Learning for Spacecraft Proximity Operations Guidance and Control in Cislunar Space

Innovative lightweight and model-free guidance algorithms are essential to achieve full autonomy of spacecraft and address future space exploration challenges. In the near future, this type of technology will be essential for cislunar space proximity operations, such as NASA’s Artemis program and its Lunar Gateway project. In this scenario, a meta-reinforcement learning algorithm is employed to address the real-time optimal guidance problem of a spacecraft in the cislunar environment. Non-Keplerian orbits pose complex dynamics, where classic control theory may be less adaptable and more computationally expensive compared to machine learning approaches. Meta-RL stands out for its ability to learn how to learn through experience, training on various tasks to enhance efficiency, and effectiveness in tackling new ones. By modeling a stochastic optimal control problem within the circular restricted three-body problem framework as a Markov decision process, an LSTM-based network agent is trained using proximal policy optimization, considering operational constraints and stochastic effects for safety and robustness evaluation. Additionally, an MLP-based agent and an optimal control pseudo-spectral solution are assessed for comparison. The resulting tool autonomously guides spacecraft in cislunar proximity operations, approximating the optimal control solution with a versatile algorithmic framework. This ensures both robustness and computational efficiency.

Location-dependent flight cost difference from the lunar surface to an orbital fuel depot and its influence on in situ resource utilisation location selection

Given the increasing relevance of lunar activities, the location selection for in situ resource utilisation (ISRU) facilities is necessary for identifying the most suitable configuration during mission planning. To gather information about the dominant location dependencies, a scenario is established wherein an ISRU product is exported to an orbital depot and its mass costs are used for classification. In the selected scenario, oxygen is produced in an ilmenite reduction plant and subsequently exported to the lunar gateway via an oxygen–hydrogen fuelled launcher operated in a round-trip to refuel oxygen at the lunar surface and hydrogen at the lunar gateway. This showed that the transport cost variations could be avoided entirely or have a recessive influence on the mission’s total costs over an extended period of time, such as 20 years. The identification of the top-10 most optimal locations for various resolutions was altered only slightly upon consideration of flight costs as compared to considering only the ISRU factors; this indicates the insignificance of flight cost dependencies for the analysed case.

Optimization, guidance, and control of low-thrust transfers from the Lunar Gateway to low lunar orbit

The Lunar Gateway will represent a primary space system useful for the Artemis program, Earth–Moon transportation, and deep space exploration. It is expected to serve as a staging location and logistic outpost on the way to the lunar surface. This study focuses on low-thrust transfer dynamics, from the Near-Rectilinear Halo Orbit traveled by Gateway to a specified Low-altitude Lunar Orbit (LLO). More specifically, this research addresses two closely-related problems: (i) determination of the minimum-time low-thrust trajectory and (ii) design, implementation, and testing of a guidance and control architecture, for a space vehicle that travels from Gateway to LLO. Orbit dynamics is described in terms of modified equinoctial elements, with the inclusion of all the relevant perturbations, in the context of a high-fidelity multibody ephemeris model. The minimum-time trajectory from Gateway to a specified lunar orbit is detected through an indirect heuristic approach, which uses the analytical conditions arising in optimal control theory in conjunction with a heuristic technique. However, future missions will pursue a growing level of autonomy, and this circumstance implies the mandatory design and implementation of an efficient feedback guidance scheme, capable of compensating for nonnominal flight conditions. This research proposes nonlinear orbit control as a viable and effective option for autonomous explicit guidance of low-thrust transfers from Gateway to LLO. This approach allows defining a feedback law that enjoys quasi-global stability properties without requiring any offline reference trajectory. The overall spacecraft dynamics is modeled and simulated, including attitude control and actuation. The latter is demanded to an array of reaction wheels, arranged in a pyramidal configuration. Guidance, attitude control, and actuation are implemented in an iterative scheme. Monte Carlo simulations demonstrate that the guidance and control architecture at hand is effective in nonnominal flight conditions, i.e. with random starting point from Gateway as well as in case of temporary unavailability of the propulsion system. The numerical results also point out that only a modest propellant penalty is associated with the use of feedback guidance and control in comparison to the minimum-time optimal trajectory.

Rapid Approximation of Low-Thrust Spacecraft Reachable Sets within Complex Two-Body and Cislunar Dynamics

The reachable set of controlled dynamical systems is the set of all reachable states from an initial condition over a certain time horizon, subject to operational constraints and exogenous disturbances. In astrodynamics, rapid approximation of reachable sets is invaluable for trajectory planning, collision avoidance, and ensuring safe and optimal performance in complex dynamics. Leveraging the connection between minimum-time trajectories and the boundary of reachable sets, we propose a sampling-based method for rapid and efficient approximation of reachable sets for finite- and low-thrust spacecraft. The proposed method combines a minimum-time multi-stage indirect formulation with the celebrated primer vector theory. Reachable sets are generated under two-body and circular restricted three-body (CR3B) dynamics. For the two-body dynamics, reachable sets are generated for (1) the heliocentric phase of a benchmark Earth-to-Mars problem, (2) two scenarios with uncertainties in the initial position and velocity of the spacecraft at the time of departure from Earth, and (3) a scenario with a bounded single impulse at the time of departure from Earth. For the CR3B dynamics, several cislunar applications are considered, including L1 Halo orbit, L2 Halo orbit, and Lunar Gateway 9:2 NRHO. The results indicate that low-thrust spacecraft reachable sets coincide with invariant manifolds existing in multi-body dynamical environments. The proposed method serves as a valuable tool for qualitatively analyzing the evolution of reachable sets under complex dynamics, which would otherwise be either incoherent with existing grid-based reachability approaches or computationally intractable with a complete Hamilton–Jacobi–Bellman method.

Cis-lunar and surface missions: Health risks and potential surgical conditions

The next goal of human space exploration is to return to the Moon to stay, and to establish a new, more advanced space station in lunar orbit: the ‘Lunar Gateway’. The authors aim to contribute to this goal through undertaking an ongoing comprehensive survey of relevant published scientific literature to seek information regarding the risk of medical conditions that might require operative or non-operative surgical solutions during long-duration spaceflight. The intended outcome is to create a roadmap for future mission planning. To date, we have identified more than 50 such potential surgical conditions. Based on disease severity and mission duration, these can be classified into: (Category 1) Time-critical conditions requiring immediate surgery; (Category 2) Urgent surgical conditions requiring minor temporising surgical intervention or conservative care (these patients can return to Earth for definitive treatment); or (Category 3) Non-urgent, as these conditions do not require immediate surgical intervention, and definitive treatment can be delayed. The proposed Lunar Gateway will be an international collaboration. Reaching Gateway is anticipated to take around three days. Gateway will operate in microgravity conditions, and include a communications lab (ground support from Earth is still available with minimal signal delay), a scientific lab, and a habitat for astronauts. Transfers to and from the lunar surface will allow astronauts to undertake extra-vehicular activities (EVA). Habitation on Gateway will present similar physiological and psychological challenges as experienced on the International Space Station (ISS), with the addition of a slightly increased communications lag. The Moon is only within Earth's magnetosphere for approximately 25 % of the time, which will increase space radiation exposure compared to the ISS. Gravitational conditions will range from microgravity on Gateway to ⅙ of the Earth's gravity on the lunar surface. Considering the duration and distance necessary in order to undertake a lunar mission, time-critical surgical interventions (Category 1) will likely be necessary, such as treating a bowel perforation, or fixation for musculoskeletal trauma. For urgent conditions (Category 2), antibiotic treatment of responsive appendicitis, drainage of uncomplicated cholecystitis, or other conservative measures might be acceptable as a temporising measure. If a return to Earth is possible within three days, delayed surgery can be undertaken if the conservative measures are unsuccessful, or the condition recurs. In the case of non-urgent procedures that can be delayed (Category 3), planned evacuation to Earth is expected to be available, for example, if a malignancy develops or is detected. Anticipating the medical and surgical challenges a lunar mission presents, and subsequent adequate planning and preparation for possible surgical emergencies, will help ensure mission success. Creating a system for triaging of surgical cases will be paramount in order to guide appropriate management.

Operational demonstration and experimental characterisation of a central cathode electrostatic thruster equipped with a high temperature superconducting magnet

Interplanetary transport of payloads of unprecedented mass, as envisaged beyond the lunar gateway, will require thrusters with high specific impulse as well as high thrust. To achieve this, innovations in propulsion are critical. Many classes of electric thruster utilise a magnetic applied field module to accelerate charged particles. Magnetoplasmadynamic thrusters exhibit improved performance with increasing field, at least up to the limit of around 0.5 T able to be provided by permanent magnets or copper electromagnets. However, superconducting magnets can generate much stronger magnetic fields. In this study, we utilised a space-relevant cryocooled high temperature superconducting magnet as the applied field module for a central cathode electrostatic thruster (CC-EST). A convex anode enabled ignition at high magnetic fields, and in this configuration the thruster’s performance was characterised in the power range of 1 kW to 2.5 kW and at steady applied fields ranging from 0.6 T to 0.8 T, representing a significant advance in achievable field strength. In combination, these operating parameters enabled the achievement of a magnet-inclusive thruster efficiency of 19%, while the cryocooled magnet was demonstrated to be thermally stable in the presence of the kW-scale plasma, demonstrating the viability of such a design for space flight applications.

Hindlimb unloading, a physiological model of microgravity, modifies the murine bone marrow IgM repertoire in a similar manner as aging but less strongly

BackgroundThe spaceflight environment is an extreme environment that affects the immune system of approximately 50% of astronauts. With planned long-duration missions, such as the deployment of the Lunar Gateway and possible interplanetary missions, it is mandatory to determine how all components of the immune system are affected, which will allow the establishment of countermeasures to preserve astronaut health. However, despite being an important component of the immune system, antibody-mediated humoral immunity has rarely been investigated in the context of the effects of the space environment. It has previously been demonstrated that 30 days aboard the BION-M1 satellite and 21 days of hindlimb unloading (HU), a model classically used to mimic the effects of microgravity, decrease murine B lymphopoiesis. Furthermore, modifications in B lymphopoiesis reported in young mice subjected to 21 days of HU were shown to be similar to those observed in aged mice (18–22 months). Since the primary antibody repertoire composed of IgM is created by V(D) J recombination during B lymphopoiesis, the objective of this study was to assess the degree of similarity between changes in the bone marrow IgM repertoire and in the V(D)J recombination process in 2.5-month-old mice subjected to 21 days of HU and aged (18 months) mice.ResultsWe found that in 21 days, HU induced changes in the IgM repertoire that were approximately 3-fold less than those in aged mice, which is a rapid effect. Bone remodeling and epigenetics likely mediate these changes. Indeed, we previously demonstrated a significant decrease in tibial morphometric parameters from day 6 of HU and a progressive reduction in these parameters until day 21 of HU, and it has been shown that age and microgravity induce epigenetic changes.ConclusionThese data reveal novel immune changes that are akin to advanced aging and underline the importance of studying the effects of spaceflight on antibody-mediated humoral immunity.

A Data-Driven Variance Reduction Technique for Efficiently Modelling Astronaut Radiation Doses in Spacecraft in High-Energy Isotropic Radiation Fields.

The ionizing radiation exposure to crew on current and future space missions can significantly increase their health risks for cancers, degenerative diseases, and other acute and late effects. A common approach for estimating risk to crew is by completing stochastic (e.g., Monte Carlo) or deterministic particle transport simulations. Within the simulated environment, a small fraction of the particle histories tracked will interact with the astronaut or detector, particularly for larger spacecraft such as the International Space Station, Tiangong Space Station or Lunar Gateway. These simulations can be computationally intensive as they require a very large number of particle histories to achieve a low statistical uncertainty. Variance reduction techniques are applied to simulations to reduce the computational time of the simulation while maintaining the same (or less) statistical uncertainty. The variance reduction technique developed herein involves applying a directional source bias to an isotropic radiation field, such as galactic cosmic rays, to reduce the quantity of particles that have a low probability of interacting with the astronaut or detector. A custom application has been developed utilizing the Geant4 Toolkit that computes the trajectories and energies of particles in three dimensions in the International Space Station using the Monte Carlo method. The results demonstrate the impact of our variance reduction technique on effective dose equivalence depending on: primary and secondary particle type (proton, neutron, photon, heavy ion, etc.), geometric volumes and spacecraft materials. Our variance reduction technique can be tuned by the user to optimize the simulation time depending on their objectives and enables rapid testing of different shield configurations and materials. This variance reduction technique is implemented easily using several input parameters for boundary conditions. Recommended values are presented for rapid implementation in simulations.

The road to on-board crew autonomy: Using ISS’ Columbus module as the basis for ground procedure automation

Future human exploration missions require new concepts of operations since the international roadmap foresees stations with uncrewed periods (e.g. Lunar Gateway) and deep space missions with communication delays making real-time monitoring and control impossible (e.g. any vehicle on its way to or in orbit of Mars). As part of the commitment to achieve human presence in lunar orbit and prepare for missions to Mars, the goal for future operations is to become independent from ground and enable crews to live and work autonomously. However, as a first step towards on-board crew autonomy, the ground segment itself needs to be automated and its functions eventually transferred on-board. For this purpose, this paper introduces a novel tool, based on Columbus operations, conducted at the Columbus Control Center (COL-CC), allowing the interaction between scheduled activities and the commanding infrastructure, by automatically generating a command sequence, transferring the command sequence to the operators’ command interface for inspection and approval, and finally sending the commands to the receiver for execution. This tool is implemented as a ground prototype, in order to show how ground operations can be automated and how such a tool can ultimately lead to increased crew autonomy.

Hybrid Optimization of High-Fidelity Low-Thrust Transfers to the Lunar Gateway

Hybrid Optimization of High-Fidelity Low-Thrust Transfers to the Lunar Gateway

Dynamics in the Vicinity of the Stable Halo Orbits

This work presents a study of the dynamics in the vicinity of the stable L2 halo orbits in the Earth-Moon system of the circular restricted three-body problem. These solutions include partially elliptic, partially hyperbolic, and elliptic quasi-halo orbits. The first two types of orbits are 2-dimensional quasi-periodic tori, whereas the elliptic orbits are 3-dimensional quasi-periodic tori. Motivated by the Lunar Gateway, this work computes these orbits to explore the 3-parameter family of solutions lying in the vicinity of the stable halo orbits. An algorithm is presented to quantify the size of the invariant surfaces which gives perspective on the size of the orbits. A stability bifurcation is detected where the partially elliptic tori become partially hyperbolic. A nonlinear behavior of the Jacobi constant is observed which differs from the behavior of the quasi-halo orbits emanating from the unstable halo orbits which makeup the majority of the quasi-halo family. Uses of the orbits in the vicinity of the stable L2 halo orbits are identified, and the results highlight characteristics and structure of the family to broaden the understanding of the dynamical structure of the circular restricted three-body problem.

The ESA Active Dosimeter (EAD) system onboard the International Space Station (ISS)

Ionizing radiation in general and mixed fields of space radiation in particular pose a risk of serious harm to human health. The risk of such adverse effects increases with the duration of the mission, and for all missions outside the protective properties of the Earth’s magnetic field and atmosphere. Accordingly, radiation protection is of central importance for all human spaceflight, which is recognized by all international space agencies. To date various systems, analyze and determine the exposure to ionizing radiation within the environment and to the crew onboard the International Space Station (ISS). In addition to this operational monitoring, experiments and technology demonstrations are carried out. This to further enhance systems capabilities, to prepare for exploratory missions, to the Deep Space Gateway and/or to enable for human presence at other celestial bodies. Subsequently the European Space Agency (ESA) decided early to support the development of an active personal dosimeter. Under the auspices of the European Space Research and Technology Center (ESTEC) together with the European Astronaut Center's (EAC) Medical Operations and Space Medicine (HRE-OM) team, a European industrial consortium was formed to develop, build, and test this system. To complete the ESA Active Dosimeter (EAD) Technology Demonstration in space, EAD components were delivered to ISS with the ESA’s space missions ‘iriss’ and ‘proxima’ in 2015 and 2016. This marked Phase 1 (2015) and 2 (2016–2017) of the EAD Technology Demonstration to which focus is given in this publication. All EAD systems and their functionalities, the different radiation detector, their properties, and calibrations procedures are described. Emphasis is first on the “iriss” mission of September 2015, that provided a complete set of data for an entire space mission from launch to landing, for the first time. Data obtained during Phase 2 in 2016–2017 are discussed thereafter. Measurements with the active radiation detectors of the EAD system provided data of the absorbed dose, dose equivalent, quality factor as well as the various dose contributions during the crossings of the South Atlantic Anomaly (SAA) and/or resulting from galactic cosmic radiation (GCR). Results of the in-flight cross-calibrations among the internal sensors of the EAD systems are discussed and alternative usage of the EAD Mobile Units as area monitors at various different locations inside the ISS is described.

Enabling deep-space experimentations on cyanobacteria by monitoring cell division resumption in dried Chroococcidiopsis sp. 029 with accumulated DNA damage.

Cyanobacteria are gaining considerable interest as a method of supporting the long-term presence of humans on the Moon and settlements on Mars due to their ability to produce oxygen and their potential as bio-factories for space biotechnology/synthetic biology and other applications. Since many unknowns remain in our knowledge to bridge the gap and move cyanobacterial bioprocesses from Earth to space, we investigated cell division resumption on the rehydration of dried Chroococcidiopsis sp. CCMEE 029 accumulated DNA damage while exposed to space vacuum, Mars-like conditions, and Fe-ion radiation. Upon rehydration, the monitoring of the ftsZ gene showed that cell division was arrested until DNA damage was repaired, which took 48 h under laboratory conditions. During the recovery, a progressive DNA repair lasting 48 h of rehydration was revealed by PCR-stop assay. This was followed by overexpression of the ftsZ gene, ranging from 7.5- to 9-fold compared to the non-hydrated samples. Knowing the time required for DNA repair and cell division resumption is mandatory for deep-space experiments that are designed to unravel the effects of reduced/microgravity on this process. It is also necessary to meet mission requirements for dried-sample implementation and real-time monitoring upon recovery. Future experiments as part of the lunar exploration mission Artemis and the lunar gateway station will undoubtedly help to move cyanobacterial bioprocesses beyond low Earth orbit. From an astrobiological perspective, these experiments will further our understanding of microbial responses to deep-space conditions.

Transfer from Lunar Gateway to Sun-Earth Halo Orbits Using Solar Sails

To extend the usability of solar sails in the sun–Earth–moon system, we analyze the transfer trajectories from the 9:2 Earth–moon near-rectilinear halo orbit (NRHO) to halo orbits around the sun–Earth L1 and L2 points under the assumption of a future mission for a solar sail spacecraft equipped with a solar electric propulsion (SEP) system deployed from the Lunar Orbital Platform-Gateway. The dynamics are modeled using the bicircular restricted four-body problem, where the gravitational forces from the sun, Earth, and moon as well as solar radiation pressure (SRP) are considered. We propose a trajectory design method that utilizes both SRP and SEP. The method consists of initial guess generation and optimization steps. The initial guess generation comprises the forward propagation of the escape trajectory from the NRHO, the backward propagation of the stable manifold of the target halo orbits, and their apoapsis patching process. Optimization is conducted to minimize propellant consumption by effectively controlling SRP. We perform optimizations with various parameters, namely, the sail area-to-mass ratio (), specifications of SEP, target sun–Earth halo orbit, and departure direction. The results validate the proposed trajectory design method and verify that solar sail acceleration can reduce the necessary amount of propellant, which indicates that such missions can be realized by small CubeSats.

Geometric Analysis of Sun-Assisted Lunar Transfer Trajectories in the Planar Bicircular Four-Body Model

This research presents a geometric analysis of Sun-assisted low-energy lunar transfers and several convenient tools that enable the systematic trajectory design in the framework of the planar bicircular restricted four-body problem. By analogy with the patched conic approximation approach for high-energy transfers, a Sun-assisted low-energy trajectory is divided into three legs. Two interior legs, departing and arriving, are located inside the Earth–Moon region of prevalence and designed in the Earth–Moon circular restricted three-body problem, whereas the exterior leg lies outside the region of prevalence and is calculated in the Earth–Moon–Sun bicircular restricted four-body model. The whole trajectory is obtained by smoothly patching the three legs on the boundary of the region of prevalence. The arrival conditions are met by targeting a specific point in the L2 lunar gateway. The interior legs are easily adjustable to the four-body dynamics. The database of planar lunar transfer trajectories can be used to select an initial guess for the multiple-shooting procedure of designing a three-dimensional Sun-assisted lunar transfer in high-fidelity dynamical models.

Implementation of Human Systems Integration technical and management process for the lunar Gateway Program

NASA recognizes Human Systems Integration (HSI) as part of the overall systems engineering and acquisition strategy for space systems. The Lunar Gateway Program is implementing HSI technical and management process across the lifecycle of the mission, as required by NPR 7123.1C NASA Systems Engineering Processes and Requirements, and led by the Gateway HSI team as required by NPR 8705.2C Human-Rating Requirements for Space Systems, now HEOMD-003 Crewed Deep Space Systems Human Rating Certification Requirements and Standards for NASA Missions. NASA has been using HSI principles for many years and has applied them to many of its previous human spaceflight Programs. As NASA returns to the Moon in a more sustainable manner, the Gateway Program is maturing the application of HSI by implementing it more visibly as part of Artemis, with guidance from the NASA/SP-20210010952 NASA HSI Handbook. This paper discusses how HSI is being implemented in the Gateway Program, challenges faced with its implementation during the development phase, and strategies/approaches used to overcome those. The paper also covers HSI implementation for flight systems, vehicle processing, and interfaces across the six identified NASA HSI domains: human factors engineering, operations, safety, training, maintainability and supportability, habitability and environment. The goal is to provide an overview of the implementation process of HSI in the Gateway Program as an example for other Programs/Projects/Missions that are looking to implement HSI.

Rendezvous trajectory design of logistics resupply missions to the lunar gateway in near-rectilinear halo orbit

Logistics resupply to the lunar Gateway is one of the candidates for the Japan's contribution to the Artemis program. The Japan Aerospace Exploration Agency (JAXA) is presently developing the HTV-X, a new unmanned spacecraft developed as the successor to the H-II Transfer Vehicle (HTV). The HTV-X will transport supplies to the International Space Station. JAXA is also investigating enhancements to the HTV-X for logistics resupply to the lunar Gateway. A Near-Rectilinear Halo Orbit (NRHO) of the L2 southern family was selected as the Gateway operational orbit. This paper proposes a trajectory design for missions to the Gateway in NRHO. The rendezvous scenario consists of a transfer from the Earth to NRHO, a rendezvous, and proximity operations in NRHO. Monte Carlo simulations are performed in all phases to identify the effects of navigation and control errors. In addition, the simulations evaluate the designed trajectory's fuel consumption, safety, and operational feasibility. This paper also identifies the GN&C requirements for rendezvous in NRHO determined by the study.

Launch parameters of a lunar ice payload traveling via electromagnetic mass accelerator

This paper describes a solution for procuring propellent needed for future space exploration missions based on the Lunar Electromagnetic Mass Accelerator (LEMMA) concept analyzed by McNab and McGlasson. This study examined the feasibility of using an electromagnetic launcher (EML) to transport raw materials used in propellent production from the lunar south pole to the National Aeronautics and Space Administration's (NASA) Lunar Gateway. The proposed Gateway space station, to be located in a lunar near-rectilinear halo orbit (NRHO), is a critical part of NASA's Artemis program. Cheaply and efficiently sourcing lunar hydrogen from surface ice to the Gateway would benefit the program's success and future exploration of the solar system. Our study of the launch requirements for a lunar EML payload are described here. AGI Inc's Systems Tool Kit (STK) was used to calculate the required launch azimuth, elevation, magnitude, epoch, and trip duration for a payload launched from the Moon to rendezvous with Gateway. The study shows that it is feasible to conduct a single launch from the lunar south pole that can intercept any point along the Gateway's orbit with variable launch conditions.

Fully Autonomous Orbit Determination and Synchronization for Satellite Navigation and Communication Systems in Halo Orbits

This paper presents a solution for autonomous orbit determination and time synchronization of spacecraft in Halo orbits around Lagrange points using inter-satellite links. Lagrange points are stable positions in the gravitational field of two large bodies that allow for a sustained presence of a spacecraft in a specific region. However, a challenge in operating at these points is the lack of fixed landmarks for orbit determination. The proposed solution involves using inter-satellite links to perform range and range-rate measurements, allowing for accurate computation of the spacecraft’s orbit parameters without the need for any facilities on Earth. Simulations using a fleet of three satellites in Near Rectilinear Halo Orbits around the Earth–Moon Lagrange point, proposed for the Lunar Gateway stations, were conducted to demonstrate the feasibility of the approach. The results show that inter-satellite links can provide reliable and accurate solutions for orbit determination with a DRMS error lower than one meter (90th percentile) and synchronization errors of around one nanosecond. This solution paves the way for a fully autonomous fleet of spacecraft that can be used for observation, telecommunication, and navigation missions.

Human movement in simulated hypogravity-Bridging the gap between space research and terrestrial rehabilitation.

Human movement is optimized to Earth's gravity and based on highly complex interactions between sensory and neuro-muscular systems. Yet, humans are able to adapt-at least partially-to extreme environments upon and beyond Earth's surface. With upcoming Lunar Gateway and Artemis missions, it is crucial to increase our understanding of the impact of hypogravity-i.e., reduced vertical loading-on physiological and sensory-motor performances to improve countermeasure programs, and define crewmember's readiness to perform mission critical tasks. Several methodologies designed to reduce vertical loading are used to simulate hypogravity on Earth, including body weight support (BWS) devices. Countering gravity and offloading the human body is also used in various rehabilitation scenarios to improve motor recovery in neurological and orthopedic impairments. Thus, BWS-devices have the potential of advancing theory and practice of both space exploration and terrestrial rehabilitation by improving our understanding of physiological and sensory-motor adaptations to reduced vertical loading and sensory input. However, lack of standardization of BWS-related research protocols and reporting hinders the exchange of key findings and new advancements in both areas. The aim of this introduction paper is to review the role of BWS in understanding human movement in simulated hypogravity and the use of BWS in terrestrial rehabilitation, and to identify relevant research areas contributing to the optimization of human spaceflight and terrestrial rehabilitation. One of the main aims of this research topic is to facilitate standardization of hypogravity-related research protocols and outcome reporting, aimed at optimizing knowledge transfer between space research and BWS-related rehabilitation sciences.