Cislunar stations in near-rectilinear halo orbit (NRHO), like the Lunar Gateway, once a part of NASA’s Artemis program architecture, pose a unique challenge for rendezvous and proximity operations. The dynamics of this orbit vary greatly over each revolution, and currently developed strategies limit approaches to a region centered on the orbit’s apolune. This work proposes an approach strategy for operators to reference as they navigate their visiting vehicle from outside Gateway’s rendezvous sphere to just outside its keep-out sphere. The strategy is composed of sets of nominal and contingent strategies predicated on Gateway’s positioning within the NRHO. The proposed strategies are prescribed for all dynamic regions of the NRHO, enabling approaches in time-critical scenarios where operators cannot wait for a particular Gateway orbital alignment. Approach trajectories, developed in a circular restricted three-body problem (CR3BP) model, are designed to maintain visiting vehicle safety in accordance with proposed flight rules while ensuring that selected trajectories are [Formula: see text] efficient. A graphical reference for the complete strategy is presented alongside nominal and off-nominal approach scenarios, demonstrating how the strategy could be executed in a real mission.
Accurate onboard navigation is fundamental to spacecraft autonomy, especially in deep-space and cislunar environments where ground-based orbit estimation may introduce unacceptable latency. Optical navigation (OpNav) offers a viable solution, but conventional geometric methods typically require high-resolution imagery and substantial computational resources, limiting their applicability under challenging visual conditions and onboard hardware constraints. This paper presents a reinforcement learning (RL) framework for autonomous optical navigation in cislunar space. A convolutional neural network is trained to correct the position estimates by processing differences between simulated and observed lunar images. Training is performed in a simulated visual environment, enabling the policy to learn robust estimation strategies under observation noise, unmodeled dynamics, and varied initial conditions. The method is demonstrated for station-keeping along a southern halo orbit around the Earth-moon L2 point. Results show that the RL-based navigation policy consistently provides position estimates within the required accuracy for the closed-loop onboard controller to successfully maintain the spacecraft along the reference orbit, despite low-quality image inputs and a low update frequency. These findings underline the feasibility of RL-driven OpNav as a computationally efficient and resilient alternative to traditional techniques, offering a promising foundation for future onboard learning-based navigation systems in the vicinity of planetary bodies.
Earth's orbital environment is becoming increasingly populated with large satellite constellations operated by a diverse range of stakeholders. Opportunities for interconstellation cooperation increase as more satellites enter orbit. It is shown that smaller constellations benefit greatly from cooperation with larger constellations, while larger constellations experience diminishing, but non-negligible, returns from this cooperation as the overall network size increases. These improvements accumulate as the number of cooperators increases, thereby incentivizing cooperation from large constellations and encouraging them to foster growth in small constellations, revealing a potential foundation for a new operational model for large constellation operators. Delay-tolerant networking protocols are applied to demonstrate the value of cooperation between constellations of varying sizes. The paper explores and quantifies the changes in data delivery times, network hop count, and traffic capacity when satellite constellations cooperate using intersatellite communication links. To generate the contact plans for large cooperating constellations, an abstraction of the orbital environment, called Matryoshka orbital networks (MatrON), is applied that consolidates multiple constellations into a single, heterogeneous system of systems. MatrON is shown to consume less CPU time and less RAM than an SGP4 propagation routine on the same platform and produces a solution with a variance of <8%.
Recent growth in space activities has led to increased interest in space mobility services in the form of refueling and repositioning. Despite this interest, limited analysis has been conducted to quantify the value and impact of these services. Currently, the consideration and selection of space servicing options rely heavily on qualitative heuristics and subject-matter-expert judgment. To address this lack of quantitatively supported decision-making, this paper provides a comparative analysis of Earth-imaging satellite designs across various lifetime scenarios of use. Using a combination of epoch-era analysis, multi-attribute tradespace exploration, and technology data provided from a quantified state of technology progression analysis, the value of including or omitting compatibility with services in the form of on-orbit refueling and repositioning (OORR) for Earth-imaging satellite owner-operators is determined. Results from this analysis show that refueling and repositioning services can offer unique and tailorable advantages to stakeholders if used in the right circumstances. The demands and relationships of client satellite parameters, the environment in which the system is used, and the stakeholders who dictate the necessary performance of a system were found to directly influence the benefit or detriment of designing for compatibility with and using OORR during a system’s lifetime.
The Boundary Layer Transition 1B (BOLT-1B) flight experiment successfully obtained detailed measurements of hypersonic boundary-layer transition and turbulent heating on a sounding rocket vehicle at Mach 7.2. The experimental forebody was instrumented with pressure transducers intended to aid in the estimation of the angle of attack; however, the pressure measurements suffered from drift during the flight. Using reasonable assumptions about the vehicle motion based on complementary sensor data, a method was devised to filter the pressure data, remove the drift, and correlate oscillatory components with computational predictions to estimate angle of attack. The resulting pressure-derived angle of attack and sideslip angles compared favorably to conventional vehicle attitude solutions, but with improved agreement to measured heating data on the experimental forebody. This paper will describe the methodology, estimated angles, assumptions, and uncertainties inherent to the method.
The Space Weather Investigation Frontier mission aims to reveal whether local or global processes drive mesoscale heliospheric structures that can affect the solar wind-magnetosphere coupling. To achieve this, a sailcraft, equipped with fields and plasma instrument suites, will be placed at at sun–Earth sub-Lagrange point [Formula: see text] to monitor Earth-bound solar wind. One possible challenge with solar sails is spacecraft charging due to the large collection area of the sail relative to the sailcraft chassis, which can interrupt instrument operation, introduce noise to scientific measurements, or potentially damage subsystems. Using Nascap-2k, simulations were performed to investigate the interactions between solar sails and the solar wind over a range of solar wind conditions and the tilt angle between the sail and sun. The electric potential of the sailcraft with respect to the plasma and sheath structure surrounding the sailcraft were determined under the various solar wind conditions. It was found that the potential relative to the solar wind is smaller than 10 V under all ambient space conditions when the solar sails were electrically connected to the sailcraft bus. This meets the requirements not only to detect superthermal electrons and energetic ions but also to detect core electron and ion populations.
The Boundary Layer Transition (BOLT) series of flight experiments was designed to study hypersonic boundary-layer transition and turbulence on a geometry with low-curvature concave surfaces and highly swept leading edges. A refly of the BOLT-1A flight experiment, named BOLT-1B, was designed, fabricated, and tested in preparation for flight from And & oslash;ya Space in Norway. BOLT-1B was successfully launched on 2 September 2024 at 0941 hrs Coordinated Universal Time. A comprehensive CFD++ database was generated to calculate aerothermal heating on the BOLT-1B payload. A finite element analysis model was developed to analyze the thermomechanical response of the payload during the hypersonic flight experiment. Thermal contact resistance across the payload nosetip joints was analyzed and validated against thermocouple data. The step heights across the joints resulting from differential thermal expansion during the flight were estimated. The analysis indicates that the steps on the primary experiment side on the BOLT-1B flight geometry remained rear-facing during the flight, which was desired to minimize roughness effects. The roughness effects with intended greater step heights on the secondary side were successfully achieved. A delayed step-height response following time-dependent aerothermal heating was observed. The analysis in this paper provides a reasonable estimate of joint step magnitudes during the BOLT-1B flight.
A full-scale model of the BOLT-1B flight experiment geometry was tested in The University of Queensland's X3/R Stalker Tube. Existing and new flow conditions for X3/R using the Mach 7b nozzle were used and developed to provide flight-equivalent flows at 10 points on the trajectory of the BOLT-1B flight at altitudes between 23 and 33 km. The freestream unit Reynolds numbers ranged between 1.81 and 7.15 million/m. Steady flow test times, after flow establishment, varied from 2.3 to 4.8 ms. Heat flux and surface static pressure measurements were made at locations matching those on the flight vehicle on the primary experimental surface. Laminar, transitional, and turbulent boundary layers were observed evolving as the freestream Reynolds number increased. The shape of the transition front across the model was similar to that in flight, but transition Reynolds numbers were much lower in the tunnel. This is attributed to higher freestream turbulence levels in the shock tunnel than in flight.
The recent BOLT-1B flight experiment collected a high-quality dataset of surface pressure and heating measurements that capture the onset of boundary-layer transition under hypersonic flight conditions. Consistent with earlier BOLT-2 observations, the data show a marked rise in surface heating, accompanied in this case by distinct spectral peaks in pressure data near the centerline and midspan regions at slightly higher Reynolds numbers. These features suggest the presence of significant instability mechanisms that precede transition and motivate the present computational investigation. This study analyzes the BOLT-1B transition process using a combination of high-fidelity baseflow solutions, stochastically forced direct numerical simulation (DNS), and plane-marching parabolized stability equation (PPSE) analysis. The forced DNS is employed to model receptivity and nonlinear disturbance amplification within the boundary layer, supported by a modal analysis of the resulting transition process. Complementary PSE calculations provide linear growth predictions for comparison with the DNS and to establish a baseline consistent with linear stability theory. Together, these methods yield a comprehensive interpretation of the instability mechanisms that likely govern transition on BOLT-1B and provide a validated reference framework for future transition modeling efforts under realistic hypersonic flight environments.
The growing number of space debris in low Earth orbit (LEO) jeopardizes long-term orbital sustainability, requiring efficient risk assessment for active debris removal (ADR) missions. This study presents the development and validation of Filtered Modified MITRI (FMM), an enhanced risk index that ranks debris, incorporating a proactive fictitious collision model and a dynamic background density within a concurrent analysis framework. Using the MIT Monte Carlo Orbital Capacity Assessment Tool (MOCAT-MC) simulation framework, we performed a comprehensive performance evaluation and sensitivity analysis to probe the robustness of the FMM formulation. The results show that, while FMM provides superior identification of high-risk targets, with a near-perfect identification rate for objects with a high statistical probability of collision, there is a critical performance tradeoff: the event-based MITRI index, despite the lower predictive accuracy, consistently proved more effective in reducing the long-term debris population. This finding reveals a divergence between accurately predicting individual collisions and effectively mitigating long-term environmental instability. The analysis also reveals that physically grounded mass terms are necessary for a feasible risk assessment. By leveraging the open-source MOCAT-MC framework and offering a validated methodology that provides critical insights into risk dynamics, this research enhances our ability to select optimal ADR targets and ensure the long-term viability of LEO operations.
Environmental uncertainty makes atmospheric passages challenging and poses risks to flight safety and mission success during planetary aerobraking. To enhance aerobraking predictor-corrector guidance under uncertainty, this paper proposes a strategy based on reachability and controllability. The reachable union set and a controllable intersection set under uncertainty are developed and integrated into the prediction and correction phases, respectively. The reachable set improves the estimation of the periapsis state distribution, supporting reliable maneuver decisions at apoapsis, while the controllable set is used to determine feasible commands so that the corrected periapsis state meets corridor constraints. For computational efficiency, several propositions are proposed and then used to transform the complex set calculations for the reachable and controllable sets into the determination of bounds for the periapsis heat flux and aerobraking maneuver sets. Simulation results show that the method enables proper decisions and effective corrections under uncertainty, improving the safety and efficiency of aerobraking.
The electrodynamic tether sling, a spinning tether with electrodynamic thrust, is described and has the ability to catapult spacecraft onto a variety of trajectories without the need for propellant. The electrodynamic force is used to recover the transferred momentum, change the orbit of the tether, and, because of its asymmetric design, alter the spin rate of the tether. A simple bang-bang current control scheme is developed for the spin-up maneuver, and an elliptical spiral current control scheme is developed to increase the energy of the orbit of the tether while maintaining the perigee close to the high-magnetic-field region near Earth. The equations of motion governing the system are derived and used to demonstrate the effectiveness of the two control schemes. An integral motion of the planar attitude dynamics within magnetic equatorial orbits is obtained, which aids in comprehending the dynamic structure of the attitude motion of the electrodynamic tether sling under the influence of gravitational and electrodynamic torques.
Prediction of the hypersonic inlet unsteady flowfield is crucial for preventing inlet unstart. By combining an autoencoder (AE) for dimensionality reduction with radial basis function (RBF) methods and long short-term memory (LSTM) networks, models for predicting the hypersonic inlet unsteady flowfield were constructed. This study compared the interpolation and extrapolation performance of these models, including several AE-RBF variants with different RBF types and shape parameters, as well as the AE-LSTM model. The results show that within the sample space, the cubic RBF method can accurately predict the unsteady flowfield, but it fails rapidly outside the sample space. The Gaussian RBF yields relatively stable prediction errors with negligible influence from the shape parameter, achieving an extrapolation prediction error of 5.7% at 70 ms after backpressure was applied. The extrapolation error of the multiquadric RBF increases with time, and a larger shape parameter leads to a greater error. Although the extrapolation error of the AE-LSTM method also rises slowly with time, it remains as low as approximately 2.01% at 70 ms post-backpressure. This study reveals that the Gaussian AE-RBF method and the AE-LSTM method have good potential for predicting the unsteady flowfield of the hypersonic inlet.
Conical cold gas thrusters are characterized for a contactless method to detumble space debris using plume impingement. Vacuum chamber experiments and matching simulations using Computational Fluid Dynamics (for continuum flow within the nozzle) and Direct Simulation Monte Carlo (for rarefied flow inside the vacuum chamber) are performed to infer scaling laws of imparted force on a 10 & times;10 cm flat plate target as a function of plenum pressure, and the target's axial and vertical displacement. The increase in vacuum chamber back pressure over time results in plume narrowing and an associated rise in pressure force experienced by the target. The simulations capture the rise and fall of the pressure force on the target in comparison with the experimental results, with the peak force discrepancy recorded to be less than 15% in the majority of cases, validating the reliability of the simulation tools for predicting plume impingement forces at related conditions and larger offset distances in a spacelike environment. The validated simulation tool highlights the challenges and constraints associated with the ground-based testing of orbital plume impingement.
