Long-haul flights often perform step-climb, where the cruising altitude is increased in steps as fuel is consumed, to increase fuel efficiency. However, in oceanic airspace, which is procedural rather than radar-controlled, intended step-climbs can be blocked by potentially conflicting traffic, sometimes for extended periods of time. Airspace design that facilitates operators to achieve their ideal flight plan trajectories, including step-climb profiles, will increase overall operational efficiency. This paper provides the results of simulation experiments of North Pacific Oceanic airspace, in which operators may plan flexible routes considering winds aloft, with the following two objectives: 1) to establish and validate a framework for the fast-time simulation of flexible route airspaces in which flights perform step-climb operations, and 2) to identify high-demand areas in the target airspace and clarify where the airspace design could be modified to improve flight efficiency and airspace capacity. In the validation, calculated minimum fuel and minimum flight time routes were compared with actual flown trajectories in terms of flight time and lateral and vertical profiles. The calculated minimum fuel routes were closest to the actual trajectories and had sufficient accuracy for the objectives of this paper. In the simulation experiments, potential loss of separation (PLOS) was used to identify high demand areas, and it was found that variation of step-climb locations of flights due to varying departure mass reduces PLOS duration. The identification of high PLOS areas in this study will serve to inform concepts to reduce PLOS and increase step-climb opportunities, such as airspace design to disperse traffic flow.

In the Martian Moons eXploration (MMX) mission aimed at sample return from Phobos, stereo observations at the requested local time are crucial for creating a local shape model of landing site candidates. To optimize the observation scheduling and facilitate as many stereo observations as possible within a limited time, we address the Phobos observation scheduling optimization problem and customize a genetic algorithm previously proposed for Earth observation satellites. Our ingenuity integrates elements related to stereo observations and local time constraints such that they can be applied to observation scheduling for planetary exploration. The scheduling demonstration results illustrate that 38 of the 50 landing site candidates can be observed during stereo viewing. Furthermore, we perform a sensitivity analysis of the number of landing site candidates to be scheduled, which will provide insights for improving the MMX operational planning.

This paper presents an analysis of the formation of an equilateral triangle for a space-based gravitational wave observatory (GWO) near a collinear libration point in the circular-restricted three-body problem. To achieve continuous observation of gravitational waves, stable triangle configurations are required. However, the motion near the collinear libration points is highly unstable. This problem is examined by employing a two-layer design. In an inner-layer loop, the tracking problem is solved by using the output regulation theory to establish equilateral triangle formation in two periods. As for the outer-layer loop, the radius, frequency, and direction angle of the formation are examined. These parameters play a crucial role in establishing a stable and efficient triangle formation configuration for the GWO. Finally, when the radius, frequency and direction angle are changed, the fuel consumption that required to initialize and maintain the desired formation is calculated.

This study addresses a quasi-steady self-field magnetoplasma dynamic (SF-MPD) thruster with water propellant. Water has no toxicity nor reactivity to materials and necessitates no high-pressure tank. Accordingly, using water as a propellant lowers thruster size and the ground-test costs. Moreover, water is abundant on Earth and accessible in space because it may be harvestable in celestial objects such as a regolith on the moon. However, the thrust-to-power ratio of the water MPD thruster was smaller than that of conventional MPD thrusters. Changing the electrode shape is a promising option to improve the thrust-to-power ratio. In this study, a 1-MW class water-propellant MPD thruster was examined to evaluate the relationship between performance and electrode geometry. The ceramic-nozzle anode produced a maximum thrust of 14 N with a corresponding thrust efficiency of 7% and a thrust-to-power ratio of 5 mN/kW at a discharge current of 10 kA. The tubular anode yielded a maximum thrust of 5 N with a corresponding thrust efficiency of 0.8% and a thrust-to-power ratio of 3 mN/kW at a discharge current of 10 kA. The nozzle divergence angle seems to produce gas dynamic thrust, resulting in enhanced total thrust. The difference in discharge path would affect propellant utilization.

Identification of the spatio-temporal structure of plasma turbulence will be key to understanding anomalous electron transport driven by plasma perturbations in Hall thrusters. A radial-axial (r–z) two-dimensional three-velocity fully kinetic particle-in-cell simulation was performed for a 100 W class Hall thruster. The electron transport across the magnetic field was estimated and compared to the fluid-based electron drift-diffusion model. The cross-field electron transport outside the channel was found to be larger than that deduced from the classical diffusion model, and the electron inertia terms were found to play a significant role. That is, the electron transport outside the channel can be explained by the so-called “Reynolds stress” derived from the plasma turbulence. The frequency of the perturbations was observed to be several tens of MHz, and the wave number was found to be several thousand m⁻¹. The perturbation is identified as ion acoustic waves; the dispersion relation agrees well with that of ion acoustic waves, and the Boltzmann relation is satisfied.