This paper proposes a new strategy to design low-thrust trajectories using a shape-based method and an alternating rotational coordinate system. The shape-based method is a well-known strategy for designing spiral trajectories. In this method, a shape of the trajectory is first given and thrust profiles are then derived so that the equations of motion are satisfied. The alternating rotational coordinate system introduced in this paper is a rotational coordinate system in which the angular velocity varies depending on the position of the spacecraft. The advantage of this coordinate system is that spiral trajectories can be described with a simple shape. By combining these two tools, the given shape in the shape-based method becomes simple. In this paper, Sun-Earth L2 to Sun-Mars L1 transfer trajectories are designed as a demonstration of this strategy.

View full abstract

We have conducted three-dimensional particle-in-cell simulations with Monte Carlo collisions method (PIC/MCC) to investigate the discharge characteristics of water for a microwave-discharge ion thruster, which can replace a high-pressure gas storage system. In the calculation model, three ion species (H₂O⁺, OH⁺, and H⁺) are taken into account. The PIC/MCC results indicate that the electron density, the potential, and the electron temperature are the highest near the ECR region, and in order to obtain a similar electron density, high absorbed power is required compared to the results using xenon as the propellant. For the ion composition ratio of the water discharges, H₂O⁺ and OH⁺ dominate over H⁺ and occupy more than 97%. However, about 10% of the ion current density is derived from H⁺ because of its lightweight and the effect of hydrogen ions would not be negligible for ion beam extraction.

View full abstract

In gas turbines, inverse diffusion flames form when film-cooling air reacts with fuel-rich packets from the combustor. Investigations have focused on the quantitative radiation heat transfer in oxygen-enriched inverse diffusion flames (IDFs) since it plays an important role not only in fundamental combustion research, but also in much research on industry combustion, such as gas-turbine engines. To investigate the quantitative radiation properties of oxygen-enriched IDFs, a mid-infrared thermal camera coupled with two different band-pass filters was selected to acquire the thermal radiation intensity of carbon dioxide and soot. The oxygen mole fraction in the oxidizer was varied from 21% to 100% using a co-flowing inverse flame burner to produce steady flames. The radiation intensities from carbon dioxide are approximately 15 to 20 times stronger than those from soot with different oxygen enrichment in IDFs. Both radiation from carbon dioxide and soot increased as the oxygen index of the oxidizer was increased, and the increase in radiation from carbon dioxide was more drastic than that from soot when the oxidizer was more enriched. However, the growth rate of the maximum radiation emission from carbon dioxide along the flame centerline decreased when the oxygen index of the oxidizer exceeded 80%. Furthermore, a second peak appeared along the flame centerline in the radiation curves from soot when the oxygen index of the oxidizer exceeded 40%. The axial position of the second peak was closer to the burner exit than that of the first peak. Moreover, the values of the second peak presented a steeper growth rate than the first one with greater oxygen enrichment.

View full abstract

As more GPS receivers are used in navigation systems to obtain precise position information, concerns about GPS jamming vulnerability are growing. The most effective way to overcome this jamming weakness is to use an array antenna that consists of many antenna elements and RF channels. However, an array antenna causes two side effects: a nulling pattern and a time delay error in positioning performance. We analyze the effects on the positioning accuracy of a GPS receiver equipped with a precise time-delay-compensated array antenna to overcome jamming situations. We present an analysis of the theoretical gain pattern of a 4-array antenna and experimental verification of GPS signal attenuation by obtaining a satellite's CN₀ value in the near jamming direction. We show the results of the time delay measurement in the array antenna system using two independent methods and present a new baseband linear interpolation algorithm that is evaluated as having a 0.95 ns RMS error after compensating for the invariant RF time delays. Finally, using the realistic gain pattern and time-delay-compensation results, we assess the position error of the GPS receiver and show the possibility of attaining a precise navigation system in jamming environments.

View full abstract