Conventional solid-propellant thrusters do not require tanks or valves and, accordingly, have high reliability and simple structures. Nevertheless, thrusters have not been applied to the attitude or station control of satellites because of problems with throttling. We therefore propose a new combustion-controllable, solid propellant microthruster using laser heating. The proposed thruster uses combustion-controllable, hydroxyl-terminated polybutadiene/ammonium perchlorate solid propellant where combustion is maintained only while the burning surface is heated with a laser. Therefore, combustion is started and stopped by switching the laser heating. In a previous study, laser-switching was used to start and stop thrust production. Stable thrusts and combustion chamber pressures with a thrust and specific impulse Isp of 0.02 N and 95 s, respectively, were obtained. However, firing tests showed an ignition delay of approximately 3 s. In this study, to shorten the ignition delay, the diameter of carbon black (C) used to absorb the laser beam was reduced from 50 to 20 μm. Thrust measurements showed that a ϕ20-μm C was comparable to a ϕ50-μm C in terms of the maximum Isp, and reduced ignition delay. Using a ϕ20-μm C produces a shorter ignition delay and 120-s-class Isp by adjusting the laser-head traverse velocity.
An experimental investigation on fuel and air mixing characteristics within a dual-mode combustor is presented. To determine the dominant parameters of mixing characteristics of fuel with airflow, fuel (H2 or C2H4) or inert gas (He, N2 or Ar) were perpendicularity injected from plural circular orifices into high- or room-temperature M2.5 airflows decelerated through pseudo-shockwave systems. Under similar dynamic pressure ratios, fuel mass flux contours downstream of the injector were similar between the H2 and C2H4 reacting cases. However, fuel mass flux contours were different between the C2H4 reacting and Ar non-reacting cases due to the heat-release effect during local mixing. On the other hand, heat-release effect on mixing efficiency was found to be minor in bulk-scale mixing evaluation. It was found that C2H4 mixing efficiency with an equivalence ratio of 1.6 could be predicted within an error of a few percent from Ar mixing results under similar dynamic pressure ratio and similar peak pressure.
This paper describes a new algorithm to determine the attitude of micro-/nano-satellites using an Earth sensor. For recent micro-/nano-satellites, the requirements for attitude determination accuracy are becoming more stringent, despite its limited volume. Since Earth sensors have the advantage of smaller size, some studies have presented using them as attitude sensors; however, they could not achieve fully automatic processing in real-time. Therefore, we have developed an algorithm that effectively combines geometrical consideration and image recognition technology, thus realizing high autonomy, robustness, and real-time processing. The validity of this algorithm is confirmed through ground experiments. The algorithm operates at a rate of 0.2 Hz and achieves an accuracy of 0.1–1 deg, which is similar to the accuracy of a coarse sun sensor. Furthermore, it is capable of determining the three-axis attitude using only an Earth sensor and a GNSS receiver for position information. This study proves that the bus equipment required for attitude determination systems in micro-/nano-satellites can be reduced, thereby contributing to increased design freedom.
Due to their suitable characteristics for throttleable rocket engines, interest in pintle injectors has been recently renewed. Many studies have focused on the correlation between spraying conditions and spray or combustion characteristics for pintle injector. However, there is no previous study on the correlation between spray and combustion characteristics due to the difficulties in controlling each spray characteristic individually. This research presents a solution to this problem. For the control group, a 400 N gas-liquid pintle injector for liquid oxygen and gas methane is designed and its spray characteristics are measured through cold-flow tests. In sequence, a `reverse injection' idea and its design are proposed to increase spray angle while maintaining the droplet size, which is represented by the Sauter mean diameter. In addition, in the design proposed, the reverse injection effect is intensified as the throttling level increases, decreasing the difference of spray angle between throttling levels. In a cold-flow test, air and water were used under an atmospheric condition for gas-liquid flow simulant. The spray angle and droplet size were measured using the shadow method. The `reverse injection' feature proposed functioned properly, increasing the spray angle of the injector while maintaining the droplet size.
Earth remote sensing from geostationary orbit (GEO) can realize high temporal resolution; however, the spatial resolution is commonly worse than observation from low Earth orbit. In order to achieve high-frequency and high-resolution GEO remote sensing, a “Formation Flying Synthetic Aperture Telescope (FFSAT)” with multiple micro-satellites has been proposed. The FFSAT greatly improves the spatial resolution using a synthetic aperture technique. Therefore the relative positions and attitudes between the optical units of each satellite must be controlled with an accuracy better than 1/10 of the observation wavelength. However, even mm-class accuracy control has not been demonstrated on orbit. As a first practical application of the FFSAT, a forest fire monitoring mission using infrared rays is being considered, in which control accuracy requirement is relaxed as its wavelength is longer than visible light. We proposed a point spread function optimization method for controlling formation flying with an accuracy of approximately 1–1,000 times the wavelength (1 µm–1 mm) in the absence of sensors, which can measure absolute distance with µm-accuracy. The effectiveness of the method was demonstrated through simulations in which the satellites’ system and the optical system are coupled. The simulation results show that the method can control the formation within the wavelength order.
A compound aircraft with a collectible rotor has the ability of vertical take-off and landing (VTOL), high-speed flight and long-range cruising. Compared to systems in other compound aircraft, the collectible rotor can work as a conventional rotor in helicopter mode and can be gathered into a disk in the center in fixed-wing mode, thereby relieving the rotor's limitations pertaining to forward flight performance. The collectible rotor is a key component in the design and realization of a compound aircraft. Based on a 35-kg-level prototype, in this study, the principle of a folding rotor is proposed, a dynamic model of the rotor is established considering the complex nonlinear compound motion of rotation and folding, and the aerodynamic and dynamic characteristics are analyzed considering the coupling of different speeds of the rotor and folding strategies for the folding process. According to the above research, a complete rotor system, including an unconventional rotor structure, closed-loop real-time control system, and high-torque driving system, is designed. A demonstration model was constructed to verify the feasibility of the folding rotor. Finally, through an on-board test, the folding rotor system was verified in a simulated real flight state. This paper provides a theoretical basis for folding rotor design and proposes a set of design methods and research concepts.