Monte Carlo simulation (MCS) has been widely applied in the preflight evaluation of flight systems because of advantages such as its ability to evaluate nonlinear systems with uncertain parameters, which are incorporated into MCS randomly and simultaneously. Some aerodynamic and control derivatives can have significant effects on flight control and vehicle performance, so it is important to evaluate the influences of their uncertainties. However, it has not been easy to incorporate uncertainties of derivatives into MCS appropriately. A derivative is the slope of a curve, such as the Cm–α curve. To randomly vary it for use in MCS, the rotation point on the curve must be determined. However, the deviation from the nominal curve becomes greater as the flight condition, such as α, moves further from the rotation point, which can result in excessive variance of the aerodynamic coefficient. This paper presents a new method to generate derivative and bias uncertainties randomly using a covariance matrix of uncertain parameters. The method is applied to the MCS of an existing experimental flight system, and the MCS results are compared with a result that excludes derivative uncertainties to show how to apply the presented method.
This paper reports the development of a 10 Ah lithium-ion pouch battery cell using stainless-steel laminated film as the casing material for JAXA’s SLIM lunar lander. By selecting the pouch format, the mass ratio of the case and electrode terminals is significantly reduced, which is superior to conventional space batteries using prismatic metal cases. A high specific energy of approximately 130 Wh/kg was achieved. In addition, unlike standard batteries using aluminum-laminated film, the battery developed during this study deforms little when subjected to a vacuum. It can thus be mounted on a spacecraft with a simple, lightweight bracket, contributing to higher specific energy as a module. This paper reports the results of environment tests for the SLIM mission and the basic electrical characteristics of the battery.
Double-gimbal variable-speed control momentum gyroscopes (DGVSCMGs) have been attracting attention as actuators for satellite attitude control. The DGVSCMG has the advantage in that it can provide three-axis torque using a single unit, and various control methods have been actively investigated. However, previous studies only evaluated control performance via numerical simulations. The authors experimentally evaluate the control performance of the proposed DGVSCMG for practical verification. An experimental DGVSCMG machine was fabricated and three-axis attitude control in the gravity environment of an indoor experiment was achieved. The results are compared with numerical simulation results to confirm the validity of the proposed dynamics model and control system.
Project Irazú was an innovative space mission that aimed to propel the advancement of the aerospace sector in Costa Rica, by developing a ground to space communication solution for daily monitoring of carbon fixation in forests and tree plantations. Irazú is Central America’s first satellite mission and is a joint endeavor between the Central American Association of Aeronautics and Space and the Costa Rica Institute of Technology, along with national and international partners. The 1U CubeSat developed in this project was deployed from the International Space Station on May 2018, commencing straightaway operations. The scientific mission demonstrated a practical novel solution to monitor daily tree growth by using wireless electronic sensors and a store and forward satellite link. This article presents an overview of the project, along with the mission architecture, summary of the Assembly, Integration and Testing (AI&T) and operations phases, and results from the scientific mission, including the sensor’s performance and measurements of the daily estimated tree diameter during six months. The impacts that the project had on an emerging space nation such as Costa Rica is included as well.
A passively adaptive variable rotor diameter is proposed to improve the flight performance of variable-speed rotors. A validated helicopter model to predict rotor performance is utilized. The analyses focus on three typical flight states (i.e., hover, cruise, high speed) to explore the potential of the passively adaptive variable rotor diameter in reducing rotor power. During hover, the variable rotor diameter can optimize the distribution of lift and then reduce the rotor power, especially at lower rotor speeds. At a cruise speed of 150 km/h, the variable rotor diameter can delay stalling and reduce the rotor power, especially at lower rotor speeds. At a high speed of 300 km/h, the rotor speed needs to be increased, and the reduced rotor diameter is beneficial reducing power. The reduced power comes from decreasing the parasitic power of the fuselage due to decreasing its longitudinal tilt, and the rotor profile power and induced power increase with relatively small magnitudes. The passively adaptive variable rotor diameter is more suitable for larger take-off weights, and can effectively delay stalling at lower rotor speeds. The strategy of varying the rotor diameter can be designed according to the performance improvement requirements.
The Jovian moons have been visited by several flyby missions and are attracting more attention for long-term observation. However, because of Jupiter’s gravitational perturbations and the J2 and C2,2 terms of the Jovian moons, orbits around these moons are unstable, especially those orbits with high inclinations. This study considers a scenario in which the spacecraft flies at a high altitude equipped with a payload having a small field-of-view angle. The coverage rate is achieved by numerical integration, and the largest coverage rate can be found using the particle swarm optimization method. The results highlight the possibility of obtaining a greater coverage rate, as well as considerable imaging resolution and mission duration by choosing suitable candidate orbits. A station-keeping algorithm is introduced to produce a more accurate estimation of gravitational models that is indexed using the station-keeping cost and estimation accuracy. Based on the five aspects mentioned above, a systematic evaluation of candidate orbits was created for orbit design.
At present, Global Navigation Satellite System (GNSS) satellites operate in medium Earth orbits (MEOs), geostationary orbits (GEOs), or inclined geosynchronous orbits (IGSOs). The QZSS consists of GEO and IGSO satellites. When we considering the QZSS skyplot in Japan and its surrounding areas, there are no satellites in the northern sky. This results in a geometric placement imbalance, and thereby, causes position errors. The fundamental method to solve this problem is to position a satellite in the vacant northern area. Therefore, in this research, the addition of navigation satellites with a high-inclination, high-eccentricity orbit (a new type of orbit) is proposed. The vacant northern area can be filled effectively by adding a satellite using this orbit. Three satellites with this orbit were added to the QZSS in a simulation. Thereby, satellites were positioned effectively in the vacant northern area of the skyplot for Tokyo and Seoul. In addition, the improvement in performance was verified quantitatively through Horizontal Dilution of Precision (HDOP) and Vertical Dilution of Precision (VDOP). Accordingly, the addition of a satellite with a high-inclination, high-eccentricity orbit to the QZSS would enable more accurate positioning in Japan and its surrounding areas.