This paper proposes a decentralized vibration control method for cable-network structures in space antennas, which are large and so flexible structures and show non-linear behaviors. The main advantage of this method is that it is possible to gain adaptability to changes of models, such as size or depth changes of parabolas that come from diversity of space mission and manufacturing errors. The control method is decentralized direct velocity and displacement feedback (DVDFB). Force Density Method (FDM) is used for structural analysis of cable-network structures. The index “Force Density (FD),” which shows tension condition of each cable, can be used for decision of the placement of sensors and actuators. The results show that, even though non-linear behaviors such as large displacement and slack of cables are occurred, vibration control of this structure system is possible. And then, it is also shown that the shape-changed model can obtain the control effect by this method.
Experimental studies on telescopic aerospikes for aerodynamic control are reported in this paper. Parametric study on the aerodynamic characteristics of the aerospike has performed including the effect of spike length L, base diameter of tip cone D, spike translating speed and direction. The Axial force coefficient Ca of the aerospike suddenly increases at L/D=3.0 due to flow mode transition from the separation to the reattachment. Reattachment/separation flow mode transition phenomenon can be applicable to a newly invented aerodynamic control device, which is called air-breathing aerospike. In this paper, verification test results of this air-breathing aerospike are also reported. A small solenoid valve in the body cylinder successfully controls reattachment/separation flow mode transition at the angle of attacks from 0 to 12 degree. The spiked bodies’ Ca varies according to the mode transition. As a result, we can control the aerodynamic property of the spiked body by opening/closing the valves periodically.
We have developed Satellite controller Integrated with Star sensors (SIS) as a prototype of a future small and low-priced satellite controller. To reduce size and cost of the controller, SIS integrates attitude sensors into star sensors with medium resolution and medium sensitivity, adopts Commercial Off-The-Shelf (COTS) electrical parts for key parts such as CPU and CCD, and integrates several electronics for star identification, attitude determination, attitude control, and data handling into a single processing unit. Newly developed computer architecture is introduced for high reliability with COTS parts under the harsh space environment. In this paper, we will focus on the new star identification algorithm dedicated for star sensors with medium resolution and medium sensitivity and evaluate it with in-orbit experiment data of SIS.
This paper discusses the conceptual trajectory design associated with the impulsive deflection of a potentially hazardous asteroid (PHA) with considering uncertainty of velocity increment that spacecraft gives to the PHA at the time of collision. The effect of the uncertainty is evaluated as the worst value of the closest approach distance between the PHA and the Earth by modeling the uncertainty as a convex model, where the uncertainties of magnitude and the direction of the velocity increments are independently varied. It is shown that the worst value is determined uniquely without searching in the convex hull. Then, the most efficient spacecraft trajectory is evaluated by maximizing the worst approach distance in terms of the Earth departure date and the asteroid arrival date of the spacecraft under C3 constraint that considers the mission feasibility. The importance of considering the uncertainty is demonstrated by comparing the optimum trajectories with and without the uncertainty. Additionally, it is shown that the uncertainty of the velocity increment direction has the significant effect on the deflection of the PHA.
Aerodynamic characteristics of NACA0012 airfoil at low Reynolds numbers (Re=1.0×104∼1.0×105) are measured systematically to clarify nonlinearity of the aerofoil characteristics. The variation of the lift curve with the angle of attack is divided into 5 sub-regions; the gradient of the lift curve much depends on the incident angle. Negative values of the gradient of lift coefficient are observed at lower angles of attack in a Reynolds numbers range. The sub-regions are summarized in a diagram of angle of attack and Reynolds numbers. The coefficients of drag and moment around 0.25 chord length have also unique characteristics.
A simple perturbation theory is introduced for modeling geosynchronous orbits. The theory uses diagrammatic representations of orbits, and derives the perturbations in a direct manner without using differential equations. Perturbations of major importance are derived, including satellite-longitude changes due to the earth’s asymmetric shape, orbital eccentricity increase due to the sun-radiation pressure, and orbital plane inclination due to the sun/moon attraction. The theory clarifies the physical/geometrical meaning of the perturbations while using minimal mathematical analysis.
Magnetic Sail is a propulsion system making use of the solar wind for deep space exploration missions. The interaction between the solar wind and the magnetic field of Magnetic Sail was simulated based on magnetohydrodynamics for various attack angles, and propulsive characteristics of Magnetic Sail were analyzed. When the attack angle is 90 degrees, the thrust is maximum: the drag coefficient (non-dimensional thrust value) is about 5, and when the attack angle is 30 degrees, the maximum steering angle (12 degrees) is obtained. The thrust direction of Magnetic Sail is stable only when the attack angle is 0 degree, whereas Magnetic Sail experiences a torque for other attack angles.