The purpose of the present paper is to examine experimentally relationship between the drag reduction of the two-dimensional square prism body and its near wake due to the cutout of its front edges. The mean velocity and the velocity fluctuation are measured by the hot wire anemometer with I type and X type probes. The present experiment shows: (1) There are typical three patterns of the velocity fluctuation against the cutout dimensions, which are almost the same as of the drag reduction shown in previous work. (2) The length of the dead water region of the near wake around the square prism with the cutout is related with the profile of the velocity fluctuation. (3) The decrease of total velocity fluctuation energy on the cross-area of the near wake reduces the drag coefficient of the square prism with the cutout.
In order to take advantage of electric propulsion for a rendezvous with a near-earth small body such as a commet or an asteroid, very long continuous thruster operation of several years is required. For the asteroid sample and return mission named MUSES-C, the institute of space and astronautical science is developing a new-concept ion engine, microwave discharge ion engine, whose cathode-less discharge chamber made the engine being free from the degradation of the electrodes. To demonstrate the new thruster's lifetime, a full-automated test facility was constructed and the endurance test of the ion engine started in February 1997. The facility consists of a large vacuum chamber evacuated by cryogenic pumps and a thruster system; the latter includes a propellant feed system, microwave power generators, power supply units for ion acceleration, and a data acquisition system. All the engine operation system is integrated into a GPIB bus interface and safely controled by computers without any on-site personnel.
Fuzzy logic control law to improve duch roll characteristics of aircraft was designed and its control performance was evaluated. First, control law was designed for a small high speed aircraft at low altitude and low speed flight condition. Then the control law was applied to flight conditions from the minimum speed to the supersonic and sea level to high altitude, and these control performances were evaluated. Additionally, this control law was adapted to a large transport aircraft without any parameter change. The evaluation showed good control performance to improve the duch roll characteristics of all flight conditions of both small high speed aircraft and large transport aircraft without the parameter change. This meant that the fuzzy control proved to provide effective flexible application to aircraft stability augmentation. In case of actual flight in strong air turburence, input to fuzzy logic controller may exceed the limit of effective range. To cope with this problem, the countermeasure method was provided and proved its effectiveness.
Navigation and guidance for in-orbit satellite servicer is discussed. Outside inspection of the target satellite in a geostationary transfer orbit by a camera is taken as an example. The nominal trajectory for inspection is selected considering orbital dynamics. Then, required control accuracy is evaluated when position control is executed only in the vicinity of the apogee point. A new image processing algorithm is proposed to meet this requirement assuming a typical CCD camera. The algorithm is applied to the simulated images of an upper stage booster of the H-II rocket to confirm its validity.
This paper discusses a method for damping the angular momentum of an uncontrolled target satellite in order to make it easy to capture using a chaser-satellite-mounted manipulator. During the capture operation of an uncontrolled floating target, it may be difficult for a manipulator to grapple it directly because of target nutation or tumbling. In this paper, we propose using a cushion type damper in order to absorb the rotational motion. The scenario is as follows: 1) a cushion type damper is attached to the end-effector of the manipulator, 2) the manipulator softly pushes the damper on carefully selected points on the target, and 3) the contact force between the damper and the target causes the angular momentum of the target to decrease. The validity and feasibility of the proposed method are verified through numerical simulations.