Yohei Kushida
(Nagoya University, Japan)

On the landing of a spacecraft, a large shock load leads to undesirable responses, such as rebound and trip. The authors have discussed the control problem of these shock responses by means of momentum exchange impact dampers (MEIDs). Conventional MEID mechanisms are classified into two types. One is PMEID (Passive-MEID) that is composed of passive elements. The other one is AMEID (Active-MEID) that includes active actuators. The speriority of the AMEID was verified by simulations. However, practical implementations of the AMEID are still difficult because the actuator cannot resist the huge shock acceleration of landing. To solve the problem, this paper proposes a novel MEID - HMEID (Hybrid-MEID). The HMEID possesses a shock absorber in the bottom of the actuator to protect it from shock acceleration. The controlled object and the damper are connected by springs as well as PMEID. Hence, additional masses of the HMEID are thrown by means of both PMEID effect and actuator force. As a fundamental study, this paper applies MEIDs to a single-axis falling type problem. Simulation studies reveals that the HMEID can effectively reduce the influence of shock responses as same degree as AMEID. Furthermore, it greatly reduces the shock accerelation of the actuator.

Munetaka Kashiwa
(Mitsubishi Electric Corporation, Japan)

A stepper motor is a highly reliable actuator because it can keep the angle of the motor shaft without leading current. Thus, the stepper motor has been utilized to drive devices in satellites which need high reliability, for example an antenna pointing mechanism and a solar paddle mechanism. However, the stepper motor generally induces high-frequency disturbance when it rotates. Since the disturbance degrades the pointing stability of the satellite, a low disturbance driving method for the stepper motor is required. In this paper, a new driving method for the stepper motor is proposed. The proposed method can compensate a detent torque of the stepper motor and reduce the disturbance without angle sensors. First, this paper describes studies on conventional driving methods for the stepper motor, full step and micro step driving method. The performance of reducing the disturbance by these conventional methods is investigated through numerical and experimental studies. Second, the details of the proposed method are described. The performance of the proposed method is compared with the conventional methods. The proposed method can drastically reduce the disturbance compared with the conventional methods (Figure). Finally, the effects of the sensor less drive on the performance are discussed.

Keita Tanaka
(University of Tokyo, Japan)

The three-dimensional reaction wheel (3DRW) is a three-axis free rotor reaction wheel, which can achieve a compact and high integrity attitude control systems. In the system we propose, a spherical rotor is levitated without mechanical contact by gas bearings and rotated by the torque generated by magnetic fields. To realize the precise control of the rotor, it is important to understand the characteristics of spherical gas bearings such as pressure distribution, load capacity, stiffness and flow rate. Some previous works clarified them but few researches are there relating the use of gas bearings in the space. What is required for the space gas bearing is having the minimum robust characteristic against various small disturbances. A big air compressor would be unnecessary. In addition, great supply pressure and flow might disturb the control of the rotor worsening the performance as an attitude control unit. The authors have developed a spherical gas bearing with a circular slot restrictor and analyzed its performance by experiments and numerical calculations. The result shows that this type of bearing can generate necessary floating force with low supply pressure and low flow rate operated by a compact pump such as piezoelectric type without sliding parts.

Kyoko Oribe
(IHI Aerospace Co., Ltd., Japan)

Reducing size, weight and cost of rocket avionics is indispensable to get competitive SLVs (Satellite Launch Vehicle) that is small and inexpensive. In order to provide the avionics at a low cost, we could choose unqualified parts like COTS product. Although applying unapproved parts as a substitute for MIL parts to the avionics would give it at a lower cost, failure rate would increase significantly when we calculate it using conventional approach. But then, according to analysis of failure event of space crafts, in fact, there were a lot of failures resulting from improper design or manufacture and that failure rate didn't correspond with the system reliability built up from failure rate of parts one by one. In other words it is possible to get the equivalent success rate to conventional rockets by considering the quality of design and production even in the use of unqualified avionics parts. We will propose new confidence assessment that counts the reliability of design and production as well. In addition, we will introduce our approach to get high reliability of both hardware and software adapting unqualified products.