Electrical Shock Absorber for Docking System in Space

Abstract

This paper presents a study of attenuation and shock absorbing characteristics of the docking system in space. A laboratory prototype of electromechanical shock absorbing system is developed in order to make a preliminary experimental study on the docking system. IntroductionThe docking system is one of the most important functions for the space station and the orbiter such as space shuttle. Recently the construction of many large scale space stations is planned. Many kinds of docking/berthing system must be required for space construction, assembly and servicing. The docking systems are usually classified mainly according to their approach speed. The docking between the station and the orbiter is the 'soft' docking where the final approach speed is ultimately slow. Precise coiitrol of velocity and alignment is performed during the approach phase to minimize contact and stroking forces. On the other hand, 'hard' docking system will be utilized for docking between objects such as small conveyer vehicles, robots, construction equipments, etc. where rather high speed docking is inevitable and force attenuation during the c a p ture phase is more significant In the latter'case, the docking system is desired to make 'hard' docking as 'soft' as possible.The development of the docking system needs variably controlled actuators for energy absorption, compliance control and adjustment of a docking interface to eliminate misalignments. In space environment a hydraulic device can not be used because of fluid leaks and difficulty of maintenance. The use of an electromechanical actuator is considered to be most suitable for docking system in space. An electric docking actuator is considered to include range, rate and attitude sensors to adjust a docking interface in order to eliminate misalignments and to minimize contact and stroking forces. This paper presents a preliminary experimental study on the docking system in space. Main purpose of this research is the study of attenuation and shock absorbing characteristics of the docking system. A laboratory prototype of electromechanical docking system is developed which uses sonar ranging system as a substitute for the laser iange sensor and is controlled by a microprocessor. The configuration of experimental system consists of a rack and pinion gear actuator, a servo motor, sensors, a digital controller and a air-lifted docking target.The motion of docking system is considered to have three phases, i.e. approach, matching and capture phases. In approach phase, relative velocity, attitude and alignment are controlled to obtain suitable docking interface. In matching phase, the actua-*Furocho Chikusaku, Nagoya, 464 Japan Te1.052-781-5111 ext.4418, Fax.052-781-4094tor is accelerated to match the velocity of the approaching target which i s assumed tohave constant velocity in this phase. In capture phase, the actuator is decelerated to attenuate the kinetic energy of the target. In this paper, control for matching and capture phases are considered.The attenuaior can be considered a...

Automatic spacecraft docking using computer vision-based guidance and control techniques

“…Docking between £ spacecraft and a space station or between two spacecraft is called "soft" if the final relative speed along their relative range direction is low. 2 Precision control of spacecraft relative velocity and alignment is required during the approach phase to minimize docking contact forces.…”