There has been increasing demand for larger space structures to satisfy the requirements of astrophysics missions. However, storage space for payloads in satellites is limited, so deployable structures are used in most space missions to minimize storage space and consequently, to reduce launch costs. This work proposes a deployable truss structure which can improve the packaging efficiency of the existing truss structure. The main feature of the proposed structure is that it can be stored in a flat form. Each unit consists of Scissor-like Elements (SLEs) and the whole structure is deployed in a three-dimensional form with a simple mechanism. The detailed configurations and mechanism of the proposed structure are discussed. The geometric constraints for folding the proposed structure into a planar form were analyzed. A kinematic analysis to describe the motion of the structure was also performed. Then the packaging efficiency with respect to length, which is an important performance index of such deployable structures, was analyzed and compared with a typical truss structure.
Recently, space structures are getting larger and more complex because of the more demanding requirements in the space mission. Constructing large structures in space has several challenging issues such as assembly, maintenance and delivering cost. Deployable structures can be the appropriate solution to construct large space structures. Employing bistable characteristics can provide additional advantages to the deployable structure for solving these issues because the overall system can be made relatively simple as well as reliable. In this study, a new concept of the deployable structure using bistable characteristics is proposed. Due to the bistability, both folded and deployed states of the proposed deployable structure can stay under the stable state. The mathematical model of the single bistable component is established to analyze the effect of the off-axis ratio on the characteristics of the proposed structure. In order to analyze the deployment behavior of the proposed structure, the dynamic model of the single bistable component is established. The driving force from the SMA spring is measured from an experiment. By applying the force profiles to the dynamic model, the simulation of the proposed structure is conducted. In order to validate the dynamic model, the experimental model is constructed and the deployment process is captured. The comparison of the simulated and experimental results shows good agreement.
In this study, the use of the twisted string concept with a pin, serving as a moment arm, is proposed to produce the snapthrough of a pre-compressed beam so that the whole system can be used as an effective on/off actuator. The twisted string mechanism is to produce a horizontal pulling force to the pin, which triggers the snap-through of the beam. The actuation moment required to trigger the bistable beam in this study is 24.3 Nmm, corresponding to a horizontal force of 0.81 N. The twisted string actuator is able to produce a pulling force of 1 N, which is further pulled through a distance of 5-mm. Static performance of the integrated system based on the effects of the length of the string on the required input motor voltage, torque, and the overall system response time is experimentally investigated. The snap-through sequence during the static experiment is also captured with a high-speed camera. The input voltage to the motor increases as the length of the string is increased. The length of the string also affects the overall system response, motor speed and torque. The whole snap-through of the beam happens within 100 msec after the trigger signal is sent.