# New Construction Solutions of Gear Using in Space Vehicle Control Systems
###### Abstract  
Outer space presents construction challenges that are completely different from the terrestrial environment. They should be characterized by high resilience and indefinite durability because there is no possibility of repair during exploitation. There are drives in spacecraft control systems that are necessary to move solar panels, robotic arms, and manipulators, and also to position antennas. In these devices, they have applications where harmonic drives are characterized by high kinematic accuracy but relatively low mechanical strength. The analysis presented in this study is aimed at modifying the shape of the harmonic drive to increase its durability and reliability. In this study, the most vulnerable damage element of the harmonic drive is the flexspline. The calculation was carried out using the finite element method (FEM) in the computer program ABAQUS. A standardized shape was tested as a basic model, and several other design solutions were proposed. For each of them, the mechanical strength was determined, which allowed the selection of the most preferred shape for the flexspline of the harmonic drive. The specific environmental requirements of the expectations for sand for gear used in spacecraft control systems were included in the analysis. The selected construction solutions of the flexspline allow for longer work and transfer of greater loads by the harmonic driver than the solutions currently used. The choice of harmonic driver design shape allows for failure-free and maintenance-free work in space vehicle control systems. h 20221228122814 November 2022 28 November 2022 2021222122814 November 2022 28 November 2022 20212212  
use in space devices. Many research centers carry out projects to improve the durability of wave gears by selecting appropriate lubrication [16; 17] or using new materials [18]. In view of the high transport costs and negligible service options, outer-space-bound devices must be characterized by high durability and reliability, which is often the main construction problem. Mechanical drives used under earth conditions are not exposed to extremely low temperatures or still contamination by very fine dust. It can also be periodically cleaned, lubricated, and preserved, which cannot be done in outer space. The Sojourner rover from the Mars Pathfinder mission ran for two and a half months, which, from today's perspective, is a short period of operation. Therefore, controlled drives in currently designed space vehicles should have greater durability to allow their application in future, more challenging space missions. One of the drives used in space vehicle control systems are harmonic drives. They are a unique type of gear transmission, not only in view of characteristic constructions but also regarding the special schemes of transferring loads. The unique character of harmonic drives is based on the relative movement of the mating gears as a result of the elastic deformation of one of them. The main components of the harmonic drive are shown in Figure 1, and include the flexspline (1), circular spline (2), and wave generator (3). The generator deforms the toothed wheel rim of the flexspline into an ellipse, and then it engages with the circular spline in the mating areas (4); limited by angle \(\gamma\) in the large axes (\(\gamma\)) of the harmonic drive, the teeth of both gears are in contact, while in the small axes (X), the teeth of these gears pass each other [19; 20; 21]. Typically, the driving element of the gearbox is a wave generator, and the driven element can be both a flexspline and a circular spline. During the transmission operation, the rotating generator causes the deformation waves to move along the circumference of the flexspline, transferring the motion to the mating circular spline. For most harmonic drives, the load is simultaneously carried by 20-50% of the total number of teeth of the flexspline [22; 23].