Evolution of Three Hold-Down Configuration for Large Antenna Mounted on a Dual Axes Steerable Mechanism

The Hold-down system is a key unit on satellite that enables rigid holding of antenna on to the spacecraft structure so as to withstand diverse loads during launch. The hold-down system gets released on orbit upon actuation command so that the antenna gets deployed to its functional orientation using various mechanisms. Thus, the configuration of the hold-down system is very critical in fulfilling the overall satellite mission. The configuration of the hold-down system primarily involves arriving at the required number of hold-downs, which depends upon several factors like stowed frequency requirements, mass, inertia, and size of the antenna. In the present work, an iterative approach has been adopted, by varying the number of hold-downs and span between them, in order to meet the satellite specifications related to large steerable antennae. Based on normal mode frequency analysis, several parametric studies have been carried out to meet the stiffness requirements while catering to mass and space constraints of satellite mission. Finally, after detailed studies, a three hold-down configuration has been arrived at for large antennae. This paper presents the evolution of this three hold-down configuration along with details on different case studies carried out and the corresponding reasons for considering the cases. The configuration has been devised so as to meet the frequency requirements of spacecraft along with confirmation of hindrance free release of the antenna after deployment, desired nominal functional movement of the antenna, and ease of assembly and testing. The FEA details of different cases along with the optimum configuration with three hold-downs integrated onto antenna bracket that has been arrived and have been presented. The methodology adopted for finalization of the hold-down configuration serves as guideline for arriving at an optimized solution for rigidly holding a large sized steerable antenna on spacecraft.