Structures and Materials

The structure of the space transportation system is the physical body of the vehicle which houses all major or minor subsystems. It consists of propellant tanks, motor cases, payload fairing and interstage structures. The entire structure of the vehicle has to support all associated secondary elements like mechanisms, pyros, avionics, actuators, etc. Structures are classified as primary and secondary structures. Load-bearing structures like the solid stage motors, liquid stage tanks, interstage structures, payload fairing and interface joints are all primary structures. Gas bottles, fuel tanks for control systems, brackets, avionics packages, etc. which do not experience direct loads are known as secondary structures. The design of structural elements has to ensure the structural integrity of the vehicle during its various phases of flight starting from lift-off till satellite injection. Loads, materials, their characteristics, structural construction, manufacturing processes, structural dynamic response, stability characteristics, development schedule, cost, etc. strongly influence the structural designs. During the structural design process the mass of the structure has to be kept minimum to maximize the vehicle performance while ensuring adequate design margin. This makes the launch vehicles very flexible and hence the detailed structural dynamic studies are essential. Therefore, selection of suitable materials for structures and their shape and construction methods are important. To ensure that the designed product meets the specified requirements, the compliance has to be checked through detailed analysis and testing. Structures designed and analyzed for various load cases are to be qualified through a series of structural static and dynamic tests. This chapter discusses in detail the STS structural design requirements, load analysis and different configurations to meet different requirements. The materials’ selection for structures, their shape and construction methods are included. Static and dynamic analyses are described and some insight on design tools is presented. The various static, environmental and dynamic tests needed for the qualification of the structures are highlighted.