The first consideration of the stru

The first consideration of the structural design is to get the telescope safely into orbit. Therefore,the ability to survival the launch environment is a key requirement. The allocation of massbetween primary mirror and its launch support system, the telescope structure itself (divided intomirror support truss, forward metering truss, secondary mirror and its spiders, baffling and sunshields) the satellite and finally but not least the instruments. As the primary mirror is both thelargest and most fragile of these elements, it becomes the major design driver. The distributionof forces into the primary mirror during launch requires a large number of axial attachmentpoints. Because it is a mirror, the front surface cannot be used for support; hence the back faceattachment locations must be capable of both tension and compression. The lateral loads can betransferred by compression only with a bumper/gap system, or, with the use of bonded pads, bothtensile and compressive loads can be utilized. Since glass (or ceramics) are stronger incompression than tension, as much of the loading as possible should be compressive. On theother hand, as a thin meniscus, the primary should not be put into bending. This dictatedavoiding edge bending and controlling the uniformity of stiffness of the back support structure.The basic design of the primary mirror support truss is to control the axial stiffness of each attachpoint to a level that a combination of support unit stiffness and truss backing stiffness in series isuniform across the whole back of the mirror. There are frequency and weight considerations thatdetermine the depth, complexity and stiffness of the truss itself and limit the range of supportstiffness (softening permissible) to avoid interaction of the primary mirror as a lumped mass withthe launch vehicle dynamics