The following is a list of the important aspects that the structure subsystem engineer has to consider, many of which are related to the fundamental requirement to survive launch:
• Low mass. Although there is a need to build a robust structure, nevertheless the structure subsystem engineer must also make every effort to minimize mass. As we said in Chapter 5, the cost of the launch rises steeply as the mass of the spacecraft increases, so this requirement becomes a critical issue about limiting the overall cost of the spacecraft project, as launch is usually a large percentage of this cost.
• Strength and stiffness. The structure must be strong and stiff enough to withstand launch and on-orbit loads without distortion. Unacceptable levels of distortion would compromise the pointing of payload instruments, such as imaging cameras or telescopes, and the pointing of subsystem elements like communications dishes and attitude sensors.
• Environmental protection. The structure must also provide an appropriate level of protection against environmental aspects (see Chapter 6), such as radiation, and shielding against impacts of orbital debris and micrometeors.
• Launch vehicle interface. The manner in which the spacecraft is attached to the launch vehicle also affects the spacecraft's overall design. The attachment must be done in such a way as to ensure a robust connection with the launcher during the ascent to orbit, but it must also be able to reliably release the spacecraft on command once in orbit. The position of this interface within the spacecraft also governs how the launch loads are distributed throughout the spacecraft structure.
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