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Q: Does a mission have to use all of the SCPS protocols? No. Each mission can choose the appropriate layers and the appropriate options within those layers. The individual protocols provide flexibility and optional features that allow designers to tailor a communications protocol to meet the requirements and constraints of a mission, without extensive software development. Q: Doesn't the availability of so many options defeat the purpose of a standard? Not really. Like most protocol stacks, SCPS provides three classes of options. First, spacecraft designers can choose which of the protocols to use. A mission might be designed to operate without one of the SCPS protocols, for various reasons. The second class of options is the choice of features to include in a specific copy of a protocol entity, to tailor that copy for use in a particular environment. Such adaptation is often made through compile-time options. Finally, some options do not affect size or overall capability of a protocol implementation, but are simply setup parameters that configure the run-time protocol entity to optimize performance or provide compatibility with peer protocol entities. Each of the options was designed to accommodate the real and unavoidable differences from one mission to another-differences in objectives, hardware, environment, or operations. These differences must be accommodated in some way. Use of a few carefully designed options within a family of protocols will lead to lower cost and lower risk than the multiple, uncoordinated, point solutions that would otherwise be necessary.
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