For the purposes of this paper, an onboard checkout system is defined as a system which is built into prime flight equipment, flies with it, and permits a checkout capability to exist during all the major phases of the test and mission life of that prime equipment. Varying degrees of capability may exist in such a system, depending on what is designed into it. This, in turn, is generally dependant on life and mission requirements of the prime equipment, degree of mission checkout required, reliability restrictions,redundancy levels, data management scheme, and equally important, state of the art . Not all checkout can be accomplished with onboard equipment. Mechanical system problems such as leak detection, for example, require techniques that cannot be remotely controlled and evaluated today. On the other hand, such things as in-flight telemetry have been used for quite a long time and will continue to be used for onboard checkout.
