Autonomous space access vehicles can be designed smaller, lighter and less complex than the current space shuttle since they do not require life support systems for human operators. The high mishap rates of UAVs and close correlation between the problems and the size of the vehicles has demonstrated that advanced health monitoring systems are needed for autonomous space access vehicles. In this paper, use of Index Based Reasoners (IBR) is proposed for interpretation of the sensory signals of Integrated Systems Health Management (ISHM) applications. A generic IBR has a classifier. For interpretation of dynamic signals, and to avoid sending out wrong values because of noise or transition, an encoder and/or an Index History Evaluator may be built into an IBR. The performance of IBRs was evaluated by analyzing the simulation results of virtually implemented health monitoring systems of a High Displacement Actuator (HDA) and a turbojet engine.