International Telemetering Conference Proceedings / October 25-28, 1993 / Riviera Hotel and Convention Center, Las Vegas, Nevada / To model the "black boxes" in a command and telemetry simulation, it is important to preserve the abstraction of a one-to-one match between the real-world interfaces and the simulated interfaces. Everywhere a physical interface exists on the box, there needs to be a simulated interface. Preserving this abstraction allows the model to evolve more naturally with real-world design changes. In most command and telemetry systems, many different types of commands and telemetry can be sent over a single interface. This creates a problem in preserving the interface abstraction if the Ada language is used for implementation. Due to the fact that Ada is a "strongly typed" language, a different or overloaded operation needs to exist for each type of command or telemetry. However, by using a "discriminated variant record" to represent the commands and telemetry streams, a single operation can be used in the Ada specification. This not only preserves the abstraction but makes the software more maintainable by allowing the data list to change during the design of the "black box" without changing the Ada specification. As a result, "loose coupling" is achieved, a common set of commands and telemetry formats can be "inherited" to promote reuse, and overall system development and maintenance costs are reduced.

International Telemetering Conference Proceedings / October 17-20, 1994 / Town & Country Hotel and Conference Center, San Diego, California / The Space Station Verification and Training Facility is using an object-oriented design methodology for software design, a rate monotonic scheduling and message passing system to support the highly distributed environment, and the Ada language to implement most of the software. One of the subsystems within the Space Station and Training Facility is the Space Network Simulator. Space Network simulators are used to provide training of ground controllers and flight crews, providing a model of real-world formats and protocols. This gives the controller the appearance of a real-world network, providing valuable training. To develop a simulation of the space network within this distributed environment, software objects are under development to dynamically simulate the existence of the space vehicle(s) and their communication components. Communication components include the on-board antennas, transponders, communication systems, and corresponding communication ground control facilities. Telemetry systems are used in the simulation to provide the control of actual data manipulation, as a function of the state of the simulated Space Network. The telemetry system automatically formats appropriate telemetry characteristics through mode and control commands. A software model is under development to provide a transparent interface between the software objects and the telemetry system, allowing the objects to execute without knowledge of the particular telemetry system in use. A transparent interface between the software and hardware, within this object-oriented methodology, reduces the propagation of change to software models as the interface requirements change.

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