The Kennedy Space Center (KSC) Simulation System is a computing system capable of large-scale mathematical modeling for real-time simulation of the behavior of a complex system that could include many different interacting machines, instruments, and/or computers along with human operators. Developed for simulating space-shuttle launches to ensure the readiness of launching systems and personnel, the KSC Simulation System could also be adapted to other (including commercial) applications in which there are requirements for real-time simulation of systems represented by large mathematical models.

Previously, launch simulations at KSC were performed on a system called the "Shuttle Ground Operations Simulator" (SGOS) that consisted mainly of a large mainframe computer running a mixture of Fortran and assembly code. The SGOS hardware and software were non-portable, very difficult to debug, and expensive to maintain. Because of increases in the cost of maintenance and aging of the mainframe computer, it became necessary to design the present KSC Simulation System as a more cost-effective, more reliable, and more maintainable replacement for the SGOS.

The new KSC Simulation System utilizes the latest technology and is designed to provide the capability to support future launch vehicles.

The SGOS was used in conjunction with a system, called the "Video Simulation Interface" (VSI), that enables communication and flow of data between the KSC Firing Room launch software and the SGOS. In operation, the SGOS appears to engineers in the Firing Room as though they were controlling and monitoring the real space shuttle and its ground support systems. The use of the SGOS thus made it possible to debug the Firing Room software in safety; that is, without jeopardizing the real space shuttle and other hardware. In addition, the SGOS made it possible to train Firing Room personnel by enabling them to experience simulated launch countdowns, into which random failure scenarios were introduced by trainers. The SGOS also made it possible to observe the effects of new hardware and software on the overall launch system before use in a real launch.

In developing the KSC Simulation System, the basic functionality of the SGOS as described above was preserved, as well as its name. The development was accomplished without any effect on the rest of the simulation infrastructure at KSC; from the perspective of human users and pre-existing simulation equipment with which the System is required to interact, the System functions identically to the earlier SGOS, except that it is an order of magnitude faster and supports higher-fidelity, larger models. Models in the KSC Simulation System can have up to 200,000 variables and >16,000 model segments, each segment representing a specific piece of hardware or software. The System can support >1,000 control-procedure programs, which stimulate the model. The System can execute a simulation model in real time in steps as small as 5 ms. It supports a sophisticated graphic display path and tracing mechanism. The system includes an extremely easy-to-use human/machine interface for all phases of development and execution of the models and of control-procedure programs that stimulate the models.

The central processing unit of the KSC Simulation System computer is a VersaModule Eurocard (VME) single-board computer that communicates with other VME boards inside the VSI. Whereas the SGOS ran on the mainframe computer that occupied more than half of the second floor of the KSC launch-control-center building, the computer hardware of the present system occupies about the same floor space as that of an ordinary desk (see figure). The computer now runs an entire space-shuttle-launch-countdown simulation of >100 MB in real time. The System takes advantage of a broad spectrum of current supporting hardware and software, including 100-Mb/s Ethernet, VMEbus, X-Window/Motif interfaces, and the Unix operating system. The software for the Simulation System itself has been written in the C, Flex, and Bison (Lex and Yacc) languages, thereby making the software portable to other systems.

This work was done by Scott Estes, Juan M. Busto, Mike Dick, Kevin J. Grant, Jimmy H. Celsor, Charles T. Lostroscio, Nathan G. Taylor, and Carlos M. Alvarado of Kennedy Space Center and P. Keith Sullivan, Thomas D. Miller, Caroline A. Achee, John Coulter, and Lauren N. Graves of United Space Alliance. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com  under the Electronic Components and Systems category.