Gateway development is part of an overall effort to replace the existing Kennedy Space Center Launch Processing System (LPS) Checkout, Control, and Monitoring Subsystem (CCMS) in firing rooms that support processing and launch of the Space Shuttle. The CLCS is made of several components, including the Gateway subsystems. Gateway subsystems are similar in function to the CCMS front-end processors (FEP’s) and provide interfaces between CLCS, the Space Shuttle, and ground support equipment (GSE). The existing CCMS was designed and built in the 1970’s with custom hardware and assembly language prior to establishment of industry standards commonly used in real-time data processing systems today. One of the Gateway’s primary functions is to perform link protocol conversion between the nonstandard Shuttle/GSE interfaces and the industry standard 100BaseT network interface. This allows Gateways to communicate with other CLCS subsystems. Gateways also perform data conversion, calibration, command routing, command authentication, measurement change checking, measurement time stamping, and link health monitoring.

Figure 1. CLCS GSE Gateway Subsystem

Processing commands and data for the Space Shuttle and GSE requires CLCS to be able to support communication via complex Pulse Code Modulation (PCM) data streams (uplink and downlink), Orbiter’s Launch Data Bus (LDB) (a variation of MIL-STD-1553), the Ground Data Bus (unique to KSC), serial interfaces (RS-232), and Ethernet for recently modernized ground systems such as the Hazardous Gas Detection System 2000. Although computing power available in today’s high-speed embedded real-time computers permits a single subsystem to process data and commands for all interfaces, safety and redundancy considerations require the deployment of separate Gateway subsystems to support each specific link. In a launch processing environment, there are six Gateway types: GSE, LDB, PCM Downlink, PCM Uplink, Space Shuttle Main Engine, and Consolidated Systems. In order to maximize reuse of hardware and KSC-developed software in the various Gateway types, an open systems architecture based on the VersaModule Eurocard (VME) standard was chosen as the hardware platform. Each Gateway consists of a 6U VME Chassis, two high-speed single-board computers (Gateway Control Processor [GCP] and Front-End Process Controller [FEPC]), disk drive, IRIG-B Interface Board, 100BaseT network interface board, and a special interface board depending on which link a particular Gateway Subsystem is required to support. A separate Signal Conditioning Chassis contains custom KSC-developed circuit boards used to sum and split LDB, GSE, and PCM signals. Figure 1 shows a single GSE Gateway subsystem VME chassis and components.

To support Space Shuttle launch countdown, 21 Gateways will be used for the large number of different Shuttle/GSE interfaces and to satisfy redundancy requirements for LDB, GSE, Consolidated Systems, and PCM Downlink Gateways. Redundant Gateways are configured as “Active Standby Pairs.” If the Active Gateway fails, CLCS will automatically switch to the Standby. In the case of the GSE Gateway, the switch time can be as little as 20 milliseconds with no loss of commands. Two Gateway groups that will eventually support launch countdown are currently deployed in the CLCS Operations Control Room One (OCR-1). One of these Gateway groups is shown in figure 2.

Initial development on 10 Computer Software Configuration Items (CSCI’s) for CLCS Gateways is complete. As with the hardware, a software architecture was developed to facilitate a high level of code reuse. Wind River’s VxWorks operating system was chosen for Gateway subsystems for its symmetrical multiprocessing features, priority-preemptive scheduling support, and deterministic context switch times required for real-time command and control systems such as CLCS Gateways.