QuickView of the SCL System

Spacecraft Monitor and Control 
using Expert Systems Technology

Reusable Software Architecture Key to Cost Savings

To achieve a competitive advantage in today’s marketplace, reusable software architecture must be employed to salvage existing infrastructures and lower recurring costs from program to program. The Spacecraft Command Language (SCL) system developed by Interface and Control Systems, Inc. is the competitive edge your next project needs.

The SCL system has been proven on Navy, Air Force and NASA contracts. The re-usable architecture of the SCL system employs Expert Systems Technology to achieve a high level of automation. The SCL product is unique in the control system field in the fact that the system can be used on Workstation class computers as well as embedded systems.

Uses of the SCL span the spectrum of spacecraft, ground stations, simulations, and industrial monitor and control. SCL is a mature product which has been fielded for many years, yet employs state of the art technology today…no vapor-ware here.

SCL enables state of the art automation using Expert Systems, Graphical User Interfaces (GUIs), Message Brokers, Object-Oriented Methodologies, Integrated Development Environments (IDE), and Application Programmer’s Interfaces (APIs). Read on none of these need to be intimidating if the system is developed for user-friendly operation. All these technologies are desirable features which allow a system to be scaleable in a heterogeneous, client-server architecture.

Automation using Expert Systems

The SCL system has its roots in the cold war era where satellites were required to take care of themselves for 180 days or more. The SCL system was born from a desire for autonomous operations of spacecraft, and a need to lower manpower requirements for tracking stations. The Interface and Control Systems (ICS) team developed the SCL system to provide a symmetrical software architecture for spacecraft and the ground stations that control them. By using an Object-Oriented approach from the beginning, the system has been applied to other disciplines and has been capable of being reused from project to project. An Internal Research and Development (IRAD) effort at ICS continues to expand the capabilities of the system to incorporate state of the art software tools and meet the needs of our customers.

The SCL system uses a core set of software built around a rule-based Expert System. In addition to rules, the SCL system also employs a high level scripting language to provide a temporal reasoning capability. Rules give the system an event-driven capability, while scripts give the system a procedural and scheduled capability. Both scripts and rules are used in conjunction with each other and share a common, HyperScripting grammar. HyperScripting languages lower the learning curve for personnel and provide a powerful machine-neutral language for capturing knowledge.

The SCL system accepts data from outside sources in the form of telemetry frames which need to be decommutated, or in the form of identified data passed in through the SCL API. Multiple copies of SCL can be used in a network topology and can communicate with each other using the SCL Message Broker. Devices can be commanded on local and remote machines.

The SCL system is the core product of a control system and its architecture provides the foundation to build a larger control system. The SCL system allows a user to add functionality to the core system by integrating other 3rd party products, custom code, graphical elements, and existing hardware and software infrastructure. Step-wise integration of the SCL product is also an option. The SCL system has been successfully fielded as a value-added product to existing systems.

For new projects, the SCL system can be installed from tape and provide functionality immediately. Desktop simulations of data can be developed quickly. User-defined extensions can be made to the grammar to customize the system to unique requirements. Custom software modules (clients and servers) can interface with SCL using our API.

Elements of the SCL Toolkit

The SCL system is composed of several processes and employs several 3rd party products to give the system a state of the art capability. Many of the 3rd party products are optional. SCL is marketed as a stand-alone or a bundled product. The core SCL system is composed of:

• A high-level HyperScripting Language (Spacecraft Command Language or SCL). This is a grammar used to support the development of SCL scripts and rules. The SCL grammar is a high-level, loosely typed HyperScripting language much like HyperTalk for the Macintosh. The SCL grammar is designed for a quick learning curve, lower skill level (no professional software developers needed), and an English-like syntax. The language allows the operator to capture knowledge in terms of scripts (time based, procedural) and rules (event driven Expert System).
• The SCL Compiler, a state-of-the-art language processing facility which translates the ASCII SCL grammar into an intermediate or tokenized form. This module allows the user to add keywords to extend the grammar and customize the system for the application. The SCL compiler also supports the SCL real-time command line interface.
• The SCL Real-Time Engine (RTE) - This is the run-time portion of the SCL system. The RTE is included in the development and run-time versions of the SCL system. The RTE is the SCL Command Interpreter and the Inference Engine for the SCL Expert System. SCL scripts and rules are compiled using the compiler, loaded to the SCL RTE and executed by the SCL RTE.
• Message Broker - the SCL Messages Broker is a software "data bus" used to move data among processes in an SCL system. The Message Broker is a "CORBA-like" messaging system which allows the user to define message formats and processes which can dynamically produce or consume SCL Message Broker packets. The SCL API defines a layer for interfacing to the other processes in a heterogeneous networked environment using the Message Broker. The user has control of the message broker communications layer and can use one of several underlying technologies depending on the operating system(s) used.
• SCL Application Programmer’s Interface (API) - SCL is generally used as a core component of a control system. The SCL API allows a programmer to extend the functionality of the SCL system using C and C++ code. User-defined processes can be written to take advantage of the flexibility of the Message Broker Data Bus. Keywords can be added to the SCL compiler and RTE to extend the functionality. Software can be linked directly into the SCL RTE, or it can be "hung" on the software bus.
• Data I/O - Data I/O is responsible for the ingestion of data from external sources. Data I/O has a heritage in flight systems and is capable of decommutating frames of data. Data is asynchronously acquired by the Acquisition Module and passed to the Telemetry Reduction Module for decommutation, change detection, Engineering Unit conversion (for analogs), storage in the real-time database, and notification messages sent to the Expert System to trigger rules. Decom records are defined in the SCL database to describe how to pick apart frames of data. The Data I/O module also accepts change packet from external processes.
• On-Line Documentation - The SCL system is delivered with the entire manual set on-line in HyperText format. All you need is a Web Browser to view the information. You can also get up to date documentation from our WebSite located at: http://www.interfacecontrol.com Use the WebSite to register for our electronic newsletter (save some trees) which will be delivered to you via e-mail. You can also visit our Frequently Asked Questions Pages at our WebSite as well as send us comments and bug reports. Developers can visit our ftp site for code examples for extending the SCL system.
• Manual Set - Included with the development versions of SCL is the SCL Toolkit Manual Set. These are a complete reference set for the SCL system. They include tutorials, installation guides, version description documents, and much more. Documentation for all 3rd party products are also included in the delivery of the SCL system.

Optional 3rd party products can be used in tandem with the SCL core product, these include:

• Visualization Tools - The SCL system is "graphics system neutral". That is, we can work with several vendor’s graphical front ends, or the user can develop a custom front end with Motif, Microsoft Foundation Classes, etc. The SCL system is most often shipped with the Sammi product from Kinesix. Other products such as LabViews from National Instruments are supported on an ongoing basis. 3D graphics products can also be used with SCL. Please call for a current list of Visualization Tools.
• Display Server - The SCL system uses "best in class" 3rd party products to provide a Graphical User Interface (GUI). We "bridge" between the SCL API and the GUI's API using display servers. Generally, we use Dynamic Data Visualization Tools (DDVTs) to handle the graphical user interface. The SAMMI and LabViews products are currently supported. Support for other products such as SL-GMS, Talarian, and DataViews is available upon request, please call for availability and platforms. The SCL Display Server provides bi-directional communication between SCL and the visualization tool. SCL commands can be "hidden" behind object on the screen to give a "point and click" functionality for a commanding system. SCL data points can be monitored using a wide variety of graphical objects.

SCL for Embedded Systems

SCL is available for embedded systems for both industrial control system and spacecraft applications. The system is composed of the RTE and the Data I/O modules and released in source code form. ICS offers Engineering Services for the incorporation of SCL in an embedded system. The embedded version of SCL is written in C and is portable to most standard microprocessors which support a Real-Time Executive (VRTX, PSOS, VxWorks, etc.) and an ANSI standard C compiler. Call ICS for a quote on an embedded version of SCL. Embedded SCL is available as a "do it yourself" kit, or as an adjunct to an Engineering Service contract.

ICS is offering a training course for Embedded SCL.

SCL Training

New Users and Developers can benefit from training on the SCL system. Training is available at the Melbourne, Florida and Columbia, Maryland offices. Two levels of training are currently available. A new user would benefit from the Introduction to SCL training class. This introductory course is geared toward the operational staff members and designed to give the student experience in the overall operation of the SCL system. The class will include an overview of the architecture and infrastructure of SCL. It will provide hands-on, task-oriented projects, useful tips, and technical information to get the student started using SCL. This class is designed to take the student from elementary tasks, such as loading and configuring the system, to more complex techniques, such as basic programming in SCL, creating a database, and developing SCL scripts and rules. Prerequisites are: a working knowledge of the UNIX operating system and the "vi" editor. Familiarity with expert system concepts are also desirable.

The Advanced SCL Concepts course is geared toward the software development team members and designed to provide the student with advanced SCL programming language techniques, the database management system structure, and rule based expert system development concepts. The student will learn through the use of hands-on, task-oriented projects, the user-oriented, integrated environment for development, simulation and test of a control system. Strategic exercises will include use of the API, message broker, and development of client/server applications. Prerequisites include "Introduction to SCL" or equivalent working knowledge of the SCL environment. C or C++ programming experience is necessary.

On-Site Training at the customer's facility is also available. Call ICS for a quote and a class schedule. Training schedules are regularly posted on our website. (http://www.interfacecontrol.com)

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