Purpose of Document

The Space Shuttle avionics system design roots are in the early 1970's, yet it remains the most sophisticated, integrated, innovative approach to an aerospace avionics system in use today - 16 years hence. It is the intent of this document to trace the origins and evolution of the system; to outline the requirements, constraints, and other factors which led to the final configuration; and to provide a comprehensive description of its operation and functional characteristics. The assumption is made that the reader is familiar with, or has access to, information about the basic Space Shuttle vehicle configuration and its subsystems.

Organization

The remainder of the document is organized into three sections.

• In Section 2 - The Design Environment, the state of the electronics and aerospace art in the early seventies is assessed. The intent is to familiarize the reader with the environment in which the design evolved.
• In Section 3 - System Design Evolution, the major requirements and other factors that led to the Space Shuttle avionics system configuration are developed. The overall design drivers and constraints are treated first, followed by a subsystem-by-subsystem discussion of the major tradeoffs and design issues that were addressed as the system evolved.
• Section 4 - System Mechanization/ Operation contains a description of the system and of its functional operation. Each function or service provided is examined from the standpoint of the data processing hardware and software attributes used as well as of the additional unique avionics subsystem hardware required.

Use

The Space Shuttle avionics system is very large and extremely complex and, therefore, is difficult to describe without becoming engulfed in details. The approach used here is to maintain a top-level perspective by frequent reference to the system block diagram contained in the foldout located inside the back cover. The reader is requested to examine the foldout at this time. Note that it can be extended without interfering with the reading of the document. To facilitate reference to various features of the system, letters (across the top and bottom) and numbers (along the sides) define zones that are used in the descriptions which follow. References to zones in the diagram will follow the alphanumeric convention (e.g., [B,3]) to identify locations. To the lower left of the diagram, note the color code legend which indicates the convention used to identify data buses. Note also that the diagram reflects the physical distribution of equipment in the vehicle. Because of the frequent references made to the diagram, it is recommended that it remain extended while the various sections, especially section 4, are examined. Even though subsystem and function descriptions may include more detailed, specialized diagrams and figures, it is very important that the overall perspective be maintained through the use of the system block diagram.

As indicated previously, the document is intended not only to describe the Space Shuttle avionics system, but to develop the thesis for its configuration and its evolution. For the user not interested in the origins and evolution, section 4 is written to stand alone and may be used as a reference description of system mechanization and operation.

Acronyms and abbreviations used herein are defined in the appendix.

In compliance with the NASA's publication policy, the original units of measure have have been converted to the equivalent value in the Système International d'Unités (SI). As an aid to the reader, the SI units are written first and the original units are written parenthetically thereafter.