NASA Office of Logic Design

NASA Office of Logic Design

A scientific study of the problems of digital engineering for space flight systems,
with a view to their practical solution.


SPACEBORNE DIGITAL COMPUTER SYSTEMS

1. INTRODUCTION

As space vehicle missions have become more complex, the use of onboard digital computers has become more prevalent. The functions which these computers are assigned to perform are also expanding in number and magnitude. As a result, the problem of specifying and designing digital computers for space vehicles has increased in complexity.

Although most spaceborne digital computers are of the type often referred to as "general purpose," they have been in fact special-purpose machines in that a particular choice of design must reflect the requirements of the particular mission application. Thus, the program manager must be aware of the capabilities and limitations of spaceborne computer systems and the design tradeoffs which might affect his application.

The flight performance of spaceborne digital computer systems has generally been successful. However, a number of recurring problems have been experienced during the design, development, and testing of these machines. Previous systems have been very costly, have required major redesigns, and have caused significant schedule delays. Most difficulties have resulted from 1) lack of adequate capacity and flexibility to accommodate expanded requirements, 2) poorly defined subsystem and interface specifications, 3) the impact on software of changing mission requirements, and 4) reliability demands.

Important factors which influence the design and performance of spaceborne digital computer systems include:

The preferred design should consider the expanding nature of the requirements, potential advances in the technological state of the art, and the entire spectrum of environmental requirements. It should strike a balance between hardware complexity and software simplicity, and facilitate simulation, testing, and checkout.

This monograph discusses considerations which form a basis for the specification, design and evaluation of digital computer systems for spaceborne applications. Detailed discussion of the following items are outside the scope of this monograph: software development, mechanical and electrical design, hardware technology, I/O equipment, displays, and test equipments or specifications.

Related documents are SP-8053, "Nuclear and Space Radiation Effects on Materials,' June 1970 and SP-8054, "Space Radiation Protection," June 1970.


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