The following is the first in a series of white papers which will be issued as a result of a task to define and qualify space grade fiber optic cable assemblies. Though to qualify and use a fiber optic cable in space requires treatment of the cable assembly as a system, it is very important to understand the design and behavior of its parts. These papers will address that need, providing information and "lessons learned" that are being collected in the process of procuring, testing and specifying the final assemblies. This installment covers information on optical fiber, coatings, cable components, design guidelines and limitations, radiation and reliability.

Fiber optic cable has been qualified and used in space by NASA GSFC and JPL. It is becoming a defacto standard for telemetry and command data transfer at GSFC and on New Millennium spacecraft through the use of the MIL-STD-1773 fiber optic bus. A new JPL design plans to use optical cable in an extra-vehicular application where additional radiation shielding will be required and atomic oxygen effects are a concern. Applications which have flown optical cable have used multimode fiber although single mode fiber is now finding its way into designs. The loss of the heritage fiber (Corning 100/140 micron fiber) requires qualifying multimode cables once more.

The original design of the flight MIL-STD-1773 bus used jacketed, buffered fiber and simplex connectors. More recent designs, including the arrangement used with the Hubble Solid State Recorder (SSR), also include buffered fiber pigtails with no strength members or jackets. This creates a significantly different cable configuration with respect its durability and ease/reliability of termination. New coating and cabling approaches have also emerged since NASA qualified its heritage design in the 1980’s. Military users have done quite a bit of work to define and test some of the new cables available but have not addressed some areas of performance of unique interest to NASA. A NASA contractor for the Space Station program has been instrumental in uncovering problems and researching alternatives. This paper is part of a larger body of work, sponsored jointly by NASA GSFC and JPL, which will communicate relevant results found to date for promising cable assembly designs and will investigate areas not covered by other users or still in need of solutions.

The information below is intended to communicate the most relevant issues being discussed at this time within the user and manufacturing community, relating to space grade optical cable designs. This information has been used to coordinate two prototype cables which are being fabricated and procured at this time. Specifications which describe these designs will be available shortly [1]. Pre-qualification testing of these designs is planned for the 2nd and 3rd quarter of 1997. Subsequent white papers will discuss issues related to optical connectors being used in space and the results of tests on protoflight cable assemblies.

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