«WORKMANSHIP STANDARD FOR FIBER OPTIC TERMINATIONS, CABLE ASSEMBLIES, AND INSTALLATION Measurement System Identification: Metric (English) NASA-STD ...»
Soxhlet Extraction: A process similar to distillation used to separate materials. Uses relative to this standard include removing oils, resins, or other contaminants from cotton swabs or wipes.
Splice: An interconnection method for joining the ends of two optical fibers in a permanent or semi-permanent fashion.
Splice, Chemical Splice: A permanent joint made with an adhesive such as UV-cured polymer or epoxy.
Splice, Fusion Splice: A splice accomplished by the application of localized heat sufficient to fuse or melt the ends of two lengths of optical fiber, forming a continuous single optical fiber.
Splice, Mechanical: A fiber splice accomplished by fixtures or materials, rather than by thermal fusion.
Splice Enclosure: A device surrounding the spliced area of an optical fiber used to protect the splice from physical damage.
Splice Tray: A container used to organize and protect spliced fibers.
Strength Member: That part of a fiber optic cable composed of kevlar aramid yarn, steel strands, or fiberglass filaments included to increase the tensile strength of the cable, and in some applications, to support the weight of the cable.
Ultraviolet (UV): Optical radiation for which the wavelengths are shorter than those for visible radiation that is approximately between 1nm and 400nm.
Working Life: The duration of time that an adhesive can be used for a process and still achieve the intended result, with the intended quality, as measured from the time it is mixed or is fully defrosted, in the case of frozen sub-batches.
General When there is a conflict between the requirements of NASA-STD-8739.6 and those herein, the requirements in NASA-STD-8739.6 shall take precedence.
When Electrostatic Discharge (ESD) control is required during workmanship operations defined herein, the ESD control requirements of NASA-STD-8739.6 shall apply.
A program shall be established to assure continuing process capability.
Special controls shall be developed for process parameters and equipment settings that influence product compliance with critical performance and quality requirements.
Design Considerations The following considerations shall be used when selecting and qualifying parts, materials and processes used for terminating fiber via splicing or when manufacturing cables that meet the
requirements of this standard:
a. Construction, weight, and physical dimension requirements for cables, splices and subsystems.
b. Tensile strength continuity between spliced cables without concentrating the cable tensile load on the splice junction.
c. Cable stress relief and environmental sealing between the cables and splice, or the cables and the connectors, to prevent the entry of external contaminants and to provide protection from both cable tensile forces and cable axial compressive forces.
d. Optical, mechanical, and environmental performance requirements for cables, splices and subsystems.
e. Physical and functional interchangeability, for all splice parts and for all connector parts of the same type without the need for modification of the parts or of the splicing or terminating equipment.
f. Use only of connector parts from the same manufacturer in a given mated connector pair to prevent connector intermateability problems.
g. Protection against electrolysis and corrosion when dissimilar metals are used in contact with each other.
h. Seals for isolating splice and connector interiors from humidity and contamination.
i. Mechanical protection parts and methods for splices. The use of splice trays is recommended for multiple splices.
j. Staking requirements in NASA-STD-8739.1.
k. Minimum fiber and cable bend radii, both short term and long term.
l. Use of clear heat shrinkable sleeving to improve ability to inspect.
TRAINING AND CERTIFICATION PROGRAMThis section has been superseded by NASA-STD-8739.6. Refer to NASA-STD-8739.6, Chapter 5 and Appendix A for applicable training requirements.
FACILITIES, EQUIPMENT AND MATERIALSEnvironmental Conditions The environmental control requirements of NASA-STD-8739.6 shall apply.
Light intensity shall be a minimum of 1077 lumens per square meter (lm/m2) (100 footcandles) on the surface where fiber optic fabrication operations are being performed, inspected, or tested. Supplemental lighting may be used to achieve the required lighting levels.
Tools and Equipment The tool and equipment selection and control requirements of NASA-STD-8739.6 shall apply. See NASA-STD-8739.6 for metrology and calibration requirements.
The supplier's process documentation for tool and equipment use and control shall be available for review and approval prior to processing mission hardware.
Fiber Stripping Tools Chemical and mechanical stripping methods and materials shall be of a design that will not impart damage to the optical fiber or termination elements. Refer to Safety Data Sheets (SDS) for proper handling of chemical stripping materials.
Fixed fiber diameter tools shall be capable of removing the coating from one specific fiber diameter (e.g., 125 microns).
Variable fiber diameter tools shall be capable of removing the coating from a range of fiber diameters by using interchangeable die to accommodate the different fiber diameters.
CAUTION: STRIPPING CAN CAUSE NICKS, SCRATCHES, OR CHIPS
THAT ARE NOT EASILY DETECTABLE. USE EXTREME
CARE WHEN SELECTING AND EVALUATING TOOLS.Fiber Cleaving Tools The fiber cleaving tool design shall be such that the cleaved fiber end is retained, thus preventing possible injury to personnel.
The following capabilities of the selected fiber cleaving tools shall be demonstrated
prior to use for producing mission hardware:
Capable of allowing a clean, fragment-free, crack-free cleave which minimizes chips or other defects as shown in Appendix A on the cleaved fiber end.
Capable of allowing the operator to control the strip length of the fiber to meet end item design and quality requirements.
Capable of producing a cleaved fiber with an end-face angle as required by engineering documentation.
Inspection Aids Magnification aids shall be capable of viewing both the bare optical fiber and the termination without imparting damage.
Magnification aids shall be capable of rendering true colors, proportional dimensions, and adequate resolution at the magnification chosen to perform the specified inspection.
For inspection of cleanliness, chemical strip wicking, cracks, nicks, and cuts in the glass fiber and coating, magnification shall be between 50X and 80X.
For inspection of connector end-faces and cleaved bare fibers, magnification shall be between 100X and 200X.
For critical end-face measurements, an interferometer shall be used for inspections.
Additional Nondestructive Inspection Methods The use of other nondestructive inspection methods (e.g., laser or automated inspection systems) is permitted. The method chosen shall be fully documented and not damage parts.
When other nondestructive inspection methods are used per 220.127.116.11, inspectors shall be trained to use the applicable controlled procedure.
Storage and Handling Containers shall be compatible with the stored materials.
Personnel shall ensure that hands and tools are clean prior to processing optical parts.
Stripped fibers or connector interfaces shall not be handled with bare hands due to risk of contamination to the fiber interface.
Parts and Materials Selection Vinyl dust caps shall not be used for flight applications.
See sections 4.2 and 9.1.3 for design considerations that should influence part and material selections.
Solvents The solvents used for the removal of grease, oil, dirt, or other debris shall be selected for their ability to remove both ionic and nonionic contamination.
The solvents used shall not degrade the materials or parts being cleaned.
Solvent containers shall be properly labeled.
Solvents shall be identified in materials lists.
SDS for solvents shall be available for personnel review and posted where solvents are being used.
When any type of water is used, drying shall be accomplished immediately after its use.
Exposure of bare fiber to water should be minimized.
Solvents have the potential of removing marking information from parts. Marking permanency testing shall be performed as part of the selection and qualification process for any solvent.
Adhesives Adhesives Selection Adhesives shall be readily dispensable. Adhesives and the cure schedule shall be compatible with the part and process and not interfere with the termination performance.
Adhesives shall be noncorrosive.
Some adhesives can become brittle when they have come in contact with solvents used for cleaning fiber optic assemblies. Process design and qualification shall include verifying compatibility between the adhesives and the solvents.
Adhesives shall be selected such that the glass transition temperature (Tg) is above the maximum temperature the assembly will be exposed to during system-level processing, during testing, and during the mission by a margin defined by project requirements.
Process Controls Dispensing equipment shall not contaminate the adhesive material (e.g., silicone lubricated syringes).
Adhesives shall not be used in the optical path of the termination.
Adhesives shall provide good wetting action that develops strong bonding between the fiber and the internal fiber channel of the connector or mechanical splice.Mixed
adhesives shall be degassed (e.g., centrifuge or vacuum) before they are applied to optical fibers and connectors.
CAUTION: CARE SHOULD BE TAKEN NOT TO INTRODUCE
BUBBLES OR VOIDS INTO ADHESIVE DURING MIXING
OPERATIONS. BUBBLES AND VOIDS IN THE
ADHESIVE SURROUNDING OPTICAL FIBERS IN
CONNECTORS HAVE BEEN CORRELATED TO FIBERBREAKAGE.
For all multipart epoxies, a record for each mix batch shall be maintained.
The mix record for the multipart epoxy shall document:
a. Unique batch identifier (e.g. serial number).
b. The unique identifier of each sub-batch if separated into sub-batches (i.e. into syringes). It is recommended that sub-batch identifiers are a derivative of the parent batch identifier.
c. Materials used (including manufacturer, part number, traceability code, expiration date) d. The mix ratio e. Ambient conditions (temperature, humidity) f. Time mixed g. Working life h. Date i. Operator j. Mix procedure name or number and revision k. Test specimen acceptance test results The mix record for premixed, preloaded syringes as obtained directly from a commercial supplier may not be available. When this is the case, the manufacturer name, product identification (e.g. part number) and lot date code for each syringe shall be recorded and used for product traceability.
When using preloaded syringes instead of a newly mixed batch, data shall be recorded to provide evidence that the working life was not exceeded.
Syringes used for epoxy dispensing shall be verified to be silicone-free prior to use.
Silicones are used by some syringe suppliers to reduce plunger friction. Silicone is detrimental to polymeric bond reliability.
A test specimen shall be produced for all mixed batches of adhesives to verify that the mix was performed correctly, prior to applying it to mission hardware. With NASA preapproval the test specimen may be cured concurrently with the material used on the mission hardware (i.e. cured with the mission hardware).
The witness sample shall be stored under the standard controlled laboratory conditions defined in NASA-STD-8739.6.
The witness sample shall be traceable to the mix record.