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control engineering data

Configuration management is the process of controlling engineering data. It includes identifying the engineering data required for manufacture (configuration identification), controlling changes, maintaining the engineering database (configuration control), reviewing and auditing the engineering data (configuration audit), and verifying that the hardware is built as designed (configuration verification). Changes to the engineering data (engineering change orders and procedure change orders) are also tracked. For military contracts, MIL-STD 483, MIL-STD 1521, and DOD-STD 480 itemize configuration-management requirements. Most aerospace contractors have systems that conform to these standards.

12.2 Manufacture of High-Reliability Hardware

The first step in manufacturing spacecraft hardware is to translate the engineering data into manufacturing plans, flows, instructions, manufacturing aids, and tooling. This occurs as the design matures and manufacturing personnel may influence the design for ease of manufacture. Engineering data is formally released at a Critical Design Review. Typically, we review manufacturing plans at this time or in a Manufacturing Readiness Review shortly afterward.

The manufacturing planning starts with subassemblies by generating parts kits, preparing detailed procedures for assembly, and identifying inspection and test requirements. We must also identify special facilities (such as clean rooms); manufacturing methods, precautions, and controls; and training and certification levels of personnel. Based on these plans, we then call out the manufacturing steps in detailed procedures. A copy of the procedures travels with the hardware and is checked off as

* Military specifications and standards are no longer being maintained and are due to be superseded by industry standards which are not yet in place.

the steps are completed. This paper becomes part of the permanent record of the assembly. Inspection and test results are also part of the record, and some installations include photographs of each assembly.

Manufacturers buy most raw materials from certified vendors, who certify the material quality. They buy electronic piece parts to meet individual specifications which call out performance and quality requirements. Under current practices, high-reliability electronic parts are constructed for a particular program. Such procurement takes a long time, and most parts undergo extensive testing before combining into components. Flight hardware usually requires the highest level of reliability, which in the past has been called S-level. Lower reliability parts may work for prototype and qualification units not intended for flight. In addition to vendor lead times, each part order must be bid and negotiated, which adds weeks to the procurement time. The current practice is to have the part supplier test each part for performance (group A tests) and a sample from each lot to extremes (group B and C tests). The manufacturer bums the parts in while monitoring their performance and does a destructive physical analysis (DPA test) on a sample.

The industry is currently undergoing a major revision in the way that parts are specified and procured. In the Department of Defense this is called "Acquisition Reform" and is characterized by elimination of government specifications and standards for parts and processes. Industry is expected to replace these specifications and standards with their own controls or use Professional Society Standards. A consistent set of such standards is not yet in place although efforts are under way to produce them (see for instance AIAA Recommended Practice for Parts Management AIAA R-100-1996). Extensive parts information is also available on the Internet at Air Force and NASA sites.

To contend with the lead times for parts and materials, manufacturers must order them before they see component engineering data. Thus, we establish a Project Approved Parts List (PAPL) and Project Approved Materials List (.PAML) early in the program. Because designers must use the preferred part or identify and justify new parts, these approved lists reduce the number of part types and allow early procurement

Manufacturing facilities cover mechanical manufacturing, electronic manufacturing, spacecraft assembly and test and special functions. Mechanical manufacturing includes standard machine shops, plus locations for mechanical assembly, plating and chemical treatment composite manufacture, adhesive bonding, and elevated temperature treatment Although most aerospace facilities are quite clean, mechanical manufacturing does not normally need controlled cleanliness. But electromechanical and optical manufacturing, as well as the tailoring of thermal blankets, do need controlled clean rooms—normally separate from conventional mechanical manufacturing. Table 12-5 shows cleanliness requirements for various operations.

Electronic manufacturing facilities include areas for building printed circuits and clean rooms for building and testing electronic assemblies. Test facilities may include anechoic chambers and screen rooms containing various types of general-purpose test equipment as well as special purpose testers for circuit boards and components. Component tests may also require environmental test facilities.

Spacecraft assembly and test operations are normally conducted in controlled-cleanliness facilities, which are often high-bay hangars. Spacecraft functional tests are conducted with special purpose test sets. Spacecraft environmental testing requires large vibration and thermal-vacuum equipment

TABLE 12-5. Facility Cleanliness Requirements (FED STD 209). Class 10,000 means less than 10,000 particles per cubic foot

Facility/Operation

Cleanliness

Mechanical Manufacturing

Not controlled

Electronic Assembly

Class 10,000

Electromechanical Assembly

Class 100

/nertial Instruments

Class 100

Optical Assembly

Class 100

Spacecraft Assembly and Test

Class 100,000

Many times a spacecraft will need a special facility to protect sensitive equipment or prevent outside interference. Because optical equipment is especially sensitive to contamination, it must be ultra-clean. Payload instruments that require cryogenic temperatures, absence of magnetic fields, or RF isolation call for special facilities which may increase program cost and schedule.

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Reasonable care has been taken to ensure that the information presented in this book is  accurate. However, the reader should understand that the information provided does not constitute legal, medical or professional advice of any kind.

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