1、Lessons Learned Entry: 1997Lesson Info:a71 Lesson Number: 1997a71 Lesson Date: 2008-11-25a71 Submitting Organization: JPLa71 Submitted by: David Oberhettingera71 POC Name: Paul Willisa71 POC Email: Paul.B.Willisjpl.nasa.gova71 POC Phone: 818-354-6998Subject: Application Notes Facilitate the Use of N
2、on-NASA Standards Abstract: NASA use of general-industry standards and specs issued by standards developing organizations and international bodies is explicitly encouraged by government policy, but these general-use documents are not typically prepared with consideration given to spaceflight applica
3、tions. NASA users of non-NASA technical standards/specs issued for industry-wide use should consult “application notes“ that clarify provisions that may not be suitable for application to NASA systems.Description of Driving Event: Technical standards capture lessons learned and new technology, provi
4、de a common base for interoperability, and facilitate engineering excellence. These include standards published by NASA, other government agencies, standards developing organizations (SDOs), and international bodies. Standards, specifications (specs), and handbooks published by NASA are particularly
5、 valuable as they provide direction that is specific to the space environments and other design challenges that are faced solely by NASA missions. However, federal government policy (Reference (1) explicitly discourages the preparation of new NASA standards and handbooks where existing industry stan
6、dards are technically adequate. Although this has the salutary effect of minimizing the maintenance of duplicative standards, it also means that a NASA system operating in the vacuum of space has had to justify non-use of a grease specification intended for army tank tracks. Another extreme- but rea
7、l- example is the designation of a paint specification for naval ships for use in spacecraft coatings. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Clearly, general-use industry standards and specs may not be optimal for spaceflight applications w
8、here, for example, the out-gassing properties of lubricants and paints must be rigorously controlled. Furthermore, many specs have recently been rewritten to require the use of recycled and commercial-off-the-shelf (COTS) materials in the production process. Requirements have been eliminated that ha
9、ve called for (1) customer notification of changes in product materials and processes and (2) testing to re-qualify the product over the full range of properties. The U.S. Office of Management and Budget (OMB) requires NASA and other federal agencies to report how many government standards were elim
10、inated and how many industry voluntary consensus standards (VCS) were adopted each year, but projects have not been required by the OMB to assess the risk of applying non-optimal requirements. To minimize this risk, NASA has pioneered the preparation of application notes that add NASA-specific cauti
11、ons or caveats to a number of industry standards adopted by NASA. The purpose of the application notes is to identify provisions in a document that may be widely applicable to general industry or even to the aerospace industry, but may be incorrect or misleading when used in the design of NASA space
12、flight systems. The application notes are prepared by the NASA Engineering Standards Panel (NESP) and made available, along with the full text of the industry documents, in the NASA-maintained standards repository (Reference (2). A pyrovalve (pyrotechnic device) specified for use as a backup in the
13、Mars Reconnaissance Orbiter (MRO) Propellant Isolation Assembly (PIA) provides an example of the need for an application note. The material used to fabricate the primer chamber component was flagged as susceptible to stress corrosion. Inspection of a previously activated unit (Figures 1 and 2) showe
14、d failure due to stress corrosion cracking of the primer chamber body (PCB) (Reference (3). The Materials Identification and Usage List (MIUL) for the pyrovalve identified the PCB as fabricated from 7075 aluminum alloy with a T651 temper. AMS-QQ-A-225/9, the industry spec adopted by NASA and DoD for
15、 procurement of this material, states that, “This alloy is intended for use where high strength and good corrosion resistance are required“ (Reference (4). In this application, however, the 4000 psi of high chloride combustion gas pressure to which the material is subjected upon firing of the booste
16、r charge causes stress corrosion cracking. Figure 1 is a high contrast photographic image similar to an X-ray. A dark circular mass lies in the upper left quadrant of the image; the periphery of the dark circle has a vaguely spongy texture. The remainder of the image is an off-white blank. Thin dark
17、 striations, similar to gullies make by running water, extend from the dark circle into the off-white Figure 2 is a color photo of a silvery metal part. Most of the photo is taken up by a barrel-shaped structure, with several thin cracks in it that extend parallel to the longest axis of the structur
18、e. A threaded extension protrudes from the right end of the barrel; its diameter is about one-half the diameter of the barrel.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-area. These represent voids where there are cracks in the material. There ar
19、e three main branches of these striations, each leading to narrower patterns of striations.Figure 1. Scanning electron microscope (SEM) image shows evidence of stress corrosion cracking of the MRO PIA backup pyrovalve.Figure 2. Effect of stress corrosion cracking on the MRO PIA backup pyrovalve.An a
20、pplication note in the NASA standards repository would alert NASA users of Reference (4) to the circumstances under which Paragraph 6.1 (Intended Use) is misleading in regard to stress corrosion resistance. The application note would point NASA users to MSFC-SPEC-522B for rating of resistance to str
21、ess corrosion cracking, and would provide guidance on the threshold crack propagation stress for NASA applications. References: 1. OMB Circular A-119, “Federal Participation In The Development And Use Of Voluntary Consensus Standards And In Conformity Assessment Activities,“ February 10, 19982. NASA
22、 Standards and Technical Assistance Resource Tool, http:/standards.nasa.gov 3. “Valves Corrosion,“ JPL Problem/Failure Report No. Z85547, January 21, 2005.4. AMS-QQ-A-225/9, “Aluminum Alloy 7075, Bar, Rod, Wire, and Special Shapes; Rolled, Drawn, or Cold Finished,“ Society of Automotive Engineers (S
23、AE), Paragraph 6.1: Intended Use, July 1, 1997.Lesson(s) Learned: NASA use of industry standards and specs issued by SDOs like the Society of Automotive Engineers (SAE) or the American Society for Testing and Materials (ASTM) is explicitly encouraged by government policy, but these general-use docum
24、ents are not typically prepared with consideration given to spaceflight applications. Application of these standards to spacecraft systems without the preparation and review of appropriate guidance may pose an unacceptable and unnecessary risk to mission success. The deregulation of industry by elim
25、ination or relaxation of government standards and specs for the procurement of qualified materials, processes, and products (formerly audited and enforced by entities such as Defense Contract Administration Services (DCAS), has further increased the risk that even products known to be acceptable wil
26、l not perform as expected.Recommendation(s): NASA users of non-NASA engineering standards issued by standards developing organizations for industry-wide use should consult application notes that alert NASA users to provisions of questionable applicability to NASA systems. NASA users should also assi
27、st in identifying such provisions that necessitate the preparation of new application notes.Evidence of Recurrence Control Effectiveness: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-JPL has referenced this lesson learned as additional rationale a
28、nd guidance supporting Paragraph 4.1.2 (Flight System Design: General- Design Standards) in the JPL standard “Design, Verification/Validation and Operations Principles for Flight Systems (Design Principles),“ JPL Document D-17868, Rev. 3, December 11, 2006.Documents Related to Lesson: Click here to
29、download document. Mission Directorate(s): a71 Space Operationsa71 Sciencea71 Exploration Systemsa71 Aeronautics ResearchAdditional Key Phrase(s): a71 Missions and Systems Requirements Definition.Level 0/1 Requirementsa71 Systems Engineering and Analysis.Engineering design and project processes and
30、standardsa71 Systems Engineering and Analysis.Level II/III requirements definitiona71 Safety and Mission Assurance.Early requirements and standards definitiona71 Additional Categories.NASA StandardsAdditional Info: a71 Project: variousApproval Info: a71 Approval Date: 2009-02-10a71 Approval Name: mbella71 Approval Organization: HQProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
