1、Public Lessons Learned Entry: 6716 Lesson Info: Lesson Number: 6716 Lesson Date: 2012-02-20 Submitting Organization: JPL Submitted by: David Oberhettinger Subject: Enforce Contamination Control Processes Abstract: Inspection of the principal OCO instrument revealed several incidents of component con
2、tamination. This indicated a lack of awareness of contamination risks, and an unfamiliarity with general contamination control practices, on the part of project personnel. Provide mandatory contamination control training for all project personnel early in project implementation. Ensure the involveme
3、nt of the cognizant contamination control engineer in the design and execution of fabrication, assembly, and handling plans for contamination-sensitive hardware. Description of Driving Event: The Orbiting Carbon Observatory (OCO), an Earth orbiting satellite mission managed by the NASA/Caltech Jet P
4、ropulsion Laboratory (JPL), was designed to make precise, time-dependent, global measurements of atmospheric carbon dioxide (CO2). The instrument, intended to detect CO2 from orbit, employed three channel-specific spectrometers. During assembly of the OCO Optical Bench Assembly (OBA) at JPL (Figure
5、1), four spectrometer lenses designed to image the strong CO2 channel were bonded into mounting rings. Following a thermal-vacuum bake-out procedure performed to complete outgassing of the silicone-based “RTV“ bonding material, visible contamination was observed on the lenses. Probable sources of th
6、e contamination included excessive curing agent in the RTV, use of a lens cleaning solvent containing aliphatic hydrocarbons and esters, use of plastic lens cases, use of gloves that had not been pre-cleaned, and parts handling procedures. The impact of the lens contamination was minimal due to the
7、performance characteristics of the instrument, but migration of the contamination to certain focal plane components would have had a major or catastrophic impact on the OCO mission. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Figure 1. Assembled
8、OCO optical bench (The telescope aperture is covered by the red cover on the right. The flight detector assemblies attach to the three camera lens exit flanges at the middle left.) The silicone contamination was documented in the Problem Reporting System (Reference (1). A detailed investigation was
9、made of the contaminant species, and evaluations were made on the potential impacts to instrument performance. A Contamination Control Engineer was assigned to OCO, and a more thorough inspection and sampling program was implemented to monitor surface cleanliness and prevent further contamination. O
10、ther sources of OCO instrument component contamination (Reference (2) included: Particulates on a telescope barrel located on a clean room bench were traced to paper (an unapproved material for use on the barrel) used to wrap painted parts. Use of a silicone adhesive tape (another restricted materia
11、l) to wrap a relay case during surface preparations prior to bonding, which caused high levels of silicone contamination of the relay. Large surfaces of the OBA were contaminated with molybdenum disulfide grease resulting from the failure to change gloves after lubricating screws and before handling
12、 the OBA. Significant labor was required in each case to identify the contamination source and clean the contaminated spaceflight hardware. The inspection and sampling activities implemented following the lens contamination event supported recovery and corrective actions prior to further hardware in
13、tegration, and they mitigated potential cost and schedule impacts from the lens contamination. The incidents indicated unfamiliarity with general contamination control practices- and a lack of awareness of project-specific contamination sources, hardware sensitivities, and risks- among project perso
14、nnel. References: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-1. “OCO Instrument Strong CO2 Spectrometer Lens Contamination,” JPL Problem/Failure Report No. 4891, August 1, 2006. 2. P.J. Guske, “OCO (Orbiting Carbon Observatory) Project Lessons L
15、earned Document (Final),” JPL Document No. D-26172, July 7, 2009, Paragraph 3.8.1. Lesson(s) Learned: 1. All project personnel should be made aware of contamination risks, material restrictions, and handling protocols prior to the beginning of flight hardware handling and assembly, including materia
16、ls processes and clean room operations. Optical assemblies are particularly sensitive to contamination sources, and certain optics may be affected by even a single particle. 2. Because the Contamination Control Engineer performs an essential role in the design and execution of fabrication, assembly
17、and handling plans for contamination-sensitive hardware, continuing oversight is necessary when working with forms of contamination that are often virtually invisible to the naked eye. This continuing oversight also involves Quality Assurance support for this activity in monitoring hardware assembly
18、. Recommendation(s): 1. Provide mandatory contamination control training for all project personnel early in project implementation (Reference (2). The training should not be limited to generic contamination control techniques, but rather should focus on control measures specific to the project facil
19、ities and hardware, including: o Instrument sensitivities and sensitive surfaces o Materials and processes approval and restrictions o Surface cleanliness requirements o Potential contamination sources o Contamination transfer mechanisms o Special handling procedures o Warning signs that require not
20、ification of the Contamination Control authority. 2. Following training of project personnel, continued involvement of the cognizant Contamination Control Engineer in the design and execution of fabrication, assembly and handling plans for contamination-sensitive hardware should be mandatory through
21、out the project life cycle to reduce the risk of unforeseen, but preventable, contamination events. The Contamination Control Engineer and clean room staff should reiterate the training and enforce clean room processes, including assuring the escorting of individuals who are not certified for clean
22、room entry and operations. Evidence of Recurrence Control Effectiveness: JPL has referenced this lesson learned as additional rationale and guidance supporting Paragraph 6.10 (“Engineering Practices: Materials, Processes, and Contamination Control”) in the Jet Propulsion Laboratory standard “Flight
23、Project Practices, Rev. 7,” JPL DocID 58032, September 30, 2008 Documents Related to Lesson: N/A Mission Directorate(s): Science Exploration Systems Additional Key Phrase(s): Integration and Testing Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,- Sa
24、fety and Mission Assurance.Product Assurance Safety and Mission Assurance.Quality Additional Categories.Facilities Additional Categories.Flight Equipment Additional Categories.Hardware Additional Categories.Payloads Additional Categories.Parts, Materials, & Processes Additional Categories.Packaging,
25、 Handling, Storage Additional Categories.Industrial Operations Additional Categories.Hazardous/Toxic Waste/Materials Manufacturing and Assembly Additional Categories.Spacecraft Additional Categories.Safety & Mission Assurance Additional Info: Project: Orbiting Carbon Observatory (OCO-1) Year of Occurrence: 2009 Approval Info: Approval Date: 2012-11-27 Approval Name: mbell Approval Organization: HQ Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
