1、Lessons Learned Entry: 2043Lesson Info:a71 Lesson Number: 2043a71 Lesson Date: 2009-02-17a71 Submitting Organization: JPLa71 Submitted by: David Oberhettingera71 POC Name: Dan Karmona71 POC Email: Dan.Karmonjpl.nasa.gova71 POC Phone: 818-354-9700Subject: Understand What Cleaning Means In The Context
2、 Of The Flight Item Abstract: Isopropyl alcohol (IPA) was used to “clean“ instrument parts. Residual IPA interfered with the instrument Level 1 requirements. Subsequent helium purging did not reduce IPA concentrations to acceptable levels. Determine what “cleaning“ means within the context of the re
3、quirements. Following bakeout to remove cleaning agents, retest over an extended period to assure that concentrations are not increasing as trapped quantities are released.Description of Driving Event: Environmental Monitors on Station (EMOS) is a NASA program to design, build, and test a series of
4、environmental monitors for installation on the International Space Station (ISS). The Vehicle Cabin Atmosphere Monitor (VCAM) is a rack-mounted EMOS instrument for monitoring the air in the ISS. VCAMs pre-concentrator, gas chromatograph and mass spectrometer will detect trace amounts of organic mole
5、cules. Internal software will perform the identification and quantification. VCAM is delivered with an Orbital Replacement Unit (ORU), a delivery system for the consumable gases (i.e., a carrier gas and calibrant mixture) required for VCAM operation. Each ORU (Figure 1) is designed for 12 months of
6、operation, followed by on-orbit replenishment. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Figure 1 is a color photo of a complex arrangement of tanks, metal feed lines, and valves mounted on a flat metal tray. The open unit appears to be roughly
7、 cubical in shape, such that the entire unit could be slid into a rack within an enclosed volume. There are two tanksFigure 1. VCAM ORUIn accordance with a standard JPL cleaning procedure, isopropyl alcohol (IPA) was used liberally on ORU parts, both prior to and during fabrication and integration.
8、The flow of helium gas at a slightly elevated temperature through the ORU units during a purging procedure was expected to remove any IPA residue. Instead, while testing the VCAM with an ORU installed, excessive levels of residual IPA were detected in both the carrier and calibrant gases (Reference
9、1). Due to the high sensitivity of the mass spectrometer, the IPA residue requirement calls for less than 200 parts per billion (ppb), whereas the detected concentration was in the double and triple-digit parts per million (ppm) range. This high level of residual IPA interferes with the VCAM Level 1
10、 requirement to detect hazardous concentrations of IPA within the range of 1 to 10 ppm in the ISS cabin air. VCAM measurements verified that IPA adsorbed onto soft goods and having filled small volumes would not likely be removed by the standard purging protocol. IPA measurements made following stan
11、dard purging trials (e.g., bakeout) indicated that the IPA continued to desorb. Thermal-vacuum purging was needed to reduce the residual IPA concentration below the 200 ppb requirement. In this ORU-specific case, placing the unit in thermal-vacuum at 10-5torr and 80 degrees C for 150 to 200 hours pr
12、oved adequate after other alternative methods were tried without success. Follow up testing confirmed that IPA levels remained at less than 200 ppb, and further desorbing of IPA was not observed. References: 1. “Isopropyl Alcohol Residue,“ JPL Problem/Failure Report No. 13449, September 5, 2008.2. “
13、General Cleaning Requirements for Spacecraft Propulsion Systems and Support Equipment, Detail Specification for,“ Jet Propulsion Laboratory (JPL) Spec No. FS504574C, May 28, 1974.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Lesson(s) Learned: 1. I
14、t can be extremely difficult and expensive to remove residual IPA from a sensitive instrument. The current Precision Cleaning practices and processes, such as those specified by Reference (2), may be inadequate to meet the needs of sensitive instrumentation. The Precision Cleaning processes commonly
15、 used by NASA does not solicit the input on customer requirements that is needed to identify special needs. These needs may include alternative chemicals and methods for cleaning and verification. 2. For an extended period following the implementation of standard purging protocols, contaminant conce
16、ntrations may increase as gases are released from soft goods and small volumes.Recommendation(s): 1. Ensure that the Precision Cleaning process is geared to unique needs and is sensitive to the possibility that the customer has failed to state special requirements. Actively involve the customer in t
17、he preparation and review of the cleaning procedure to assure that special requirements are identified. 2. Verification that flight hardware contaminants have been fully purged should include retesting over an extended period to assure that concentrations have not increased as trapped contaminants a
18、re released.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 Project Practic
19、es, Rev. 7,“ JPL DocID 58032, September 30, 2008.Documents Related to Lesson: N/AMission Directorate(s): a71 Aeronautics Researcha71 Exploration Systemsa71 ScienceAdditional Key Phrase(s): Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-a71 0.a71 0.a
20、71 1.Engineering design and project processes and standardsa71 1.Level II/III requirements definitiona71 0.a71 1a71 1a71 0.a71 1.Product Assurancea71 1.Qualitya71 1.Flight Equipmenta71 1.Hardwarea71 1.Industrial Operationsa71 1.Parts, Materials, & Processesa71 1.Payloadsa71 1.Safety & Mission Assurancea71 1.SpacecraftAdditional Info: a71 Project: Vehicle Cabin Atmosphere MonitorApproval Info: a71 Approval Date: 2009-05-06a71 Approval Name: mbella71 Approval Organization: HQProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
