1、Lessons Learned Entry: 1334Lesson Info:a71 Lesson Number: 1334a71 Lesson Date: 2003-04-21a71 Submitting Organization: JPLa71 Submitted by: Carl S. Guernsey / David J. OberhettingerSubject: Cleanliness of Diaphragm Propellant Tanks (2000) Description of Driving Event: The propellant tanks on the Gene
2、sis spacecraft were filled with isopropyl alcohol (IPA) prior to modal and acoustic vibration testing in order to obtain the proper spacecraft dynamic response. IPA was used as a referee fluid in place of the hydrazine propellant because of its similar mass, as well as for safety reasons. When the G
3、enesis tanks were drained about ten days later, levels of particulate and non-volatile residue (NVR) were found that significantly exceeded the cleanliness specification. Both the particulate levels and the NVR were brought back into specification by filling the tank with IPA and draining it several
4、 times, followed by vacuum drying. A cleanliness demonstration test was subsequently performed on an Atlas Centaur propulsion system hydrazine tank that was of a design similar to Genesis. The Atlas tank was also found to be out-of-specification with respect to particulate contamination. After the t
5、ank was exposed to the IPA cleaning fluid for about a day, it was also found to be out-of-specification on NVR. A total of 16 Atlas tanks were subsequently returned to the vendor. The Genesis tank is a titanium sphere with a diaphragm fabricated from AF-E-332 rubber material. The diaphragm is incorp
6、orated to ensure gas-free propellant expulsion. When empty, the diaphragm conforms to the lower wall of the tank. As the tank is filled, the diaphragm reverses toward the upper dome of the tank. The tank is cleaned at the piece-part level and subjected to a final cleaning at the assembly level. The
7、ability of cleaning fluids to remove particulate from the assembled tank during this final cleaning may have been limited by the fact that the vendor used only 1 liter of IPA for this procedure. Furthermore, the vendor has asserted that transportation of a “clean“ tank may result in particulates bei
8、ng released from the faying surfaces near where the diaphragm is attached to the wall and/or in generation of particulates due to rubbing of the diaphragm on the tank wall. It is likely that the out-of-specification particulate seen in the Genesis and Atlas tanks was a result of imperfect cleaning a
9、nd/or this self-generation mechanism. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Further materials testing verified that the NVR contamination was a substance leaching out of the rubber diaphragm material following prolonged exposure to IPA. Thi
10、s AF-E-332 diaphragm material has been used in this application since 1974, and contact with hydrazine does not produce degradation of the material or performance problems in propulsion systems. Exposure to IPA for periods of over 4 hours, however, can produce excessive NVR. Similar tank vendor clea
11、ning processes were used on the Deep Impact project, but it was found that conservative propulsion system filter sizing mitigated the threat of high particulate levels. References: Genesis Tank NVR Contamination Interim Report, (contractor document), September 15, 2000. Additional Key Words: cleanli
12、ness verification, decontamination, environmental test, alcohol flushLesson(s) Learned: Following delivery, diaphragm-type propellant tanks may exhibit particulate contamination levels that exceed the vendors cleaning tag results and also the customer specification. Additional particulate contaminat
13、ion may be generated by subsequent transportation of the tank and/or the system. Isopropyl alcohol can leach out-of-specification amounts of NVR contaminant from AF-E-332 diaphragms in propulsion tanks when exposed for periods significantly longer than 4 hours. Recommendation(s): 1. Conservatively s
14、ized propulsion system filters should be used immediately downstream of diaphragm propellant tanks in order to accommodate particulate levels which may exceed the specification levied on the tank.2. Vendor procedures for cleaning of diaphragm propellant tanks should be carefully reviewed to ensure t
15、hat adequate quantities of cleaning fluid are being used to ensure the internal surfaces are fully wetted and agitated.3. Propellant tank cleaning procedures should limit the time the diaphragm is exposed to isopropyl alcohol to no more than 4 hours. Exposure should be followed immediately by vacuum
16、 drying of the tank.4. Do not introduce isopropyl alcohol into diaphragm-type propellant tanks for extended periods during system test unless the tanks are subsequently re-cleaned, verified clean, and vacuum dried.Evidence of Recurrence Control Effectiveness: N/AProvided by IHSNot for ResaleNo repro
17、duction or networking permitted without license from IHS-,-,-Documents Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): a71 Flight Equipmenta71 Hardwarea71 Parts Materials & Processesa71 Pressure Vesselsa71 Spacecrafta71 Test ArticleAdditional Info: Approval Info: a71 Approval Date: 2003-05-14a71 Approval Name: Carol Dumaina71 Approval Organization: JPLa71 Approval Phone Number: 818-354-8242Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
