1、Public Lessons Learned Entry: 6056 Lesson Info: Lesson Number: 6056 Lesson Date: 2010-02-2 Submitting Organization: JSC Submitted by: Kristen Kinder Subject: Liquid Oxygen (LO2) Purity Impacts Engine Performance Abstract: STS-114 experienced a very low Fuel Bias which lead to an investigation regard
2、ing possible causes. One item that was reviewed was the effect that LO2 purity would have on Space Shuttle Main Engine (SSME) performance. Investigation yielded large differences between LO2 purity requirements between Stennis Space Center (SSC) and Kennedy Space Center (KSC) and that LO2 purity was
3、 not accounted for in overall performance predictions. It was also identified that the current LO2 purity requirements were not adequate with the use of Flight Derived Dispersions to protect for an abnormally low LO2 purity day. Description of Driving Event: STS-114 experienced a very low Fuel Bias
4、which lead to an investigation regarding possible causes. The LO2 purity at SSC where the SSMEs are tested was found to be very different than the LO2 purity at KSC and not accounted for in performance predictions. In addition, the run tanks at SSC are pressurized with Gaseous Nitrogen (GN2) which i
5、ntroduces more contaminant in the LO2. Actions taken: 1. LO2 purity requirements were tightened to guarantee adequate LO2 at KSC on day of launch. 2. Additional LO2 purity sampling was implemented to every flight instead of every six months to ensure adequate LO2 on day of launch. 3. Increased LO2 p
6、rocurement requirements at KSC only. 4. Provisions were put in place to adjust APM on day of launch should we have lower than expected LO2 delivery (but still within procurement requirements). Lesson(s) Learned: 1. By ensuring adequate LO2 purity, the likelihood of an LO2 Level Cut Off (LLCO) was dr
7、astically reduced due to off-nominal engine performance. 2. By knowing LO2 purity prior to launch, the ability to hold back APM to offset for a low LO2 purity day was also achieved. Recommendation(s): *TEST AS YOU FLY, FLY AS YOU TEST* 1. Would strongly recommend future LO2 based engine programs imp
8、lement a method to sample LO2 purity in-line/in-run during engine acceptance testing to establish a baseline. 2. Would recommend future programs maintain a preflight measurement capability of LO2 purity to ensure adequate performance during flight. 3. Would recommend implementing LO2 purity requirem
9、ents for both test and flight that are compatible and correct for any differences in pre-flight predictions. 4. Would recommend not pressurizing LO2 run tanks at SSC with GN2, this only worsens the purity of the LO2 in the stand. Instead consider pressurizing with GO2. Evidence of Recurrence Control
10、 Effectiveness: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-N/A Documents Related to Lesson: SE-S-0073, NASA Specification Fluid Procurement and Use Control Mission Directorate(s): Space Operations Additional Key Phrase(s): Launch support systems
11、 Vehicle concepts Acquisition / procurement strategy and planning Cryogenic Systems Propulsion Level II/III requirements definition Additional Info: Project: Space Shuttle Program Approval Info: Approval Date: 2011-09-14 Approval Name: mbell Approval Organization: HQ Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
