Status Report

NASA Lessons Learned: SSME 0523 Test 902-772 Major Mishap

By SpaceRef Editor

October 1, 2003

Filed under NASA Public Lessons Learned System (PLLS) Database, Space Shuttle, US

PLLS Database Entry: 0934

Lesson Info

Lesson Number: 0934
Lesson Date: 16-jun-2000
Submitting Organization: MSFC
Submitted by: Tom Hartline

Subject/Title/Topic(s):

SSME 0523 Test 902-772 Major Mishap

Description of Driving Event:

Space Shuttle Main Engine (SSME) test 902-772 was conducted Friday, June 16, 2000, on engine 0523 with High Pressure Fuel TurboPump (HPFTP/AT) 8109R1, and High Pressure Oxidizer Turbopump (HPOTP/AT) 8308. The test was prematurely cutoff at 5.2 seconds due a violation of the High Pressure Fuel Turbine (HPFT) temperature limit of 1860 degrees Rankine. The high temperature led to High Pressure Fuel Turbopump turbine damage and the declaration of a type A mishap.

The major objective of this test was to characterize the effects of Chamber Coolant Valve (CCV) position on HPFT temperature. Engine 0523 was in the Block Ia configuration (small throat Main Combustion Chamber) with the exception of the Pratt & Whitney High Pressure Fuel Turbopump. It had previously been tested for 119 starts and 59,278 seconds. It was the fleet leader in both starts and seconds.

Nominal operation was planned for the first 90 seconds of the test. The first indication of abnormal performance occurred 2.7 seconds into the start transient. High Pressure Fuel Turbine temperature measurements in two of the four locations began increasing beyond predictions. Other two measurements remained normal. All other engine performance parameters indicated normal engine operation at this time. The two high measurements reached the 1860 degree limit at 4.04 seconds. At approximately 4.97 seconds, the High Pressure Fuel TurboPump vibration levels increased sharply and engine performance dropped. The HPFT temperature limit was activated at 5.04 seconds and a failure identification (FID) was issued, accompanied by a major component failure (MCF). The control and data simulator (CADS) commanded shutdown. The turbine temperature measurements continued to increase after shutdown, reaching a high of 2165 degrees Rankine.

Post test inspections revealed heat damage to the High Pressure Fuel Turbine. The Fuel Preburner fuel manifold was heavily contaminated with “LOX” tape.

During the assembly of SSME 0523, tape was introduced into the fuel system during some “hands on” process (temporary closure, contamination barrier, unintentional introduction, etc.). The tape contamination went unnoticed and was left in the fuel system during the remainder of assembly and pre-test activities.

On June 16, 2000, Stennis Space Center conducted test 902-772. SSME 0523 was to be tested for a scheduled duration of 210 seconds. At engine start the tape contamination was forced downstream in the fuel system, eventually coming to rest as debris in both the Fuel Preburner (FPB) injector and Oxidizer Preburner (OPB) injector. The amount of debris in the FPB was sufficient to block the fuel inlet holes to several FPB injector elements in a localized area. This blockage caused a localized high mixture ratio area in the preburner without affecting overall engine system performance. Data analysis indicates a localized temperature increase occurred in the vicinity of HPFT DS T CH A measurement and the HPFT DS T measurement at joint KG2dt beginning at approximately 2.7 seconds.

At approximately 4.9 seconds, the localized temperature increase caused melting of the support struts and first stage vanes in the HPFTP/AT. The melting of the turbine stator caused local structural failure. The liberated material continued down the hot gas flow stream, impacting the first stage blades, causing the first stage blades to fail due to impact. This caused significant HPF turbopump imbalance. Data analysis indicates synchronous vibrational level increases of approximately 8 Grms on the pump end and 20 Grms on the turbine end. The levels continue to increase with the increase of imbalance of the turbopump; eventually reaching approximately 16 Grms on the pump end and 83 Grms on the turbine end. At 5.04 seconds, the HPFT DS T Launch Commit Criteria (LCC) was activated. At 5.08 seconds, 2 Failure Identifications (FID’s) were issued indicating that HPFT DS T CH A2 and HPFT DS T CH A3 had exceeded the 1860 degree Rankine redline. These FID’s were accompanied by a Major Component Failure (MCF) indication. The Facility Command and Data Simulator (CADS) was set to respond to an MCF indication before 6.6 seconds with a command to perform engine shutdown. The CADS unit issued a shutdown command and the engine entered shutdown phase at 5.18 seconds. The engine powered down nominally with the exception of the HPFTP. Its spindown was much faster than nominal. It stopped at approximately 4 seconds after shutdown (expected for a pump with severe imbalance).

Lesson(s) Learned:

1. Early on in the investigation there was much concern regarding the lack of damage to the FPB faceplate. Past failures in the FPB injector and OPB injector suggested that faceplate damage was common for fuel flow loss due to contamination. Model analysis performed during this investigation suggests that with a short-duration test and with the fuel cavity contamination type and quantity observed, damage to the FPB faceplate does not necessarily occur. In other words, there exists a substantial range of contamination levels within which it is possible to effectively destroy the HPFTP without melting the FPB faceplate. This conclusion is supported not only by the post-test hardware inspections from this test, but also by mathematical modeling analysis performed by MSFC and Rocketdyne.

2. The Pratt & Whitney HPFTP/AT has shown that it can endure extreme levels of imbalance and damage without engine catastrophic results.

Recommendation(s):

1. Verify that all systems are free of foreign object debris prior to hot-fire. Limit the opportunity for contamination introduction by minimizing the use of potential contaminants and using permanent closures on joints were applicable. Keep joints closed at all times when access is not required to perform work.

2. Implement an improved method of dealing with loose, non-serialized materials to ensure full accountability. Additional inspections and checkouts should be considered to verify that the engine is contamination free, prior to any hot-fire.

3. The use of reusable joint barriers, which can be controlled and accounted for, should be investigated.

4. Provide clear instructions in processing paperwork and discrepancy paperwork. Use positive identification of engine hardware to ensure that the work is being done on the correct part.

5. Correct electronic paperwork systems, to either prevent changes or provide a clear tracking of change activities. Further ensure that all SSME changes can be tracked.

6. SSME Project should investigate evidence to ensure that SSME 0523 Powerhead structural properties were adequate. Ensure that an unacceptable condition does not exist in the flight fleet.

7. The SSME Project should understand the mechanism causing roller bearing failure and ensure that conditions experienced were outside the designed capability of the roller bearing.

8. The agency and its contractor teams need to avoid schedule practices that create undue risks.

Evidence of Recurrence Control Effectiveness:

N/A

Applicable NASA Enterprise(s):