SSME 0523 TEST 902-772 FAILURE INVESTIGATION FINAL REPORT

Space Shuttle Main Engine (SSME) 0523 was assembled as a unique development engine
for a specific series of tests. The plan for the test series was to demonstrate safe operation
of the Pratt & Whitney High Pressure Fuel Turbopump (HPFTP/AT) at the High Pressure
Fuel Turbine discharge temperature (HPFT DS T) redline values. The engine was in a
hybrid Block I/II configuration with a standard throat Main Combustion Chamber (MCC)
and a HPFTP/AT. The major objective of the first test in the series was to characterize
the effects of Coolant Control Valve (CCV) position on HPFT DS T.
During the assembly of SSME 0523, Permacel P-670 (LOX) tape was introduced into the
fuel system during some “hands on” process (temporary closure, contamination barrier,
unintentional introduction, etc.). A list of the probable locations of introduction is
discussed in Section 7.6. Despite normal processing inspections, the tape contamination
went unnoticed and was left in the fuel system during the remainder of assembly and pretest
activities.
On June 16, 2000, test number 902-772 of SSME 0523 was conducted on test stand A2 at
Stennis Space Center (SSC). The test was scheduled for a total duration of 200 seconds.
A thrust profile of the planned test is provided in Figure 6.0-1.
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 multiple fuel inlet holes of several FPB injector elements in localized areas. 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 Channel A (flight instrumentation
location) and the HPFT DS T KG2dT (ground test instrumentation location) beginning at
approximately 2.7 seconds. The HPFT DS T Channel B measurement and the HPFT DS
T measurement at KG2cT remained at nominal values. All other performance parameters
indicated normal engine operation at this time.
The localized temperature increase caused melting of the turbine inlet housing struts and
first stage vanes in the HPFTP/AT. At 4.97 seconds, all three airfoils on a first stage vane
segment were melted through the chord, causing local structural failure of that segment of
vanes. The inner platform of the vane segment fell into the hot gas flow stream impacting
the first stage blades. This caused the first stage blades to fail creating significant
HPFTP/AT rotor imbalance. Data analysis indicates that the HPFTP/AT synchronous
vibration amplitudes increased sharply to levels significantly higher than nominal
operation. The sharp increase in vibration levels were followed by a drop in HPFTP/AT
performance and a corresponding response by the engine control system attempting to
recover performance.