Investigation called after STS-127 SSME 1 found to have 100s of leaks
A failure investigation team has been created for Endeavour’s Number One Space Shuttle Main Engine (SSME) that was used during STS-127, which was found to have hundreds of leaks in its nozzle tubing during post-flight inspections. The engine – which was passed to fly after suffering from contamination at the pad ahead of flight - thankfully enjoyed a nominal performance during powered ascent.
Following her STS-127 mission, Endeavour has been in processing inside Orbiter Processing Facility 2 (OPF) for the February 4, 2010 flight to carry Node 3 and Cupola to the International Space Station (ISS).
This week has seen work being conducted on replacing Fuel Cell 3 – which will be completed after the holiday weekend – and reinstalling her Orbiter Boom Sensor System (OBSS)
“Orbiter: OV-105 (OPF Bay 2): Fwd Sep Pyro Harness Installation was completed yesterday. APU (Auxiliary Power Unit) catch bottle drain SCAPE operation was completed this morning,” noted Friday processing information on L2.
“Fuel Cell hydrogen separator R&R work continues and should complete today. Fuel Cell 3 R&R work picked up yesterday with mechanical de-mates and the removal of the replacement fuel cell from its shipping container.
“Electrical de-mates are scheduled for today, and the R&R is scheduled for (next) Tuesday. OBSS installation into the Orbiter is scheduled for today.
SSME 1 Leaks:
As part of the normal processing flow, all three SSMEs were recently removed from Endeavour, ready for their turnaround on a future flight. However, one engine will require a new nozzle – following inspections.
“Were working post STS-127 Engine inspections in the engine shop. On Engine #1 (2045), got into nozzle tube leak checks,” noted the first memo on the observations (L2). “Ended up with over 100 leaks on the hot wall side of that nozzle.”
This engine (2045) is set for turnaround in order to be ready to fly with Discovery on STS-131 next year. It is also designated as being on standby for installation on Atlantis for STS-335 – the Launch On Need (LON) mission in support of STS-133, which is currently the final mission on the shuttle manifest.
The memo confirmed the engine in question was the SSME that required specialist cleaning ahead of STS-127, when a brown – rust-like – contamination was observed on the nozzle out at the pad.
“Corrosion/contamination has been noted on two SSME nozzles at Pad A for STS-127 (engines 1 and 3). ME2045 (Main Engine) has a significant amount in the first few inches downstream of the MCC/nozzle interface joint G15, and ME2054 has a minor amount approximately 10 inches below G15,” noted a pad flow report ahead of STS-127.
“Completed polishing. During normal nozzle inspection, identified two issues: engine 1 and 3 have some corrosion at G15 area. It looks unusual, and have asked corrosion expert from Canoga Park to look at it.”
Those experts deemed the engine to be in good shape, confirmed by successful leak checks at the pad.
The SSME nozzle tubes are made of A286 iron based steel and are nickel plated primarily to make the brazing of the tubes to operate nominally. It is deemed to be completely normal for these tubes to rust in the Florida coastal pad environment. However, the tubes – which are put under 6000 psig pressure during engine operation – are at risk of rupturing if corrosion has reduced their integrity.
An example of tube damage on the SSME nozzles was seen during STS-93’s infamous launch, where three tubes were damaged by a blown injector pin, leading to the engine controller assuming more hydrogen was being burned and compensated by injecting additional LOX – ultimately resulting in the ECO (Engine Cut Off) sensors shutting down the engines slightly ahead of time, leading to an underspeed at MECO (Main Engine Cut Off).
While Columbia’s engine only suffered from three punctures on her SSME during STS-93, a tube split or rupture would be a more serious event. **Click here for clips from the L2 STS-93 Internal Loop Video of Columbia’s ascent**
How close Endeavour’s number one engine came to suffering a major problem is unknown, with no performance issues noted in the post flight IFA (In Flight Anomaly) review on the SSMEs. However, with the engine passed as fit to fly, before failing leak checks upon its return is under investigation.
“2045 is the engine that had brown contamination prior to STS-127, which was cleaned a couple of times. That came as a surprise because they did not think that the brown contamination would pit the nozzle tubes,” added the memo.
“Will have some folks come out this week to take a good look at it. They have taken carbon tape samples, and done some digital microscopic work on the nozzle tubes. Engine 3 also had some brown residuals. (However,) post-flight leak checks look within family, nominal.”
A later memo noted engineers had then conducted a full mapping of the engine to get an exact count of leak areas. More than triple the original number were found.
“SSME (Pratt & Whitney Rocketdyne/KSC): On Engine 2045 that came out of position 1 for STS-127, had over 100 nozzle tube leaks on that nozzle,” added the latest Shuttle Standup/Integration report on L2. “Finally completed mapping that nozzle, and had a total of 340 tube leaks of various classes.
“Have a team, formed, working through a fault tree and a history of that nozzle to find out how it turned up in the corroded state we have here. Will report on that information once the failure investigation team is concluded.”
Further articles will follow as the investigation produces its findings and any potential impact on the remaining SSMEs set to fly.
L2 members: Documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4000 gbs in size.