# Space Shuttle and SSME Servicing Procedures for Re-Launch

There's been a lot of discussion about SpaceX's ~30% price reduction from re-use of the first stage, which got me to wondering: why exactly was the Space Shuttle so expensive to service and prep for re-launch?

I'm mostly interested in the actual servicing of the SSMEs themselves. They're fiendishly complicated, but does anybody know exactly what the main procedures were, and how much they cost? Or was it the case that other Orbiter processing tasks and low launch tempo were the biggest contributors to the cost?

It varied throughout the program - the SSMEs changed a lot over its course. Columbia's original FMOF engines were only marginally OK for flight. Until the Pratt turbopump redesign, the high pressure turbopumps had to be overhauled after every mission. By the end, overhaul requirements were somewhat reduced.

Here is overview information on SSME ground servicing procedures as they were in 1989. All information is from SSME Pocket Data, RI/RD87-142. The table of contents lists the major procedures performed. I have included a scan of page 3-3.

• Thanks, that helps. This sounds like the long pole in the tent was the maintenance on the HPxTP interseals and the damage done to the bearings from the seals being not-quite perfect. Gotta love those lift-off valves! The main reason I came back to this topic was that I'm trying to get a handle on the maintenance load that SpaceX will carry in servicing the Merlins. Gas generator engines don't have to worry about interseals, so there's a reasonable chance that maintenance will be considerably diminished. That, and the whole decision not to fly a little brick spaceship, of course. – TheRadicalModerate May 17 '16 at 18:05
• I'm also watching that with interest. Wish their process wasn't so opaque! – Organic Marble May 17 '16 at 18:11

Besides the SSME, I've seen estimates that a new external tank cost \$40-\$50 million and each SRB cost \\$40 million to refurbish/rebuild. Add to that the cost of inspecting and replacing the TPS tiles, and pretty soon you're talking real money.

I do not know the answer to the SSME specific thing, but the main cost driver for the shuttle was the standing army of 20,000 some odd folk employed by NASA, ostensibly to support the Shuttle program. If you launch 0 times a year, you cost is almost the same as if you launch 10 times a year, for those 20,000 salaries and benefits, and offices for them to work in.

SpaceX is using a much smaller workforce.

• "ostensibly to support"? – Organic Marble May 17 '16 at 15:23
• @OrganicMarble Did the shuttle really need all those people? Could they have done it with less? of course they could of. So what is their purpose? Ostensibly to support the shuttle. In reality, a jobs program. Look at SLS, same issues. – geoffc May 17 '16 at 16:44
• Since I worked in the program, I strongly disagree with your assertions. Could the manpower have been cut down? Somewhat. Was it solely a jobs program? No. – Organic Marble May 17 '16 at 16:48
• If you are disagreeing on absolutes, sure. Of course real people worked real jobs. But all 20,000 of them? Far too many employees, too top heavy. – geoffc May 17 '16 at 17:12
• I know you are just repeating things you have read, but you might want to think a little. What is your opinion that that number is too high based on? Compared to what? Other reuseable space planes designed in 1975? Come up with some facts about how the cost could have been reduced to operate the shuttle we had, not some magic vehicle, and I'll give your comments some weight. – Organic Marble May 17 '16 at 17:14

The shuttle was built with lots of unknowns, there were so many unknowns that the designers just could not think about unimportant things like the cost of reusing it. If there was a mark2 and then a mark3, mark4, etc the costs could have come down - but that would have required people admitting that got something wrong.

SpaceX is a set of changes to rocket designs that were already well understood, with the willingness to learn for each launch. Just think if the shuttle failed to land in one bit on it first few uses, but SpaceX got paid for doing their landing experiments, as they charge for the loads that they sent up.

• Do you have any references to back up your assertion that designers of the shuttle "could not think about...the cost of reusing it"? Cause I'm pretty sure that's 100% incorrect. – Organic Marble May 19 '16 at 14:13
• Look at what Feynman said about the disconnect between NASA's engineers and executives when he investigated the Challenger disaster. It the executives that had to believe in cost effect reusability so as to keep getting the funding….. – Ian Ringrose May 19 '16 at 14:25