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Space Forum / Shuttle / February 2004Question about SSMEs
At the point where the fuel and oxidizer actually enter the combustion chamber are they still liquids or have they changed into a gaseous state? I just realized I never knew the answer to that. My guess is that they're still liquid since transition to a gas would entail boiling at some point and that's something you'd want to avoid in the plumbing. On the other hand the heat absorbed via the regenerative cooling of the nozzle seems like it would be substantial, and maybe transition in those little cooling tubes wouldn't be a big problem.  Signaturebp Proud Member of the Human O-Ring Society Since 2003 > At the point where the fuel and oxidizer actually enter the combustion > chamber are they still liquids or have they changed into a gaseous state? [quoted text clipped - 6 lines] > nozzle seems like it would be substantial, and maybe transition in those > little cooling tubes wouldn't be a big problem. I found my answer. Gaseous H and LOX. Signaturebp Proud Member of the Human O-Ring Society Since 2003 "Bruce Palmer" > I found my answer. Gaseous H and LOX. Hydrogen in gas form and oxygen in liquid form......? ------- You can't put too much water into a nuclear reactor. > "Bruce Palmer" > >> I found my answer. Gaseous H and LOX. > > Hydrogen in gas form and oxygen in liquid form......? It's the impression I got. H2(g) & O2(l). (I never seem to see (g) notation used, much - am I just misremembering it?) Signature-Andrew Gray shimgray@bigfoot.com > > "Bruce Palmer" > > [quoted text clipped - 4 lines] > It's the impression I got. H2(g) & O2(l). (I never seem to see (g) > notation used, much - am I just misremembering it?) The hydrogen is at about 6000 psi as it comes out of the turbo pump. This is well above the critical pressure, and hence the terms "liquid" and "gas" have no meaning. At this pressure the fluid just heats up and density goes down. This reduces thermal problems, as there is no phase change or boiling to worry about. As hydrogen does not act as an oxidizer it can be used with hot metals with out the fear of an exothermic reaction. Super critical hydrogen is an excellent heat transfer media. Mike Swift > "Bruce Palmer" > >>I found my answer. Gaseous H and LOX. > > Hydrogen in gas form and oxygen in liquid form......? It would appear so. Some of the liquid hydrogen is drawn off and circulated for cooling. That portion is in gaseous form when it finally gets to the injector for the combustion chamber. The rest of it - almost all of it - goes through the pre-burner and is converted to gas there before making its way to the injector. It goes without saying that that's a simplified description :0 Signaturebp Proud Member of the Human O-Ring Society Since 2003 >> I just realized I never knew the answer to that. My guess is that >> they're still liquid since transition to a gas would entail boiling at [quoted text clipped - 5 lines] > > I found my answer. Gaseous H and LOX. One point that hasn't been mentioned is that the hydrogen is at a pressure well above the critical pressure, so it can't 'boil' in the conventional sense in the regenerative cooling channels -- it just gets less dense in a continuous manner as it is heated. Paul >>> I just realized I never knew the answer to that. My guess is that >>> they're still liquid since transition to a gas would entail boiling [quoted text clipped - 10 lines] > in the conventional sense in the regenerative cooling channels -- it > just gets less dense in a continuous manner as it is heated. Good point. One of the things that make it a complicated beast is that there are all kinds of different pressures at various points in the system. I guess that's what makes the start sequence so tricky. Pretty amazing that they actually destroyed a _lot_ of hardware while trying to work out the start sequence. I wonder if development of the RS-68 was any smoother. They must have learned a lot of lessons from the RS-24. An interesting tidbit I picked up recently is RS-24 = SSME. Signaturebp Proud Member of the Human O-Ring Society Since 2003 > Good point. One of the things that make it a complicated beast is > that there are all kinds of different pressures at various points in [quoted text clipped - 5 lines] > learned a lot of lessons from the RS-24. An interesting tidbit I > picked up recently is RS-24 = SSME. Considerably. Rocketdyne claims development of the RS-68 cost about $500 million, compared to the billions SSME has cost (the F-1 cost as much as SSME to develop). But it's a much simpler design and probably benefited from lessons learned with SSME. And they did break a few parts getting the RS-68 up to speed, but there were no major failures. --Damon > > Good point. One of the things that make it a complicated beast is > > that there are all kinds of different pressures at various points in [quoted text clipped - 13 lines] > > --Damon Here's the cost breakdown for the F-1 and the SSME (in current dollars): F-1: Design: $800M. Production of 98 flight engines: $1.1B Operations support: $200M BTW: the production cost of the 98th engine was about $8M SSME: Design (1973-82): $3B Production (1978-83): $1.3B Operation (1983-2000): ~$4B Upgrades (=Pratt & Whitney turbopumps, 1986-2000): $1.4B The SSME inventory in the year 2000 totaled 55 engines. The unit manufacturing cost of the SSME is in the $45-60M range. You can get more info on these engines in Chapters 12 and 33 of my recent (2002) book on U.S. manned spaceflight in the 20th century. Later Ray Schmitt >>>Good point. One of the things that make it a complicated beast is >>>that there are all kinds of different pressures at various points in [quoted text clipped - 35 lines] > Later > Ray Schmitt 75 F-1s were used on the 15 Saturn Vs. Any idea what happened to the other 23? Mothballed? There should have been a few extras on the Saturn Vs that never flew as well. It's nice to have a few around to gawk at but it seems like such a waste to build them and then not use a third of the production run. Signaturebp Proud Member of the Human O-Ring Society Since 2003 > 75 F-1s were used on the 15 Saturn Vs. Any idea what happened to the > other 23? Mothballed? There should have been a few extras on the > Saturn Vs that never flew as well. It's nice to have a few around to > gawk at but it seems like such a waste to build them and then not use a > third of the production run. Test articles? Cannibalism? There's definitely some in inventory - there's been proposals to use them. http://groups.google.com/groups?selm=HrGp0x.CxK%40spsystems.net "[Hudson] said that 7 F-1s and 10 J-2s were available in 1987." Signature-Andrew Gray shimgray@bigfoot.com > 75 F-1s were used on the 15 Saturn Vs. Any idea what happened to the > other 23? Mothballed? There should have been a few extras on the > Saturn Vs that never flew as well. It's nice to have a few around to > gawk at but it seems like such a waste to build them and then not use a > third of the production run. What would it take to re-certify such old engines for flight? > What would it take to re-certify such old engines for flight? Just look at what was done to refurbish and recertify old Russian rocket engines. http://www.aerospaceguide.net/rocketengines/nk-33.html http://www.aerojet.com/program/display.pl?program_ID=18 Jeff SignatureRemove "no" and "spam" from email address to reply. If it says "This is not spam!", it's surely a lie. >> Considerably. Rocketdyne claims development of the RS-68 cost about >> $500 million, compared to the billions SSME has cost (the F-1 cost as [quoted text clipped - 24 lines] > You can get more info on these engines in Chapters 12 and 33 of my > recent (2002) book on U.S. manned spaceflight in the 20th century. Interesting. Rocketdyne/Boeing's viewgraphs paint a different cost figure in reasonably current dollar equivalents. --Damon > > Here's the cost breakdown for the F-1 and the SSME (in current > > dollars): [quoted text clipped - 20 lines] > > --Damon That's not surprising. I haven't seen the VuGs you mention so I don't know which SSME costs Rocketdyne is including. The cost data in my book is based on NASA's budget documents for the 1973-2000 period and my aim was to determine the total cost to NASA of SSME ownership (design, testing, manufacturing, quality assurance, flight operations, sustaining engineering, failure analysis, redesign, improvements, upgrades, etc.) . I tried to identify every element of SSME cost in those documents, which is a real chore since NASA changed the shuttle bookeeping system twice during that period (in the late 1980s and again in FY94). That makes tracking cost categories very difficult. Having 32 years of experience as an aerospace engineer, including work on the early shuttle program and being a part of management of other large programs, was a big advantage here. Consequently, my cost data contain much more information than just Rocketdyne's SSME design and manufacturing costs. Since the shuttle became "operational" in July 1982, NASA has been averaging about $200M (current dollars) per year to maintain the SSME inventory. NASA personnel charge quite a bit to the SSME budgets for management, Q/A, and testing at the facilities in Mississippi. USA also charges a hunk for all the SSME work that's done at KSC. Most of the pertinant SSME cost info is contained in NASA-MSFC's RedStar database. Unfortunately, the interesting info is marked "contractor proprietary" and/or "competition sensitive", so ordinary citizens like myself can't get access to these numbers. So, you do the best you can with what you have. Later Ray Schmitt > That's not surprising. I haven't seen the VuGs you mention so I don't know > which SSME costs Rocketdyne is including. The cost data in my book is based [quoted text clipped - 8 lines] > engineer, including work on the early shuttle program and being a part of > management of other large programs, was a big advantage here. That's quite a chore, Ray. The devil is in the details as they say. Having had a modicum of experience myself with government contractor cost accounting, let me ask you... Did you find a lot of nebulous tasks charged against a "level of effort" catch-all category, or was everything pretty well accounted for? Signaturebp Proud Member of the Human O-Ring Society Since 2003 > That's quite a chore, Ray. The devil is in the details as they say. > Having had a modicum of experience myself with government contractor > cost accounting, let me ask you... Did you find a lot of nebulous tasks > charged against a "level of effort" catch-all category, or was > everything pretty well accounted for? I didn't have that level of visibility. The RedStar database probably has some of this info. You would have to be a forensic accountant to do justice to that type of investigation. Later Ray Schmitt |
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