I think part of the reason you might be getting confused is because the PASS TRAJ displays were recently modified (in OI-32, STS-120 I believe) – the picture I posted reflects my understanding of what the current displays look like for nominal ascent.
Probably a dumb question and has been answered before although I wasn't able to find it on a search. With the SSME having LO2 and LH as fuel, when the engines are first started, is it with the Liquid or gaseous O2 and H. I was just wondering how it is vaporized before the engines are started or is it liquid when it ignites and during the flight?
Only liquid is fed to the engines. The start sequency is complex and I never understood it completely. For example in a running engine the hydrogen runs in tubes in the nozzle to cool it. This vaporizes the hydrogen. When I taught an MPS class, I crossed my fingers no one whould ask how the darn thing starts. I would admit I didn't have a clue, but had the name and number of a booster flight control they could bug. I found saying "I don't know" was better than making up stuff.Danny Deger
Quote from: Lawntonlookirs on 10/01/2009 04:39 pmProbably a dumb question and has been answered before although I wasn't able to find it on a search. With the SSME having LO2 and LH as fuel, when the engines are first started, is it with the Liquid or gaseous O2 and H. I was just wondering how it is vaporized before the engines are started or is it liquid when it ignites and during the flight?Only liquid is fed to the engines. The start sequency is complex and I never understood it completely. For example in a running engine the hydrogen runs in tubes in the nozzle to cool it. This vaporizes the hydrogen. When I taught an MPS class, I crossed my fingers no one whould ask how the darn thing starts. I would admit I didn't have a clue, but had the name and number of a booster flight control they could bug. I found saying "I don't know" was better than making up stuff.Danny Deger
Thanks DD, so I guess it wasn't a dumb question after all. Maybe a post on L2 would get an answer. I checked the SSME Bible and it gives a lot of the information, but will take some time to digest for me. "Download 2"http://forum.nasaspaceflight.com/index.php?topic=4413.0
snipApparently only liquid head pressures and the ASIs sparking is actually needed to start, but I'd love to hear an expert explain or illustrate this!
I think a key must be to get a fire going to blow hot gas through the turbines that drives the main pumps. I don't think there is any kind of starter that spins the pump up.
Quote from: Danny Dot on 10/01/2009 11:15 pmI think a key must be to get a fire going to blow hot gas through the turbines that drives the main pumps. I don't think there is any kind of starter that spins the pump up. One of the first things that happens is the Main Fuel Valve ramps fully open, this allows LH2 to get to the preburners. Both the Oxidizer preburner and Fuel preburner valves also ramp open (but not fully) in the same time period. I'm thinking that the requirement for head pressure to start simply forces LOX and LH2 into the preburners (and the ASIs (igniters). Pressure has forced LOX and LH2 into the preburners. This burns which causes a small amount of hot gas, this spins the turbines which in turn causes more LOX and LH2 to reach the preburners (which causes the pumps to spin faster, pumping more to the preburners, and so on). At some point the igniters will stop since combustion in the preburners will become self sustaining.
This link has been posted here before...the material there is at least historically related:http://www.enginehistory.org/ssme.htm
It has a spark plug in the preburner that uses a LH rich fuel for the turbo pumps and then they adjust the final fuel mixture in the Main combustion chamber. Not sure if they have just the one spark plug for ignition or one in the preburner and one in the MCC.
Quote from: Lawntonlookirs on 10/02/2009 06:41 pmIt has a spark plug in the preburner that uses a LH rich fuel for the turbo pumps and then they adjust the final fuel mixture in the Main combustion chamber. Not sure if they have just the one spark plug for ignition or one in the preburner and one in the MCC.There are six "spark plugs". ASIs, Augmented Spark Igniters. They are found in pairs (for redundancy) in both pre burners and in the main injector. The fuel:oxidizer ratio is controlled by the fuel preburner oxidizer valve (FPOV) only and is NOT adjusted at the MCC. The thrust level is controlled by the oxidizer preburner oxidizer valve (OPOV) and the FPOV moves to maintain the correct mixture. I believe the MOV (Main Oxidizer Valve, lets LOX into the MCC) is open 100% during the entire mainstage. Digest the flow paths through the engine and (it took me quite a long time), you'll have a eureka moment when it all kind of makes sense. It's a beautifully complex but remarkably simple engine in many ways..I think 'elegant' is the better word.
In 28.5 degree shuttle missions, does the shuttle make a 90º counterclockwise roll program??
Is there a reason they flew 17 days apart, or was it just that they wanted to go as many as possible in 1985?
The latter -- they were working towards a flight rate of 24 flights per year.
Question regarding Ferry Flights:Does the Shuttle's wings provide any lift during the flight, or is the orbiter just dead weight atop the SCA?