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#680
by
kneecaps
on 28 Sep, 2009 20:00
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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.
Thanks, that explains why i've never even seen those displays! The old PASS TRAJ was very RTLS orientated. I'll try and find some docs detailing the new displays.
Thanks.
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#681
by
Lawntonlookirs
on 01 Oct, 2009 16:39
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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?
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#682
by
Danny Dot
on 01 Oct, 2009 19:06
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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
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#683
by
kneecaps
on 01 Oct, 2009 19:31
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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
I was considering giving my understanding of what happens, but thinking about it i'm not sure of some specific details. Specifically when the ASIs (Spark igniters) actually start sparking.
Apparently 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!
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#684
by
Lawntonlookirs
on 01 Oct, 2009 19:48
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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
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
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#685
by
kneecaps
on 01 Oct, 2009 20:02
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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
It doesn't answer the question in a succinct way (if at all).
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#686
by
Danny Dot
on 01 Oct, 2009 23:15
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snip
Apparently 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!
God himself spins up the turbopumps and breaths fire into the combustion chamber. That's my story and I am sticking to it.
If someone figures out how those pumps go from zero to 100,000 hp in a couple of seconds -- please tell us all.
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.
Danny Deger
Edit: Ask more shuttle question, please. The status of Ares I is getting old.
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#687
by
kneecaps
on 02 Oct, 2009 08:01
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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.
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.
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#688
by
psloss
on 02 Oct, 2009 11:59
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#689
by
Danny Dot
on 02 Oct, 2009 12:53
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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.
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.
OK. I just thought of a key in starting the turbo pumps, vs. starting a gas turbine engine. The preburner is where the fire is on the SSMEs. There is only one way out -- across the turbine. In a gas turbine, there is an opening at both ends and the turbine and compressor must be spun up by some means so the fire doesn't just go out the compressor.
I wish I would have thought of this while I still teaching the Main Propulsion System classes.
Danny Deger
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#690
by
Lawntonlookirs
on 02 Oct, 2009 18:41
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This link has been posted here before...the material there is at least historically related:
http://www.enginehistory.org/ssme.htm
Thanks psloss and DD for the information. More than I can digest, but interesting on the development of the engines. I assume the engines still run the same way and adjust for the oscillations after the main fuel valve is opened. It also tells about how many problems they had during the development of the engine.
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.
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#691
by
kneecaps
on 02 Oct, 2009 21:25
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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.
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.
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#692
by
Lawntonlookirs
on 03 Oct, 2009 15:28
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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.
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.
Yes kneecap. I am starting to understand quite a bit about it. It is just hard to imagine the liquid H and O going from the cyrogenic temp to 6000 F instantly. I guess one could say it is one H*** of a controled explosion.
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#693
by
C5C6
on 03 Oct, 2009 20:10
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In 28.5 degree shuttle missions, does the shuttle make a 90º counterclockwise roll program??
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#694
by
psloss
on 03 Oct, 2009 20:24
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In 28.5 degree shuttle missions, does the shuttle make a 90º counterclockwise roll program??
Yes.
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#695
by
Ford Mustang
on 03 Oct, 2009 21:29
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Okay, I'm confused. I heard some talk about pad time on one of the prior flights, maybe it was LON for STS-125 if they needed to use one pad.. something like 25 (I'm not sure, but it's at least that many IIRC) days at the pad, with a few days turnaround before rolling out.
STS-51D launched on April 12th, 1985, landed 7 days later.
STS-51B launched on April 29th, 1895... that's a whole 10 days after 51D landed, so that's 17 days between launches, and both were on Pad-A.
Is there a reason they flew 17 days apart, or was it just that they wanted to go as many as possible in 1985?
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#696
by
psloss
on 03 Oct, 2009 22:20
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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. (This has been discussed here before.) Since the 51-B payload was a Spacelab module (already loaded), that probably shortened the pad time a little bit.
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#697
by
MKremer
on 05 Oct, 2009 23:49
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The latter -- they were working towards a flight rate of 24 flights per year.
And we look back now and think:
"Six flights a year
per orbiter? They must have been nuts to even imagine that could happen!"
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#698
by
K466
on 06 Oct, 2009 15:05
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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?
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#699
by
astrobrian
on 06 Oct, 2009 15:25
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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?
The shape of the wing provides some lift, but given the relatively slow airspeed while on the SCA it probably doesn't help a lot
