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#11
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Used, beaten up rockets gaining popularity !
In article ,
says... David Spain writes: JF Mezei writes: On 2020-11-08 23:32, Greg (Strider) Moore wrote: The SSME were not designed to have relight capability. I don't know the details, but a pad abort for example required them to do servicing. Since there was no real reason for inflight reignition ability, my understanding is they never put it in. In a previous message, it was alluded that some nasty chemicals used to ignite engiunes (I assume hydrazyne, right?). Isn't it just a question to grow the tank and have the pump disperse finite amount such that theu can ignite 3 or 4 times during a flight? If you are interested in re-igniting a LH2/LOX engine go do a web search on the Saturn V third stage. It had to light both for Earth orbital injection as well as for Trans Lunar Injection. https://en.wikipedia.org/wiki/Rocketdyne_J-2 The above answers the question: to wit: spark plugs, ullage and pre-chill. SSMEs are fuel rich staged combustion cycle which required ground support equipment to start. Ares I was initially spec'd for SSME upper stage. NASA had forgotten just how complicated it would be to start an SSME in flight. So, NASA switched to the J-2X. J-2 was a gas generator, and it was designed from the start for in- flight restarts. Jeff -- All opinions posted by me on Usenet News are mine, and mine alone. These posts do not reflect the opinions of my family, friends, employer, or any organization that I am a member of. |
#12
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Used, beaten up rockets gaining popularity !
On Fri, 13 Nov 2020 13:50:50 -0500, JF Mezei
wrote: On 2020-11-13 13:40, Jeff Findley wrote: SSMEs are fuel rich staged combustion cycle which required ground support equipment to start. I know they had spark generators below engine bells, but was repeatedly tols this was to burn off any stray Hydrogen , not to ignite engines. So I am very curious how grouns equipme t intefaces with the engine to get them started. Is there a pole that goes up the engine bell right into combustion chamber to ignite things? or it is a question of ground pumps pushing some hypergolic through interface pipes and those end up mixing at the right location in the engine to get it started? If som why couldn't that be moved ob-bard? If ignition is done by the ground, how come control is transfered a minute or two before T-0 ? https://forum.nasaspaceflight.com/in...p?topic=1958.0 |
#14
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Used, beaten up rockets gaining popularity !
In article ,
says... On 2020-11-13 15:31, Ed Ruf wrote: If ignition is done by the ground, how come control is transfered a minute or two before T-0 ? https://forum.nasaspaceflight.com/in...p?topic=1958.0 All I have found in that thread is that a 1970s ground computer is needed to sequence the engine start. an iPhone has more power than a 1970s mainframe. It's not the computer "power" that's the big issue. From that link above: As a second stage engine, it could be conditioned until T-0 by ground commodities but during the 2 minute first stage burn, some combination of liquid and cold gaseous He, N2, H2 and O2 would have to be used. It's the added mass of those gases and tanks to hold them that would reduce payload. Jeff -- All opinions posted by me on Usenet News are mine, and mine alone. These posts do not reflect the opinions of my family, friends, employer, or any organization that I am a member of. |
#15
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Used, beaten up rockets gaining popularity !
On Sat, 14 Nov 2020 04:09:45 -0500, JF Mezei
wrote: On 2020-11-13 15:31, Ed Ruf wrote: If ignition is done by the ground, how come control is transfered a minute or two before T-0 ? https://forum.nasaspaceflight.com/in...p?topic=1958.0 All I have found in that thread is that a 1970s ground computer is needed to sequence the engine start. an iPhone has more power than a 1970s mainframe. When the SSMEs were transformed into RS25, it consisted mostly of changing the electronics, so I am disapointed they wouldn't have given it autonomy to start its own engine without requiring a ground computer to do it. They mention needed pressure. Can't that be controlled by the exhaust valve for the tanks? close it till you have the right pressure for engine start. With regards to sea level vs vaccuum start, does that make a difference when the engine is enclosed and operates at far higher pressure? I understand the engine bell differences, but from the actual engine itself, with turbopump, nozzles that mix fuel and O2, are they even aware of the pressure, tempoerature and weather outside? But notable in that thread, there is no mention that it is the groudn that generates the sparks to ignite. Only computer management of engine spin up. How about learning to do a simple search for yourself? Do you always need to be spoon fed here? https://www.google.com/url?sa=t&rct=...wLafYMNf3TdBuo |
#16
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Used, beaten up rockets gaining popularity !
On Nov/15/2020 at 09:47, JF Mezei wrote :
On 2020-11-14 12:10, Ed Ruf wrote: How about learning to do a simple search for yourself? Do you always need to be spoon fed here? So this group should return to the sex discussions then? No Mr Mezei, feel free to ask space related questions here. Don't worry about those who tell you not to ask those questions and do web searches instead. For sex topics, I think web searches will work :-) Alain Fournier |
#17
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Used, beaten up rockets gaining popularity !
Jeff Findley writes:
Since the SSME is a fuel rich staged combustion engine, you have to things to start: 1. The combustion chamber for the turbopump (whose combustion exhaust goes into the engine). 2. The main combustion chamber. Starting all that up was a complex process, so NASA put as much of the equipment and consumables to do so on the ground (since that's the only place the SSME was ever started). https://en.wikipedia.org/wiki/RS-25#Constellation From above: It would be expensive, time-consuming, and weight-intensive to convert the ground-started RS-25D to an air-started version for the Ares I second stage. Jeff Hence the revival for Constellation (as long as it lasted) of the restartable J-2 LH2/LOX engine from Apollo. It then re-incarnated as the new and improved J2-X. Remember those days. Wasn't the J2-X supposed to be part of the 2nd stage for the Aries-I 'stick' vehicle? The only version of this that flew was with a dummy mass simulator upper stage. As the PAO called it during the launch, "exploring new concepts..." Dave |
#18
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Used, beaten up rockets gaining popularity !
On Sat, 07 Nov 2020 23:08:34 -0800, Snidely
wrote: Wikipedia suggests that the RS-25 has it still ... dual-redundant spark igniters in the injectors of the preburners. |
#19
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Used, beaten up rockets gaining popularity !
On Sun, 15 Nov 2020 09:47:09 -0500, JF Mezei
wrote: On 2020-11-14 12:10, Ed Ruf wrote: How about learning to do a simple search for yourself? Do you always need to be spoon fed here? So this group should return to the sex discussions then? No just that is you took a little initiative to look down a provided path you might get to your desired answer sooner. Or you might come across a reference with a large amount of info such as the Stanford PDF I linked to which came up among the first entries in a google search and shows where the MCC igniter is. On Sat, 07 Nov 2020 23:08:34 -0800, Snidely wrote: Wikipedia suggests that the RS-25 has it still ... dual-redundant spark igniters in the injectors of the preburners. If you follow this Wiki article on the RS-25 to the MCC section you would see it says the same. "The mixture is ignited by the "Augmented Spark Igniter", an H2/O2 flame at the center of the injector head." |
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