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  #11  
Old November 13th 20, 07:40 PM posted to sci.space.policy
Jeff Findley[_6_]
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Default 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
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These posts do not reflect the opinions of my family, friends,
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  #12  
Old November 13th 20, 09:31 PM posted to sci.space.policy
Ed Ruf[_2_]
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Default 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

  #13  
Old November 14th 20, 05:59 PM posted to sci.space.policy
Jeff Findley[_6_]
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Default Used, beaten up rockets gaining popularity !

In article ,
says...

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.


Yes, those external sparklers were there to burn off excess hydrogen.
They had nothing to do with starting the engine.

So I am very curious how grouns equipme t intefaces with the engine to
get them started.


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
--
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.
  #14  
Old November 14th 20, 06:09 PM posted to sci.space.policy
Jeff Findley[_6_]
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Default 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  
Old November 14th 20, 06:10 PM posted to sci.space.policy
Ed Ruf[_2_]
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Default 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  
Old November 15th 20, 04:19 PM posted to sci.space.policy
Alain Fournier[_3_]
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Default 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  
Old November 16th 20, 05:28 PM posted to sci.space.policy
David Spain
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Posts: 2,901
Default 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  
Old November 17th 20, 08:34 PM posted to sci.space.policy
Ed Ruf[_2_]
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Default 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  
Old November 17th 20, 08:41 PM posted to sci.space.policy
Ed Ruf[_2_]
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Posts: 10
Default 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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