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#440
by
DaveS
on 25 Jan, 2011 17:25
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I recalled that there was a 'strong' concern regarding to the exhaust duct at SLC 6 to safely funnel the rocket plume exhausts away from the Shuttle. At the time, turbojet engines were used to provide suction power to draw the exhaust plumes away, but there were enough concerns voiced at the time.
Incorrect. The jet engines were to be used to heat the ET to prevent ice formation in foggy/rainy conditions.
The problem you're talking about is called hydrogen entrapment. Hydrogen would be trapped in the closed exhaust duct leading to significant build-up prior to engine start.
The fix was steam injection which would would dilute the hydrogen preventing an explosion.
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#441
by
Jim
on 25 Jan, 2011 17:58
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I recalled that there was a 'strong' concern regarding to the exhaust duct at SLC 6 to safely funnel the rocket plume exhausts away from the Shuttle. At the time, turbojet engines were used to provide suction power to draw the exhaust plumes away, but there were enough concerns voiced at the time.
Not true.
A. the duct of concern was dedicated for the SSME's, It can be seen in some of the photos and is filled with concrete. The Shuttle SRB's had dedicated ducts were were modified for Delta IV
2. I see DaveS had answered.
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#442
by
Nick L.
on 25 Jan, 2011 18:20
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Some discussion in this thread about whether certain NRO payloads can fit on a M+(5,x) vehicle.
http://forum.nasaspaceflight.com/index.php?topic=11127.45The 5m fairing on the M+ models is shorter than the one on the Heavy. Can the long Heavy fairing (the composite one, as opposed to the aluminum trisector fairing) be used on the M+?
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#443
by
Jim
on 25 Jan, 2011 18:36
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Some discussion in this thread about whether certain NRO payloads can fit on a M+(5,x) vehicle.
http://forum.nasaspaceflight.com/index.php?topic=11127.45
The 5m fairing on the M+ models is shorter than the one on the Heavy. Can the long Heavy fairing (the composite one, as opposed to the aluminum trisector fairing) be used on the M+?
aluminum trisector is only for the heavy and certain missions.
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#444
by
Lars_J
on 25 Jan, 2011 23:38
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Strictly speaking LOX hydrogen engines run rich of stoichiometric, so there's plenty of free hydrogen in the plume at any time.
Yes, but not all LOX/H2 engines exhibit this amount of free H2 at startup to generate such a fireball as the RS-68 does. For example, the
SSME and
Vulcain engines have remarkable clean startups in comparison. Either that, or the excess H2 is vented away much more efficiently.
I know you are not arguing this personally, but it seems like several people here have been suggesting that this kind of start is a "feature" of all LOX/H2 engines. But this is clearly not the case.
Clearly the RS-68 was designed to do what it does, and it works, but it still raises eyebrows.
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#445
by
Jim
on 25 Jan, 2011 23:55
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Strictly speaking LOX hydrogen engines run rich of stoichiometric, so there's plenty of free hydrogen in the plume at any time.
Yes, but not all LOX/H2 engines exhibit this amount of free H2 at startup to generate such a fireball as the RS-68 does. For example, the SSME and Vulcain engines have remarkable clean startups in comparison. Either that, or the excess H2 is vented away much more efficiently.
I know you are not arguing this personally, but it seems like several people here have been suggesting that this kind of start is a "feature" of all LOX/H2 engines. But this is clearly not the case.
As stated earlier, the RS-68 has only 25% more H2 at start. The water system at LC-39 help suck it away
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#446
by
Antares
on 26 Jan, 2011 00:15
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A tighter start sequence also has a greater possibility of going "hardware" rich. Pick your poison.
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#447
by
Nick L.
on 26 Jan, 2011 00:31
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Some discussion in this thread about whether certain NRO payloads can fit on a M+(5,x) vehicle.
http://forum.nasaspaceflight.com/index.php?topic=11127.45
The 5m fairing on the M+ models is shorter than the one on the Heavy. Can the long Heavy fairing (the composite one, as opposed to the aluminum trisector fairing) be used on the M+?
aluminum trisector is only for the heavy and certain missions.
Understood, but is it possible to use the Heavy fairing on the M+, for payloads that need more volume but not more payload capacity?
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#448
by
Propforce
on 26 Jan, 2011 00:48
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I recalled that there was a 'strong' concern regarding to the exhaust duct at SLC 6 to safely funnel the rocket plume exhausts away from the Shuttle. At the time, turbojet engines were used to provide suction power to draw the exhaust plumes away, but there were enough concerns voiced at the time.
Incorrect. The jet engines were to be used to heat the ET to prevent ice formation in foggy/rainy conditions.
The problem you're talking about is called hydrogen entrapment. Hydrogen would be trapped in the closed exhaust duct leading to significant build-up prior to engine start.
The fix was steam injection which would would dilute the hydrogen preventing an explosion.
Thanks. But I believe the correct word is called Hydrogen
Entrainment. The RS-68 has a much higher gaseous hydrogen "lead" during engine start-up than SSME. The fear was that these GH2 will be "pre-mixed" with air in the exhaust duct so, when engine ignites will set up a perfect bomb scenario, creating a detonation wave blow back to the vehicle. The Delta IV fix was to install ROFIs (sparklers) in the duct to burn away as much pre-mixed hydrogen/air as possible.
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#449
by
Propforce
on 26 Jan, 2011 00:50
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Strictly speaking LOX hydrogen engines run rich of stoichiometric, so there's plenty of free hydrogen in the plume at any time.
Yes, but not all LOX/H2 engines exhibit this amount of free H2 at startup to generate such a fireball as the RS-68 does. For example, the SSME and Vulcain engines have remarkable clean startups in comparison. Either that, or the excess H2 is vented away much more efficiently.
I know you are not arguing this personally, but it seems like several people here have been suggesting that this kind of start is a "feature" of all LOX/H2 engines. But this is clearly not the case.
As stated earlier, the RS-68 has only 25% more H2 at start. The water system at LC-39 help suck it away
Huh? Explain how does water "suck" away gaseous H2
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#450
by
Propforce
on 26 Jan, 2011 00:52
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Clearly the RS-68 was designed to do what it does, and it works, but it still raises eyebrows.
It was not designed to do this on purpose. It was a by-product as the design of vehicle and ground system came together. But it was an acceptable outcome as it posed no threat to the vehicle and missions.
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#451
by
Jim
on 26 Jan, 2011 01:19
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Some discussion in this thread about whether certain NRO payloads can fit on a M+(5,x) vehicle.
http://forum.nasaspaceflight.com/index.php?topic=11127.45
The 5m fairing on the M+ models is shorter than the one on the Heavy. Can the long Heavy fairing (the composite one, as opposed to the aluminum trisector fairing) be used on the M+?
aluminum trisector is only for the heavy and certain missions.
Understood, but is it possible to use the Heavy fairing on the M+, for payloads that need more volume but not more payload capacity?
The 5m composite fairing is the same on the heavy and Medium + (5,X)
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#452
by
Jim
on 26 Jan, 2011 01:27
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Huh? Explain how does water "suck" away gaseous H2
Hydraulic ventilation
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#453
by
Jim
on 26 Jan, 2011 01:29
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I recalled that there was a 'strong' concern regarding to the exhaust duct at SLC 6 to safely funnel the rocket plume exhausts away from the Shuttle. At the time, turbojet engines were used to provide suction power to draw the exhaust plumes away, but there were enough concerns voiced at the time.
Incorrect. The jet engines were to be used to heat the ET to prevent ice formation in foggy/rainy conditions.
The problem you're talking about is called hydrogen entrapment. Hydrogen would be trapped in the closed exhaust duct leading to significant build-up prior to engine start.
The fix was steam injection which would would dilute the hydrogen preventing an explosion.
Thanks. But I believe the correct word is called Hydrogen Entrainment. The RS-68 has a much higher gaseous hydrogen "lead" during engine start-up than SSME. The fear was that these GH2 will be "pre-mixed" with air in the exhaust duct so, when engine ignites will set up a perfect bomb scenario, creating a detonation wave blow back to the vehicle. The Delta IV fix was to install ROFIs (sparklers) in the duct to burn away as much pre-mixed hydrogen/air as possible.
The term used wrt to SLC-6 was entrapment
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#454
by
Propforce
on 26 Jan, 2011 01:45
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I recalled that there was a 'strong' concern regarding to the exhaust duct at SLC 6 to safely funnel the rocket plume exhausts away from the Shuttle. At the time, turbojet engines were used to provide suction power to draw the exhaust plumes away, but there were enough concerns voiced at the time.
Incorrect. The jet engines were to be used to heat the ET to prevent ice formation in foggy/rainy conditions.
The problem you're talking about is called hydrogen entrapment. Hydrogen would be trapped in the closed exhaust duct leading to significant build-up prior to engine start.
The fix was steam injection which would would dilute the hydrogen preventing an explosion.
Thanks. But I believe the correct word is called Hydrogen Entrainment. The RS-68 has a much higher gaseous hydrogen "lead" during engine start-up than SSME. The fear was that these GH2 will be "pre-mixed" with air in the exhaust duct so, when engine ignites will set up a perfect bomb scenario, creating a detonation wave blow back to the vehicle. The Delta IV fix was to install ROFIs (sparklers) in the duct to burn away as much pre-mixed hydrogen/air as possible.
The term used wrt to SLC-6 was entrapment
So the physics is different at SLC-6 than at LC-17?
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#455
by
Nick L.
on 26 Jan, 2011 04:27
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Some discussion in this thread about whether certain NRO payloads can fit on a M+(5,x) vehicle.
http://forum.nasaspaceflight.com/index.php?topic=11127.45
The 5m fairing on the M+ models is shorter than the one on the Heavy. Can the long Heavy fairing (the composite one, as opposed to the aluminum trisector fairing) be used on the M+?
aluminum trisector is only for the heavy and certain missions.
Understood, but is it possible to use the Heavy fairing on the M+, for payloads that need more volume but not more payload capacity?
The 5m composite fairing is the same on the heavy and Medium + (5,X)
Really? The Payload Planners' Guide shows 14.3 m length for the (5,x) fairing and 19.1 m for the Heavy fairing.
I know the long fairing is not currently offered on 5-meter versions. I guess what I'm trying to get at is, is using the longer fairing on a M+ something that they could do relatively easily if the customer requested it?
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#456
by
Downix
on 26 Jan, 2011 05:26
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I recalled that there was a 'strong' concern regarding to the exhaust duct at SLC 6 to safely funnel the rocket plume exhausts away from the Shuttle. At the time, turbojet engines were used to provide suction power to draw the exhaust plumes away, but there were enough concerns voiced at the time.
Incorrect. The jet engines were to be used to heat the ET to prevent ice formation in foggy/rainy conditions.
The problem you're talking about is called hydrogen entrapment. Hydrogen would be trapped in the closed exhaust duct leading to significant build-up prior to engine start.
The fix was steam injection which would would dilute the hydrogen preventing an explosion.
Thanks. But I believe the correct word is called Hydrogen Entrainment. The RS-68 has a much higher gaseous hydrogen "lead" during engine start-up than SSME. The fear was that these GH2 will be "pre-mixed" with air in the exhaust duct so, when engine ignites will set up a perfect bomb scenario, creating a detonation wave blow back to the vehicle. The Delta IV fix was to install ROFIs (sparklers) in the duct to burn away as much pre-mixed hydrogen/air as possible.
The term used wrt to SLC-6 was entrapment
So the physics is different at SLC-6 than at LC-17?
Same Physics, different physical situation.
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#457
by
Jim
on 26 Jan, 2011 10:19
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Some discussion in this thread about whether certain NRO payloads can fit on a M+(5,x) vehicle.
http://forum.nasaspaceflight.com/index.php?topic=11127.45
The 5m fairing on the M+ models is shorter than the one on the Heavy. Can the long Heavy fairing (the composite one, as opposed to the aluminum trisector fairing) be used on the M+?
aluminum trisector is only for the heavy and certain missions.
Understood, but is it possible to use the Heavy fairing on the M+, for payloads that need more volume but not more payload capacity?
The 5m composite fairing is the same on the heavy and Medium + (5,X)
Really? The Payload Planners' Guide shows 14.3 m length for the (5,x) fairing and 19.1 m for the Heavy fairing.
I know the long fairing is not currently offered on 5-meter versions. I guess what I'm trying to get at is, is using the longer fairing on a M+ something that they could do relatively easily if the customer requested it?
I was getting at that the aluminum one is not used on any type of non Heavy vehicles. As for different lengths of composite 5m fairings, ULA should be able to meet any request.
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#458
by
rklaehn
on 30 Jan, 2011 09:49
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Another question about the fireball:
if the same amount of H2 that is producing the fireball during a delta IV heavy launch were to somehow thoroughly mix with air prior to ignition, you would have a much more violent explosion.
Is the delta IV designed to handle that as well? And if not, how is it ensured that the H2 does not mix with air? CFD simulations of the volume around the vehicle in all possible weather conditions?
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#459
by
gospacex
on 30 Jan, 2011 12:51
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Another question about the fireball:
if the same amount of H2 that is producing the fireball during a delta IV heavy launch were to somehow thoroughly mix with air prior to ignition, you would have a much more violent explosion.
Is the delta IV designed to handle that as well? And if not, how is it ensured that the H2 does not mix with air? CFD simulations of the volume around the vehicle in all possible weather conditions?
I guess sparklers' purpose is exactly to prevent that: they guarantee that LH ignites before there is a big amount of it released and mixed with the air.
