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#300
by
kevin-rf
on 25 Jan, 2008 12:09
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Tru Grit said something interesting over in one of the Ares-1 threads :
http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=11584&start=61&posts=72And finally... By the time the administrators successor gets around to begging from congressional money for the heavy booster ULA will have moved on to RL-60 and ACES. They'll also conveniently forget this speech when the same successor comes asking for support because NASA is stuck in LEO again.
Is ACES really moving foward at ULA and more interesting will it also replace Centuar on the ULA Atlas V?
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#301
by
Big Al
on 01 Feb, 2008 23:55
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I have some questions about the RS-68 start sequence. I was watching a movie of the last Delta IV flight. Since it was at night, you could see some interesting thing happening.
1) The engine pump starts at T-15 seconds. This seems like along time before start up, my guess is that there is a chill sequence before start.
2) The engine nozzles appear to be below the three holes in the flame chute. Does anyone have close up photos on how the rocket mounts on the pad? It would be interesting to see detail on this
3) When the turbo pump starts it is only pumping hydrogen. The oxygen is shut off, I would be curious to see how they handle the O2 during that part of the startup. Most high-pressure pumps are very unhappy running with the flow shut off.
4) At T-5 is when you get the fireball; I assume that is when the igniters are turned on.
5) You notice also that the tapered aft end of the first stage allows the hydrogen to vent upward quickly
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#302
by
Jim
on 02 Feb, 2008 00:11
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1. It starts later than T-15,
2.Each CBC sits on 4 posts of the Launch Mate Unit which in turn sits on the launch table
http://www.ulalaunch.com/index_gallery.html3. It is pumping both LO2 and LH2 at the sametime
4. No, that is caused by the burn off igniters (ROFIs) which are like the shuttle's and are lit at L-15
5. Inconsequential. That is just the aeroshell of the engine section. The H2 is going to rise no matter what.
Will have more info on Monday.
Some of the real details will touch upon propriety and ITAR issue.
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#303
by
Nick L.
on 02 Feb, 2008 17:42
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The pumps start about T-8.5 seconds (right about when the TCSR takes control of the vehicle), this can be seen as the smaller flames coming from the heat exchanger and roll control nozzles on either side of the aft cone. This is the gas generator exhaust and indicates that the gas generator has begun operating and producing gas to run the turbines.
The fuel rich exhaust from the turbopumps/gas generator is ignited by the radial outward-firing ignitors (ROFIs), which as Jim stated are lit off at T-15.
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#304
by
Big Al
on 02 Feb, 2008 18:55
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Thanks for the great pictures!
Upon further review I realized that the RS-68 uses two turbo-pumps, this would give a lot more flexibility in the start sequence. I guess I was thinking of the Spacex Merlin with its single turbo-pump when I asked the question.
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#305
by
Jim
on 02 Feb, 2008 19:26
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Big Al - 2/2/2008 2:55 PM
Thanks for the great pictures!
Upon further review I realized that the RS-68 uses two turbo-pumps, this would give a lot more flexibility in the start sequence. I guess I was thinking of the Spacex Merlin with its single turbo-pump when I asked the question.
It uses one (corection) gas generator. Even, vehicles with two, like the shuttle, would start them at the same time. An engine can not run unbalanced
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#306
by
Big Al
on 02 Feb, 2008 19:37
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I bet my timing was off too. I have been watching the video over at Spaceflight Now.com and as soon as The Fat Man Doing The Countdown (he looks just like me!) says “15” you see the red glow of hydrogen deep within the flame chute
Another comment on the taper of the aft end of the rocket is that the heat blankets on both the Delta and Atlas have a very tight fit. I’m sure this is good for aerodynamics, but I would think it would trap all the heat generated buy the upper part of the engine, but it does work and is widely used.
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#307
by
Jim
on 02 Feb, 2008 20:00
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Big Al - 2/2/2008 3:37 PM
1. I bet my timing was off too. I have been watching the video over at Spaceflight Now.com and as soon as The Fat Man Doing The Countdown (he looks just like me!) says “15” you see the red glow of hydrogen deep within the flame chute
2. Another comment on the taper of the aft end of the rocket is that the heat blankets on both the Delta and Atlas have a very tight fit. I’m sure this is good for aerodynamics, but I would think it would trap all the heat generated buy the upper part of the engine, but it does work and is widely used.
1. That is from the ROFI's
2. If Spacex had such a structure,they are purged with conditioned air prelaunch, they wouldn't have had the corrosion on the first launch. Most launch vehicles enclose the upper engine sections, not just the EELV's. Thor, Atlas I & II, Jupiter, Redstone, etc
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#308
by
Big Al
on 02 Feb, 2008 22:09
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Are you sure about the single turbo pump?
Wikipedia in their write up states that it has two pumps. Also over at Spaceandtech.com they have a very nice CAD rendering of the RS-68 with a good view of the top of the engine. It shows two pumps. Each pump exhausts on the opposite side of the engine. One of them, which I think is the hydrogen pump because it looks like it has bigger scroll housing, has a high pressure nozzle on it which I assume is used for roll control. The other pump looks like it uses a lower pressure exhaust system.
The over all design looks like a classical rocket engine…except it burns hydrogen….and its on the first stage of a rocket…..and it has an ablative lower nozzle…
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#309
by
Jim
on 02 Feb, 2008 22:13
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I corrected my post to single gas generator
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#310
by
AnimatorRob
on 23 Apr, 2008 20:07
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Over on the Ares I TO thread it was mentioned that the RS-68 uses quite a lot of He and that was a potential problem due to the limited supply of He. Can someone explain exactly what the He is used for and why can't another inert gas be used, say N?
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#311
by
nacnud
on 23 Apr, 2008 20:26
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Well N freezes at LH temps while He stays a gas. So purging the system with cold He gas gets rid of all the air with might freeze just where you don't want it, but I'm no expert, best check with them.
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#312
by
Rocket Rancher
on 23 Apr, 2008 20:40
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nacnud - 23/4/2008 4:26 PM
Well N freezes at LH temps while He stays a gas. So purging the system with cold He gas gets rid of all the air with might freeze just where you don't want it, but I'm no expert, best check with them.
You very correct on that description. Frozen air in the RL-10 was the cause of 2 failures for the Atlas II program back in the late 80's.
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#313
by
Jim
on 23 Apr, 2008 20:42
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Rocket Rancher - 23/4/2008 4:40 PM
nacnud - 23/4/2008 4:26 PM
Well N freezes at LH temps while He stays a gas. So purging the system with cold He gas gets rid of all the air with might freeze just where you don't want it, but I'm no expert, best check with them.
You very correct on that description. Frozen air in the RL-10 was the cause of 2 failures for the Atlas II program back in the late 80's.
early 90's
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#314
by
Ronsmytheiii
on 23 Apr, 2008 22:43
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This may not be as sophisticated as the other questions, but what is a good book as an overview of the Delta IV system and its development? And if any other books of other launchers if know.
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#315
by
Analyst
on 24 Apr, 2008 06:13
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Jim - 23/4/2008 10:42 PM
Rocket Rancher - 23/4/2008 4:40 PM
nacnud - 23/4/2008 4:26 PM
Well N freezes at LH temps while He stays a gas. So purging the system with cold He gas gets rid of all the air with might freeze just where you don't want it, but I'm no expert, best check with them.
You very correct on that description. Frozen air in the RL-10 was the cause of 2 failures for the Atlas II program back in the late 80's.
early 90's
Atlas II never failed. It has been Atlas I.
Analyst
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#316
by
Antares
on 24 Apr, 2008 15:40
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Ronsmytheiii - 23/4/2008 5:43 PM
This may not be as sophisticated as the other questions, but what is a good book as an overview of the Delta IV system and its development? And if any other books of other launchers if know.
Rocketdyne had an internal and PR magazine called Threshold. There was one called "First Flight Edition" for RS-68 that gave a very good overview of the development of the engine. I can't find it on Google. Maybe a request to Canoga to get a soft copy of it.
Doubtful there's a book on this, exactly. I suggest looking at AIAA papers over the 1997-2004 and more recent time period.
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#317
by
Analyst
on 24 Apr, 2008 15:51
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Antares - 24/4/2008 5:40 PM
Doubtful there's a book on this, exactly. I suggest looking at AIAA papers over the 1997-2004 and more recent time period.
These papers are extremly expensive. Sadly its very often this way in academics and engineering. $30 for a pdf with 15 pages - while I am interested in this stuff, I have to pay my bills too.
Analyst
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#318
by
Antares
on 24 Apr, 2008 20:00
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Libraries, anyone? Many companies, agencies and universities have subscriptions to pdf-dot-aiaa-dot-org.
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#319
by
Nick L.
on 27 Apr, 2008 07:11
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