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#20
by
tnphysics
on 14 Aug, 2007 23:15
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What payload do you calculate?
Could anyone calulate the numbers with POST, etc?
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#21
by
Propforce
on 14 Aug, 2007 23:26
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edkyle99 - 14/8/2007 1:17 PM
I'm assuming a 5.1 x nearly 23 meter fairing that weighs close to 5 tonnes. I'm also assuming payload adapter hardware that adds an extra three-quarters of a tonne. I'm guessing that something in the neighborhood of 9,500 meters/second ideal delta-v would be budgeted for a LEO ascent, which provides a bit of padding for unknowns like gravity losses and covers a variety of inclination assumptions. I'm remembering my propellant residuals (something like 1%). I'm guessing a bit when it comes to the CBC throttling and burns, and trying to be conservative with the specific impulse numbers during the first four minutes of flight. As I mentioned before, I've also gone ahead and offloaded five tonnes of upper stage propellant.
With all of that, I'm still coming up with no less than 9,800 meters/second ideal delta-v, roughly.
- Ed Kyle
At risk of pointing out the obvious, we're talking about
existing DIV-H capability, right?
If that's the case, although I don't have the LEO delta-vee number but I do have the GTO detla-vee number (for GTO: 167 x 35,788km (90 x 19,323 nmi), 27 deg). I get the delta-vee of 11.8 km/sec on the DIV-H based on a payload weight of 13,130 kg (13.13 tons?). I assume a metallic fairing weight a little over 4 tons, plus payload adaptor weight.
This works out roughly about 9,800 m/sec for 28.5 mt payload but I did not adjust the fairing weight.
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#22
by
Propforce
on 14 Aug, 2007 23:29
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tnphysics - 14/8/2007 4:15 PM
What payload do you calculate?
Could anyone calulate the numbers with POST, etc?
POST doesn't help you if you don't have all the right models (aero, etc.).
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#23
by
edkyle99
on 15 Aug, 2007 05:00
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Propforce - 14/8/2007 6:26 PM
edkyle99 - 14/8/2007 1:17 PM
I'm assuming a 5.1 x nearly 23 meter fairing that weighs close to 5 tonnes. I'm also assuming payload adapter hardware that adds an extra three-quarters of a tonne. I'm guessing that something in the neighborhood of 9,500 meters/second ideal delta-v would be budgeted for a LEO ascent, which provides a bit of padding for unknowns like gravity losses and covers a variety of inclination assumptions. I'm remembering my propellant residuals (something like 1%). I'm guessing a bit when it comes to the CBC throttling and burns, and trying to be conservative with the specific impulse numbers during the first four minutes of flight. As I mentioned before, I've also gone ahead and offloaded five tonnes of upper stage propellant.
With all of that, I'm still coming up with no less than 9,800 meters/second ideal delta-v, roughly.
- Ed Kyle
At risk of pointing out the obvious, we're talking about existing DIV-H capability, right?
If that's the case, although I don't have the LEO delta-vee number but I do have the GTO detla-vee number (for GTO: 167 x 35,788km (90 x 19,323 nmi), 27 deg). I get the delta-vee of 11.8 km/sec on the DIV-H based on a payload weight of 13,130 kg (13.13 tons?). I assume a metallic fairing weight a little over 4 tons, plus payload adaptor weight.
This works out roughly about 9,800 m/sec for 28.5 mt payload but I did not adjust the fairing weight.
Yes. Existing Delta IV-H, or at least what we *think* the existing Delta IV-H is.
Playing around with what was reported about the first Delta IV-H, it appears that the 6 tonne payload ended up 476 meters/sec short of the planned near geostationary orbit. My model shows that the 8 second short CBC strap-on and 9 second short core CBC burns would have caused a shortfall of nearly 600 meters per second. The timing is important, but only rough numbers were provided in the Air Force press release about the failure. As a first guess, then, I'm going to assume that the upper stage must have had a bit more than 120 meters per second of planned delta-v margin that it ended up burning off in this instance, making up part of the loss.
That planned orbit would have required roughly 3,940 meters per second more delta-v than a circular 185 km orbit. My model gives about 13,720 meters per second ideal delta-v for a Delta IV-H with a 6 tonne payload. Subtracting 120 meters per second and 3,940 meters per second from that gives 9,660 meters per second to get to a 185 km LEO. There's a lot of wiggle room in there, of course, that makes it easy to see how a 9,700 to 9,800 meters/second ideal delta-v to LEO range might be expected.
9,700 to 9,800 meters per second means 1,900 to 2,000 meters per second worth of drag, gravity, and steering losses. That is high compared to Shuttle's 1,700 meters per second, Ariane's 1,300 meters per second, or the old Saturn IB's 1,400 meters per second, or Atlas V's 1450-ish meters per second. If true, then that apparently is the price paid to fly a pure hydrogen machine with its bigger tanks and lower-than desirable upper stage thrust.
- Ed Kyle
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#24
by
yinzer
on 15 Aug, 2007 07:50
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edkyle99 - 14/8/2007 10:00 PM
9,700 to 9,800 meters per second means 1,900 to 2,000 meters per second worth of drag, gravity, and steering losses. That is high compared to Shuttle's 1,700 meters per second, Ariane's 1,300 meters per second, or the old Saturn IB's 1,400 meters per second, or Atlas V's 1450-ish meters per second. If true, then that apparently is the price paid to fly a pure hydrogen machine with its bigger tanks and lower-than desirable upper stage thrust.
- Ed Kyle
It's not the pure hydrogen nature of the rocket that affects this, it's almost all down to the upper stage design which one can only assume was influenced by the choice of reference missions, although some Delta folks may be able to come in and confirm or deny. GTO (and GSO) missions are much higher energy than LEO missions and so involve a lot more flight at low vertical accelerations and hence gravity loss.
The Atlas V mission planner's guide clearly shows this in the section on intermediate orbits from CCAFS. Looking at a 63.4 degree MEO and the 531/532 pair, the second RL10 buys you 1400 kg additional payload to a 1000km orbit but only 500 kg more to a 9000km orbit. Lockheed and now ULA only offer single-engine Centaurs to GTO.
Boeing designed the Delta III second stage around a single RL10-B2 for GTO missions with maybe the odd MEO flight here and there. 700 second burn time to GTO isn't so bad, especially with that big nozzle giving you 462 (!) seconds of specific impulse. Add 23,000 pounds of propellant and switch to an LEO mission, and all of a sudden you have a 900-second second-stage burn before you get to SECO-I, 1200 seconds after liftoff. Adding a second engine would really help things, but there's you can't fit two 2.2 meter diameter nozzles in a 5-meter stage with plausible clearances. So higher gravity losses it is.
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#25
by
meiza
on 15 Aug, 2007 13:45
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What if you used two short nozzle (Centaur like) RL-10:s on the upper stage, what would the numbers look like then? And which would be easier, making a short nozzle version of the current engine or use the Centaur engine?
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#26
by
Jim
on 15 Aug, 2007 14:05
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The Delta-IV doesn't have the attachments for a 2nd engine
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#27
by
Thorny
on 15 Aug, 2007 15:23
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Could a Centaur be mated with Delta IV?
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#28
by
Skyrocket
on 15 Aug, 2007 16:12
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not without a rather complex redesign
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#29
by
MKremer
on 15 Aug, 2007 16:34
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Thorny - 15/8/2007 10:23 AM
Could a Centaur be mated with Delta IV?
Sure, with lotsa time and lotsa, lotsa money.
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#30
by
yinzer
on 15 Aug, 2007 20:41
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You'd have to redesign a large part of the upper stage. Which is why Boeing was looking at using larger engines such as the MB-45 or RL-60. Again, no money, either on their part or on the part of their Japenese partners.
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#31
by
tnphysics
on 16 Aug, 2007 00:21
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What about adding a second engine and having both engines feed into one nozzle?
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#32
by
Jim
on 16 Aug, 2007 13:50
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tnphysics - 15/8/2007 8:21 PM
What about adding a second engine and having both engines feed into one nozzle?
??
Why?
why start a new engine development, especially a concept that hasn't been done?
It would be better to have engine that is twice as large.
I have notice a trend in your suggestions, tnphysics. They don't take into account the time or money needed to solve engineering issues. There always is an "easy" answer for problems, the hard part is doing it for less cost or time
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#33
by
kevin-rf
on 16 Aug, 2007 16:22
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Quick question on the RS-68 upgrades. When done what will the Delta IV be renamed to? Delta IVb? Delta IV+? Delta V?
Also, how many 'origonal' RS-68's is ULA on the hook for? I assume they will not start building the upgraded RS-68's until they burn through the current inventory. At the current flight rate are we talking years? decades? It would make sense to me to switch it out on vehicles where a new RS-68 will save having to bump up to the next more expensive Delta IV model.
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#34
by
Jim
on 16 Aug, 2007 19:09
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It won't be renamed. there are that many RS-68"s made
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#35
by
kevin-rf
on 16 Aug, 2007 19:30
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Jim - 16/8/2007 3:09 PM
It won't be renamed. there are that many RS-68"s made
Jim, Please clarify, where you trying to say "there are not that many" or there are billions and billions of RS-68 already made.
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#36
by
Jim
on 16 Aug, 2007 19:38
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I meant "aren't". Just had carpal tunnel surgery, and trying to minimize words
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#37
by
kevin-rf
on 16 Aug, 2007 21:01
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Jim - 16/8/2007 3:38 PM
I meant "aren't". Just had carpal tunnel surgery, and trying to minimize words
Sorry to hear that, hope things heal up.
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#38
by
nacnud
on 16 Aug, 2007 21:23
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If you are using windows then I think there are passable speech recognition tools built in, you feel like a dork talking to your computer at first but once trained it's faster than typing.
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#39
by
Propforce
on 16 Aug, 2007 22:23
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nacnud, LTNS.
Glad to see you surfaced on *this* site :cool:
??