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#240
by
Propforce
on 28 Dec, 2007 21:04
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OK... can someone tell me how to up load a 8 megabytes PDF document ? This thing won't let me upload anything more than 100K :frown:
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#241
by
Antares
on 29 Dec, 2007 06:09
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Hmmm. I'm not sure which takes precedence, that the paper was produced by taxpayer dollars or AIAA (copy)rights. I've had problems uploading too. I can't remember what I did to fix it. Maybe PM Chris.
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#242
by
meiza
on 29 Dec, 2007 11:23
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Interesting, how were these improvements discovered? Were they in the pipeline during the original RS-68 development but time ran out since EELV had a deadline?
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#243
by
Damon Hill
on 29 Dec, 2007 21:04
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The RS-68 was biased towards cost rather than performance; the current round of enhancements mostly involve improving the existing design without major changes like a fully regenerative nozzle. Others, like reduction of the hydrogen flare at ignition, are driven more by possible safety issues, or just reducing the appearance of problems. I'd like to see a COBRA-style high-performance engine (sort of a simplified SSME with higher thrust), but the money isn't there for radical changes in design.
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#244
by
kevin-rf
on 30 Dec, 2007 00:13
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Interesting how much they are trying to reduce helium use ... Any chance that by the time they are done it will use less helium than LH
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#245
by
Antares
on 30 Dec, 2007 03:05
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Helium requirements are almost entirely driven by KSC infrastructure limits. Future helium costs were secondary when the requirements were written, though the white papers have helped make the point.
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#246
by
Nick L.
on 01 Jan, 2008 02:35
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Wow, so much great info! This thread is this forum at its best. That's why I love this place.
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#247
by
sticksux
on 01 Jan, 2008 23:02
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Why it was decided to use LH+LOX first stage for Delta IV? It seems to be a step backwards from Delta II and III.
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#248
by
Jim
on 01 Jan, 2008 23:11
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Clean burning.
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#249
by
McDew
on 02 Jan, 2008 01:42
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Actually the decision was driven by what was available in the US industry. Atlas wanted LOX/RP, but Rocketdyne could not develop a cost effective current technology high thrust/performance engine which led them to go the RD-180 route. Boeing's strategy was to stay with a US built engine which drove them to a RS-68 shuttle derived engine with the hope of maintaining shuttle/NASA cost synergy which is paying off with planned upgrades.
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#250
by
Jim
on 02 Jan, 2008 01:47
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McDew - 1/1/2008 9:42 PM
Actually the decision was driven by what was available in the US industry. Atlas wanted LOX/RP, but Rocketdyne could not develop a cost effective current technology high thrust/performance engine which led them to go the RD-180 route. Boeing's strategy was to stay with a US built engine which drove them to a RS-68 shuttle derived engine with the hope of maintaining shuttle/NASA cost synergy which is paying off with planned upgrades.
Not quite. RS-68 was designed specifically for the Delta-IV. Atlas went to the RD-180 when Rocketdyne couldn't handle two engine developments.
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#251
by
Propforce
on 02 Jan, 2008 01:54
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Jim - 1/1/2008 6:47 PM
Atlas went to the RD-180 when Rocketdyne couldn't handle two engine developments.
Rocketdyne could not compete with the price of RD-180 offerred by the Russians.
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#252
by
Propforce
on 02 Jan, 2008 01:59
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sticksux - 1/1/2008 4:02 PM
Why it was decided to use LH+LOX first stage for Delta IV? It seems to be a step backwards from Delta II and III.
Why is it backward to have a H2 first stage?
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#253
by
McDew
on 02 Jan, 2008 02:01
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Boeing did not go the Rocketdyne LOX/RP route for the same reasons as Atlas. The US was 20 years behind in the LOX/RP engine technology and the cost to catch up would kill any proposal.
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#254
by
tnphysics
on 02 Jan, 2008 04:19
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Couldn't you just restart RS-84 development?
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#255
by
sticksux
on 02 Jan, 2008 09:54
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Propforce - 2/1/2008 2:59 AM
sticksux - 1/1/2008 4:02 PM
Why it was decided to use LH+LOX first stage for Delta IV? It seems to be a step backwards from Delta II and III.
Why is it backward to have a H2 first stage?
Because LH stage costs more than equivalent (in lifting capability) kerolox one. Ask yourself - why SpaceX didn't go LH route?
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#256
by
meiza
on 02 Jan, 2008 11:45
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sticksux - 2/1/2008 10:54 AM
Propforce - 2/1/2008 2:59 AM
sticksux - 1/1/2008 4:02 PM
Why it was decided to use LH+LOX first stage for Delta IV? It seems to be a step backwards from Delta II and III.
Why is it backward to have a H2 first stage?
Because LH stage costs more than equivalent (in lifting capability) kerolox one. Ask yourself - why SpaceX didn't go LH route?
An LH2 gas-generator engine (with an ablative nozzle!) is much much simpler and cheaper than an oxygen rich kerolox staged combustion one, if produced in the US. And still has better ISP. I bet that was one of the reasons... There was LH2 experience from the SSME and STME that were clearly assets and competetive advantages.
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#257
by
TrueGrit
on 02 Jan, 2008 16:22
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The Delta IV decision on LH2/LOx first stage is an example of a decision based on all four aspects of real-world engineering performance-cost-schedule-manufacturing (both recurring and nonrecurring). Anyone who considers it a "step-backward" isn't taking into account all considerations... Delta (under MacDac) traded LH2 and RP1 during the proposal phase and found significant benefits to go with LH2, a big one being the high maturity of the Rocketdyne engine proposal. While I don't want to go into details the Delta and Atlas trades are good examples for those of you guys in school planning on joining us in the real-world... Real trade studies often involve all the aspects of the business.
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#258
by
meiza
on 02 Jan, 2008 17:09
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TrueGrit - 2/1/2008 5:22 PM
The Delta IV decision on LH2/LOx first stage is an example of a decision based on all four aspects of real-world engineering performance-cost-schedule-manufacturing (both recurring and nonrecurring). Anyone who considers it a "step-backward" isn't taking into account all considerations... Delta (under MacDac) traded LH2 and RP1 during the proposal phase and found significant benefits to go with LH2, a big one being the high maturity of the Rocketdyne engine proposal. While I don't want to go into details the Delta and Atlas trades are good examples for those of you guys in school planning on joining us in the real-world... Real trade studies often involve all the aspects of the business.
Well, LH2 seems to lose on all the other sectors than ISP (which is an important thing ofc).
Ground equipment: pumps, vacuum jacketed piping, hydrogen leaks easily, issue of fuel cost and storability, density, temperature...
Rocket (other than the engine): Low density makes a bulky stage which is expensive to make and transport and is draggy in flight, low temp means you need more insulation, purges, bellows in the lines etc...
But there was experience in all of this.
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#259
by
edkyle99
on 02 Jan, 2008 17:34
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TrueGrit - 2/1/2008 11:22 AM
The Delta IV decision on LH2/LOx first stage is an example of a decision based on all four aspects of real-world engineering performance-cost-schedule-manufacturing (both recurring and nonrecurring). Anyone who considers it a "step-backward" isn't taking into account all considerations... Delta (under MacDac) traded LH2 and RP1 during the proposal phase and found significant benefits to go with LH2, a big one being the high maturity of the Rocketdyne engine proposal. While I don't want to go into details the Delta and Atlas trades are good examples for those of you guys in school planning on joining us in the real-world... Real trade studies often involve all the aspects of the business.
The results of this very interesting "trade study" are still pending, but seem, based on recent and projected EELV flight rates, to be leaning right now toward the Atlas staged combustion RP/LOX choice. The results are not final. One monster Atlas pad explosion, Sea Launch style for example, could change everything.
- Ed Kyle
