-
#60
by
tnphysics
on 03 Sep, 2007 23:41
-
How much larger should the first stage tanks have been?
-
#61
by
tnphysics
on 04 Sep, 2007 22:49
-
How large would the upper stage of an LEO-optimized Delta IV be?
Assume that the CBC is unchanged (or offloaded, if necessary, although adding SRBs would be preferable)
-
#62
by
Propforce
on 04 Sep, 2007 23:12
-
CFE - 3/9/2007 10:26 AM
Nick L. - 3/9/2007 1:23 AM
As for why they went with a cryogenic first stage, I don't know. Increased ISp maybe? The RS-68, even with its simplified design, has a better ISp than the much more complex RD-180 (408 vs 338 sec, respectively). But then you do give up thrust, so I don't really know.
IIRC, When D4 was initially designed, McDonnell Douglas had conducted studies showing that using the same propellant combos for both stages would reduce overall costs.
In hindsight, most people will look at D4 and say that LOX-LH2 was a pretty bad choice for the lower stage. A better choice might have been a two-stage rocket with LOX-Kerosene in both stages. That seems to be SpaceX's reasoning.
1) Choosing a LO2/LH2 cryo first stage has NOTHING to do with sizing engine THRUST. What I mean is, one could have sized the RS-68 to 800K lbf if McDD chose to. The fact was that RS-68 thrust level was picked before all the weight growth were frozen.
2) One could argue all day till the cows come home between a LOX/LH2 vs. a LOX/HC first stage. A LOX/HC first stage would've required a much higher thrust engine because of lower Isp of LOX/HC engine and heavier HC propellant weight ( a combination of low Isp engine requires MORE propellant + higher density of HC fuel).
3) DIV was designed for high energy, high performance missions to GTO. It is NOT optimized for LEO missions. The market study said that the money is on the GTO comm sat missions.
4) Until I see an Atlas V Heavy and how much they'd charge for a heavy launch. DIV Heavy is still the only game in town for U.S. government missions.
-
#63
by
tnphysics
on 12 Sep, 2007 03:19
-
How much would developing the RS-800 cost? Probably no more than $470 million, or 2 Heavy launches.
-
#64
by
Jim
on 12 Sep, 2007 03:41
-
tnphysics - 11/9/2007 11:19 PM
How much would developing the RS-800 cost? Probably no more than $470 million, or 2 Heavy launches.
more and who is going to pay. But anyways, you just only got an engine so what are you going to do with it. integrating it into a vehicle costs big money
-
#65
by
tnphysics
on 16 Sep, 2007 12:27
-
The RS-68 cost only $470 million to develop. That is where I got my cost number.
The AUS could have helped tremendously because a Medium+ (5,4) with an AUS could have replaced a Heavy without one.
-
#66
by
Jim
on 16 Sep, 2007 14:04
-
tnphysics - 16/9/2007 8:27 AM
The RS-68 cost only $470 million to develop. That is where I got my cost number.
The AUS could have helped tremendously because a Medium+ (5,4) with an AUS could have replaced a Heavy without one.
No, the AUS was not big enough to make a 5,4 equivalent to a heavy
-
#67
by
Nick L.
on 16 Sep, 2007 21:46
-
tnphysics - 16/9/2007 8:27 AM
The RS-68 cost only $470 million to develop. That is where I got my cost number.
The AUS could have helped tremendously because a Medium+ (5,4) with an AUS could have replaced a Heavy without one.
How are you coming up with these assertions? IIRC there have been no published data regarding the planned performance of the AUS. A Medium+(5,4) with the AUS could fill the gap between the standard M+(5,4) and the Heavy, but it could never replace it. There are also probably cheaper ways of boosting the performance other than developing an all new upper stage.
-
#68
by
tnphysics
on 20 Sep, 2007 23:56
-
Why is the Delta IV Medium+ (5,2) unable to lift as much to LEO as the Delta IV Medium?
And why is there no Delta IV Medium+ (4,4)?
Or even (5,6) or (5,9)?
And why does the Delta IV cost more than the Delta II?
-
#69
by
Nick L.
on 21 Sep, 2007 00:09
-
tnphysics - 20/9/2007 7:56 PM
Why is the Delta IV Medium+ (5,2) unable to lift as much to LEO as the Delta IV Medium?
And why is there no Delta IV Medium+ (4,4)?
Or even (5,6) or (5,9)?
And why does the Delta IV cost more than the Delta II?
1) Because of the extra weight of the larger second stage and fairing, it creates more gravity loss on LEO missions. On GEO missions the bigger upper stage makes up for the added weight.
2) It wasn't worth the cost of certificating it considering the lack of payloads in the weight range.
3) It would require extra cost to add more GEM attach points.
4) Because it's bigger and has more payload capability.
-
#70
by
ryan mccabe
on 21 Sep, 2007 00:14
-
tnphysics - 20/9/2007 6:56 PM
Why is the Delta IV Medium+ (5,2) unable to lift as much to LEO as the Delta IV Medium?
And why is there no Delta IV Medium+ (4,4)?
Or even (5,6) or (5,9)?
And why does the Delta IV cost more than the Delta II?
1. It has the same thrust but is lifting a wider, heavier payload fairing. Atmospheric drag loss and mass properties probably account for most of the 1,600 kg discrepancy to GTO.
2. Probably because most of the heavy payloads that need 4 GEMS are also wide enough to need the 5-meter fairing.
3. That's the purpose of the Delta IV-H
4. The smallest Delta IV lifts twice the payload of the Delta II. It's just a more capable vehicle and that translates into cost. The Delta IV is also newer and has very low flight rate, which does nothing good for costs.
-
#71
by
tnphysics
on 21 Sep, 2007 00:17
-
Why is it more expensive to build from a supply side point of view?
-
#72
by
Jim
on 21 Sep, 2007 00:29
-
tnphysics - 20/9/2007 8:17 PM
Why is it more expensive to build from a supply side point of view?
supply side
It is bigger, more material therefore more costs
It also has to buy down development costs
-
#73
by
Jim
on 21 Sep, 2007 00:32
-
tnphysics - 20/9/2007 7:56 Pm
Or even (5,6) or (5,9)?
The pad can't support the installation of anymore than 4
-
#74
by
tnphysics
on 21 Sep, 2007 00:48
-
Jim - 20/9/2007 8:29 PM
tnphysics - 20/9/2007 8:17 PM
Why is it more expensive to build from a supply side point of view?
supply side
It is bigger, more material therefore more costs
It also has to buy down development costs
What about all those SRBs on the Delta II?
-
#75
by
Jim
on 21 Sep, 2007 01:05
-
So what about them? They work.
-
#76
by
tnphysics
on 21 Sep, 2007 01:34
-
Why they don't drive up the costs.
-
#77
by
Jim
on 21 Sep, 2007 01:59
-
Drive up what costs? Delta has been using 9 SRM for more than 35 years
-
#78
by
Nick L.
on 21 Sep, 2007 02:00
-
Because Delta II was designed with the GEMs. It needs them to be able to fly at all. Delta II is also only a derivative of the early Delta (1000/2000/3000 series), so it was cheaper to develop, so development costs are already paid for, which makes the cost lower. Delta IV is a clean-sheet design and the development costs haven't been paid off yet which drives up the per launch cost.
-
#79
by
TrueGrit
on 21 Sep, 2007 07:50
-
As for the question about more solids on a Medium+… Delta has looked at configurations other than the 4 currently offered. That includes the neccessary pad mods. Its less developed than AUS or RS-68A, but Delta has invested some time and effort to develop conceptual designs that have up to 8 solids on a “single stick”… But these have not been put on the manifest because of a lack of need. Right now the customer needs are at the high end of the vehicle capability, to upgrade the Heavy as indicated on the COTS RFI response. Quite simply there isn’t a costumer need for a better Medium. But there’s enough work to feel confident that everything from a 4/4 to a 5/8 could be quickly brought on-line if a costumer indicates a need.
