Author Topic: The design of the Delta IV  (Read 16004 times)

Offline Jim

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Re: Why did was Delta IV designed like it was?
« Reply #20 on: 05/12/2013 12:13 pm »

Didn't most people in the industry also have RP-1 experience?

No, as I said, only sustaining engineering on RS-27.  There hadn't been a new RP-1 design for years.

Offline Jim

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Re: Why did was Delta IV designed like it was?
« Reply #21 on: 05/12/2013 12:15 pm »

And I can understand a common propellant.  The Russians and SpaceX went that route too. 
But...take Atlas V.  You have three liquids.  LH2, LOX, and RP-1.


That was already LM experience base and that was what they chose.  And they ended up with a non US RP-1 engine.  MD trades said to do otherwise.

Offline Jim

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Re: Why did was Delta IV designed like it was?
« Reply #22 on: 05/12/2013 12:18 pm »

1.  If you want to remove one to make things more simple and streamlined, it doesn't seem like removing the most simple and easy to pump, transport, and store really helps things much.  You'd think they'd remove the most difficult by far to work with...LH2.

2.  I mean, I understand the higher performing LH2...but if you are going for simplicity, it seems a little counter intuitive to cut out the most easy liquid to work with and make it so you need even more of the most difficult liquid to work with.


1.  LH2 was going to be needed on the upperstage to meet the USAF performance requirements for any vehicle.

2.  MD chose to simplify ground infrastructure by having one propellant combination.

Offline edkyle99

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Re: The Design of the Delta IV
« Reply #23 on: 05/12/2013 04:24 pm »
So the ratio you're saying that if we want to launch the same amount of payload to orbit, the rough rule of thumb is that a 1% increase in booster engine Isp results in a 2.33-2.66% lighter rocket?  With regards to the Delta IV though, wouldn't the superior impulse density of the RD-180 make the Atlas V the more optimized LV?
My example was only for a hypothetical H-1 powered Delta IV versus Atlas V, and only for the two-stage "Medium" version, and depended on assumptions about the second stage.  It can't be a universal "rule of thumb".
Quote

There's one other thing about the Delta IV that bothers me besides an all-hydrolox design.  It's the complete and utter lack of common bulkheads anywhere in the design.
Common bulkheads cost more, and in the age of composites don't save as much weight as they once did.  Like Delta IV CBC, Atlas V CCB also uses separate bulkheads.  Centaur uses common bulkheads because its design dates from the 1960s, when NASA was trying to squeeze maximum payload from an Atlas that only produced 367,000 lbs of liftoff thrust. 
Quote
I'm looking at the design overview diagram of the Ariane 5 ECA and it's clear that LV was mass-optimized.  That in turn allows Ariane to use less expensive engines for the same level of performance.  Why, if the Delta IV has to overcome the drawbacks of an all-hydrolox design, did they not follow Ariane's lead?
First, USAF emphasized cost savings as a primary goal for EELV, so it is only natural that McDonnell Douglas would have followed that lead.  Second, and I'm thinking out loud here, Delta IV had to be designed to cover a lot more payload range than Ariane 5.  It had to have structural margin to handle the triple-barrel Heavy loads, etc.  Third, Ariane's core is naturally more mass sensitive than Delta IV CBC because the EPC (core) burns almost to orbit and it depends on the solids for the initial boost.  CBC is a traditional first stage.  The comparison isn't Vulcain 2 versus RS-68.  It is Vulcain 2 plus two EAP-E boosters versus RS-68.

 - Ed Kyle
« Last Edit: 05/12/2013 09:52 pm by edkyle99 »

Offline Lobo

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Re: Why did was Delta IV designed like it was?
« Reply #24 on: 05/12/2013 04:53 pm »

Didn't most people in the industry also have RP-1 experience?

No, as I said, only sustaining engineering on RS-27.  There hadn't been a new RP-1 design for years.

That's a fair point.  But what about RS-84?  Wasn't it in development while Delta 4 was?  Or was it later?

And could PWR modernize the F-1 as they might do now for Dynetics?
Not a new design, but a design they already had with several working units of the F-1 and F-1A.
Or was the deign that became the RS-68 farther along that a modernized F-1 would have been?
« Last Edit: 05/12/2013 04:58 pm by Lobo »

Offline Nick L.

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Re: The design of the Delta IV
« Reply #25 on: 05/12/2013 08:38 pm »
RS-84 was later I think - it was still being developed after the Delta IV's first flight.
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Offline Proponent

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Re: Why did was Delta IV designed like it was?
« Reply #26 on: 05/13/2013 11:52 am »
And the initial RS-68 only put out 668klbs of thrust.  Three H-1B would get you close to that.

This is a nitpick, but 205,000-lb-thrust H-1 engines would have to be H-1Cs or H-1Ds, both of which also had 200,000-lb-thrust versions.  The H-1Cs where the central four on the S-IB stage and the H-1Ds were the outer four.  Details can be found in the Rocketdyne document attached to this post.

Offline Prober

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Re: The design of the Delta IV
« Reply #27 on: 05/14/2013 01:31 am »
What type of core design does the Delta IV have.  What LV can it be traced to?
 
Understand the Atlas V has some iso grid back to the Titan.  What of the Delta IV?
 
 
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Offline Hyperion5

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Re: The Design of the Delta IV
« Reply #28 on: 05/14/2013 05:32 am »
So the ratio you're saying that if we want to launch the same amount of payload to orbit, the rough rule of thumb is that a 1% increase in booster engine Isp results in a 2.33-2.66% lighter rocket?  With regards to the Delta IV though, wouldn't the superior impulse density of the RD-180 make the Atlas V the more optimized LV?

My example was only for a hypothetical H-1 powered Delta IV versus Atlas V, and only for the two-stage "Medium" version, and depended on assumptions about the second stage.  It can't be a universal "rule of thumb".

Alright, I understand that, but your example does help to explain how methalox needs only a 7-8% increase in Isp over kerolox to compensate for lessened impulse density (~16% I believe).  There might not be a magic number ratio, but it does make it far easier to understand why t/w ratio often plays second fiddle to an engine's impulse density & Isp. 


There's one other thing about the Delta IV that bothers me besides an all-hydrolox design.  It's the complete and utter lack of common bulkheads anywhere in the design.
Common bulkheads cost more, and in the age of composites don't save as much weight as they once did.  Like Delta IV CBC, Atlas V CCB also uses separate bulkheads.  Centaur uses common bulkheads because its design dates from the 1960s, when NASA was trying to squeeze maximum payload from an Atlas that only produced 367,000 lbs of liftoff thrust. 

They might cost more to design, but they don't seem to have much effect on a rocket's crucial cost-per-kg to orbit that they need for commercial success (besides reliability).  The Ariane 5 is cheaper per kg than the EELVs and features them, as does the Falcon 9.  If Spacex can pull these off on the cheap chances are common bulkheads are not that expensive of a design feature. 


 I'm looking at the design overview diagram of the Ariane 5 ECA and it's clear that LV was mass-optimized.  That in turn allows Ariane to use less expensive engines for the same level of performance.  Why, if the Delta IV has to overcome the drawbacks of an all-hydrolox design, did they not follow Ariane's lead?
First, USAF emphasized cost savings as a primary goal for EELV, so it is only natural that McDonnell Douglas would have followed that lead.  Second, and I'm thinking out loud here, Delta IV had to be designed to cover a lot more payload range than Ariane 5.  It had to have structural margin to handle the triple-barrel Heavy loads, etc.  Third, Ariane's core is naturally more mass sensitive than Delta IV CBC because the EPC (core) burns almost to orbit and it depends on the solids for the initial boost.  CBC is a traditional first stage.  The comparison isn't Vulcain 2 versus RS-68.  It is Vulcain 2 plus two EAP-E boosters versus RS-68.

 - Ed Kyle

Though to be fair the Delta IV regularly uses SRBs, which while not as powerful as the Ariane's, certainly have performance characteristics (launch, handling, etc) that make the two LVs similar in certain layouts.  I would think the lack of man-rating for the Delta IV also plays a prominent part in design choices.  I've noticed the Delta IV Heavy has sometimes had its exhaust flames climb back up the rocket and set the insulation alight (temporarily).  I can't recall anything like this ever happening with the Ariane 5, which was meant to be man-rated.  If the Delta IV had been meant to be man-rated and the RS-68 were more like the Vulcain 2, would this insulation issue still be happening? 

Offline Jim

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Re: The Design of the Delta IV
« Reply #29 on: 05/14/2013 10:58 am »
The Ariane 5 is cheaper per kg than the EELVs and features them, as does the Falcon 9.  If Spacex can pull these off on the cheap chances are common bulkheads are not that expensive of a design feature. 


Ariane is subsidized.  Spacex has yet "to pull" this off.

Offline edkyle99

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Re: The Design of the Delta IV
« Reply #30 on: 05/14/2013 04:06 pm »
Though to be fair the Delta IV regularly uses SRBs, which while not as powerful as the Ariane's, certainly have performance characteristics (launch, handling, etc) that make the two LVs similar in certain layouts.
Delta IV was designed from the outset to lift off without solids.  Ariane 5 requires the solids, and can't lift off without them.  That's the difference. 
Quote
I would think the lack of man-rating for the Delta IV also plays a prominent part in design choices.  I've noticed the Delta IV Heavy has sometimes had its exhaust flames climb back up the rocket and set the insulation alight (temporarily).  I can't recall anything like this ever happening with the Ariane 5, which was meant to be man-rated.  If the Delta IV had been meant to be man-rated and the RS-68 were more like the Vulcain 2, would this insulation issue still be happening? 
This is not a problem.  It is a design feature!  Delta IV is designed to "set itself on fire" at T-0!  This burns off residual hydrogen from the engine start process.  I believe that the lack of a water deluge system plays a role, along with the fuel-lead RS-68 startup.  The amount of excess hydrogen in these fireballs seems to have been reduced as launch experience increases. 

NASA sought to reduce the fireball for RS-68B, but it really isn't a crew safety issue because the crew already can't be outside the spacecraft at liftoff!  (The safety issue arises if the hydrogen does not ignite.  Shuttle had this same concern.)  The hydrogen burns off in a second or two.  Boeing did a static test at SLC 37B once.  The fireball quickly dissipated and I don't recall any residual flames after shutdown.

 - Ed Kyle
« Last Edit: 05/14/2013 04:20 pm by edkyle99 »

Offline Lobo

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Re: The Design of the Delta IV
« Reply #31 on: 05/14/2013 09:55 pm »

NASA sought to reduce the fireball for RS-68B, but it really isn't a crew safety issue because the crew already can't be outside the spacecraft at liftoff!  (The safety issue arises if the hydrogen does not ignite.  Shuttle had this same concern.)  The hydrogen burns off in a second or two.  Boeing did a static test at SLC 37B once.  The fireball quickly dissipated and I don't recall any residual flames after shutdown.

 - Ed Kyle

Could D4/D4H utilize the STS style sparklers to burn off that GH2 prior to ignition?

Offline Jim

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Re: The Design of the Delta IV
« Reply #32 on: 05/14/2013 10:00 pm »

Could D4/D4H utilize the STS style sparklers to burn off that GH2 prior to ignition?

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