Author Topic: Delta IV Q&A  (Read 243068 times)

Offline publiusr

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Re: Delta IV Q&A
« Reply #320 on: 06/26/2008 05:37 pm »
Space News carried an op-ed critical of RS-68, but a simpler engine always looks like a better deal.

  The processes and time required to manufacture a 5m tank is equivelent to that of a 3m tank.  In the end the 5-engined Ares V will have less of a fireball the the 3-engined Shuttle.

Interesting points

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Offline Propforce

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Re: Delta IV Q&A
« Reply #321 on: 07/01/2008 07:36 am »

As for the launch fireball...  That is more of an unintented consequence of how PWR and Delta does the RS-68 start sequence.  Call if a lesson learned...  RS-68 is completely new and you wouldn't expect the first Block to be perfect.  PWR with Delta and NASA assistance have developed start sequence and design changes to mitigate the fireball.  In the end the 5-engined Ares V will have less of a fireball the the 3-engined Shuttle.

I think this worth some clarification.

The main reason for the "fireball" on the RS-68 and the Delta IV has much to do with how the exhaust duct was designed as well as with the RS-68 itself.

The Delta IV chosed an "enclosed" exhaust duct design over the water suppression approach, such as used on the Shuttle launch pad, for the simple reason of economic.  They did not want to spend the money to put in a water-suppression system during the early development days when money was tight (keep in mind that the majority of development cost was paid for by Boeing and not by the government).  The enclosed duct satisfied the main concern at the time, which was Ignition Over Pressure (IOP) that could adversly impact payloads acoustic qualification requirements.

The realization of have a pre-mixed detonable hydrogen-air inside the duct was an after-thought.  Internal trades were conducted to evaluate the alternatives, including what was proposed for the Shuttle pad at Vandenberg of using a jet engine to pump out the exhausts.  Again, the key figure of merit (FOM) was cost.  The radially outward flame ignitor (ROFI), a.k.a. the sparklers, used for the Shuttle launch pad, were slected out of pure economics and not that it was the most effective solution.  In fact, I doubt that they really make that much difference at all.   

The physics problem was equivalent to pumping gas into your oven for ~30 seconds before you light a match to it.  You get a big BANG and that pressure wave doesn't just go out the back end, it goes toward the vehicle as well.  They had to structurally beef up the engine aft-section as well as adding extra thermal insulation as a result.  Since hydrogen gas is lighter than air, some do floated up via the gap between the launch table and the vehicle.  So as flame propagates forward, you see a nice flash and burning of these hydrogen next to the vehicle, resulting in the charring of vehicle paints on lift-off.

Another unwelcome result is losing some initial vehicle thrust due to drag.  When the 3 engines going on full blast, e.g., 104% power level, it created a 'jet pump' effect inside the duct which created a suction at the based of vehicle.  This further reduces vehicle's T/W ratio at take-off.

But this will NOT happen on Ares 1 or V, unless NASA fails to learn this lesson from Delta and use the same enclosed exhaust duct approach.  If the vehicle is on an 'open-air' plateform, such as the current Shuttle launch pad, the hydrogen pumped out during engine start will quickly dissipate and not accumulate at the based of vehicle to cause the similar problem.


Offline TrueGrit

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Re: Delta IV Q&A
« Reply #322 on: 07/21/2008 07:17 pm »
While the flame-duct does have some influence on the "fireball" that is release when the Delta IV is started it is not the primary reason.  The primary reason is the way the RS68 is started...  I've seen simulations of the predicted Ares V start that shows a very similar situation as Delta IV, even with an open duct and water suppression.  That's the reason NASA has identified "start sequence" changes for the RS68B program.  Heck even the CBC during its stage test had similar problems with "fireballs" despite being multiple stories in the sky on an open test stand.  The primary reason for the water on the Shuttle pad is for sound/acoustic suppression due to the two massive SRBs, not fireball control.

The reason for the "fireball" is that RS68, like most LO2/LH2 engines, has a "fuel lead" during the start sequence.  This means the first thing the RS68 does when it starts is to dump a heck of a lot of hydrogen... 

As the risk of getting off topic...  It is this initial dump of hydrogen why the Delta IV, like Shuttle and SSME, has "sparklers".  The "sparklers" only try to assure the hydrogen released doesn't poll anywhere.  The "sparklers" do this job, and without them there's a risk of the hydrogen pooling and exploding when the engine is ignited.  On the test stand they have the same concerns, but utilize propane torches (like the flame stack). 

Getting back to the start fireball...  This initial release of hydrogen is lit by the "sparklers" which adds to its buoyancy...  It's is this "free hydrogen" that floats up and becomes the "fireball" seen prior to each launch.  What happens is that once the engine is started the duct aspiration you mentioned start to suck down the air around the vehicle, including any remaining fire around the bottom of the vehicle.  So the problem is that the amount of hydrogen released combined with relatively long time it takes to achieve aspiration results in too much fire released.

The NASA RS68B plan to take some conservative margins out of the start sequence to both reduce the "free hydrogen" and quicken the time to reach aspiration.  As I said these design changes are known and will reduce the amount of "free hydrogen" of 5 RS68s to that of 3 SSMEs.

Offline kevin-rf

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Re: Delta IV Q&A
« Reply #323 on: 08/01/2008 08:25 pm »
Okay here is a tinker toy question on something that has been bugging me since the DOD is ending the Delta-II 30 day callup for launching GPS birds.

Different Delta-IV cores are used for different Delta-IV configurations. In the case of the GPS, where the Delta-IV M is not maxed out can the heavier M+(4,2) and M+(5,4) core (ment for a different launch that is being bumped) be used in zero solid Delta-IV M configuration to launch a GPS bird quickly?
« Last Edit: 08/01/2008 08:26 pm by kevin-rf »
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Offline Jim

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Re: Delta IV Q&A
« Reply #324 on: 08/01/2008 08:44 pm »
Okay here is a tinker toy question on something that has been bugging me since the DOD is ending the Delta-II 30 day callup for launching GPS birds.

Different Delta-IV cores are used for different Delta-IV configurations. In the case of the GPS, where the Delta-IV M is not maxed out can the heavier M+(4,2) and M+(5,4) core (ment for a different launch that is being bumped) be used in zero solid Delta-IV M configuration to launch a GPS bird quickly?

Not the M+(5,4) core, it has a 5m interstage.  Interstage is part of the core. 
Physical at M+(4,2) core could be used but all the analyses would have to be done before hand

Offline Antares

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Re: Delta IV Q&A
« Reply #325 on: 08/03/2008 05:30 am »
The acoustic environments that solids put out could easily prevent a payload from moving off of an all-liquid stack.  G's would be higher too since there's about 2/3rds more thrust while the solids are on.  That could even present a problem for max-Q violations on the rocket, not just the payload.
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Offline Nick L.

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Re: Delta IV Q&A
« Reply #326 on: 08/04/2008 11:43 am »
The acoustic environments that solids put out could easily prevent a payload from moving off of an all-liquid stack.  G's would be higher too since there's about 2/3rds more thrust while the solids are on.  That could even present a problem for max-Q violations on the rocket, not just the payload.

I think he is asking if it is possible to fly a Delta IV M+ core (which is structurally different from the Medium core) without solids if the need arises.

I wonder now, with the RS-68 performance boost in the cards (for Ares V), is it possible that now they can do away with having separate, lighter parts specifically for the Medium and just use the M+(4,2) core, reducing cost?
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Offline Antares

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Re: Delta IV Q&A
« Reply #327 on: 08/04/2008 02:37 pm »
Very good, sir.  That precisely is or has been investigated.  The performance boost is not for Ares V.  Ares V is using the performance boost from the Delta IV Heavy Upgrade.
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Offline TrueGrit

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Re: Delta IV Q&A
« Reply #328 on: 08/05/2008 01:38 am »
GPS IIF's are currently planned to be launched on a M+ with 2 GEMs, not a Medium.  And would be by default capable of living with the environments from the 2 GEMs.  As for the launch vehicle...  The GPS IIF SV is similar in mass to the GOES SV and as such would result in similar loads.

As for flying a M+ CBC without GEMs...  The M+ structure is heavier and stronger than the Medium and therefore would be capable of flying without GEMs if the situation called for it.  The question is a matter of performance...  The M+ is multiple thousands of lbs heavier than a Medium.

As for use of the upgraded RS68A being developed for the USAF...  There are specific Heavy EELV performance needs driving its development.  That engine once developed is getting a close look at for "single stick" Delta IVs.  Part of that trade involves more commonality across the range.  But is being traded against other considerations, including performance...
« Last Edit: 08/05/2008 01:52 am by TrueGrit »

Offline Nick L.

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Re: Delta IV Q&A
« Reply #329 on: 01/21/2009 12:40 am »
What would the performance of a D-IV Medium with an RS-68A look like? Assuming everything stays the same as it is now except for the engine.
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Offline TrueGrit

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Re: Delta IV Q&A
« Reply #330 on: 01/30/2009 05:45 am »
As it has been said "rockets are not legos"...  Nothing is completely unchanged with the RS-68A incorporated.  Everything in the rocket will get a second look and some minor changes are needed at a minimum. 

The Delta IV perfromance with the upgraded RS-68A is detailed in back of the mission planners guide, which is available on the ulalaunch.com website.  Assuming the RS-68A full thrust option is pursued performance to a 19,323 nmi x 100 nmi minimum at 27.0 deg orbit is:

Medium: Current 9.4 klb - Upgrade 10.5 klb
M+4,2: Current 13.1 klb - Upgrade 14.0 klb
M+5,2: Current 10.3 klb - Upgrade 11.3 klb
M+5,4: Current 14.1 klb - Upgrade 15.1 klb
Heavy: Current 28.4 klb - Upgrade 32.1 klb

In the same section there is detailed proposals for additional M+ configurations.  The most ready to go is the M+4,4.  But also M+5,6 and M+5,8 configurations.  And has a more upto date version of the potential future Heavy growth chart.

Offline Nick L.

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Re: Delta IV Q&A
« Reply #331 on: 01/30/2009 11:45 pm »
Cool, thanks. Didn't think to look in the PPG.
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Offline Nick L.

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Re: Delta IV Q&A
« Reply #332 on: 06/26/2009 11:37 pm »
'Nuther question:

On today's launch before the scrub one of the cameras on the east LPT was showing "LOW PRESSURE". Also saw this too on a couple other videos. What pressure is this referring to?

Nick
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Offline DansSLK

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Re: Delta IV Q&A
« Reply #333 on: 06/27/2009 06:23 am »
'Nuther question:

On today's launch before the scrub one of the cameras on the east LPT was showing "LOW PRESSURE". Also saw this too on a couple other videos. What pressure is this referring to?

Nick

I suspect the camera's have enviromental enclosures with a positive pressure seal and that is what the message is referring to, i could be wrong on that since i know next to nothing about the GSE in question but i can almost guarantee you its not related to the LV.

Offline mmeijeri

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Re: Delta IV Q&A
« Reply #334 on: 06/27/2009 02:15 pm »
As I understand it currently you have to throttle down anyway so you don't exceed constraints on acceleration and/or dynamic pressure. If
The Heavy doesn't have this issue.

So why does the center core throttle down? Just to allow the outer cores to be jettisoned early? And does that outweigh gravity losses from not running at full thrust?
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Offline Danny Dot

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Re: Delta IV Q&A
« Reply #335 on: 06/27/2009 02:17 pm »
Does anyone know what the max q of the heavy is?

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Offline Jim

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Re: Delta IV Q&A
« Reply #336 on: 06/27/2009 02:40 pm »
As I understand it currently you have to throttle down anyway so you don't exceed constraints on acceleration and/or dynamic pressure. If
The Heavy doesn't have this issue.

So why does the center core throttle down? Just to allow the outer cores to be jettisoned early? And does that outweigh gravity losses from not running at full thrust?

The  strap on's aren't jettisoned early, they are jettisoned when they burnout.

The core throttles down to reduce propellant consumption, so that it can burn after the strap on's are jettisoned and function as another stage.   It is similar to the booster package on the heritage one and half stage Atlas.
« Last Edit: 06/27/2009 02:42 pm by Jim »

Offline Danny Dot

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Re: Delta IV Q&A
« Reply #337 on: 06/27/2009 03:07 pm »
snip

So why does the center core throttle down?

So the outers will use their fuel before the core does.

Quote

Just to allow the outer cores to be jettisoned early?


If you realize the outers are empty when jettisoned, the answer it yes.

Quote

And does that outweigh gravity losses from not running at full thrust?


It must or they wouldn't do it.

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Offline sdsds

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Re: Delta IV Q&A
« Reply #338 on: 11/09/2009 04:24 am »
If I understand correctly, the DoD had a concern about the nozzle extension of the RL10B-2 being provided by a French company.  To mitigate the perceived risks associated with that, DoD funded the purchase of a "large number" of the nozzles and is warehousing them.

I have not found a source indicating the exact (or even approximate) number of nozzles purchased.  Does anyone know?  Also, given the large inventory is it fair to assume the French manufacturer's production line is "cold", i.e. it could take them awhile to resume production?
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Offline Propforce

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Re: Delta IV Q&A
« Reply #339 on: 11/09/2009 07:48 pm »
Does anyone know what the max q of the heavy is?

Danny Deger

In the last AIAA JPC, Jim Sponick (VP of Delta) said the max q for DIV-H is down to the low 300s.

He is citing this as 'advantage' because of the benign environment.

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