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SLS / Orion / Beyond-LEO HSF - Constellation => Heavy Lift Launch Vehicle (HLV/SLS) => Topic started by: neutrino on 07/18/2010 06:55 AM

Title: Maximum number of SRB segments
Post by: neutrino on 07/18/2010 06:55 AM
What is the maximum number of SRB segments?

I mean - the 4-segments SRB are "easily" stretched to 5 and even 5.5 segments ("easily" = no one talks about major technical hurdles). I therefore ask: how far can this design be stretched before significant changes are required?

And, what can be done if significant changes are allowed? (preferably: changes in manufacturing and materials before changes that require one to change the ground infrastructure or ET interface).
Title: Re: Maximum number of SRB segments
Post by: Michael Bloxham on 07/18/2010 07:11 AM
As far as I am aware, the 5.5 segment talked about for the Ares V was just a standard 5-segment SRB with an extra *empty* half-segment (essentially an extra bit of steel so that the SRB could mount with the interstage of the lengthened core tank). I'm pretty sure the 6-segment design was the same.

- Mike
Title: Re: Maximum number of SRB segments
Post by: Robotbeat on 07/18/2010 07:24 AM
4
:)
Title: Re: Maximum number of SRB segments
Post by: sdsds on 07/18/2010 08:07 AM
I mean - the 4-segments SRB are "easily" stretched to 5 and even 5.5 segments ("easily" = no one talks about major technical hurdles).

That's true if "easily"= $1.8 billion, solely for "development and testing," when a five segment engineering test motor had already been successfully fired, and with no "production" motors included in that price.

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how far can this design be stretched before significant changes are required?

If changing the diameters of the segments is considered "significant" (and it should be) going to five segments was already pushing the limit of insignificant changes.  To get five segment motors, ATK required both a nozzle throat diameter increase and incorporation of an extended exit cone.

Note however that at the time of the five segment ETM-03 work circa 2004 (ETM = engineering test motor), ATK did also fire a sub-scale six segment motor several times.
http://www.csar.illinois.edu/F_viz/gallery/AIAA/RSRMV/McMillinETM-03-AIAA-2004-3895.pdf

The really big questions are, "How much would these motors really help in getting a vehicle off the pad?" and  "What would it cost to modify LC-39 so that they could be used?"
Title: Re: Maximum number of SRB segments
Post by: MP99 on 07/18/2010 02:49 PM
Chris has documented that 6.5 seg SRB's were considered for an 'Ares V Max' vehicle. See http://www.nasaspaceflight.com/2008/08/new-engine-configuration-under-evaluation-for-ares-v-ptv-fails/ (http://www.nasaspaceflight.com/2008/08/new-engine-configuration-under-evaluation-for-ares-v-ptv-fails/). With upper stage and PLF, this seems to be the max that could be assembled in the VAB :-

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It’s still early days in the development of the mammoth Ares V, with further configuration changes not ruled out – especially based on gaining performance. The largest ‘viable’ Ares V to be noted is ‘Ares V Max’ – which consists of seven RS-68s and two 6.5 segment boosters.

Even taller variants have also been documented, but all are too tall to fit inside the Vehicle Assembly Building (VAB), and are classed as requiring a new giant Vehicle Integration Building (VIB) to be built – which would not be viable on associated costs.

cheers, Martin
Title: Re: Maximum number of SRB segments
Post by: Jorge on 07/18/2010 06:45 PM
There are also diminishing returns on performance. Going from 5 to 6 doesn't add as much performance as going from 4 to 5. At some point (believe it was at 6), the new segments do not pay for their own weight performance-wise.
Title: Re: Maximum number of SRB segments
Post by: Damon Hill on 07/18/2010 08:36 PM
Apart from being essentially a complete redesign, would there be any advantage by increasing the diameter of the segments?  Obviously pad compatibility goes out the door along with a lot of other things but a six-segment motor is already getting unwieldy and heavy.

Why hasn't a filament-wound (lighter) motor been reconsidered?  Haven't filament SRB motors been built and test-fired?
Title: Re: Maximum number of SRB segments
Post by: Jim on 07/18/2010 09:16 PM
Apart from being essentially a complete redesign, would there be any advantage by increasing the diameter of the segments? 

yes, that provides for a longer burn duration.  More segments more thrust, wider segment longer duration
Title: Re: Maximum number of SRB segments
Post by: Jorge on 07/18/2010 09:18 PM
Apart from being essentially a complete redesign,

"But aside from that, Mrs. Lincoln, how did you like the play?

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would there be any advantage by increasing the diameter of the segments?

Opens the door for increased performance.

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  Obviously pad compatibility goes out the door along with a lot of other things but a six-segment motor is already getting unwieldy and heavy.

Why hasn't a filament-wound (lighter) motor been reconsidered?  Haven't filament SRB motors been built and test-fired?

That horse has left the barn. Filament-wound has been dead for a long time and it would take considerable development cost to resurrect and field it. It would not improve operational costs. The original rationale for filament-wound is obsolete; it was developed to improve shuttle performance but the shuttle orbiter is going away.

The only valid reason to keep SRBs for a future HLV is to reduce development costs by retaining existing infrastructure and industrial base; once you start contemplating major changes beyond the fairly-mature 5-segment design, it's time to scrap SRBs altogether and go clean-sheet liquids. Going larger diameter, filament-wound, or >5 segments makes no sense.
Title: Re: Maximum number of SRB segments
Post by: sdsds on 07/19/2010 04:33 AM
It's worth mentioning that ATK/Thiokol has developed quite a bit of deep knowledge about super-huge solid rocket motors.  Not meaning to invoke "the rocket that shall not be named," but the Monty Python skit with the catch phrase, "I'm not dead yet" undoubtedly applies.  The Thiokol dream of powering the first stage of a medium-lift vehicle with a single solid-propellant motor is not yet dead. 

It's just that they cannot possibly fund it internally.
Title: Re: Maximum number of SRB segments
Post by: TyMoore on 07/19/2010 04:14 PM
Back in the mid sixties (1965?) (Aerojet or Morton Thiokol?) tested a 260 in solid motor for the Air Force that delivered almost 6.5 million pounds of thrust. That was a monster much bigger than the SRB's of today.
Title: Re: Maximum number of SRB segments
Post by: simonbp on 07/19/2010 04:21 PM
Back in the mid sixties (1965?) (Aerojet or Morton Thiokol?) tested a 260 in solid motor for the Air Force that delivered almost 6.5 million pounds of thrust. That was a monster much bigger than the SRB's of today.

Yes, it was intended to be the first stage in a new version of the Saturn I with a large solid first stage and J-2 powered second stage. Three guesses where the idea for Ares I came from...

But if you think thrust oscillation was bad with the 5-seg, it was 100x worse with the big monolithic solids. Essentially, the amplitude of the oscillation is mostly a function of the motor's diameter...
Title: Re: Maximum number of SRB segments
Post by: neutrino on 07/19/2010 06:36 PM
Back in the mid sixties (1965?) (Aerojet or Morton Thiokol?) tested a 260 in solid motor for the Air Force that delivered almost 6.5 million pounds of thrust. That was a monster much bigger than the SRB's of today.

Yes, it was intended to be the first stage in a new version of the Saturn I with a large solid first stage and J-2 powered second stage. Three guesses where the idea for Ares I came from...

But if you think thrust oscillation was bad with the 5-seg, it was 100x worse with the big monolithic solids. Essentially, the amplitude of the oscillation is mostly a function of the motor's diameter...

Firstly - read this piece of history: http://www.astronautix.com/stages/aj260.htm (http://www.astronautix.com/stages/aj260.htm)

Extraordinary. Unbelievable indeed. TWICE as powerful as the current SRBs.

Anyway, getting back to thrust oscillations: remember - if we are talking about cargo-only launcher, these oscillations may be less important. Also, Ares I-X (yes, that one) proved that these can be mitigated efficiently (and that the simulations are sound). So, I think it is not in the "impossible to do" domain.
Title: Re: Maximum number of SRB segments
Post by: Jim on 07/19/2010 09:37 PM
Also, Ares I-X (yes, that one) proved that these can be mitigated efficiently

It did no such thing.  Orion would still have to carry extra hardware
Title: Re: Maximum number of SRB segments
Post by: TOG on 07/22/2010 05:53 PM
Also, Ares I-X (yes, that one) proved that these can be mitigated efficiently

It did no such thing.  Orion would still have to carry extra hardware

Which, IIRC, was the reason that Orion's original design was being bastardized so brutally - the rocket couldn't lift the weight.  So if that reasoning is maintained, the bigger you make the stick, the more weight penalty you have for mitigating thrust oscillation.

Did I get that one right, Jim?

Edit: secondary question - IIRC, there was a limit to the width of the srb segments due to them being transported on railroad cars.  Would that prevent the external dimensions from being increased?  Sure you could probably transport them some other way, but what would be the economic impact of having to do that?  How much would this affect the cost per launch?
Title: Re: Maximum number of SRB segments
Post by: Gambina-GSFC on 09/02/2010 02:50 PM
Does anyone have links or pdfs to drawings of the current SRBs employed on the shuttle?
Title: Re: Maximum number of SRB segments
Post by: Proponent on 09/02/2010 02:54 PM
IIRC, there was a limit to the width of the srb segments due to them being transported on railroad cars.  Would that prevent the external dimensions from being increased?

Before Shuttle, 156" segmented solids (about 10" larger than Shuttle SRBs) were tested.  I presume these were rail-transportable.  One question I've long had about Shuttle is why weren't existing 156" solids used rather than brand new ones.