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I was reading the wikipedia article about the SRBs, which were retrieved, refurbished, updated and re-used. I understand that if they were taken apart and pieces were replaced, that there was a 'new two' for each flight.

However, I'm looking for a rough idea of how many SRBs there were - surely it wasn't the same two, and obviously the four that weren't recovered - so how many were made? If they're famously recoverable, I would understand that they didn't make all 270 of them.

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    $\begingroup$ This question is impossible to answer as written. The SRBs were made up of segments, and the reuse was at the segment level. So each flight SRB was a mixture of different segments from other flights (or new ones). @TidalWave provided this link collectspace.com/news/news-051010a.html which has graphics in it showing the mismash of segments used in the boosters for the final flight. $\endgroup$ – Organic Marble May 31 '15 at 15:29
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    $\begingroup$ The segments were also redesigned throughout the program, first to save weight, and then to fix the design after 51-L. A complete history would be fun to look at, but it would be a huge data dump, and would probably have to come from Thiokol. $\endgroup$ – Organic Marble May 31 '15 at 15:29
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The answer to the question is an ancient philosophical question: Ship of Theseus. As Organic Marble mentioned in his comment which could have been an answer:

The SRBs were made up of segments, and the reuse was at the segment level.

The obvious lower bound for number of SRB segments produced would be eight: four SRB segments per side per launch. We can double that to 16 as this photo shows two STS stacks on the pad together.

Each SRB segment was rated for 20 launches. This document for the SLS Qualification Motor shows booster segment serial numbers in use on that test:

O32, O89, O43now, L82, L89n, L109, L98n, L92, L95n, O59

I'm sure that I've misread or misinterpreted that slightly, but for purposes of estimating population the numbers will do.

If we apply the German tank problem to that data, then we can estimate 120-130 total segments that were given serial numbers, as the higher serial numbers are better represented. Divide 120 by 4 segments per SRB, and I would say that enough SRB segments were produced to build about 30 SRBs, given enough nose caps, nozzles, and other components.

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    $\begingroup$ Thanks. Also, my God, that is a beautiful photo of Endeavor & Atlantis. $\endgroup$ – Mikey Jun 8 '15 at 20:06
  • $\begingroup$ +1 for mentioning the german tank problem. My favourite tank problem. $\endgroup$ – Ingolifs Nov 8 '18 at 6:12
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The following table lists the number of booster segments flown by type.

All shuttle missions and Ares-1X are included, no ground tests are included.

Here is a picture to help interpret the results. The red letters are the nomenclature I used for each booster segment.

enter image description here

(original diagram from Collectspace here)

  • Forward domes flown: 57
  • Upper cylinder segments flown (FC, FCF, or ACF) (all types): from 159-161 (ambiguities exist in the data - I believe the answer is 159)
  • Lower cylinder segments flown (FA, FCA, or ACA) (all types): 226
  • ET attach segments flown: 61
  • Stiffener segments flown (AS1 or AS2): 148
  • Aft domes flown: 60 or 61 (an ambiguity exists in the data, I believe the answer is 60)

Booster segment data from the paywalled http://www.spaceshuttlealmanac.com/

Caveat: Please treat this as a "best-guess". My attempts to validate the data from the paywalled site have not been completely successful. I am seeking additional shuttle flight segment data to continue the validation.

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Production for SRB segments was as follows:

$$\Tiny\begin{array}{lllllllllll} \textbf{Production Batches} & \text{STD FWD} & \text{STD} & \text{newCF} & \text{LWT} & \text{newCF} & \text{STD} & \text{LWT} & \text{STD } & \text{LWT } & \text{STD AFT} \\ & \text{Dome } & \text{CYL} & \text{SCYL } & \text{CYL} & \text{LCYL } & \text{ATT} & \text{ATT} & \text{STIFF} & \text{STIFF} & \text{Dome} \\ \text{Actual} & 61 & 94 & 77 & 124 & 101 & 15 & 62 & 73 & 97 & 65 \end{array}$$

Segments came in several flavors. STD=Standard Weight (original production run) LWT=Lightweight (MTI shaved the case down to reduce weight, with the consequent increase in ovality) newCF=new configuration (the RSRM with capture feature as a newly manufactured segment)

All existing segments were remilled to include the capture feature.

newCf were manufactured in both:

SCYL= Standardweight Cylinder LCYL=Lightweight Cylinder.

 As far as the placement of the cylinders there is 4 segments in a SRB.

 FWD segment made up of a fwd dome and two STD cylinders
 FWD CNTR segment made up of two cylinders
 AFT CNTR made up of two cylinders
 AFT segment made up of the ET ATT cylinder, two stiffener cylinders and the AFT Dome
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    $\begingroup$ Can you explain what those columns actually mean, or link to a source which does? $\endgroup$ – Russell Borogove Jun 14 '17 at 20:45

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