# How many Solid Rocket Boosters were there in the Space Shuttle program?

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.

• 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. Commented May 31, 2015 at 15:29
• 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. Commented May 31, 2015 at 15:29

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.

• Thanks. Also, my God, that is a beautiful photo of Endeavor & Atlantis. Commented Jun 8, 2015 at 20:06
• +1 for mentioning the german tank problem. My favourite tank problem. Commented Nov 8, 2018 at 6:12
• Actually you can increase the lower bound to 24 segments, as there was at least one occasion when three full stacks were assembled at the same time: STS-35, STS-38 and STS-41 in August 1990. See this forum thread on NasaSpaceflight : forum.nasaspaceflight.com/index.php?topic=3830.0 And, well, this was after the Challenger accident, so the lower bound is 32. Commented Apr 28, 2021 at 15:55
• @Nimloth That is interesting to know, thanks. But I'll not edit the answer with those numbers as that part of the answer is to demonstrate the process behind determining the bounds and does not affect the final estimate. Commented Apr 28, 2021 at 22:23

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.

(original diagram from Collectspace here)

• Forward domes flown: 57 (1 per booster)
• Upper cylinder segments flown (FC, FCF, or ACF) (all types): from 159-161 (ambiguities exist in the data - I believe the answer is 160) (3 per booster)
• Lower cylinder segments flown (FA, FCA, or ACA) (all types): 226 (3 per booster)
• ET attach segments flown: 61 (1 per booster)
• Stiffener segments flown (AS1 or AS2): 148 (2 per booster)
• Aft domes flown: 60 or 61 (an ambiguity exists in the data, I believe the answer is 60) (1 per booster)

So, if one took every segment ever flown, and ignored segments that were lost or scrapped, there would have been enough segments to build 53 boosters, with the upper cylinder segments being the limiting factor. (160 were flown, it would take 159 to build 53 boosters). Note that this is a purely hypothetical situation.

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.

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

• Can you explain what those columns actually mean, or link to a source which does? Commented Jun 14, 2017 at 20:45