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New image with Cross SectionsI understand the 11-point star perforations in the solid fuel in the top-most SRB section. Several articles say that the remaining sections had a double-truncated-cone perforation.

Double-Truncated-Cone?

Is my illustration correct for that shape-name? If it is, was there one of these per SRB fuel section? Were the top and bottom of the illustration the top and bottom of each fuel section?

I would have thought that they would have been simple right-circular cylinders, since that would be their shape as they were burning. Can someone enlighten me on this? It's merely out of interest since there is the whole discussion of the 11-point star perforation for the first section to give the rockets the most thrust at lift-off.

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These schematics from the Press Reference Manual and Space Shuttle Systems Handbook show a side view of the shuttle solid rocket booster motor grain shape.

The void in the motor doesn't "neck down" as in your sketch, it opens up continuously until it reaches the nozzle.

A 1990 Thiokol document describes the grain thusly:

The propellant grain design consisted of an 11-point star with a smooth bore-to-fin cavity transition region that tapered into a center perforated (CP) configuration in the forward segment (Drawing No. 1U77186). The two center segments (Drawing No. 1U77190) were double-tapered CP configurations and the aft segment (Drawing No. 1U76676) was a triple-taper CP configuration with a cutout for the partially submerged nozzle.

Press Manual SRB Schematic

SSSH Schematic

This snippet from the Systems Handbook drawing shows the star grain at the right (section A-A in the diagram just above) and at the left, shows a view looking up the motor.

view looking up the pipe

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  • $\begingroup$ I suspect the image is out dated... many booster images and video of grain pouring show a constant ID cylinder for mid sections and star at bottom. I've not seen any that show star section at tip if booster. Of course, I'm open to learning that I'm mistaken. $\endgroup$
    – BradV
    Commented Jan 1, 2023 at 1:31
  • $\begingroup$ You don't think the forward segments had a star grain? I'm away from my good references. $\endgroup$
    – Organic Marble
    Commented Jan 1, 2023 at 1:32
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    $\begingroup$ the 1982 "press manual" says I'm wrong. On page 60 " The propellant is an 11-point star-shaped perforation in the forward motor segment and a double-truncated-cone perforation in each of the aft segments and aft closure. This configuration provides high thrust at ignition, then reduces the thrust by approximately a third 50 seconds after liftoff to prevent overstressing of the vehicle during maximum dynamic pressure (max q)." SO... "perforations" is a correct term and it appears (so far) that my understanding of which combustion surface shapes are located where may be really flawed. $\endgroup$
    – BradV
    Commented Jan 1, 2023 at 1:40
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    $\begingroup$ my "pulled from somewhere" response is completely wrong and so I've deleted. The 1990 test report from joint redesign is very interesting. THANKS for the education. $\endgroup$
    – BradV
    Commented Jan 1, 2023 at 2:20
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    $\begingroup$ I'm trying to get the definitive document but it is a sloooow download here $\endgroup$
    – Organic Marble
    Commented Jan 1, 2023 at 2:24

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