The Amazing Engineering Behind Solid Rocket Boosters

The solid rocket motors on the space shuttle accounted for the majority of the launch mass and launch thrust. They're the most powerful rocket thrusters ever flown, at least until the 5 segment versions take flight with SLS in the next year or so.
I've often described solid rocket motors as being relatively simple compared to the complex plumbing, pumps and turbines of liquid rocket motors. However there's still a huge amount of critical engineering and science that goes into these boosters.
The design of the boosters were also partly responsible for the accident that destroyed Challenger during launch.

[Torjus_]

I wish documentaries were like this. Not the over dramatic dumbed down version we usually see. This is great, learned a lot of stuff I've never heard about anywhere else. Fascinating stuff

[RepRapper]

From someone who lives in Utah with 40 years of experience building rockets including the shuttle boosters. I don't know how you got your footage but it's the most accurate and informative video I've ever seen on this subject.

[unistrut]

When I was at Space Camp back in the day one of us asked what would happen if the explosive bolts didn't fire. "They get torn off and the SRB leaves anyway."

[mattattwell]

One of my favs Scott. I knew the general “leaking seal” conclusion for the mission disaster but you’ve just added a vast amount of fascinating info with a presentation skill that assumed reasonable intelligence.

Thank you very much and please carry on.

[ellenbryn]

Fantastic breakdown of the boosters. My dad worked for Thiokol, but I was a little young for him to explain them in this much detail when the boosters were first designed (I would've been about four or five), and after Challenger it was a little painful for me to quiz him about the specifics, especially with my classmates tormenting me about it.

He worked at the small plant in Elkton Maryland that made the little kick motors like the separation boosters, probably the ignition booster and firing latches for the bolts at the bottom. I only realized recently that my whingeing about not wanting to move to Utah, which caused him to turn down a promotion, turns out to have saved him from being caught up in the O-ring debacle a few years later.

When I was little they were doing a lot of interesting experiments in the physical properties of the rubber matrix of the propellant at his lab. He had bread mixers to mix little bitty test motors, scale models of satellite motors! I loved all the interesting forms they used trying to figure out the best interior shapes to achieve different rates of burn. They settled on star shapes with those long vanes, but it took them a while to refine that core. And there was a really messy few years in the satellite industry when Thiokol's original set of outer casings were used up and they went to a secons set and suddenly the propellant started peeling away from the interiors because the adhesive was just ever so slightly different! Gaps go boom. Gave my dad a lot of headaches back in the day.

It was so early that they were using slide rules, so I know they couldn't have been doing computer modeling yet. Early shuttle design was a very hands-on, physical sort of ship design with a lot of scale model experimentation, since it couldn't be computer modeled yet.

Somewhere in my parents house is a toy box with my childhood blocks made of honest to gosh rocket propellant. There was a "safe" version which was missing the oxidizer… It was just the rubber matrix, dyed green to show it wasn't explosive, used for tensile strength and other physical stress tests. Lab always ended up with all these oddly-shaped scraps that the scientists took home to their kids. I look for those blocks every time I visit my parents, but they're buried somewhere. They were great; they bounced! I'm sure that wouldn't be allowed now.

[guintube]

Another part of each booster's propellant was about 18, 500 pounds of Dow Chemical's DER 331 epoxy resin. It was used as a binder.

[Xatzimi]

This is one of your best videos yet. I like it when you just talk about something you know, but 100% footage/diagrams really helps with the explanations, and a lot of the videos you used were just gorgeous to look at too

[isaid]

Wow thank you for answering the o-ring fix for challenger. The netflix doco only states the issue was the o-ring but didn't mention how they fixed it.

[TheSpatulaCity]

After 30+ years of knowing common knowledge about the Challenger disaster, this video really helped me understand the problem back then. Thank you.

[jaredhenderson]

My father started working for Thiokol on the shuttle booster program back in the 80's, and now I work for Northrop Grumman on GEM 63, so it's nice to see SRB's get some love. Thanks for another great video!

[Henchman]

I was today years old when I learned the SRBs are lit from the top.

[crafty_crumbs]

One time my friends and I were making solid rocket fuel in the backyard using a coffee grinder.. the sparks in the grinder ignited the fuel quite explosively!

[CH-zwti]

I truly appreciate the beauty of the engineering films from this era!

[spaceflightbricks]

Great video as always! One correction though: at 13:58 you state that the extra segment means a longer burn time. I thought this was the case until recently too, however, the extra segment only adds extra thrust. The burn time is more of a function of the radius of the booster (propellant burns from centre outwards). It turns out the 5 segment SLS boosters burn for 1 second less than the 4 segment shuttle SRBs!

[devgru]

As a military veteran, aerospace and aircraft enthusiast, and electrical engineer, I absolutely love your videos. Very very informative and detailed. Strait to the point. As a child growing up in the 1980’s, I would’ve loved to have these videos then. I was always fascinated with NASA, the military, and more specifically, the space shuttle.
Keep up the good work!

[garfield]

That was really interesting. I always wondered how the shuttle joint was improved after Challenger. It makes the original look high risk after all the fail-safes added in the redesign.

[rorypenstock]

Finally, I get to learn about the space shuttle booster TVC! I've been wondering about it for a long time.

[jfischer]

"backbone of the shuttle" more like the glutes and quads

[michaelzilkowsky]

Fun Fact: The boosters acted totally differently than they had been designed to work, or to be more accurate, than the engineers anticipated. Engineers envisioned a uniform outward expansion of the booster case at the moment of ignition, which would have pressed the tang and clevis together and squeezed the O Rings.

However, when they conducted the first pressure test of the booster, they were astonished / surprised / shocked / confounded / flabbergasted to discover that the casing ballooned outward above and below the field joints, aka joint rotation. Instead of the joint sealing tighter as they assumed, it opened up (this is a separate phenomenon from the 3 to 4 flexes per second that released the built up pressure of The Twang).

Joint rotation was an even more serious threat to the shuttle program than the resultant O Ring erosion (which was waived as an acceptable risk) because a complete joint redesign would have not only been expensive, it would have required grounding the shuttles until the joint was fixed properly.

[wacojones]

Good Report.
Back in 1971 I was at Indianhead Maryland Naval Ordnance station when a disposal burn of a cracked Polaris motor detonated 1/4 of the way through the burn. Shockwaves from the blast carried by the limestone bedding layer cracked the Capitol basement wall. Both the test fixture and the Capital rest of the same rock layer. 3, 000 pounds of propellant went bang in a split second.