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

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."

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.

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.

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

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.

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.

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

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

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.

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

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!

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!

Never knew that about the wind shear on challenger’s last flight.

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.

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!

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

ah just when I was about to go to sleep, thanks scottt sleep safe

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.

That’s some Solid engineering there

More than twice as powerful as the most powerful liquid fuel rocket engines.

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

When I was a kid in the 70s we moved to Utah because my dad was a supplier for the Solid Rocket Motors being built by Thiokol. We made some great memories with a lot families whose parents worked on the program.

Guy In Charge: This is your first day working so we'll make it easy on ya. Just gonna have you crawl in here and pull that pin. Newbie: Pull a pin? The one with the big red tag that says danger don't pull this pin? GIC: Yep, no worries. You did kiss your wife and tell your kids you loved them this morning right? On a side note, I remember Feynman's ice water demonstration. They were not happy about that.

The SRBs were a terrible idea, but at the same time absolutely amazing.

Than you Scott, this is actually a very, very well done video. I researched the crap out of this and am so happy you put together what I thought of. :)

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.

The most informative, and comprehensive video about solid propellant rockets on UKposts so far. Very good job 👌👍 thank you Scott!

Thing I learned today thanks to this video: that Richard Feynman was on the Challenger accident commission. Of course, didn't know who he was back then...

This may be the only channel to ever give SRB's some love. I've heard Thiokol invented the modern car airbag based partly on the booster ignitor. SRB's have been saving millions of lives ever since! ;)

Really great video. Thanks for a more robust explanation of the O-Rings and of the boosters themselves. So much technical info you gave but in a way that was really easy to understand. Great job!

Fantastically complex. This is a standout video, Scott, with exceptional graphics and footage. My favorite of yours. Thanks!

I am a shuttle GEEK, but I never knew what the splash was pre-splash of the booster. Thank you!

Awesome video! One thing you may be interested in looking was the precursor work done by Thiokol, who developed the SRBs as you mentioned. Their experience with solid fuel came from their earlier work for the Air Force on the Minuteman ICBM program. Back in the 60s, if you wanted to launch an ICBM, you had one of two options: You could use cryogenic propellants, but these meant the the rocket had to be fueled before use. This meant the rocket force was at risk of being taken out on the ground before they were fully fueled, and once fueled, they had to be used within a period of time before too much propellant boiled off. The alternative was hypergolics, which, while storable, were incredably toxic as you've covered before. This was undesirable in a silo, and a non-starter on say, a submarine. A solid fuel ICBM on the other hand, was safe to store for long periods and didn't need to be fueled. It was groundbreaking in the 60s, and gave them the experience needed to adapt it to the SRB.

I love all your videos, but this one is at the top of my list of favorites. Great job, so much information. Thank you Scott Manly for the time and effort you put into this.

Enjoyed your deep dive on this. Especially getting a chance to see a lot of archival footage that I have not seen before. Great stuff.

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!

Thank you for not premiering this!

This was a great video, loved getting a peek at some of these more "out there" projects. Thanks for the collation and presentation. Well done.

You have an amazing way of presenting complex material. I never get bored watching your channel. 16 minutes of jam packed learning. Thankyou!

Learning about shuttle era technology makes my rocket motor solid

Why do we bother abbreviating MAX Q? I've literally never heard anyone say it without following it with an explanation of maximum dynamic pressure.

Thanks for your pure dedication and enthusiasm on these topics, Scott. Im constantly seeking out "space content" and this is exactly the type of video that some of the lazier youtubers would make a 3 minute bullet point video.. I really appreciate your content, you obviously put the knowledge over the incoming clicks. You got me into this interest through KSP, and continue to hold up to your own standards all these years later. You're the man, Mr Manley.

That shuttle video is one of my favourites - the clarity of the slo-mo video is outstanding. Good choice.

11:44 "another factor," upper atmosphere winds. Thanks Scott, new to me. 3:07 cc: reads "very high quality high strength miraging steel" (sic) *Maraging steel* en.wikipedia.org/wiki/Maraging_steel

What I find interesting is that many composite commercial model rocket motors use the same APCP propellant as the Space Shuttle SRBs

Scott. Love your work. The info is fantastic. Thank you!!! Love the technical jargon. Keep it up!

Good update on the SRB's. You have demonstrated the sophisticated technology that went to these boosters and they do seem to be still a very useful tool in enhancing booster lift capability.

"Somebody has to go into the nose of the booster to pull the pin." - Wonder if they drew straws.

6:00 "remove pin before flight?"

Your videos are always so interesting and lots of information that is completely new to me; despite watching 4 space shuttle launches and loving the awesome force of the acoustic shock wave hit you. I cannot wait to see a full Starship launch.

Just want to thank you for the amazing footage you include in your excellent videos.

Amazing explanation, as always, Scott, though I'm sure I'm not alone in being instantly nauseated seeing the disaster again. May they, and indeed all those lost in the quest for space, never be forgotten

SRBs are crazy beasts!! :)

I enjoyed every minute of that video, very well done. So much information on things I had wondered about, especially the consistency of the fuel mix.

Honestly watching your videos and wondering where you get all these photos and videos is amazing. I LOVE this channel!

A rather odd factoid: According to an old BBC show called "Connections", the size of the solid boosters was limited by the width of the railway cars and tunnels from the Utah facility, and those in turn were based on the track widths, which in turn were based on the width of common horse drawn carriages of the day when railroads started, which in turn were based on the ruts in the dirt roads that criss-crossed Europe, which dated back to the days of Roman chariots, which were designed based on the average width of two horses running side by side. So the SRBs owe their design width to the width of two horses asses!!!

Hey Scott, what was the documentary footage of the srb's from? I would love to watch it! Another amazing vid as always. Fly safe.

Stage tree to orbit is evoked. Thanks for covering all that, I was loving the throttling achieved with the shaped core.

Your content is high quality, i really enjoy watching it! Yo are one of the reasons i love rocket science.

hello. another awesome vid, you just boosted my day...thx!

There research you do for these videos is great! Thank you so very much for what you do. :)

30some years later and I still can't watch that footage. Takes me right back to middle school every time.

Fantastic and eye-opening mini-doc...cheers Scott!

Worked as a Minuteman III ICBM mechanic in the 70's . Was always glad to work around the solid propellent systems . Seems to be much safer than the liquid fuels .

"let's talk about the joints" I agree, let's!

Thanks Scotty, as usual I love learning rocket things from you.

It's nice to see solid propellant motor technology finally getting some love! Thanks for this.

Just finished the Netflix series, Scott! Excited to see what you have to say!

idk man seems kinda easy to build multi-ton boosters for rocket science.

Incredible! Your videos are always so in depth! I love it! Thanks for all the videos!

Brilliant doc and so well delivered too. Keep them coming , they are addictive viewing .

I wonder what kind of redundancies they built into the explosive bolts that held down the boosters (1:30). Once you light the boosters they're firing for the full duration, and it no bueno if one bolt didn't go off.

You just clicked on a Scott Manley video..now be prepared to learn something new.

the feynman pop science explanation was pure genius. if people here haven’t already done so, read or listen to the oral history of the challenger disaster that popular mechanics (i think?) did. brilliant

One of your best videos in a while. Nice job.

9:54 I was hoping to not hear those dreadful words that defined absolute "incompetence" on so many levels in 1986 and beyond.

6:00 So the takeaway from all this is that SRBs are overgrown grenades. Gotcha

I had forgotten the wind shear. Great video again. Keep them coming. And proper Scott Manley music too ! Thanks.

Loved the details. Lots I had no idea about. Many thanks, Scott.

Damn that safety pin means the move Space Camp couldn’t have happened.

One of my engineering goals is to one day work on these big dumb pieces of awesomeness

I always wondered about what they actually fixed in the booster, and I even saw some drawing where they showed the third o-ring to just be in row with the other two. Thanks for this excellent video, once again TIL something new :)

Your information delivery is seamless and engaging. At the end of all of your videos, I am well informed and I definitely learned something. Cheers

* mostly amazing when warm enough.

So you're saying these are *slightly* more complicated than the good old Estes B6-4 engine?

They need to back log this video in every documentary ever made about Challenger. Because to me "an O-ring got cold and failed " never made sense. Hell, That's not even the half of it. Best explanation ever! Thank you.

I often watch your videos twice as so much information is present 👏🏻👏🏻👏🏻👍🏼

2:28 Temperature limits 40-120 F... someone ignored that...

So if the assembled booster is hit by a lightning strike on the pad, when the safety pin has been removed, there is a non-zero chance the booster could light taking everyone on a one way journey?

Awesome explanation of the solid fuel, the Challenger O-ring issue and the complex improvements that worked, plus great footage of the booster assembly and launches. In my mind the shuttle had launched military missions from Vandenburg so I am now straight that it hadn't.

BRILLIANT booster doco, from Scott. Your work is enjoyed by so many! .. Subbed.

lol, just finished watching Challenger: The Final Flight on Netflix, and this came up.

"Will continue to do so for the SLS" Me: If we get it to fly :(

Excellent explanation of the o-ring problem and its solution. Thank you!

Great video! I have wondered for years how solid rocket nozzles gimballed. The solid rocket is a great example of all the effort it takes to simplicate and save weight

6:16 *Seperatrons

The new netflix show “the challenger: the last flight” tells us that the O ring, which was a part of the solid rocket booster was the cause of the tragedy for the challenge. The O ring was used for sealing the components of the rocket booster, but they had a massive issue with low temperature. The elasticity were inversely proportional to the temperature and hence making it more fragile under extremely cold conditions.

I read a bit about the boosters when they were the latest technology - and a fair few of the details mentioned here were not noted. Thank you yet again Scott.

Great video, Scott! It would also be cool if you mentioned the BOLE boosters being developed for SLS block 2, as they are quite interesting, and similar to the composite boosters Thiokol started on.