The Amazing Engineering Behind Solid Rocket Boosters

hello it's scott manley here and today i want to talk about the massive solid rocket boosters which were the backbone of the space shuttle and will continue to do so for the sls these were the largest and most powerful rocket propulsion systems ever used in flight and they're getting even bigger for sls when i've talked about rocket propulsion systems in the past i've often focused on liquid fueled engines and their complex plumbing and high pressure pumps and sort of dismissed solid rocket motors as being relatively simple because they don't really have any moving parts but of course that is far from the truth these are incredibly high-tech items that were developed back in the 1970s and were continuously improved even before the challenger accident forced them to take a hard look at certain features of the booster but we'll get to that later at launch the boosters accounted for more than half the mass of the space shuttle stack each booster was about 600 tons and the total shuttle stack was about 2 000 tons each booster would generate about 1250 tons of thrust whereas the core would only generate about 600 tons so these boosters for the first two minutes of flight would provide about two-thirds of the thrust needed to get the vehicle up and moving even before that the boosters were critical because the entire structure was anchored to the launch pad through the boosters there were eight massive bolts that would hold the boosters down with frangible nuts that would be detonated at t equals zero simultaneously the igniter at the top of the booster would be triggered and the booster would start running and it wouldn't stop running for the next two minutes no matter what the propellant was a hard rubbery substance made primarily of ammonium perchlorate which covered about 70 percent of the mass there was about 16 percent uh aluminium powder which would provide most of the energy for the combustion there would be a tiny amount of iron oxide to act as a catalyst and all this would be bound together by something called p-ban because saying polybutadiene acrylonitrile all the time is quite a mouthful this material would be mixed at a factory and then molded inside the solid rocket motors and they would have a material around the outside with a hole down the entire length of the booster when the booster lit the combustion is happening on the internal surface of this and the hot gases are escaping down this interior channel toward the nozzle at the far end the boosters were originally manufactured by thiacol the contract was awarded in the mid-1970s now they are based in utah and they needed to move the boosters which were very large to florida which meant the boosters weren't moved in a single piece they were made of multiple pieces which were joined together in florida so the main booster casings were constructed from cylinders of steel they would be 3.7 meters in diameter and about four and a half meters long and about 12 millimeters thick made of a very high quality high strength miraging steel they would take eight of these sections and join them together in pairs using a factory joint which would be permanent and then it would fill each section with the material but there's a little more that goes on than just pouring the propellant in first of all there is an insulating layer on the outside it's about four and a half centimeters thick and it's a like asbestos-filled rubber that's what they used on the space shuttle and this is of course isolates the interior of the booster from the steel stops it getting too hot isolates it from vibration and electrical um your currents and things like that now for the sls they are actually replacing this with a new material because asbestos has many problems and that's one of the reasons why we've seen tests of the booster rockets that are going to be used on the sls because they need to validate the new materials there are some other insulating layers interior to that but they're pretty thin and then you have the bulk of the propellant the propellant layer is just over a meter thick although i this varies depending upon where you are in the booster because the thickness will help control the burn rate during the flight but that means there's a fairly large wide section in the middle wide enough for somebody to crawl down if they were you know crazy at both ends of each section there is a layer of inhibitor material added this is like in a blade of heat shield that stops the propellant from burning on the ends there's a gap between each segment and the booster and if hot gases flowed in there then you would have extra combustion there they don't want that so they control it with a material that will essentially ablate away and control the combustion to only be along that interior channel on the very front segment of the booster there is a an 11 pointed star that is cast into the structure this will burn faster early on giving them a little boost to launch and then that those veins will burn away and the combustion will slow down a little which of course helps them by reducing the thrust during the point of maximum aerodynamic pressure or max q this section also includes the ignition system which is up at the very front of the booster the way it works is it's essentially a very small rocket booster it's actually a multi-stage system where you have a pyrotechnic igniter which ignites a bigger charge which blows hot gas down the middle starting the booster and this happens in a fraction of a second and since triggering this is the point of no return there are many locks to make sure this doesn't happen by accident there's actually a physical pin that has to be pulled out before the system can even be used that pin stops the hot gas channel from rotating into position so if a stray electrical charge triggers this while they're setting things up it can't actually start the booster somebody a couple of days before the launch has to go into the nose cone of the boosters and essentially pull out this pin to make sure the boosters are armed and ready for flight in front of this the booster also has most of the recovery hardware including the parachutes separation rockets it also includes a set of rate gyroscopes to detect booster motion these are independent from the gyroscopes on the space shuttle itself and of course having separate readings from both of the boosters was critical in figuring out what happened to challenger since the rage arrows from each booster started to show very different values seconds before the destruction now if you move to the aft end of the booster you of course have the nozzle now the nozzle has to interface to the the rest of the pressure casing but the nozzle also has to move so the nozzle moves on a two axis pressure sealed joint that can handle the 60 atmospheres of pressure and the thousands of degrees of temperature and this bearing is made by having many layers of plates that are essentially sections of a spherical shell so these are stacked on top of each other and then they're joined together by a rubber like layer but it's of course a rubber that can handle the temperatures and pressures so each layer allows a small amount of lateral motion and overall the whole nozzle can gimbal by about 8 degrees the nozzle is moved by two separate hydraulic actuators which are at 90 degrees to each other to provide a full range of motion the hydraulic system is pressurized by two separate redundant hydraulic pressure units these are self-contained power units they have a hydrazine fuel supply which decomposes drives a turbine and then that pressurizes the hydraulic system so they can handle a failure of at least one of these the nozzle also has a nozzle extension attached to the back of it which of course improves the efficiency but just before the boosters land in the ocean this is removed it's severed by uh like a pyrotechnic device and you'll see that sometimes fault the water separately from the main booster so a lot of this hardware is contained inside another component called the aft skirt that will also include some some of the avionics and it includes the aft separation motors which are used to push the um the booster away from the spacecraft the aft propellant section also has some extra features not seen in the rest the other segments of the booster it has extra reinforcement rings because this booster is one of the places where it attaches to the external tank running vertically up the side of the rocket you'll also see the electrical tunnel which contains your cables that need to run the length of the booster to communicate between the front and the rear but you'll also find the explosives for the flight termination system which runs down the side if they're going to terminate the flight of the booster then the charge splits the thing along its length and that of course stops the thing flying as the single mass and reduces the combustion of course one time this flight termination system was actually used was on challenger after the breakup of the stack the two boosters kept on going under their own power and had to be destroyed in case they went somewhere where they shouldn't so let's talk about the joints as i said the booster on the shuttle was made from four segments and each segment was itself made from two separate sections of steel now the sections were all joined together by a clevis tang joint and this is where on one side the steel would split into two and form a y shape and on the other side this the other piece would slide into the gap and then a pin would slide through now if you have this in a complete cylinder on the wall of a cylinder you have many pins that go all the way around now mechanically this is a very secure joint but it isn't pressure sealed so to stop the get hot gases from the inside coming out on the interior side of the clevis there's a pair of o-rings that were added in the original design and these would cut or go around the entire circumference and when the interior was pressurized these would get pushed into the gap and stop the gases leaking through the o-rings have to have some flexibility because this is a mechanical system and when those boosters are firing they are bending and flexing under the loads during early part of launch these boosters are sort of flapping back and forth like strings on a guitar three or four times per second so the factory joints were generally more secure because interior to those there was a continuous layer of insulation and the liner but the field joints which were assembled when the booster was being put together on the pad those necessarily had a discontinuity in the insulating layer so as they were assembled they would put a putty around the outside and that would push itself into the gaps but of course the gases were expected to push past this the o-rings were still very much the primary protective system so in the case of challenger it was very cold and those o-rings didn't respond fast enough to fill the gap as the booster was oscillating it would find one side would be under tension and as those joints were pulled under tension one side would get peeled away just because of the shape of the mechanical mechanical coupling and that would pull those joints with the o-rings wider and then as it was compressed they would get pushed back together but that of course in that moment you would let gas get by and it would start to erode the o-ring as challenger was leaving the pad the cameras recorded puffs of smoke three or four times per second consistent with the oscillations of those boosters but this smoke actually stopped after a few seconds and you know challenger might have safely made it to orbit if it hadn't been for another factor about 37 seconds into flight they started experience wind shear and it was the strongest wind shear on any shuttle flight so the boosters are now having to correct for these aerodynamic forces they're working much harder and of course these forces that are being translated into these boosters causing those joints to flex again and at some point the joint again starts to come loose and starts leaking and that's when we start to see the real erosion happen and the jet of flame start to shoot out and that flame of course damaged the external tank and it damaged the coupling to the external tank and eventually tank starts leaking the booster comes loose at the bottom and the vehicle it breaks up under aerodynamic stress so of course the challenger investigation happens richard feynman does his amazing pop science experiment and a number of recommendations are made to fix these joints so first thing they did was in the forward side they add a new flap that stops the o-ring section from being pulled away as tension is applied on that they add a third o-ring as well the pins are lengthened and on the outside they add a retainer ring to hold the pins in place and to this they also add a heater to make sure the o-rings never get too cold and on the interior they just redesign the insulation so that there's something called a j-slit and this is a gap in the insulation layer at the back and what it's designed to do is the hot gases will flow into this gap and push the slit apart and this will actually force a section of insulation across the gap and therefore increase the seal hopefully it'll act as like another pressure seal helping to protect the o-rings so these changes were made and the boosters flew largely trouble free for the rest of the shuttle program and of course they're now being re-engineered for the sls program there's lots of subtle changes to materials the o-rings now handle low temperatures which means they don't have the heaters to keep them warm the insulating material no longer contains asbestos and the boosters are now five segments long providing for more thrust and a longer burn time they are still using steel casings though while many modern solid boosters have switched over to use composite or filament wound casings but the space shuttle actually looked at filament wound casings very early on back in the early days of the space shuttle they really wanted to launch the space shuttle into polar orbits from vandenberg and because it wasn't launching eastwards they needed to have a bit more performance so there was a program to develop these lighter boosters using modern composite materials unfortunately of course that program shut down when challenger happened there were more pressing concerns and the space shuttle never launched from vandenberg there was one other rocket that flew with this booster design that was the aries 1x that flew back in 2009 the constellation program of course was planning to use these to deliver cargo and crew to the space station back in the days when many people didn't trust outside contractors like spacex to do the same thing to be honest the aries 1x wasn't much of a launch vehicle it was all boilerplate with the exception of the main booster and a single unit that provided roll control everything else was a dummy the booster wasn't even a full five-segment booster that was supposed to be used on the real thing and it you lifted off and showed that well a shuttle booster can indeed lift lots of mass but it was a very expensive launch for not even a fully functioning launch vehicle and commercial vehicles are doing this so much cheaper these days so these big dumb solid rocket boosters that propelled the space shuttle and will carry the sls are by no means low tech items by any means they are very much the product of rocket science i'm scott manley fly [Music] safe [Music] you

Channel: Scott Manley

Views: 725,490

Rating: 4.9606147 out of 5

Keywords:

Id: Eis3A2Ll9_E

Length: 16min 4sec (964 seconds)

Published: Mon Sep 21 2020