How To Start The Massive F-1 Rocket Engine - Explaining "Ignition Sequence Start"

although it's Scott Manley here with the 50th anniversary of Apollo 11 already being celebrated you're no doubt seeing pictures like this all the time plenty of articles about these amazing f1 engines and the raw power they produced to get the Saturn 5 moving and so I think it's appropriate do we actually learn how the engines themselves started you see a rocket engine is a complex piece of machinery and it doesn't simply go from zero to a hundred percent thrust in a fraction of a second it's not just turned on simply there are multiple moving parts that all need to synchronize their activities so that we can see this gorgeous sequence here as their engines light and they suck the gas around them and of course the whole vehicle eventually begins to move under thrust and so this is what the mighty f1 engine looks like it is a simple pump fed engine burning kerosene and liquid oxygen it's pump is powered by a gas generator which means that it dumps its exhaust over the site actually it dumps its exhaust around the inside of the engine Bell now because this is a NASA program we have lots of documentation including this page in the manual that has the exact startup sequence so I took these resources and drew my own diagram with nice color-coded lines so you can see what's what at the top we have the low-pressure fuel and oxidizer lines going into the turbo pump out of those come the red and the blue high-pressure oxygen and fuel lines getting tapped off of those there's a small pair that gets fed into the gas generator to power the turbine and then min output goes straight into the main rocket engine and that's where the thrust comes from no the question is how do you get to this state this is what it's like winners operating and the turbine is spinning but obviously it doesn't start like this for most of the time the rocket is sitting in the pad there is no fuel or anything in any of these lines the flow of the propellant into the engine is blocked by these three prevails up the very top now about 10 minutes before launch that's when these valves open in the let fuel and oxidiser a flaw into the engine but it doesn't flow out of the engine Bale because we have the mean fuel and the mean LOX valves holding the these back the next critical moment is about t-minus nine seconds when you hear the announcer say ignition sequence start the first thing happens is four pyrotechnic devices get fired they're there in two redundant pairs two are in the gas generator and two are in the engine Bell to catch the gas generator exhaust these devices will burn for about six seconds and while they burn they will burn through a little metal wire which is connected to a circuit so when all four of those wires are broken the sequencer knows to trigger the next step in the ignition process the sequencer will then direct the mean oxygen valves to open and that allows liquid oxygen to flow into the engine bell into the combustion chamber but there is no combustion happening at this point we do get a cloud of liquid oxygen coming out and you can see this in some of the videos this flaw is largely driven by the fact that the oxygen tank is pretty high up so this is gravity just pooling the oxygen down and it's developed several atmospheres of pressure because the first stage of the Saturn 5 is over a hundred feet tall and that corresponds to several atmospheres of pressure when you account for the the mass of the Lak oxygen that oxygen also flows through the turbo pump and it actually starts driving the turbo pump causing it to turn which also then applies pressure to the fuel side of the system the next step is the fuel and oxidizer valves leading to the gas generator are opened this lets the propellants flow in there they start combusting and they start generating exhaust gases which drive the turbine which drives the turbo pump and as the pump picks up speed the pressure downstream from it starts to get higher also the exhaust gases from the turbo pump finally start arriving in the nozzle and those are getting burned off but they're not like a raw high-energy rocket flame they're more like a casual combustion they're not generating any thrust but it's important that it gets burned up so that it doesn't accidentally flow back through the system and cause problems when they really ignite early on in the ignition you can obviously see these billowing flames that aren't generating any thrust when sensors detect the pressure in the main fuel line is about 26 atmospheres it then opens a valve to the hyper gall cartridge this is a small part of the fuel line with a burst disks at either end so when the fuel is allowed to flow through it it breaks these disks and the contents of that pipe get pushed through the engine and into the combustion chamber so this contains the starter fluid this is the triethyl aluminium and the trifle boring that ends up going into the engine and when it contacts the oxygen that's when the main combustion starts with a combustion chamber being fed a small amount of fuel the pressure inside the chamber rises and that pushes against sensors in the injector plate which when they reach a certain threshold they then send a signal to trigger the final operation opening the main fuel valve and as both the fuel and the oxidizer valves are open the engine then ramps up to full power and about a second before liftoff they should be generating over 700 tons of thrust per engine if all the engines are generating that thrust the main computer gets the signal and liftoff occurs there's a few other wrinkles are important first of all the valves are actuated by a high pressure hydraulic fluid as is the engine gimbal on the ground they have a high-pressure hydraulic line that comes in but once the fuel loop gets to high enough pressure this thing switches over and it uses the high pressure fuel coming out of the turbo pump to open the valves and of course to move the engine once it's in flight secondly when you are bringing 700 tons of thrust per engine you don't light all the engines at once because that would create too big a shock to the spacecraft instead they light the middle engine then another pair 200 milliseconds later and the third pair 200 milliseconds after that that all gives them enough time to ramp up to a hundred percent thrust before launch while not hitting the structure with too much thrust at once another step the engineers took to smooth the engine thrust buildup is that the combustion chamber is regenerative Li cooled that means the floor the fuel through the walls to keep it cool but before they launch they actually pre fill all these pipes that run through the combustion chamber walls with ethyl glycol so that that has to get pushed out of the way first by the fuel flowing through these so so initially the fuel flowing into the combustion chamber is diluted by this ethyl glycol which reduces its energy and as that gets flushed out then the fuel gets to its fuel concentration and the engine reaches fuel thrust now of course we have all the telemetry so you can actually see this thrust build up in graphs this is Apollo 11 this is the inner the thrust being built up over time and you see that roughly one second before launch they're all generating pretty much 100% thrust you can see that the engine five in the center goes first and then engine three and four one go second and then you get engine tuned for those go last but around two and a half to two seconds you'll notice there's a little kind of blip in the thrust buildup on four of those engines but not in engine five in the center and that is a result of helium from the Pogo suppression system getting ingested into the oxygen two pipes now engine 5 in the middle doesn't have any of the Pogo suppression hardware so this only affects the four outer engines but once the flow settles down the engines reach stable levels of thrust and of course everything works just fine and so there you have it that's how you turn on a 700 ton thrust engine that's consuming more than two tons of propellant per second I'm Scott Manley fly safe [Music] [Music]

Channel: Scott Manley

Views: 1,220,477

Rating: 4.9513998 out of 5

Keywords: f-1, saturn v, apollo, apollo 11, rocket science, liquid oxygen, lox, rp-1, kerosene, rocket engine, nasa

Id: 2cldgl9IIyY

Length: 8min 38sec (518 seconds)

Published: Thu Jul 18 2019