Neil deGrasse Tyson Explains the Rocket Equation

[Music] i'm back chuck i know well that means it's time to talk about something that you thought you knew but you didn't really know everything you thought you know about or even if you never knew to think anything about it sometimes there's those things as well uh you know one of our most successful of these was on water towers wasn't that amazing it's got millions and millions of views and nobody thinks about watertown so it's just but it's a reminder that there's physics in everything so today today i want to talk about the rocket equation did you know that did you know there was such a thing come on now no you could say i'm sure there's an equation for everything yeah i'm sure there is yeah that's got to be right well actually one of our friends of star talk um max tegmark uh he he wrote a book a little while back on uh why he felt we're all in a simulation and one of the the evidence for that was everything that you see happening in the world can be described mathematically mathematically right even a rock even barack yeah what do you talk about the forces and pressures within it that comprise it and make it so if everything can be described mathematically then why can't we just all be in a simulation where someone programmed it in right and and it was like i had no rebuttal to that so you would expect even in that world the rockets would have their own equation and they do okay all right all right so here's how it goes have you ever wondered why let's take the saturn v rocket for example all right for those who remember it or we can do the the space shuttle any rocket at all but the saturn 5 is sort of the best a measure of what i'm about to describe right okay the rocket was 34 stories tall yeah okay 34 stories right and all right uh where were the astronauts in half a story they are crammed into the capsule right way at the top okay okay so well what's the rest of it is it payload is it their food supply for while they're on the moon no that sits just behind them a little bit in the rest of the command module okay there's a little b section they're sitting up front to three of them and there's a little sort of store called storage closet oh my god it's like a cosmic tractive trailer okay so there it is everything else is rocket fuel that's ridiculous everything and you can say to yourself well how come cars don't look like that right all right if you if you're going on a trip how come most of your car is not it's not your gas tank it's not your gas tank that's just not the case by the way i am not getting in a car that is 98 gas tank if you pull up in a car that's 98 gas tank i'm like bruh i'm taking the bus i will see i'll see you when we get there i'll walk i'll still get there that's right all right so so here's what's going on a rocket uh when you launch you say well how much fuel do i need to launch a certain amount of payload okay because that's it's all about the payload all right how you know the astronauts i forgot which mission where they first took the rover uh you know their automobile on the moon uh i heard jerry seinfeld joke about this he said you know guys invented this idea say why because here you have a rocket going to the moon and the first thing they said is let's bring a car just the car culture in america is like written all over that you know we you gotta rock it guys so you're not happy enough with that that makes sense that's funny so uh so here's the point we have the payload and it weighs whatever it does you say how much fuel does it take to get that payload to the mu to the moon okay so you can calculate that and it'd be like this much fuel i'm just gesturing with my fingers here i'm not the amount doesn't matter for what i'm about to describe so that's how much fuel it takes to get to the moon all right but there's a problem chuck the pay the weight of the payload is not only the stuff you're bringing to the moon right it's the stream also the weight of the fuel you haven't burned yet right so now i need more fuel to get my fuel correct that gets my stuff to the moon thank you okay so you need the fuel to get the fuel to burn the fuel to get your stuff to the moon now that bit that you added what's getting that to the moon now i need my fuel to get my fuel that's getting my fuel to get my stuff to the moon exactly okay so the branch of math called calculus is exquisitely conceived for just this kind of problem okay all right and so what it tells you is that the amount of fuel you need okay to deliver a certain payload grows exponentially okay cool for every extra pound of payload that's why the birth of the space program you had trim astronauts that we had to miniaturize everything and in fact the miniaturization of electronics which we all take for granted today you got stuff that fits on your hip in your pocket going back to the sony walkman where you put a cassette tape and you walk around the miniaturization of electronics was driven by the urge to put this stuff in space wow and so not this not sony walkman in space but just just circuits and the things that enable electricity to do interesting and important things for you on your journey right so the urge to miniaturize it and make it lighter and lighter and lighter because you you couldn't keep making a bigger and bigger gas tank okay so that that's what it was so you get the the slimmest possible payload now there's nothing an engineer likes better than constraints never you know think about it that way engineer says what do i have to do i need you to do xyz lmnop okay and you but you have to do it for this much money on this time frame and you can only use copper zinc and aluminum okay that's where ingenuity comes in right okay and that is also why architects hate engineers they've had they've been tussling from from the beginning absolutely so i saw jokes about that with the sphinx back in ancient egypt um it's like no you can't have the nose stick out over the front it's not gonna work we're gonna do it the nose falls off oh that's hilarious doesn't have a nose that's a funny engineering toe guy right there's nothing holding up the nose right it's just exactly that's dangling out there so the sphinx snazz that's very funny okay go ahead all right so there's a couple of things we can do about this okay because it's all about the weight oh by the way i forgot this if you have a gas tank and then all the fuel has been exhausted from that tank but you have other tanks um the empty tank has weight yes so what are you gonna do now now it's just not right now it's just a it's useless so you just it's useless useless okay so werner von braun knew this werner von braun was the the german rocket engineer that we brought over after the second world war and we said build us a rocket to the moon and so he did and he realized that you don't want to carry useless weight with fuel that you need to ultimately get your payload so he built the rocket into multiple stages it's brilliant multi-stage rocket so the first stage is the first set of fuel that burns and there it goes it gets up to a certain speed a certain altitude it is done what do you do with that stage jettison it right you say get it the hell off of my ass here okay then you kick in the next stage oh god i wish nasa talked like that okay god that'll be so great mission control we have reached the altitude of all right get that off your ass so anything you're not gonna use get it the hell off of your body right so you shed the shell the rocket shell and so so if you're high up and you shed it it'll burn up in the atmosphere now what what um spacex is doing is for the set of rockets that jettison low enough to not burn up okay you know what they do they left some fuel in them for them to guide their way back autonomously to a launch pad and then they've reused them that's even more brilliant that's that's there it is and a bit scary why because i got used rockets that i'm going to space with no you refurbish them no no wait wait chuck when you get in an airplane are you saying wait has this airplane ever been used before no but that airplane has never been to space before and i'm not going to space okay so i'm just saying all right but okay but you do get on an airplane that's been used a gazillion times before that's true that's if you had to if you if every time you got on it you got off an airplane they threw away the airplane that's a different business model and your airplane ticket would cost a whole lot more if that's what was going on [Laughter] i only flying planes once okay if you reuse things then you get the the the benefits of the economy of scale for that and that is the main contribution that spacex is making to this whole enterprise okay so they reuse the rockets that they jettison the remaining fuel has less weight to then push to its destination it's utterly brilliant okay so just to be clear the rocket that went to the moon needed enough fuel to leave earth go into orbit leave earth orbit go to the moon go into orbit around the moon land on the moon come back to moon orbit leave earth moon orbit and come back to earth all that fuel had to be in that vessel okay and they're just leaving stuff left and right so on the moon they left the landing pad they left the rovers they brought some rocks but and so by the time they got back they just did the capsule that was there at the top of the 36 to 34-storey building okay that's yeah okay so now the reason why you don't have cars with 98 of their mass and fuel by the way you would need such a car if you were driving from here to california where in new york now if you're not from here to california and there were no fill-in stations you'd have to carry all your fuel that's right and you would and some of the energy burned in that fuel would be to move not only your ass and your luggage and your family but the other fuel that is not yet to burn that's right in fact the gas mileage for those still using internal combustion engine cars the gas mileage of your car gets better the less gas you have in the tank right because it's pushing something it's fueling something that's lighter it's lighter precisely and so i when i was on a budget and i had to work i actually calculated that and i would save a few dollars a month by driving half empty down to like a fifth empty rather than a full tank down to half tank so anyhow did you also calculate how to draft trucks so you could save i did that once no no watch watch no no the problem is this doesn't work in space that's the problem because it requires air all right there you go right but but um my first car that i got that actually told you your active miles per gallon in a readout okay they calculated that right so i could see when i'm accelerating hard the miles per gallon drops as you'd expect cruising that's higher so i said let me try something i went up behind a big old 18 wheeler and i got closer and closer and closer to it now it can't see me in its rear view mirrors right so it doesn't know i'm there i didn't feel safe doing this but it was for science okay so i did that and as i got closer i watched the miles per gallon go up and at one time at one point in there i was getting 100 miles a gallon oh that's great yeah because you were just using their all of the uh i was drafting off the office off the truck that's that's cool that's cool anyhow so the real way to travel through space just to bring this to closure is you need filling stations in space that way i don't need all that fuel i just need fuel to get to the filling station now while these filling stations have mini marts i need a candy bar you pull up hey can you can you check the oil all right tuck the oil i'm going to go inside and get some chips and juice [Laughter] so the future of space travel is going to have to be that or you find a way to make fuel at your destination and there are people thinking about that for mars uh mars especially um but also the moon which has fewer chemical resources but anyhow the rocket equation tells you how big ass your rocket has to be because it's the fuel that carries the fuel that carries the fuel that carries the fuel that carries your stuff that's pretty cool and calculus makes that a continuous equation where you make the calculation perfect and we've been doing that ever since the dawn of the space program chuck we got to call it quits there all righty there you go now you know how to get to mars yes i do practice all right as always keep looking

Channel: StarTalk

Views: 166,093

Rating: 4.9621525 out of 5

Keywords: startalk, star talk, startalk radio, neil degrasse tyson, neil tyson, science, space, astrophysics, astronomy, podcast, space podcast, science podcast, astronomy podcast, niel degrasse tyson, physics, Chuck Nice, rocket equation, rocket launches, simulation, mathematics, space travel, rocket equation explained, SpaceX, reusable rockets

Id: -73MZsj8bVI

Length: 15min 10sec (910 seconds)

Published: Tue Feb 09 2021