Why Do Ion Thrusters Use Xenon? KSP Doesn't Teach.....
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- Опубліковано 16 січ 2017
- Xenon is the most common propellant used on electrical propulsion systems in space, it's also one of the more expensive gasses, so what makes it especially suitable to Ion propulsion?
- Наука та технологія
Q: Why Do Ion Thusters Use Xenon?
A: Because it's the most futuristic-sounding possible reaction mass. Why would you use anything else? The 'x' makes it at least 2.75 times cooler than argon. Can't use the other noble gases either: neon is too film noir, krypton belongs in comics, and radon sounds like something from the naffer, more day-glo parts of the 80s.
Yeah, and what Scott said about energy efficiency. That too.
I thought radon sounded the coolest, but maybe it's because xenon makes me think of headlights
WHAT ABOUT UNOBTAINIUM?!?
Personally I would have used Radon but generating enough and using it quickly would be a massive challenge.
Oganesson?
Oganesson will be for the relativistic drive engines in Kerbal Interstellar Program
I was quoted 1,600$ for a lecture bottle of xenon (with 50L of gas) I want it for for my gas collection and for my attempt to float a liquid on a gas. I might need a few more experiments to make it worth while... any thing you want done with xenon?
I wish I had ideas, but if you're going to float something on gas isn't Sulphur Hexafluoride the way to go, presumably it's a hack of a lot cheaper.
eat it
Cheaper yes but the critical density is much lower at .7g/cm^3 where xenon can be made to have a density of 1.3g/cm^3 at pressures that are reasonable for me to produce.
Make Xenon Hexafluoride or another noble gas compound.
I'd really like to see you make some fluorinated xenon compounds...
I just love how the "Fly safe!" send off always sounds like a threat.
Fly safe!
*It is inevitable.*
@@General12th Lithobraking is !!FUN!!
It's from Eve Online, where "Fly safe!" often is a bit of a threat
Did you know that he actually want’s us to fly a safe, he doesn’t want us to fly safely
@@draftymamchak He wants us to fly a safe so he can steal it.
Space piracy, eh Scott? I see your game, you maverick renegade you!
"But in KSP, it's a lot easier to just add more and more boosters"
*Laughs in Russian*
Are you going to mention that the thrust of the KSP ion engine is about 1000x the thrust of the best real-life counterparts?
Gstrangeman96 KSP's parts are heavier though.
MrSh1pman a little bit heavier doesn't excuse 1000x times the thrust
Justin Koenig gameplay reasons I guess.
the engine would go from being used situationally to being abandoned completely if they decreased the thrust by 1000x
Jack Vernian yes, I know. it would have just been nice to have him bring it up to shatter the dreams of all the kids that might think ion engines would be viable to propel interstellar spaceships from playing ksp
Just watched your video “Why Do Ion Thusters Use Xenon?”. Your discussion of the nobel gasses, particularly when you listed them, reminded me of a story from my high school years. Our neighbor, Dr. B, was the head of the chemistry department at the local university (where my father taught astronomy.) Once, Dr. B was lecturing to his students discussing the nobel gasses. He listed a few to remind the students of the names, like this: “….the nobel gasses, neon, argon, krypton, and so on,….” At the end of this discussion, on of the students asked, “Please tell us more about this new nobel gas you’ve discovered -- ‘so on’”. Dr. B and the entire class burst into laughter.
Enjoy your videos immensely.
clever people. i love it.
Thank you for this but we totally ignored krypton and now it turns out that starlink has krypton thrusters.
He he, same comment I wanted to made :D
Argon now
Scott Manley actually, you got it wrong at around 5:00 - each individual Xenon atom DOES NOT have 80% more momentum than each Argon atom. This is because Momentum = m * v, and while each Xenon atom has more mass, it is moving more slowly. Each Xenon atom has almost the same momentum as each Argon atom if it is 2x more massive but moving 1/2 as quickly, for instance. Rather, you can accelerate 80% more Xenon atoms with the same amount of electrical energy because E = 1/2 * m * v^2, and thus each Xenon atom takes less energy to accelerate to the same momentum. Proximately, this is because each Xenon atom spends a longer period in the electrostatic field due to accelerating more slowly, which means that you can have a weaker field but pass more Xenon atoms through per second, and still end up with the same momentum per atom... THIS is where the higher thrust comes from- each atom is less energetic, but you can pass proportionally more atoms through the engine per second...
What does the formula of kinetic energy have to do with momentum?
You f'd up the math too, if xenon moves at 0.5 of argon's speed, squared, it would resuilt in 0.25 of argon's energy (not counting the mass).
WARSSS11 the formula for kinetic energy is relevant because with different fuel-types you divide up the same kinetic energy over different amounts of mass. You're right that I messed up the math (and I've completely re-written the comment as a result), but not in the way you think. Thrust = exhaust mass * exhaust velocity, so if your propellant is moving 1/2 as fast it is 1/4th as energetic but produces half the thrust per unit mass. This means you can accelerate 4x the mass with the same energy (so 2 atoms instead of 1 if your propellant has 2x the atomic mass and 1/2 the exhaust velocity), resulting in 2x the thrust per kW on this basis alone, not 4x (that's BEFORE accounting for the reduced ionization energy or the different levels of surface interactions with the engine walls...)
Okay got it now.
In short
*Mo' powah beybeh!*
I am from Germany and my English is not too good to understand everything exactly the right way, but what I understood of your mention is in short:
You are able to reduce the energy generation of your craft, and that means less mass of the vehicle which is to thrust up.
Its like the Diesel engine vs. the gas engine. It does more momentum while it is turning slower. Okay there is a leverage thing also, but your mentions are reminding me how the momentum and RPM thing is.
Like a bike with gears, you climb up that mountain (high momentum) while you are turning faster in the first gear but your are slow.
Or you are driving fast while slowly but HARDLY pushing into the pedals, and this time YOU must bring the momentum into the system.
I know with my English it is a nice thing to read that.^^ xDDD
But I think I've catch ya.^^
Ignition! is such a good book. One of my favorite parts is the discussion of a Li-F-H tri-propellant rocket, its wonderful ISP potential, and its terrifying practical problems of getting a heated liquefied alkali metal, a ferociously poisonous, super reactive and corrosive liquefied halogen gas, and just about the coldest possible cryogenic liquid to play nice enough together for long enough to get vroom instead of boom.
Because the name "Xenon" sounds cool and everybody agreed to use that as the main propellant(ksp xenon tank part description :D)
When you think about it, KSP may not teach these things...but it makes us ask the questions in the first place, and that's something! Great video, Scott. :D
no this is how video games teach
your voice is so soothing to hear, It´s wonderfull to just use this kind of video as background noise while I study for my electronical engenieering exams.
How much more vitamin D do bald people get compared to say, someone with long hair?
thatoneguy33198 I don't think he's technically bald, he cuts his hair that way it's a look he's cultivating.
Jason Henderson he's being aerodynamically efficient. :P
This is what the Bird people would call a, "Dick move".
More like a bowling ball
less then 15% percent more i guess if your naked
When I am dictator I shall make Scott Manley director of NASA. Then I shall write him a blank check, point to Mars and say "Make it happen."
As long as he starts every press conference with "Hulloooo, Scott Manley here."
Von Neely make it happen
Von Neely yeah
Okay with that as long as you get Isaac Arthur working on the long-term program asap
"Then I shall write him a blank check, point to Mars and say 'Make it happen.'"
...and a few hours later, after a Kerbonaut walks on mars, Scott will be laughing as he cashes the one billion dollar check. :)
Hello Scott Manley I just want to say thank you from Here in Colorado, USA. I have found that your help with explaning things I dont always think about has helped me over the years. I started watching your KSB videos and ended up geting the game just to have some thing to do with my time and learn some thing new. I still have not got docking down very well but its alright. I find that your help has also given me some thing to do and keep my mind going and learning. my two year old son and I were watching a video of yours and i opened up ksb and stared to build with him last nite at my side as he thought it was the coolest game there ever was. I have been on bed rest for almost 4 years and the time messing with ksb and learning is just fun for me. I want you to know that I really like the talks you have and your videos are doing some great things for me so keep up all the work you do for us and thank you.
Thank you never even considered the subject. Love series like this where you explain real science, please keep it up.
I love these KSP doesn't teach videos! You should make them more often
Love the callout to John D. Clark's Ignition! one of the best reads in the rocket biz.
Thank you for this; you've just answered the question I was wondering, and in very clear terms.
Love the videos scott, please never stop em coming
I would say biggest core. More mass, radius and you can plasmarize it easier :>
This would be such a good sci-fi element, Oganesson engines. :)
Some kind of superheavy Island of Stability Noble Gas would make more sense. More mass, lower ionisation energy, less horrible, horrible radiation.
I assume this is even possible, I'm not a chemist or a nuclear physicist.
by conventional definition, it isn't, unfortunately.
Yuri Oganessian has hypothesized that a second Island of Stability might be located around element 164 (unhexquadium). So perhaps the existence of an "ultraheavy" stable element capable of providing even more thrust in an ion engine than a stable isotope of Flerovium is not entirely impossible.
I do suspect though, that a civilization capable of producing large quantities of ultraheavy IoS2 elements might not really care about ion engines anymore.
Well, "stable" is unlikely because a stable element would have been found naturally by now. What I think you mean is a long half-life.
***** I would not be difficult to get the right number of neutrons from an exploding supernova. Seeing as exploding supernovae produce neutron stars, it seems they can produce a pretty much unlimited amount of neutrons per nucleus.
Thanks Scott for another great video. You helped a LOT getting me started in KSP so please, keep them coming
Thanks for the tip on "Ignition!" Scott. Loved it. If anyone is interested, it's available as an audiobook as well (at Audible, among others).
I wonder, would you be willing to expand on to the various other types of Ion and Electromagnetic thrusters (VASMIR, magnetoplasmadynamic thrusters, Pulsed Inductive Thrusters, etc; basically all of the types shown in Near Future Propulsion)?
When you're supposed to be watching a video about Xenon propulsion but you're too busy looking at a comment by Cody'sLab.
Now THIS is a good explanation video! Thank you Scott.
this is my favorite channel to watch because i learn stuff i find interesting i wish there where more YT channels like this
"because of that whole quantum wave function thing" lol
best way to describe my physical chemistry classes from college.
Love this thank you. I learned something (imagine!)...
This needs a 2021 update. Super interesting. Thank :)
Thank you - you answered my engineering questions quite well - it too thought that Argon would have been the best choice
This is cool!I ever wanted to know how ksp íon engines works
what ?
This doesn't really explain that... but there might be another video.
Scott Manley U type thusters in the title
He doesen't explain how, he explains why. With my english I am pretty sure that is two different statements with two different meanings.
Well, he explained both. He explains how ion engines work, and then why xenon is the go-to option.
"quantum wavefunction thing" +1 :)
Neat. I work on ion implant equipment, and I learned some stuff pertinent to my job. Thanks!
This video right here is the main reason i subscribed. Knowledge, never cease to learn.
It's worth mentioning that the original design had a base plate of prefabulated amulite, surmounted by a malleable logarithmic casing in such a way that the two spurving bearings were in a direct line with the pentametric fan.
Eh? You talking latin or what? Seeiously what do these things mean?
They forgot the turbo encabulator though.
Bless
xenon is like a nerd who doesn't like friends
Pedro Rocha You know what would be funny? If two helium atoms were to bond. He-He
and hydrogen is the nerd who really wants to make friends, but always ends up blowing it up
Carbon on the other hand, well everybody loves carbon (except the sky, but that's a different story)
And florine is that guy who wants to be friends with everyone
I should change my name to xenon. I don't mind friends but it's so much easier to sit here alone.
Now i know why this robot race in X is called Xenons.
My favorite series of yours.
Thorough, cogent, and well presented. A skillful melding of physics, chemistry, and engineering.
I may have said this before, but,
I ABSOLUTELY LOVE THESE VIDEOS
But what happens if you accelerate your reaction mass to relativistic speeds? Let's say you shoot single protons at 299 Mm/s out of your engine. Does that have an effect on the spec. impulse and thrust, because the particles get much heavier at these speeds?
but the energy!
But the energy required would be so humongous that it isn't even worth thinking about?
You get a very efficent engine! But it will have appaling thrust and very high power consumption.
It basically comes down to two equations; P=MV and E=1/2*MV^2.
P is momentum, E is energy, M is mass, and V is velocity.
From newtons laws we know that every reaction has an equal and opposite reaction, so based on that we can work out the thrust(which is just momentum change per second) based on the velocity and mass flow(Mdot) of its propellent.
So we can express the thrust of a rocket engine as; Ve*Mdot, Ve is the "effective exhaust velocity" basically just a convention to make comparing engines easier as the actual velocity varies with pressure. (worth noting ISP=Ve/g)
Writing the thrust out in momentum form gives;
T=Ve*Mdot
Now to work out the power needed to run the engine;
E=1/2MV^2 can be rewriten as; P=1/2*Mdot*Ve^2
Now what does this mean?
Basically it means if you double the Mass flow you get double the thrust but need double the energy
yet if you double the Exhaust velocity you need quadruple the energy (and if you quadruple it you need sixteen times the energy, and so on)
So using your example of a photon thruster, and assuming a thrust of 1N for ease
Ve=299*10^9 m/s
T=1N
We can work out Mdot as;
Mdot=T/Ve
Mdot=1/299*10^9=3.344*10^-12
And from that we can work out the power required to run this thruster;
P=1/2*Mdot*Ve^2
P=1/2*3.344*10^-12*(299*10^9)^2
P=150Gw
which is quite a lot for a newton of thrust!
(of course relatively rears its ugly head to make the problem worse, but this is just to explain the theory and methods used when working with rocket engines in general)
It's also a tyranical rule, as the power increases thrust does increase but so does the mass of the powerplant.
This same rule applies to all rocket engines, and can not be avoided, power generation is the true barrier to efficent engines. Doubling the power generation only helps if it doesn't also double the spacecraft mass.
(incidently you can work this backwards to work out the thrust of just about anything you know the power and velocity of, for example a laser.)
If you shoot a proton with a massive energy, like you said, you will indeed get lot of momentum but the energy used to accelerate the proton will decrease the mass of your spaceship by E/(c^2) this mean that your specific impulse will never get bigger than c.
A proton weights 130 times less than a Xenon atom. In order to make the relativistic mass of the proton the same as the mass of the Xenon atom, the proton has to to be accelerated to 99.997% the speed of light. This acceleration requires 121GeV (gigaelectron-volt). As Scott said ionizing one Xenon atom requires 12.13eV and it is accelerated with 2500eV, or 2.5keV (kiloelectron-volt).
So accelerating a proton to a speed where it has the same mass as a xenon atom requires about 48 million times as much energy.
Edit: made a mistake in the conversion from giga to kilo. It is 48 million times the energy, not 48.
I swear this is my favourite series of videos.
Very nice video on the Xenon propulsion. I learned a lot. Thx
I once knew a joke about Xenon... but it never got much of a reaction.
😉
But Xenon is VERY reactive after you knock one e- out. it's got 7 electrons in its outer shell, so it's essentially a free radical. Why is it still used?
because most astronauts aren't vegans anyway
But now that it's charged, it's controlled by the electric field and is shot out the back of the spacecraft.
+Vampyricon
I never entirely understood ion thrusters until your comment. Thanks.
Given how some of the most calorie dense foods are vegan that is a non-issue. Just compare seitan to beef in term of protein per gram.
Also, once space colonies are a thing, eating mostly plants will be the only sensible choice for a while. Sending cows or chickens in a several months long space trip would be stupid, and raising them on Mars would be a big pointless waste of calories. Growing food on mars is expensive already without livestock to feed.
Of course you could send them already dead but that is pretty costly long term.
The water that makes most of the mass of something like a cabbage will be peed out and reused, its not dead mass.
Rawbots Vids the fuck is seitan
I love these kinds of videos! Keep it up Scotty!
Thanks Scott for sharing this Information !!! This is Sarabjeet Singh from Chandigarh, INDIA
Your title and thumbnail have a typo Scott.
Myztkl-Kev what? Where? There's nothing wrong with either.
it says Thusters... you people blind.
Myztkl-Kev didn't notice the title. But there's nothing wrong with the thumbnail.
It got fixed, but youtube takes days to replace the thumbnail universally.
Scott Manley typo's happen to the best of us. Even to rocket surgeons such as yourself, Scott. Much love from South Africa!
Wow! I just got a 52 Inch Tv, and you look so High def. LOL
Also, very good video!!
Thank you Mr Manley, that was very interesting.
i actually unserstood all of that.... gj Scoot!! keep it up!
All this talk about thrusters keeps me panicked that we're exhausting the earth's resources, and I fear one day we'll discover a secret among the stars, and we can't reach it, because we've ran out of fuels and we are stranded to die on our planet. :(
Alucard Pawpad Don't be silly...
We have plenty of mass to chuck out the back of rockets here on earth. We'll have plenty of time to get out to space and begin mining operations among the stars for more better masses to chuck out the back of our rockets.
Hydrogen is a rocket fuel commonly used. It is also the most abundant element in the universe. So I wouldn't worry too much about that. ;)
Just use dirt and throw it behind the ship really fast.
Element Zero.
for another episode, alternators in rocket engines. are they real?
Another great explanation Mr. Manly
Videos like these are the only time I will ever apply stuff I learned in Chemistry class to real life.
how overpowered are ion engines in startrek?
5
Well, its hard to say honestly. They use "impulse" engines, which *could* be ion engines. And they can accelerate a MANY ton Enterprise (insert letter here) to a decent fraction of the speed of light within a reasonable amount of time. If impulse engines are ion engines, they are pretty freaking powerful.
Impulse engines uses plasma as propellant. Electrified plasma, apparently, which is also how they move the enormous quantities of power various systems use, the EPS (Electrified Plasma System) conduits. So no, impulse engines are not ion thrusters, they're plasma thrusters, like the VASIMIR.
Above all else, impulse engines are fictional! ;)
+kokodin there aren't ion engines in startrek, the impulse engines are just magical (think control wheel in KSP, but with the ability to change delta-v instead of just direction), and then the light speed that they do is using a separate tech using anti-matter/matter reactions to power a (similar to alcubierre drive) warp drive, (IDK about modern star trek movies, but this is how it was in the old ones like Voyager and TNG)
A xenon atom and a argon atom walk into a bar they didn't react!!!
sounds like my love life
Until some fluorine walks in xd.Then the xenon might do something! :)
walking into a bar hurts
bars are made of metal
I've always wondered why xenon works the way it does. Very informative. Reminded me of a SciShow video. ^^
love the lessons scott. keep it up
What would happen if you put your hand in front of an Ion thruster? Specifically Xenon. Asking for science.
why ask? let's do our own research
ok now where can I buy an ion thruster
John Wayne Tingley Multiply its Isp by g and picture a single atom hitting your hand that fast.
It would probably tale it right off? I dont know what kind of mass fluclx they have but they have exhaust velocities in the ballpark of 100kmps.
+sevenbrokenbricks A single atom wont do much even at the 40 km/s of a Xenon ion thrusters exhaust velocity sure it's fast but each ion still only weighs a mere 2.18*10^-22g.
+I need no channel youtube! Well NASA's NEXT thruster apparently consumed 890 kg of Xenon in 48,000 hours so around 4.97*10^-6 kg/s, with it's exhaust velocity of 40 km/s then would be 800 MJ/kg but of course we are talking millionths of a kg here so the power would be closer to 4 kW.
This would be spread throughout most of the volume of your hand as you would likely not fully stop all the particles so it would be less than the full 4 kW but I don't see that saving you as we are still talking about the sort of thermal power dissipation equivalent to having a 250V 13A space heater element implanted directly into your tissue.
Fortunately this is likely to induce sufficient pain to make even the dumbest person* instinctively remove their hand from the area quick enough that you would likely be on a trip to hospital to be treated for severe burns but they might possibly be able to salvage the limb provided that secondary infection or similar doesn't develop.
* I think it's safe to assume that anyone who would willingly put any part of themselves in the path of a high energy particle beam like this would have to qualify as dumb.
Incorrect use of 'begs the question'. Begging the question is an informal logical fallacy indicating a circular argument whereby the conclusion is also stated in one or more of the premises. You should have said 'raises the question' instead.
thank you.
Common usage has given that phrase two meanings. Ain't living languages weird?
I'm glad I'm not the only one bothered by this.
No. Begs the question is originnaly used as synonimous to raises the question. The fallacy got named later.
Great video. Thanks Scott.
Really good explanation knock out all my questions :)
very good video, now i have some understanding of the hall thruster i recently worked on. and before you think how can you work on something you dont understand i answer i did a computed tomography scan on a unit meant for flight and i dont need to understand how it works before scanning it.
I've been waiting for another one of theese!!
...thanks for the easy layman syle understood info
Hear dear Scott ! Thanks for the video & while we're on the topic of ion thrusters, LISA used _colloid_ thrusters for RCS. Basically, these use charged droplets as propellant/reaction mass (ideally: ionic liquids). Pros: permits alternative current mode, no need for a neutralizer, much cheaper than Xenon; cons: very low thrust (microNewtons).
Thanks Scott :) well done. Regarding the cost of Xenon, I'm sure that isn't even considered when the spacecraft plus launch costs would eclipse it
As a chemist, I'm always happy to see my two loves - chemistry and rockets - paired together. Excellent explanation, Scott, both chemically and practically.
Thank you Scott!
At the end, when you were taking about using Cesium, two problems I thought of is that the cesium would almost certainly react with almost any of the parts in the payload (probe or manned station), as well as that the fueling process, whether it's done during or after manufacturing, would have to take place in a near perfect vacuum.
I'm fine with being corrected, but I thought I should point those out.
this is really interesting man, nice simple explanation! 10/10
Great vid. Be interesting to see how VASIMR fits in to all this.
All the explanations about ionization energies brings back wonderful memories of AP Chem
Haowei Shi - Ive got an AP chem test Monday =(
It's also worth pointing out the Xenon has a much larger cross-sectional area than lighter noble gases, and so the probability of knocking off an electron is much higher.
Electronic shell shielding makes it easier to knock off those outer electrons as well.
All those 1s 2s 3s orbitals and such get in the way of the previous ones.
Ignition I love that book it really is a fun read and I can highly recommend it. it's out of print but you can get digital copies
this channel is a goldmine
I'm actually impressed that I remember enough from inorganic chemistry to guess three of the big reasons: "it's inert", "it's heavy", "it's not radioactive".
Another great episode! Just curious, any thoughts on the Expanse book series? First solar-system based series I've read that remembers relative position in travel, pretty neat.
Good craic, Scott!
Wow, there was more to it than i thought. I always thought Xenon was used simply because it was more massive, and therefore, provided more thrust.
Educational and relevant to my interests.
great Job.
Yesterday I was wondering when a new "KSP doesn't teach..." and now I'm very happy :D
Very interesting thanks scott
I was I the team by astrium that builds them great explanation thanks
I love this series
Simply Amazing!
thanks for explaining this
As a trained and practicing chemist, this video made me happy. :)
Very interesting, thanks for the video :)
Back in the early 60's when I was grade school, I read about ion propulsion and remember a diagram and the device looked simple and easy for a science nerd grade school boy like I was, the working fluid was Caesium, Xeon was also mentioned ... Caesium was tried in the 1960's ... in high school we made a plasma jet using argon .... maybe take about plasma jet propulsion in space ....
This has helped me out👏👌
Very interesting! More of these types of videos please! Maybe some "challenges of building a permanent moon base" videos?
more science videos pls
btw I love your channel
I love these videos!
Can you do Decouplers next? Like how they work, or how to succesfully and cleanly decouple something like a radially attached booster.
thanks for this, awesome.