Why Are There Two Different Types Of Electric Space Engines, And How Do They Work?

[@scottmanley]

For everyone asking why it’s important to neutralize the exhaust, if you don’t then the positively charged Ions will get pulled back towards the spacecraft, and that will result in the thrust being cancelled out. So, it’s essential that the charge on the ions get removed in the process.

[@mattparker9726]

you forgot about the new electrically throttled solid rockets.

[@mikldude9376]

I was just going to ask why the protons have to be neutralised :) thank you !

[@TheWadetube]

I believe you could magnetize the back end of the engine to keep those ions from coming back, but I also believe that you could extend a tube a great many meters behind this and use pulsing magnetic fields to continue accelerating the ions to over 100 thousand kilometers per second. I hear a report recently, may have been Helion, of an ion thruster that uses regular metal as fuel, vaporized as in a plasma cutter and shot out the back with a better thrust and better seconds of impulse. Any news on that?

[@alexandermarsteller7848]

Solar panels and sensor electronics also like ion bombardment a lot less than than the walls of a thruster, so preventing erosion is also a big concern besides thrust efficiency

[@MadMorgie6318]

Literally scrolled down down to ask this, thank you!

[@ostlandr]

Wonderful to hear that "It doesn't match the models, but it works, so we'll just go with that." And the fact that it doesn't match the models means that the models need to be reworked, which means we'll learn cool new stuff.

[@HelenaOfDetroit]

I'm working on a new model that explains this, and it also happens to explain other phenomena like the estimated size of galaxies recently viewed by JWST. Gonna take a while, but yea, kinda fun.

[@raifikarj6698]

In what timestamp?

[@stormy0307]

@@raifikarj6698 12:35

[@termitreter6545]

Its always good to keep in mind that models are usually just simplifications. Even stuff like newtonian physics might be heavily evidence based, but they dont actually seek to understand "why" things happen on a suabtomic level and lower, and thus cant explain some things.

[@petlahk4119]

@@HelenaOfDetroit - Would be very curious about this when your research is completed haha.

[@reeeeeeee2143]

A correction is that the electrons do hit the walls. At 11:53, it is shown that the electrons orbit along the magnetic field lines. And from the thruster illustration, the magnetic field lines do not go around the annulus; the field lines cross the gap radially outwards. This means the electrons are constantly orbiting the field lines and reflecting from each wall of the annulus, this causes erosion in the anode channel. The electrons slowly drift in a circle (but in fact they are bouncing back and forth between the inner and outer wall) due to the hall effect. The hall effect is a side effect, it does not play a critical role in confining the electrons. The mechanism responsible for confining the electrons is the gyration of the electrons about the magnetic field lines. Thus "Hall Effect thruster" is a bit of a misnomer, "Hall thruster" would be more accurate. Regarding the higher mass flow rate of the Hall thruster, this is not really the major mystery. The reason why Hall thrusters can achieve a higher thrust density is because it effectively avoids the space-charge effect. In an ion thruster, the space between the grid only contains positively charged ions. This means there is a critical density where the amount of ions per unit volume is so high they start to repel each other. This prevents scaling the thrust up on a gridded ion thruster without scaling the size. In a Hall thruster, the ions and electrons exist in the same space, so the plasma is effectively quasi-neutral, and the electrons and ions shield each other (sort of) from the space-charge effect. This allows for higher thrust density. However, the mystery lies in how to confine the electrons within the magnetic field effectively. The electrons diffuse out of the magnetic field at a higher rate than expected of classical models, but also slower than other proposed models, so we dont have a complete understanding of the mechanism that allows electrons to escape being trapped by the magnetic field lines.

[@u1zha]

Thanks for the valuable nuggets of information! Yeah this is exciting to think about... Completely bonkers for me as a layman to imagine the conditions in various points throughout the apparatus, like when and what fraction of atoms would get ionized, and where there is surplus of electrons and where there is not, and what happens with ions that get created late down the road at the exit and dive in backwards... Fascinating that even the manufacturers of the actual thrusters don't possess the theoretical underpinning of what the thing will do but go hey, the proof in the pudding is in the eating.

[@Takeshi_9000]

Excellent comment thank you

[@thecma3]

An interesting consequence of the design of the hall effect thrusters is that they impart a swirl torque on the spacecraft along the axis of the thruster, so spacecraft using hall effect thrusters may need to desaturate inertial attitude control systems (reaction wheels/CMGs) periodically

[@Thefreakyfreek]

Normaly you woud solve this by adding a second one spinning the opasite direction. But that would not work because you can't just flip electron rotation around magnetic field ( or something like that)

[@mytube001]

@@Thefreakyfreek You could mount two some distance apart, angle them very slightly in opposite directions, enough to cancel such a rotation. Thrust vector roll!

[@gavinkemp7920]

can't they inverse the magnetic field for that ?

[@ENCHANTMEN_]

Huh, I wonder if a small portion of the thrust could be vectored to counter it? Almost like vernier engines

[@AlanTheBeast100]

I read your comment and was wondering why - when I saw those electrons circling, then it was clear. Solution: 2 thrusters with the coils wound oppositely (or current in opposite direction).

[@jonathanedelson6733]

Small correction at time 4:50. If you double the exhaust velocity you quadruple the energy needed per unit reaction mass, but you also double the thrust. So for the same thrust you only need half the reaction mass and double the power. Jon

[@andytroo]

this - this is why efficient + high power engines can never be a thing - because you have to pay double - once for efficiency and once for thrust, and untll you have a mega-watt power source, you aren't going to be doing mega-newtons of thrust at high isp, and when you run to ultimate limits you discover that even antimatter doesn't have enough energy density to power the rocket if you want to get to a large fraction of the speed of light.

[@riccardoorlando2262]

@@andytroo I suppose the main use cases are automated very small vessels - sub-kg minicomputers stuck to a thruster and some solar panels. The other option is beaming energy from a remote source.

[@SephirothRyu]

@@andytroo Compared to today's engines, they could be possible. Relative to today's, that is. If we get fusion reactors functional and in space, they could create enough power to shove a sufficiently high amount of power into a sufficiently large amount of matter to be both efficient and high power. Again, relative to current ionic engines.

[@SBImNotWritingMyNameHere]

Jon Garfield died 6 years ago you have to let him go you need to move on

The Hall effect thruster sounds something straight out of a science fiction book. It is unbelievable that we can build it and it works.

[@matsv201]

Well the core idea of it is not very different to a particle accelerator, or even a cathode ray

[@Randelia]

Thank you so much for the ion/hall breakdown! Fascinating content. NASA continues to ignore my resume but thanks to you, KSP is ready to hire me!

[@realulli]

Same here! The bribe for the people in charge at the KSP wasn't even that high... 🙂

[@ProjectPhysX]

Cool video, thanks! Small correction at 8:04: the gap width has no effect on ion velocity. Only the electric potential/voltage dictates ion velocity, not the distance between the charged grids.

[@colinmaynard2879]

Why? Surely the potential gives an acceleration and the longer the ion is undergoing this force the faster it will be travelling at the end?

[@torstenmautz195]

With higher voltage comes higher distance. Electric Engines follow the spiderman rule😂.

[@ProjectPhysX]

@@colinmaynard2879 the gap distance cancels out. At the same voltage difference between places, the acceleration on the ion becomes larger when the gap becomes smaller. In the end you get velocity v = √(2qU/m), with q and m being the charge and mass of the ion and U being the voltage difference between plates. No gap distance in the equation. Making the gap larger probably has some engineering reasons, but doesn't affect ion velocity.

[@DrDeuteron]

@@colinmaynard2879 in a conservative field, all that counts is start potential (voltage) and end potential. Ofc, if the acceleration is to too strong, you may start losing energy to bremsstrahlung (photons of all energies)...ofc, photons carry the most momentum per unit energy, so maybe that's a good thing?

[@colinmaynard2879]

@@ProjectPhysX thanks

[@Chooie6]

Some years ago I used to work in an inspection lab with a very nice computed tomography system, that is to say a machine built to take 3d x-rays of what was put in there simply speaking and outputting a volume of data that could be analyzed. The customer was aerojet rocketdyne and what I was inspecting was the rear outer rings of hall effect thrusters that were being tested for lifetime limits and erosion is definitely the best way to describe the appearance of the ceramic material. There were straight channels along the direction of thrust I forget how long they were running but for that to happen it was definitely a long time.

[@azmanabdula]

What does it look like? Like a river bed thats dry?

[@Chooie6]

@@azmanabdula straight and jagged like

[@azmanabdula]

@@Chooie6 Isnt that contradictory?

[@Chooie6]

@@azmanabdula its a bit hard to describe but the best comparison is its similar to a sloppy water jet cut. like if you used a extremely rough grinding surface in the same spot to the point that it leaves distinct grooves. as was the case they had extremely long runs of consistent wear.

[@azmanabdula]

@@Chooie6 Oh I see So its like a flat burred surface

[@heiner8991]

Great explanation of Hall Effect Thrusters, I have heard a lot more about ion thrusters previously on ESA missions. Just to add FEEPs (Field Emission Electric Propulsion) may gain in popularity after decades of struggle. The slit FEEPs were actually removed from LISA Pathfinder spacecraft and replaced with a cold gas subsystem previously flight qualified for GAIA. But now various Cubesats are using the Enpulsion supplied needle FEEPs, which hopefully will meet lifetime requirements as there are proposed for missions like the AWS Protoflight model with a total spacecraft mass of about 135kg. So it could be that FEEPs are used for smallest spacecraft and the other electric propulsion technologies for larger satellites.

[@clevergirl4457]

A man of his word! Scott said he'll make a video on this subject in the last deep space update and he delivered!

[@James27Simko]

I could listen to you speak all day... something about the way you can get information across is amazing

[@Deltarious]

Ion thrusters have always been one of the very few real technologies that seem truly "SciFi" to me

[@grn1]

It probably helps that a lot of SciFi shows use ion thrusters as a plot device.

[@anonymous-rb2sr]

they're basically just magnets at the end of the day, same concept as a coilgun, optimised for a different purpose, any engine that uses either beamed energy reception or nuclear reaction is a lot more sci fi than ion engines, "ion" sounds sci fi but it's just the basic building block of all chemistry, it's just magnetically charged atoms being pushed by a magnetic field, and they chose chemically inert noble gasses because they react with the walls, they sound sci fi, they look sci fi (with their blue or purple glow), but when you get down to it they're very basic and low technology

[@SephirothRyu]

@@anonymous-rb2sr Magnetic Sails are basically also just magnets at the end of the day. Except applied to the solar sail concept. If you accept the downside of them needing power, they are basically superior to a normal solar sail in just about every other way. Their wind catching area is not limited by the physical shape, but but the fields they produce. I like to describe it as: Solar Sails = the square rigging on many large age of sail ships. Can really only sail downwind. Magnetic Sails = the triangular sails seen on many ships throughout the ages, as well as being the primary sail type used for conventional sailing vessels today. You can sail at various angles due to them being wing-like in that they deflect the wind rather than just being pushed by it. You can even sail into the wind up to a certain angle. Fun fact, a magnetic sail can actually sail closer to directly against the apparent wind angle than an actual naval sail.

[@0OolIi]

Scott I gotta say, your old OG explanation space vids thought me more science than school. Its amazing to see you still going keep it up✌🏼✌🏼

[@richb313]

Thanks Scott for explaining how these thrusters work and applications.

[@matterwave2331]

Yeah!! Ion source time :D I'm working on electron impact ion source, your videos on ion thrusters are always a good discussion material with my colleagues, thank you for the good work Scott!

[@carltheshivan]

Scott, I'd like to see a follow up about plasma thrusters. There are designs that do away with electrodes so the erosion problem is avoided. Stuff like helicon and mpd thrusters are cool bits of tech that we could use if space agencies ever considered doing more ambitious missions.

[@ericlotze7724]

I second this! Things like V A S I M I R Granted in that “Future Rocket Technologies” mod or whatever he covered in a video for KSP 1, he may have mentioned these to an extent, but yeah a dedicated video would be neat!

[@thekaxmax]

@Eric Lotze vasimr has the tiny problem of requiring high temp superconductors. But they'd be useful for all thrusters. Side note: my cousin was on the helicon dev team.

[@ericlotze7724]

damn, didn’t realize that. Also that’s cool you had someone you knew working on it!

[@anonymous-rb2sr]

YES PLEASE!!!!

[@davidking972]

Bravo Scott Manley for a concise review and explanation of state of the art Electric Propulsion, from an EP expert of 4 decades. I find your description of the devices accurate and meaninful. I am proud to have contributed to several of these at JPL, Aerojet Rocketdyne, and SpaceX.

[@peterpeterson2430]

I second David comment, from a 2.5 decades of EP experience ;)

[@johndododoe1411]

From the properties quoted, ion-grid thrusters can achieve significant fractions of c for interstellar probes, while hall effect is great for repositioning satellites and impact avoidance .

[@matsv201]

that is great, in steed of the traveling taking several 100 years... now the acceleration will instead.

[@anonymous-rb2sr]

​@@matsv201 lol 100s? you're generous, maybe you forgot a few 0s there! I did the math, and ignoring any relativistic losses should there be any, to reach half of c (which is extremely slow compared to interstellar distances let's not forget that, c is SLOW, half c is DOUBLE slow) it would take around 60 thousand years to reach half of c from standstill and at half c it would take 8 years to reach proxima centauri I can't be bothered to do a differencial equation to calculate what the shortest travel time achievable with it would be, but I expect several tens of thousands of years with the thruster burning 100% of the way yeah ion engines just suck, let's be honest

[@arneschroder2033]

10:06 made my laugh! Electron „I wanna go there!“ „Eh eh“, answers the magnetic field, „you‘re gonna go sideways!“

[@vonrechner9618]

Hello from DE.

[@erichazuriki2947]

poggers, on my part aswell

[@Nuschel]

Moin!

[@BackYardScience2000]

Delaware? Germany? Denmark? They all use DE as their abbreviations. Well, Denmark doesn't, but you'd think that they would by way of reasoning.

[@raulkaap]

In a CRT, the electrons that shoot out from the gun in the back are easily steered by the coils but any residual stray ions (chlorine, oxygen) tend to fly in a straight line and, if not accounted for, create an ion spot in the middle of the screen. This ties in well with the fact that in Hall effect thrusters, electrons swirl around but the ions just shoot through the magnetic field. I like it when facts from different fields of technology help understand each other.

[@donjones4719]

Thank you, Scott. Just what I've been waiting for since the announcement of argon thrusters on the new Starlinks. 556 days from clean-sheet to multiple deployed production articles. SpaceX just keeps outshining (and probably dismaying) the competition.

[@Danuxsy]

Starship was supposed to fly to Mars with cargo in 2022, it has yet to reach space...

[@Pharisaeus]

One clarification: you definitely can build propellant-less electric thruster - the Photon Rocket, but with 1N/3GW of power it's not a particularly practical idea. Still, in theory you could accelerate just by shooting a laser, without any reaction mass involved.

[@TwinPeaksIndustries]

Also, you would vaporize anything that is behind you, with a laser that powerful xD

[@user-si5fm8ql3c]

Well, really you are using energy, as your reaction mass, energy also has mass

[@Pharisaeus]

@@user-si5fm8ql3c but you don't need to carry a tank with photons or worry they will run out.

[@Phlosioneer]

You’d also need to be careful with the photon thruster about heat dissipation (which emits photons), solar panel use (traveling towards a light source acts like a reverse solar sail), and for radioactive power, gamma ray momentum losses.

[@anonymous-rb2sr]

has this ever been tested in space or not because if not I feel like you're making the mistake of extrapolating things a step too far, so far the two studies that tried to measure the mass of photons both came out with positive results, and we know that photons have inertial mass (they impart a velocity change upon interaction with matter), and gravitational mass (they get affected by gravity in the same way as everything else) now I am fully aware that it's not what einstein says, I'm just saying, if all experiments and all logic points to photons having a small mass... maybe it's worth considering and what better experiment to test that than to put a big flashlight in space, then test it's resistence to change in velocity vector before and after releasing a large ammount of EM radiation because at the end of the day, if we could make a reactionless engine, that would kinda break the universe, even if it takes millions of years to get up to speed, it eventually would, so pardon the skepticism but until it has been properly tested, I won't put blind faith in the word of mathematicians who have a long history of closing their eyes to anything that goes against their nice little theories

[@tevvya]

Really nice to finally see how these work. One question: Why is neutralizing the outflow necessary in these thrusters?

[@joshuasteele343]

If you don't, the ions may be electrically attracted back to the spacecraft, negating the thrust.

[@hanelyp1]

You don't want charge building up on the spacecraft and dragging the ions back.

[@noop9k]

You want ions to leave roughly at constant speed, carrying your delta impulse. If you emit charged particles, your vehicle will attain the opposite charge and after a while the particles won't leave it anymore due to electrostatic attraction, nullifying thrust.

[@ManBearPigCreative]

Always a treat to see a new video!

[@brianmatthews232]

Very interesting video. I've worked a lot with ion beam millers using these guns based on the same technology to produce mems.

[@rhofer99]

Great job capturing the salient details of our historically obscure field that is now going mainstream.

[@peterpeterson2430]

Go Blue

[@randomm9683]

Thank you for that explanation of the hall effect. From watching AVE teardowns i knew that the hall effect had to do with magnets and electricity but didnt know what it was

[@mkllove]

Hi Scott ! I had the privilege of working for an industrial ion source company started by Dr Kaufman ( & Dr Brown ) here in VA called Commonwealth Scientific in the 90s.... Glad to see you credited him for his contributions to EP systems in US. We made Gridded and HE Sources and Custom Power Supplies for the majority of computer chip, hard drive and surface treatment plants worldwide. I still have a book he wrote ( with his later partner Robinson ) "Operation of Broad Beam Sources" by Kaufman & Robinson sitting on my bookshelf !

[@rubikfan1]

Yea. Ion engines are so underrated in media. Thank you for the very extensive video about all the variants

[@MoritzvonSchweinitz]

Well, Twin Ion Engines are actually very popular in the media! Whole movies feature them prominently! :-)

[@MCsCreations]

Fascinating stuff indeed. Thanks, Scott! Stay safe there with your family! 🖖😊

[@nanev1976]

Worth mentioning the Magnetoplasmadynamic thruster, which combines both insane Isp and high thrust. It is still experimental, though

[@leonfa259]

Anything that results in high Isp and high thrust uses a lot of power and power is currently the bottleneck.

[@nanev1976]

@@leonfa259 Cathode erosion is the bottleneck for this type of engines now. However, the video is about el. engines, so, as I said, this type is worth mentioning.

[@alexanderstone9463]

Not to be pedantic but it’s more like highER thrust. We’re still talking about millinewtons of thrust here.

[@mech____]

12:28 i wonder if theres some form of resonance that would allow particles to flow progressively faster as burn time goes up maybe explained by the more 'closed loop' nature of hall effect thrusters? the gridded design using a more acceleration-staged method would in theory have a more instantaneous activation therefore have less of a charge gradient and a lower tendency to generate said resonance. im really curious to know the actual answer, hope we find out sometime!

[@kyon10]

Hey, @scottmanley if you had a 1000 kg spaceship exclusively dedicated to accelerate, that used a mix of solar and nuclear power to fuel the ion thruster (solar panels could be ejected when they became useless, thus reducing total mass) what would be the top speed that it could achieve? If it would it be possible to mix it with gravity assists how much more speed could it get? Could it get somewhere near relativistic speeds before the fuel ran out?

[@TheEvilmooseofdoom]

Wow, you don't ask easy questions!!

[@dabs4270]

it depends too much on many variables. how heavy the rest of the space ship is, how much is fuel, what kind of engines you have, how much money you're willing to put in, how much time you're willing to wait, etc

[@kyon10]

@@dabs4270 the ship should be just engine, fuel, solar panels and nuclear RTG, nothing less, nothing more. It should the best engine possible, with no time or money limits. I just want to know what would be theoretically possible

[@codacoder]

Yeah, (when?) could we overtake the Voyagers this way?

[@bluetube8824]

To do this, you would probably want like 90% fuel, 9% RTG, and 1% everything else. Skip the solar panels, run purely on a 50 W RTG, and use a FEEP thruster at a truly ridiculous accelerating voltage, and a truly abysmal thrust level. Say you use 130,000s of ISP and a 90% fuel mass fraction - you have 2.9 million m/s of delta-v. But, with a 50 W powers supply, and 900 kg of fuel, it will take about 950,000 years to fully accelerate. That's way too many half-lives of plutonium for the RTG to continue working - you get like 80 years at best. So, not feasible. But, it gives you a sense - With Xenon,130,000s of ISP only requires like 200,000V of accelerating potential. That's like a decent high-school Van de Graaff generator. Just need a power supply that weighs little enough to make it make sense.

[@shmookins]

7:20 Why is it necessary to neutralize the exhaust?

[@GilgaFrank]

Bizarrely, the description of how the grids work in the ion thruster and the addition of screens and suppressor grids is precisely the way that audio vacuum tubes (valves) were developed from triodes to tetrodes to pentodes. So my question is this - can I stick four ion thrusters in my Marshall amp?

[@spagamoto]

Alternatively, if you just needed a few more Ns impulse to reach a rescue craft a la Martian and had nothing but your great-grandpa's Fender amp, could you use it to rendez-vous? What guitar tab would be best?

[@GilgaFrank]

@@spagamoto I'll knock the tops off a few EL34's and contact you from orbit

[@Spacedog49]

While working on the Deep Space One NSTAR engine, the JPL people asked where I gained my knowledge about Ion engines. I told them I made a few in 1966 from old vacuum tube components.

[@GilgaFrank]

@@Spacedog49 There's nothing new that hasn't been forgotten!

[@robbo307huron]

I wish you had mentioned Deep Space One which made a lot of the ion thrusters assumptions valid. I remember following that spacecraft at the time, as difficult as that was back when. Great video though.

[@mosiprop]

Brilliant video! I'm very interested in knowing more! Can you please post the sources of the information presented? Thanks! ( Fly safe!) :D

[@austinskylines]

Thank you so much for such an in depth look at this tech! Super interesting! There is alot of work to come out of Electric Thruster Design in the coming years! Applied Ion Systems has off the shelf products you can buy as a civilian too now!

[@lake5044]

An electric thrust engine with no propellant is of course possible, just have an LED and emit light behind you and you'll get thrust. Sure, that thrust will be insanely low and you'll need a way to cool down the LED or have some sort of superconductive LED... but possible and practical are different things of course 😅

[@gerthddyn]

This is great! You can almost completely replace the AIAA/IEEE electric propulsion class with this. Can you add another pair of these? One for generic electric propulsion that includes the equation relationships between specific impulse, voltage, thrust and power and a second that covers the other forms of elecitric propulsion? Cover Arcjets (flown), pulsed plasma thrusters (flown), VASIMR and the various cubesat EP systems (you hinted at FEEP, but there are vendors that have flown dozens or hundreds)? Seriously. Having someone that is charismatic like you do this series would make it so I don't have to teach new mission designers anymore.

[@scottmanley]

That sounds like… work :)

[@luckyirvin]

when i worked at the Redmond rocket factory, i had played a small part building circuit boards for the development program. when i saw a Hall Effect thruster firing in the vacuum chamber, i was gobsmacked watching the future with my own two eyes. blue energy

[@pineapple2703]

My favourite thing about these videos is I don't understand most of what's being said, and yet... I still love it, love science and I love spaceeeee

[@smokeydops]

The chart at 13:56 has the "PIT" Ammonia thruster on it. Google told me something surprising; ammonia electric thrusters have flown in space before on test flights but are not Hall Effect or Gridded thrusters. Maybe video that?

[@bazem]

I always get alarmed with the abrupt end of Scott's videos, you get used to him talking many interesting things nonstop during a period of time and then suddenly "I'm Scott Manley, fly safe"

[@cmilkau]

I always thought plasma thrusters count as electrical thrusters, too. I guess they don't use electric fields as directly as ion thrusters, but what else would you call them?

[@anonymous-rb2sr]

"I always thought plasma thrusters count as electrical thrusters, too." They do! And they're awesome, the current problem with plasma thrusters is that they get too hot and melt down all known materials, but if we managed to solve the heat issue, they would be WAY better than ion engines Plus the heat management issue is also the thing that is preventing us from using advanced fusion, fission antimater etc engines, so solving that would open the door to truly magnificient engine types

[@c182SkylaneRG]

Your disclaimer about "pure electric" thrusters still being Science Fiction is exactly why I clicked this video: your title/thumbnail citing "electric thrusters" had me scratching my head, and wondering if I missed the next major spaceflight revolution.

[@Andrew5347d]

So, if you had a big fusion reactor and some very large banks of electric thrusters, could you generate some significant thrust? I'm thinking The Expanse.

[@allineedis1mike81]

We can build powerful fission reactors right now that could do all kinds of awesome things in space. Like getting humans around the solar system in amounts of time we could handle. We just don't have the drive to do it yet. That could change in the relatively near future as we learn to gather and use resources in space. If your into this stuff I'd read Delta-v and Critical Mass by Daniel Suarez. They're novels about mining in space and saving the world but are scientifically accurate. Good reads for space nerds.

[@General12th]

It's not just the raw power requirements that make ion (or plasma) engines bad for moving humans, but also the efficiency of the parts. If you strap a gigawatt nuclear reactor to one of these engines, you won't be able to funnel all that power into engine thrust. You'll just melt the components.

[@harryganz1]

In theory, you could generate a lot of energy from nuclear fission/fusion which could drive an ion engine, but I doubt it would be better than using the thermal energy to expand a gas and use that. Right now, most energy production from nuclear is via heat, so it is more efficient to use that heat energy to produce kinetic energy than to have efficiency losses by converting it to electrical energy then to kinetic energy.

[@mrpicky1868]

fusion reactor would be an engine in itself) double-quadruple conversion is pointless

[@allineedis1mike81]

@@General12th Kinda like changing to a different propellant, it's building a whole new engine. I didnt mean to imply that all we need is huge source of electricity and bam its The Expanse. But there are many different propulsion concepts that become possible when you effectively have a your cities power plant on board. Nuclear Thermal will probably be the first one we'll see that makes Human exploration beyond the Earth Moon system feasable. Or maybe something like the vasimir plasma engine powered by an electricity producing fission reactor. Still have to get rid of waste heat one way or another which can be a real bitch in vacuum. People much smarter than myself will hopefully be stressing over all of this sooner rather than later.

[@shmookins]

1:06 Why does the exhaust need to be neutralized?

[@flymypg]

I've always liked Hg thrusters because they make it easy to have solid propellant, so you only need to vaporize the atoms you need when you need them, right there in the cavity, with no need for pressurized bottles and nozzles.

[@stevecoates3799]

Nicely done Scott, a timely topic that needed discussion. Kudos!

[@michaelcooney7687]

As a Luddite, I must say, this episode was almost understandably descriptive… I love rocket technology and spend way too much time lurking in this space… It’s staggering how much time this tech has been around and I’ve learnt of it now.. Obviously my time in space needs to be accelerated in order to catch up.. 🤣🤣🤣🥰😎

[@famguy2101]

I work with very similar technology on a daily basis, but for thin-film optical coatings. We actually use pretty much both types and we also use argon for cost reasons

[@mitchellminer9597]

Excellent information, great explanations. Thank you!

[@mr1enrollment]

thx Scott, cool topic. stretches my 45 year old EM studies to the max.

[@benjaminshropshire2900]

Finally an explanation of why Xe is so popular. It's always seemed odd to me given that for a fixed ionization state (e.g. +1) the Iₛₚ goes up as the species mass goes down. The explanation here suggests that thrust-per-power dominates over total ∆V as a priority. Hydrogen would make the best fuel, yet again, for max ∆V over very long missions... as long as storing it isn't a major concern. The species I've thought would be an interesting candidate would be Br: it's cheap, light, not horrendously corrosive, has a comparable first ionization energy to Xe and can be stored as a liquid in the structural equivalent of a pop-can.

[@williamduffy1227]

How about Radon? How well would that work?

[@benjaminshropshire2900]

@@williamduffy1227 the entire Radon content of Earth's atmosphere is less than 1kg and it has a half-life of less than a week. I suspect the logistics alone would rule it out.

[@lightkeeper917]

Thanks Scott! This is very educational and extremely interesting.

[@michaellove9831]

Scott, I actually worked for one of Dr Kauffman's companies here in VA called Commonwealth Scientific working with all varieties of ion beams for industrial purposes and research ! Pleased that someone remembers his contributions...

[@xymaryai8283]

if you can dump more power into the thruster, can you get more thrust linearly? does the design need to be changed for higher throughput?

[@frankgulla2335]

Scot, thanks for the nice explainer and great graphics.

[@NET-POSITIVE]

It seems to me if you have counter rotation at speed em fields while blasting the propellant, you can take advantage of the field differences, helping the acceleration of the craft?

[@djredrover]

I love how you have Slack open on your laptop with a link to the Terran 1 Launch Live stream!!!! Awesome!

[@peterbalholm2138]

The first experiments in electric propulsion for spaceflight were made in May, 1912, by the Norwegian physicist Kristian Birkeland (most famous for discovering the cause of the Northern Lights). He built and tested it, said to his assistant, "It's nice!", and never published anything. According to Frank Winter, former curator of space at the Smithsonian, Birkeland's vacuum chamber he tested it in, which is now on display in Norway's Teknisk Museum, is the oldest spaceflight artifact in the world.

[@JulieanGalak]

Great video, as always! I'm wondering, do you know anything about the thruster used by Team Miles on their cubesat, which was launched on the Artemis 1 mission? A video about it would be great.

[@tillthiemann6448]

The best thing about electric thrusters is, that they look super cool

[@KyleBrubakerrekaburBelyK]

You should look into RF ion thrusters. You basically microwave the propellant until it ionizes and flies out the back. There's at least one example in space at the moment, but I'll leave finding the company as an exercise to the reader.

[@SirDeadPuppy]

thats....crazy!!! lol

[@SephirothRyu]

Pure electric engine that works: A magnetic sail. Its like a solar sail, but it uses magnetic fields to redirect solar wind instead of just bouncing it directly off a surface. It has much greater control over the way its thrust is used, and can in theory be used to sail "against the wind." The thrust is, of course, quite low, though possibly a bit better than a normal solar sail. Just make sure you have them at both the aft and the bow (relative to facing at the sun) so you can use them to steer and to cancel out each set of sail's torque. Edit: technically, it does need "fuel." But that fuel is given to it constantly by the local star in the form of solar wind and energy that can be harvested by solar panels that then power the magnetic fields of the sail system (the masts that have the field generators can also double as mounting points for the panels).

[@iitzfizz]

Great video, as always!

[@jonathangra-v6l]

Thanks Scott!

[@citizenblue]

8:49 "where the action happens" - Scott Manley

[@pauljcampbell2997]

Thanks Scott. Another very interesting and informative video!

[@LukasSMF]

Those videos are sooo interesting I wish u were the one making all of my thermodynamics classes

[@michaelmurray2595]

Thanks, Scott: great episode!

[@tbix1963]

Thanks for sharing your thoughts and ideas. Always interesting and entertaining. Are there any other types of electric rocket engines that could work within the atmosphere. I’m often pondering if the thorium liquid salt reactors can be refined for space use since one of their primary waste products is xenon gas. While powering your way to orbit you might be able to produce your propellant needed for space. Although no expert by a long shot I’m stuck liking the idea that your nuclear fission fuel contains both your energy and propellant in one compact element.

[@dustinmorrison6315]

2:23 Could we capture matter from the exosphere and use that as propellant?

[@dungeonkeeper42]

@7:17 why does the exhaust need to be neutralized?

[@gutterhalo]

Thank you so much i've been a fam for a long time ABBA

[@jackb3822]

Just clicked the notif on accident but I’m not complaining!

[@ReadTheShrill]

How big would you have to build one of these drives to provide 1G acceleration on a ship large enough to maintain a complete biosphere, such that it could be useful as a generation ship?

[@TheEvilmooseofdoom]

I don't think you could, the power requirements would be tremendous.

[@anonymous-rb2sr]

I don't think you could ever reach 1G of acceleration, it's not about size, it's about the weight to thrust ratio of the entire system, you need power generation, power cables and an engine that is powerful enough to create enough thrust to accelerate itself at 10m^2 so basically if we had magical star trek power generation/batteries etc sure we could overclock those thrusters to 1G, but I don't see how we could make a system that powerful yet light enough with known materials and technologies if you want high thrust you need hot engines, that's kinda how it goes (thinking of, it would be possible if your power supply was not on the ship, beamed power would work, but only in range of the power supply)

[@bozhijak]

Damn! I could write a paper (for REAL) using this information. Thanks Scott and keep it up!

[@mm-yt8sf]

if one didn't mind super low thrust, could shining a laser out the back work as a thruster? if light has momentum..shouldn't that work?

[@Br3ttM]

The amount of light required means either absurd amounts of energy, or miniscule thrust. The effect of reflected sunlight and emitted heat radiation is enough to be detectable with careful measurements over years. It can even cause asteroids to spin after a very long time. The solar wind is a bigger effect.

[@theharbinger2573]

Shockingly good video, I really got a charge out it.

[@Fantic156]

OK, cards on the table I barely understood anything, but man, do these thrusters look cool! Great video, thanks. 😜

[@lelandrogers1078]

Would it be possible to put enough of these on a ship like Starship to accelerate it at near 1G to provide artificial gravity as well as shorten the transit time?

[@petamerican2588]

No. They have way too little thrust and way too steep of a power requirement to be of any use on anything manned.

[@moonshine7753]

No. But for fun let's do a small calculation. Using the thrust from 4:13, about 250mN, you'd need 39 or these to accelerate 1kg of material at 1g. Every one of these engines alone weights 12kg.

[@exo_2171]

Shortening the transit time by increasing the velocity sounds like a good Idea at first but you have to keep in mind that in order to land on another celestial body you have to bleed of all that speed again as well or you just burn up in the atmosphere/ slamm into the planet.

[@moonshine7753]

@@exo_2171 just aerobrake really hard, smh. It works in kerbal space program. But actually I think the idea is to have enough fuel (somehow) to accelerate for half the travel and decelerate for the other half.

[@Gregorius421]

What happens to living tissue (ex. your hand) if put in front of an operational ion thruster?

[@mine4me403]

Excellent animations❤

[@EvocativeKitsune]

Always answering the questions on my tiny mind.

[@circogalactico3820]

"It's like having a mouse push your space craft around" lol Totally picturing a mouse in a spacesuit with a jetpack. hahaha

[@SinisterMD]

I love to listen to smart people talk about things. The accent really brings it full circle though.

[@katm9877]

Is there a typo in the chart at 13:50? NSTAR design and tested... did they really test it to work nearly 4x longer than designed?!

[@Only1Orinthal]

2:58 Prettiest thing I've seen today

[@RobinWootton]

Impressive stuff!! Thank you

[@undertow2142]

Have you done a video on magnetic sails? I know Zubrin did some work on using a metal wire array to create a sail in which an electric field could be generated and propel the spacecraft by pushing against the solar wind and other ionized atoms in space.

[@Archgeek0]

BaHAHah, love that table at 13:57 That 100N hydrogen MPD : "Isp (S) - Very high"

[@carlrossi7989]

(Apologies if duplicate post) The USA tested electric engines using both suborbital missions [SERT-1], and an orbital mission, SERT-2. The latter was launched in 1970 and operated until.....1991! Not continuously of course, but one of the thrusters onboard SERT-2 ran for a total of over 3,700 hours with multiple restarts. In particular, SERT-2 [BTW, the acronym stands for Space, not Solar, Electric Rocket Test] really paved the way for the increasing use of electric propulsion that we are seeing today.

[@darylmunton6262]

So there's a propellant, Argon or what ever it is. How much of this do these thrusters consume? Is it a really tiny amount and they can store enough onboard to work for years? Or untill the thruster erodes and stops working?

[@ClaimsDelegates]

Why does the exhaust need to be neutralized? Is it no possible to nozzle or cone the output? At the micro scale?

[@crangos]

How has the available power for a spacecraft evolved over time, with improvements to energy required for other mission specific hardware and solar collection? Is the available electrical power a contributor to the late adoption of these devices?

[@bluetube8824]

Yes; it is a huge factor, and it is improving. With electric propulsion, the optimum ISP depends on the specific power (W/kg) of available power supplies. Solar panels at LEO typically provide ~100-150 W/kg, though this is improving - some solar providers I am seeing now talk about 400W/kg panels. However, the further you are from the sun, the worse this gets; at Jupiter, you get 1/50th the power from solar. Modular nuclear fission reactor designs can get to 300+W/kg which would work all the way to Neptune. Since ISP increases proportional to power squared, a 3-4x improvement in specific power yields about a 2x increase in optimal ISP (there are some other factors that play into this too). But, with thin-film ultra light solar, we should see a shift to higher ISPs, and nuclear in space would likely cement ion thrusters as the main workhorses for high-mass interplanetary cargo - not for humans because it will be too slow, but good for everything else.

[@gordonstewart5774]

How effective is the neutralizing of the thrusted particles typically?

[@nordithen]

I assume it doesn't matter if the discharged ions ever actually recombine with the electrons, you just need to also shoot electrons out to avoid the spacecraft building up net charge.

[@gordonstewart5774]

@@nordithen Makes sense, thanks!