Small Hall thrusters can generate much more thrust than previously believed

[Vl3d]

Running with krypton researchers maxed out their power supply at 45 kilowatts (starting from 9 nominal). At an overall efficiency of 51%, they achieved their maximum thrust of about 1.8 Newtons, on par with the much larger 100-kilowatt-class X3 Hall thruster.

https://phys.org/news/2023-01-plasma-thrusters-satellites-powerful-previously.html

[Shpaget]

No mention of ISP in the article.

[kerbiloid]

6 hours ago, Shpaget said:

No mention of ISP in the article.

 

18 hours ago, Vl3d said:

100-kilowatt-class

18 hours ago, Vl3d said:

1.8 Newtons

100 000 / 1.8 ~= 50 km/s

[farmerben]

Its 45kw.  Isp = 2,550 s

[darthgently]

On 1/25/2023 at 5:12 AM, Vl3d said:

Running with krypton researchers maxed out their power supply at 45 kilowatts (starting from 9 nominal). At an overall efficiency of 51%, they achieved their maximum thrust of about 1.8 Newtons, on par with the much larger 100-kilowatt-class X3 Hall thruster.

https://phys.org/news/2023-01-plasma-thrusters-satellites-powerful-previously.html

Efficiency goes down quite a bit, but does open up more uses

[Nuke]

the biggest hold up on electric propulsion is always the electric part. solar is fine for the inner solar system, but we dont need electric propulsion for that. 

[AckSed]

Idea: I did hear of one proposal in the 90s to use buckyballs (C60) as ion engine propellant. Apparently they are not only tough enough to survive impacts with metal surfaces at 15,000mph, they also have a lower ionisation energy than xenon and more than five times its molecular mass (Xe - 131.3; C60 - 720.3). Theoretically, it could have 1.5 times the thrust to power ratio of xenon.

Now combine that with this finding and we might see something special.

...though now I look further, the price might make one pause: high-purity 99.9% fullerene is available from Merck at an eye-watering £538 ($660) per gram. The Deep Space 1 probe carried 82 kilograms of xenon; the Dawn probe 425kg. Xenon prices are considered high but this would make them seem reasonable.

Ironically, producing the buckyballs is simple, it's purifying them that's expensive... and ion engines tend to need pure propellants. Someone did discover a process to purify them with silica gel, heat and dienes, but so far as I know nothing's come of it.

[CBase]

19 minutes ago, AckSed said:

... and ion engines tend to need pure propellants

the question is how pure: as I understand it, the tricky part is seperating C60 from C70, C72, ... but does it matter that much for an ion thruster ? And even if you loose some efficiency and thrust, as long as you are better than xenon who cares ?

So actually a quite kerbal idea

[AckSed]

33 minutes ago, CBase said:

The question is how pure: as I understand it, the tricky part is separating C60 from C70, C72, ... but does it matter that much for an ion thruster? And even if you lose some efficiency and thrust, as long as you are better than xenon who cares ?

So actually a quite kerbal idea

I am told ion engines tend to have the highest efficiencies when all the ions have the same mass/charge ratio. According to Messer, who supplied the xenon for the Dawn probe, propulsion-grade xenon is 99.9995% pure; the largest impurity allowed is krypton, at a 'generous' 5 parts-per-million. Prices were not given, but if you have to ask, you can probably afford it.

How much a mix of different-sized buckyballs  would affect efficiency for the already over-amped, lower-efficiency ion thruster is something you could only discover through experimentation. There might be knock-on effects or it could be fine. If 98% pure C60 still works, it goes down to a more reasonable £182 ($223) per gram. If it would cause a 10% decrease in specific impulse but still retains the increase in thrust, people might begin to take interest.

I can think of a further advantage to buckyballs as a propellant - no need for cryogenic storage. That'd save a fair bit of mass, even if the transfer of an atomically fine powder in zero gravity is by no means a solved problem, and the buckyballs might be less dense than LH2. It'd essentially be a big plastic bag of soot.

Edited February 2, 2023 by AckSed
Adding prices

[Nuke]

im partial to hydrogen mpd thrusters. but those things are power hogs. 

[AckSed]

12 hours ago, Nuke said:

I'm partial to hydrogen mpd thrusters. but those things are power hogs. 

*nods* Somewhat related, I've been following Momentus Space purely because they have microwave electro-thermal thrusters on their satellite tugs. Rotten specific impulse for electrical thrusters - something like 10kw of solar panels creating 900s for their largest proposed tug - but the propellant is simple water that's cracked into hydrogen and oxygen by microwave-induced plasma. It recombines in the nozzle to give 10s to 100N of thrust, and it's electrically neutral so you could cluster them to push a larger vehicle. Plus the actual engines aren't much more complex than a microwave.

It could be the basis of a very cheap inflatable spacecraft that uses water-walls as radiation shielding, fuel tank, life-support and structure, mining fuel from asteroids and comets as it goes.

This finding, though it needs cooling (which is a big, heavy can of worms by itself) could also be a basis for the same concept, since it seems to work better with lighter, more available noble gases. Mars' atmosphere is about 2% argon.

[Nuke]

i think you could do more with 10kw with a normal hall thruster. they have gotten really good in the last few years. but if you could source a megawatt or two. obviously solar is not going to do that unless you use some kind of large mylar reflector supported by solar wind to cut down on weight. keeping that sail billowed and in the right orientation while under thrust will be somewhat difficult. this will allow constant (slow) acceleration in the inner solar system to enable faster than hohmann trajectories for human crew transfer from earth, mars, the belt, and venus if we do a cloud city there (cargo can use hohmann to save fuel). getting travel time down for humans is important for colonization.

with a fission reactor, now your talking, but where you had panel mass you now have radiator mass, which as far as i know you cant cheat with a big mylar reflector. but with higher power available, you open up the outer solar system. just use whatever thruster makes the most sense (highest isp or cheapest/most available/locally minable propellant or some tradeoff of the two). 

[AckSed]

Other recent technology that might make this better:

The iROSA recently fitted to the ISS and the former DART are lightweight, high-efficiency roll-out solar panels. Each one fitted to the ISS masses 325kg and generates 20 kilowatts of electricity in Earth orbit. A hypothetical spacecraft would have to massively overbuild (8 panels, about 3 tonnes) to have a reasonable power supply out to Mars, but it could be done today.

MIT is building the miniaturised SPARC tokomak, using electromagnets wound with superconducting tape that works at liquid nitrogen temperatures. The tape is capable of carrying kiloamps of current and creating 10 tesla of magnetic containment. The relatively modest electromagnets and cathode/anode in a HET would be much easier. Imagine the electron density inside a superconducting HET: it'd be the size of a dinner plate but rated at *pulls numbers out of air* 300kw and 50 N of thrust; VASIMR would be proud.

Now, you're exchanging one form of cooling with another, but I think in space it's simpler to keep something at 77K than shedding kilowatts of waste heat - something like the JWST's layered mylar infra-red shield plus a helium/neon heat-pump?

[Nuke]

we could do pulsed fusion too, little brother to "old boom boom" orion drives. theres a uk company doing projectile based ignition, where they slam a fuel pellet with a copper disk and really high velocity, i think using a gas gun. the are mostly experimenting with fuel pellet design. so do that in a magnetic nozzel using something like p-b11. i figure have 2 guns pointed at each other shooting fuel pellets at each other, cased in a material that is non magnetic and will ionize on impact, from both fusion and the physical impact. they just have to collide in the bottle and a magnetic mirror at one end will make sure they go out the throat of the magneticv nozzel. you could have 2 gatling gun type dispensers mechanically linked and brrrrrrrrrrrrrrrrrrrrrrrt your way to the planets.

[AckSed]

Huh, it turns out I was accidentally right: increasing magnetic field strength is key to making smaller, more powerful Hall thrusters.

It's just a comment, but this student of UMich's Plasmadynamics and Electric Propulsion Laboratory says they hope to achieve power densities that reach 10N of thrust within a device a square foot across.