I caught up on this the other day and had no idea that plasma rocket engines were a thing. Almost sounds too good to be true. Anyone know any more about them? Pros and cons?
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If it works on large craft Iâm guessing it s a slow build up to speed. And then turn around and fire the engine again for a long time to slow down. Sort of like the TV show âThe Expanseâ use of the Epstein Drive. In that it has constant thrust and then the craft flips around and uses the engine for a long burn to decelerate. (not the actual engine tech)
Iâm guessing many years away from testing this on a human large interplanetary craft. Must be other ideas in the pipeline that NASA is also looking at the same time. Seeing which pans out. I assume some ideas have already been tested up in space on a small scale. (ION engines etc), Iâm not familiar with any others.
I never thought all my research on this topic would be useful. This is my moment! When first applying to grad school I actually applied to a phd program for plasma propulsion. Didnât get in but I love the field.
Theyâre similar to to conventional electric thrusters in the fact that they use electrical power to accelerate the propellent as opposed to chemical reactions. However Ion drives, Hall thrusters, and Plasma thrusters all differ on what parts of electrodynamics they use to achieve this and technically all 3 of them create plasma in the chamber and itâs neutralized at some point along the way.
I wrote a paper on electric propulsion for my physics E&M class in my undergrad so I can upload that too if youâre interested but itâs basically a bit more detail about the differences.
Basically gridded Ion drives use a large E field to ionize the propellant and because the positively charge gas is repelled from the E field plate towards a charged grid which the ions pass through where then the exhaust is then neutralized with an electron gun. This has negative effects due to lifetime of that grid because of the many impacts by charged particles.
In the Hall thrusters the gas is still ionized by a large E field(this is the similarity) but the plasma is accelerated by B fields due to the right hand rule out the nozzle. In this case I think an electron gun isnât necessary and definitely not the grid, so these thrusters are all the rage right now because they have a higher life time of a traditional gridded ion drive.
The best example of what we would call a âplasma driveâ is VASIMR which stands for Variable something something something magnetohydrodynamic something. Itâs been too long and a simple google would solve that but I thought that sounds funny. At any rate, in these thrusters the plasma is created by microwave radiation. The plasma is then controlled and modulated using âplasma physicsâ and shoved little by little towards the nozzle with asymmetric frequency modulation. Basically move 1 to left, 2 to the right. Eventually you leave the right side of the engine. Using this technique you can choose how long you keep the plasma in the âcombustionâ chamber. This is the entire advantage of this engine type. The longer you keep the propellant spends in the chamber the hotter it gets, and the higher its exhaust velocity. This increases the specific impulse of these engines at the cost of thrust. On the other hand, you can modulate faster and have more propellant leave per unit time. More mass flow means more thrust at the cost of a cooler propellent so lower ISP.
These engines allow you to dynamically change your thrust and specific impulse just by changing the frequency inside the engine. Itâs cool shit. This means you could have high thrust when you want to leave/enter an area fast(such as the initial thrusting phase when leaving or entering a new sphere of influence) and switch to lower thrust by higher efficiency during the transfer phase.
To finally answer your pros and cons of electric engines:
Pros: High efficiency due to large specific impulse
Cons: Expensive electricity wise. You need kV and a lot of current to run these suckers. In addition to that low thrust trajectories are typically much longer than a traditional trajectory with a chemical engine due to the time it takes to impart significant deltaV. I just wanted to reemphasize how much power these requireâŚespecially vasmr. It would need a nuclear reactor or an insanely huge solar panels to run. We have hall thrusters in use and the dawn mission actually used a set of 3 hall thrusters through the course of its missions, but even these 3 tiny thrusters require like 20m long solar panels to accelerate a relatively light satellite. To use these on human bearing spacecraft to get people places in a reasonable time requires a lot more power.
VASIMR is the Variable Specific Impulse Magnetoplasma Rocket. I should have remembered that.
Let me know if you have any more questions!
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Awesome post, thanks! Sounds like a good step away from traditional chemical rockets, but yeah, those power requirementsâŚ
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All we need to do is convince the world that nukes in space is a good idea, and weâd be good to go! 
Letâs compromise with nuclear reactors in space ;). Nuclear warheads in space is a bad idea both politically and in implementation. Iâm pretty sure ICBMs would reach a target faster than a warhead in LEO. Itâs funny how orbital mechanics work.
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Yeah just say that! People generally have a lot of trust for nuclear reactors these days.
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Unless said warhead is the multi-gigaton Orion-propelled orbital nuke the USAF envisioned at a time. No need to de-orbit, itâs big enough to fry the Soviet Union from where it is!
For some reason, it never went beyond a few plans on paperâŚ
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City-Size Lunar Lava Tube Could House Future Astronaut Residents - space.com
A newly discovered moon tunnel could be the perfect place for a colony, scientists say - washingtonpost.com
This could work out if humans can get enough heavy lift machinery onto the surface of the Moon on the edge of these large lava tunnel openings. Send lots of drones down into them first to survey using what ever technology they need to invent to keep large drones aloft on the Moon.
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Heh, I was just listening to Isaac Arthurâs video on that yesterday
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NASA reveals Curiosity 2020âs 23-camera payload - theregister
Curiosityâs cameras - Image NASA JPL & Caltech
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These are really worth a watch, very interesting.
The Jet Propulsion Laboratory W/ Doug Ellison - Part 1
The Jet Propulsion Laboratory W/Doug Ellison - Part 2
Jet Propulsion Laboratory w/Doug Ellison - Part 3
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Keepâin on trucking along
Voyager 1 fires thrusters last used in 1980 â and they worked!
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Bruce McCandless, who made first untethered space flight, dies at 80 -bbcnews
Humans done this in 1984!
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Can Wind Turbines Really Work On Mars? Scott Manley discusses.
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Iâve seen things you people wouldnât believe.
Time to die⌠maybe
Opportunity knocked? Rover survives Martian winter, may not survive budget cuts
