Plasma Fusion Thruster

[jqavins]

@NTP2, I immediately thought of you.

(She's worth subscribing to in general.)

 

[NTP2]

Yup I’m a fan of hers, my dad put me on her. I haven’t had a chance to see this one yet so I’ll hold my opinions for a little

 

[NTP2]

Ok I saw it, it’s definitely interesting but I agree that it’s probably requiring massive amounts of energy to operate, you would need to do the math but the temperature the plasma needs to reach would be extremely high so it’s still the same trade off. And that means you’re better off with a regular thruster.

 

[jqavins]

Does it? In some situations and applications, such as for station keeping thrusters on GEO satellites, electricity is nearly free. You've got big solar arrays in order to operate your payload (the stuff that does the mission that you're there to do) and batteries to keep operating the payload while in Earth's shadow, so you use those same solar arrays and batteries to run high current station keeping thrusters while you're not in shadow. When I left that industry (not by choice ) there were two kinds of thrusters in use after the satellite reached it's designated orbit.

• Hydrazine monopropellant thrusters with decent I_SP for "momentum shedding", which is when the reaction wheels used for attitude control have to be spun down due to accumulated angular momentum, and you need a decent amount of thrust to stay still during the process.
• Arcjets, which use the same hydrazine, run it over the same or a similar catalyst, then use an electric arc to heat the decomposition products further, giving much greater I_SP, but only at low thrust. The arcjets require a lot of electric power.

The batteries, sized to keep the spacecraft running through eclipses* are also sufficient to run the arcjets, so long as you don't ty to run those during an eclipse.

At the time I left, ion thrusters for this purpose were just being developed. I'm pretty sure they were to use the same hydrazine fuel (not PTFE) since the tank and plumbing were already there, but I won't swear to that. It looked, as far as I ever learned, like swapping out the old arcjet for the new ion thruster and changing very little else save for the power supply, so you could use more of that basically free electricity to get better performance from your low thrust thrusters. No brainer. That was about 2010.

Now, skip ahead to today, and there may be a way to throw in some ¹¹B and another whole bunch more of the free electricity to get another big increase in performance, and that sounds like another no brainer to me. Maybe. Well, no.

It's all about mass. The thruster will be more complex, and has to contain the boron supply, and that means it's heavier that the arcjets or ion thrusters. I don't know how much more electricity it takes, and it might mean you need bigger batteries. So you have to evaluate the improved thruster performance against the increased system mass to come to a conclusion, so it's definitely a brainer. But it sounds very promising.

You might be wondering, is the I_SP of the station keeping thrusters really such a big deal? The main limiting factor in the lifetime of a GEO comsat is running out of fuel for station keeping. So yes, it's a huge deal.

* A GEO satellite passes through the Earth's shadow way more often that the Earth and moon pass through each other's. Lot's more. Like, every day for a couple of week season twice a year.

 

[NTP2]

electricity is nearly free….

I don't know how much more electricity it takes…

Well do you have 10 GW available?

Ps there is very little available about how much energy you need to dump in (probably because it’s not helping you sell your research) but I found This paper in nature where they used a 10GW laser.

 

[cls]

Well do you have 10 GW available?

Ps there is very little available about how much energy you need to dump in (probably because it’s not helping you sell your research) but I found This paper in nature where they used a 10GW laser.

Remember, they claim the thing is "pulsed", so it may be 10GW peak for... 1 nanosecond... So 10 watt-second input power.

I find the same kind of accounting in high fi equipment. 1kW Peak Power from this 6" subwoofer! Ahhh, bullshit.

I had a real 1kW for my bass when I played in metal bands. That would dim the lights and blow breakers.

 

[cerving]

Here's the answer...

 

[jqavins]

Well do you have 10 GW available?

Ps there is very little available about how much energy you need to dump in (probably because it’s not helping you sell your research) but I found This paper in nature where they used a 10GW laser.

Well, no, that much would be a problem. Even in a short pulse, because the pulse rate has to be high. A 10 GW, 1 µs pulse at 1000 pulses per second, for example, is still 10 MW averaged out. If that's what this thing takes, then I take it all back.

(Still, ¹H + ¹¹B → 3∙⁴He is intriguing.)

 

[NTP2]

Well, no, that much would be a problem. Even in a short pulse, because the pulse rate has to be high. A 10 GW, 1 µs pulse at 1000 pulses per second, for example, is still 10 MW averaged out. If that's what this thing takes, then I take it all back.

(Still, ¹H + ¹¹B → 3∙⁴He is intriguing.)

I’m afraid so, that paper was supposed to be about how you could use LESS power than before! But I agree it’s super cool and maybe if nuclear reactors become common on space craft it’ll be practical…

Ps and they are probably heating it less efficiently than a laser would, because you can’t heat a large area with one of those, it’s the entire point of a laser.

 

[Art Upton]

Remember, they claim the thing is "pulsed", so it may be 10GW peak for... 1 nanosecond... So 10 watt-second input power.

I find the same kind of accounting in high fi equipment. 1kW Peak Power from this 6" subwoofer! Ahhh, bullshit.

I had a real 1kW for my bass when I played in metal bands. That would dim the lights and blow breakers.

The Old appliance store commercials [at least in the Midwest] "One Thousand Watts per channel Baby Cakes"

Edit: yes I know it was said at 50 watts on the TV, but the Stereo stores were pushing 1K watt car stereo speakers, BS of course.