|
Post by srbrant on Nov 8, 2019 6:04:18 GMT
While I was tinkering around with module design, listening to the same main menu music over and over again, a thought struck me: If a fusion reaction is magnetically-contained and the resistojet coils can only get so hot...why not use the heat of an isolated fusion “beam?”
I definitely know that there are holes to this theory, but I don’t know exactly what and where. And that it will most-likely require a bit of carefully-applied handwavium. So...what’s wrong and what’s right with this?
|
|
|
Post by dragon on Nov 8, 2019 18:23:18 GMT
It's a fusion thermal engine, in other word. If you want decent thrust, any fusion engine will have to work like that. With magnetic containment you can jack the temperature up quite a bit.
|
|
|
Post by srbrant on Nov 8, 2019 20:50:38 GMT
It's a fusion thermal engine, in other word. If you want decent thrust, any fusion engine will have to work like that. With magnetic containment you can jack the temperature up quite a bit. Thing is, how would it function? In my story, there’s FTL travel, so torch drives are very rare. In my eyes, a fusion resistojet would be perfect for making a ship more than just a cabin strapped to a rocket, able to complete a cis-lunar tour and back without refueling but without the relativistic travel speeds that makes every nearby world soil itself.
|
|
|
Post by srbrant on Nov 8, 2019 20:55:05 GMT
It's a fusion thermal engine, in other word. If you want decent thrust, any fusion engine will have to work like that. With magnetic containment you can jack the temperature up quite a bit. Thing is, how would it function? In my story, there’s FTL travel, so torch drives are very rare. In my eyes, a fusion resistojet would be perfect for making a ship more than just a cabin strapped to a rocket, able to complete a cis-lunar tour and back without refueling but without the relativistic travel speeds that makes every nearby world soil itself. I can get some damn good thrust-mass ratio if I can get a resistojet coil to not melt at temperatures over 5000K.
|
|
|
Post by dragon on Nov 10, 2019 20:13:24 GMT
Try looking up arcjets. They're just like resistojets with the heating element made of plasma. They might have other limits though.
For fusion, though, it doesn't work. Heating propellant up with a fusion reaction is what works. Then you have a "normal" fusion thermal engine. Really, just use that.
|
|
|
Post by srbrant on Nov 11, 2019 1:37:45 GMT
Try looking up arcjets. They're just like resistojets with the heating element made of plasma. They might have other limits though. For fusion, though, it doesn't work. Heating propellant up with a fusion reaction is what works. Then you have a "normal" fusion thermal engine. Really, just use that. That’s kind of like what I meant, but I imagined the story’s paragravity technology being used to make a coil that pushes the superheated propellant out at a greater velocity, drastically improving the vessel’s thrust-to-mass ratio. Like the offspring of a rail gun and a fusion engine.
|
|
|
Post by bigbombr on Nov 11, 2019 16:55:47 GMT
Try looking up arcjets. They're just like resistojets with the heating element made of plasma. They might have other limits though. For fusion, though, it doesn't work. Heating propellant up with a fusion reaction is what works. Then you have a "normal" fusion thermal engine. Really, just use that. Arcjets tend to suffer from elektrode erosion IIRC. They're also in a bit of an awkward spot in regards TWR and I sp when compared to NTR's and electromagnetic drives.
|
|
|
Post by srbrant on Nov 11, 2019 17:48:17 GMT
Try looking up arcjets. They're just like resistojets with the heating element made of plasma. They might have other limits though. For fusion, though, it doesn't work. Heating propellant up with a fusion reaction is what works. Then you have a "normal" fusion thermal engine. Really, just use that. Arcjets tend to suffer from elektrode erosion IIRC. They're also in a bit of an awkward spot in regards TWR and I sp when compared to NTR's and electromagnetic drives. Electrode erosion? You mean like neutron embrittlement? EDIT: Also, arcjets tend to suffer a lot in the thrust department. I figured that the combination of superheated plasma being safely contained by handwavium antigravity coils that are accelerated further outwards by the same system would push the thrust-to-mass ratio off the charts. How does that sound?
|
|
|
Post by AtomHeartDragon on Nov 11, 2019 18:35:49 GMT
Resistojets are rockets that heat the propellant with resistive heating element by passing electric current through it. What does "fusion resistojet" even mean? Arcjets tend to suffer from elektrode erosion IIRC. They're also in a bit of an awkward spot in regards TWR and I sp when compared to NTR's and electromagnetic drives. Electrode erosion? You mean like neutron embrittlement? No, he means like electrode erosion. You have an electrode and use it to create that hot and energetic electric arc made of plasma. Turns out this is bad for your electrode because hot and energetic electric arcs tend to be hard on stuff they touch.
|
|
|
Post by cipherpunks on Nov 11, 2019 21:22:00 GMT
DOI://10.2514/6.1996-2703 - this is an older paper but I believe it is still relevant w.r.t. electrode erosion. Electric propulsion is a good and easy read, recommended. Alternatively, here. There were some grants given a couple of years ago by US.mil to develop and test advanced composite (not Zirconium Copper) electrodes for arcjets, but I do not know their results (if any). That said, there is an " arcjet lab" where they use arcjets to test various materials with (for example heat shields) - you may want to dig for some reports on erosion from there; probably they do publish. Me, personally - I like A2100 approach (either burn Hydrazine for higher thrust, or heat it via resistivity for higher I sp), and this one seems promising too. Not saying that I do not want to see VASIMR tested. Other than that - matterbeam's post here and some of his other postingss p.s. oh, and what is " whiskering" problem with arcjets? I do not know, but the problem exists.
|
|
|
Post by bigbombr on Nov 12, 2019 7:18:42 GMT
Arcjets tend to suffer from elektrode erosion IIRC. They're also in a bit of an awkward spot in regards TWR and I sp when compared to NTR's and electromagnetic drives. Electrode erosion? You mean like neutron embrittlement? Elektrodes have nothing to do with neutrons.EDIT: Also, arcjets tend to suffer a lot in the thrust department. I figured that the combination of superheated plasma being safely contained by handwavium antigravity coils that are accelerated further outwards by the same system would push the thrust-to-mass ratio off the charts. How does that sound? Why not use a regular nozzle? With some additional cooling, it should be fine. If you really can't use a physical nozzle, a magnetic nozzle doesn't really need any handwaving, unlike antigravity.
|
|
|
Post by srbrant on Nov 12, 2019 20:06:38 GMT
Electrode erosion? You mean like neutron embrittlement? Elektrodes have nothing to do with neutrons.EDIT: Also, arcjets tend to suffer a lot in the thrust department. I figured that the combination of superheated plasma being safely contained by handwavium antigravity coils that are accelerated further outwards by the same system would push the thrust-to-mass ratio off the charts. How does that sound? Why not use a regular nozzle? With some additional cooling, it should be fine. If you really can't use a physical nozzle, a magnetic nozzle doesn't really need any handwaving, unlike antigravity.My apologies. Brain fart. But can a magnetic nozzle really contain something over 25,000K?
|
|
|
Post by cipherpunks on Nov 12, 2019 23:53:00 GMT
can a magnetic nozzle really contain something over 25,000K? Any physical reason why it can't? I mean, if the " stuff" is susceptible to deflection by magnetic field, why not then?
|
|
|
Post by srbrant on Nov 14, 2019 2:54:38 GMT
can a magnetic nozzle really contain something over 25,000K? Any physical reason why it can't? I mean, if the " stuff" is susceptible to deflection by magnetic field, why not then? True. Just worried about really low thrust. Any non-handwavium way to fix that?
|
|
|
Post by srbrant on Nov 17, 2019 23:34:41 GMT
Allow me to clarify: I believe that a handwavium "anti-grav coil" would be better because it would "squeeze" the plasma together and force it out at a higher velocity, as opposed to a magnetic field that would simply contain it otherwise.
|
|