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Post by ash19256 on May 31, 2017 2:15:34 GMT
From what I've seen from the Homecoming thread, MPDs aren't really useful if you have sub-mg acceleration. You spend a lot of delta-v that you wouldn't think you'd need to spend to exit a planetary system, and you can't accelerate as much.
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Post by concretedonkey on May 31, 2017 3:35:59 GMT
I had worries about this too but this is why you have the resistojets. The idea was to use them to brake away from the gravity well, then when you are farther switch to mpds on long run. Its pretty much given that you are not going anywhere very fast but the alternative was to use an additional higher density propellant (I see that apophys is fond of neon) for the MPDs and that will turn the methane in to that much dead weight, the ship would grow... how much I'll have to test , I don't have any non-methane mpds at the moment. I've tested it braking away from Earth and atleast there there wasn't much of a problem with this approach - boost for around 800m/s beyond moon's orbit and then do what you want. Admittedly I haven't tested it on lower Jupiter orbits for example and that might be a problem but I see no reason for this ship to be there on the first place. Its a long range / long term support vessel not a fast transport. Still all of this is very much WIP, I'll try denser propellants or even might switch the main propellant to something else entirely for the whole fleet if it turns out to be more beneficial. Or alternatively I can go the easy way and just use NTR instead of the resistojets as on my military ships that will have enough punch for sure  . |
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Post by apophys on May 31, 2017 5:20:07 GMT
concretedonkey - The simplest way to improve acceleration is to upscale the power generation and the MPD. I'd say 208 kt is quite a bit too much to handle with only ~10 GW; more appropriate for this mass would be 1 TW. Or alternately, reduce the mass to around 10 kt. Also, I notice the MPD you are using seems to have comparatively low exhaust velocity for an MPD of that power. (I use neon a lot just because it's the cheapest, and my big ships don't need any propulsion other than MPD. Methane is a fine multipurpose propellant.)
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Post by concretedonkey on May 31, 2017 5:58:40 GMT
concretedonkey - The simplest way to improve acceleration is to upscale the power generation and the MPD. I'd say 208 kt is quite a bit too much to handle with only ~10 GW; more appropriate for this mass would be 1 TW. Or alternately, reduce the mass to around 10 kt. Also, I notice the MPD you are using seems to have comparatively low exhaust velocity for an MPD of that power. (I use neon a lot just because it's the cheapest, and my big ships don't need any propulsion other than MPD. Methane is a fine multipurpose propellant.) mmm I'm not prepared to go there, I have psychological boundaries with high power builds, you may have noticed  .... and now its around 10 GWs , the power plant is one of yours btw.... The way I see it we play this game in two completely different ways - some people like to go way overboard with everything - large ships and terawatt reactors and so on. Mess around with the limitations of the game. I on the other had constantly worry about limitations that the game doesn't take in to account, for example on this build you may notice that the radiators are relatively short - this is because as I was scaling them up I got worried if there shouldn't be some kind of degradation of effectiveness as the radiator gets too long and if there shouldn't be power and additional mass taken in to account for that coolant on the heat pipes running to and in the radiator. Call me a party pooper. On the other hand if I think that what I did was going to work in real life and is relatively realistic I always get a warm feeling inside ... .. The MPDs are 70km/s 2GWs around 50kN if I remember correctly (I'm at work now and can't check), I'm not very experienced in them and most of mine are slapped on to warships because why not - you really have no downside of adding them if they use the same propellant, but none of my ships designed around them, so I never really payed much attention to them. Also I usually do not have that much power available , from what I see they really start to shine with more juice  . |
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Post by RiftandRend on Jun 3, 2017 7:39:35 GMT
I made a fusion ship that's fairly realistic. The engine does use graphene, but only in single atom thick layers  |
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Post by The Astronomer on Jun 3, 2017 7:40:53 GMT
I made a fusion ship that's fairly realistic. The engine does use graphene, but only in single atom thick layers Why Deuterium-Tritium? You'll face some horrible amount of neutron radiation. |
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Post by RiftandRend on Jun 3, 2017 7:54:02 GMT
I made a fusion ship that's fairly realistic. The engine does use graphene, but only in single atom thick layers Why Deuterium-Tritium? You'll face some horrible amount of neutron radiation. Because it takes much less energy to ignite and has an enormous cross section? The neutron radiation isn't all that bad, 2 meters of boron completely protect the crew module. |
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Post by The Astronomer on Jun 3, 2017 7:57:46 GMT
Why Deuterium-Tritium? You'll face some horrible amount of neutron radiation. Because it takes much less energy to ignite and has an enormous cross section? The neutron radiation isn't all that bad, 2 meters of boron completely protect the crew module. I wonder why nobody else ever think about D+T, then... ._. Is it because of that 12 years of half-life? |
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Post by RiftandRend on Jun 3, 2017 8:16:35 GMT
Because it takes much less energy to ignite and has an enormous cross section? The neutron radiation isn't all that bad, 2 meters of boron completely protect the crew module. , then... ._. Is it because of that 12 years of half-life? What. D-T fusion is practically the only type of fusion being realistically considered for any practical application, with p-B11 in a far, far second. |
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Post by bigbombr on Jun 3, 2017 8:17:22 GMT
Because it takes much less energy to ignite and has an enormous cross section? The neutron radiation isn't all that bad, 2 meters of boron completely protect the crew module. I wonder why nobody else ever think about D+T, then... ._. Is it because of that 12 years of half-life? Neutron activation and neutron embrittlement I presume. Neither are modeled in CoaDE. |
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Post by The Astronomer on Jun 3, 2017 8:21:05 GMT
I wonder why nobody else ever think about D+T, then... ._. Is it because of that 12 years of half-life? , with p-B11 in a far, far second. You've got to be kidding me. D+T fusion is only used in nuclear warheads, while D+He-3 is considered one of the most promising power source of the world. Research more. |
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Post by RiftandRend on Jun 3, 2017 8:51:03 GMT
What. D-T fusion is practically the only type of fusion being realistically considered for any practical application, with p-B11 in a far, far second. You've got to be kidding me. D+T fusion is only used in nuclear warheads, while D+He-3 is considered one of the most promising power source of the world. Research more. My apologies, I was vague and somewhat rude. By practical application I meant current, modern, applications. D+ 3He Fusion is alright on paper, but has some significant issues. It requires a higher temperature and 3He is impossibly rare. You would have to process several million tons of lunar soil or gas giant atmosphere to acquire enough for large scale power production. Additionally, it is not totally aneutronic due to D+D side reactions. Because of this, it is usually ignored in favor of the somewhat more difficult p+ 11B fusion. D+T fusion is far easier to achieve and the reactants are vastly more plentiful. The rarest reactant, tritium can be bred by encasing the reactor in lithium to take advantage of n+ 6Li>T+He and n- 7Li>T+He+n fusion. |
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Post by The Astronomer on Jun 3, 2017 9:00:14 GMT
You've got to be kidding me. D+T fusion is only used in nuclear warheads, while D+He-3 is considered one of the most promising power source of the world. Research more. My apologies, I was vague and somewhat rude. By practical application I meant current, modern, applications. D+ 3He Fusion is alright on paper, but has some significant issues. It requires a higher temperature and 3He is impossibly rare. You would have to process several million tons of lunar soil or gas giant atmosphere to acquire enough for large scale power production. Additionally, it is not totally aneutronic due to D+D side reactions. Because of this, it is usually ignored in favor of the somewhat more difficult p+ 11B fusion. D+T fusion is far easier to achieve and the reactants are vastly more plentiful. The rarest reactant, tritium can be bred by encasing the reactor in lithium to take advantage of n+ 6Li>T+He and n- 7Li>T+He+n fusion. Where will you find all those Li-6 required, then? |
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Post by RiftandRend on Jun 3, 2017 9:08:21 GMT
My apologies, I was vague and somewhat rude. By practical application I meant current, modern, applications. D+ 3He Fusion is alright on paper, but has some significant issues. It requires a higher temperature and 3He is impossibly rare. You would have to process several million tons of lunar soil or gas giant atmosphere to acquire enough for large scale power production. Additionally, it is not totally aneutronic due to D+D side reactions. Because of this, it is usually ignored in favor of the somewhat more difficult p+ 11B fusion. D+T fusion is far easier to achieve and the reactants are vastly more plentiful. The rarest reactant, tritium can be bred by encasing the reactor in lithium to take advantage of n+ 6Li>T+He and n-7Li>T+He+n fusion. Where will you find all those Li-6 required, then? As I stated, 7Li works as well. |
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Post by samchiu2000 on Jun 3, 2017 9:14:02 GMT
My apologies, I was vague and somewhat rude. By practical application I meant current, modern, applications. D+ 3He Fusion is alright on paper, but has some significant issues. It requires a higher temperature and 3He is impossibly rare. You would have to process several million tons of lunar soil or gas giant atmosphere to acquire enough for large scale power production. Additionally, it is not totally aneutronic due to D+D side reactions. Because of this, it is usually ignored in favor of the somewhat more difficult p+ 11B fusion. D+T fusion is far easier to achieve and the reactants are vastly more plentiful. The rarest reactant, tritium can be bred by encasing the reactor in lithium to take advantage of n+ 6Li>T+He and n- 7Li>T+He+n fusion. Where will you find all those Li-6 required, then? Ocean. Google for more details |
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.... and now its around 10 GWs , the power plant is one of yours btw....
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