acatalepsy
Junior Member
Not Currently In Space
Posts: 97 
|
Post by acatalepsy on Oct 4, 2016 18:46:07 GMT
Wikipedia defines in-situ resource utilization thusly: In a trivial sense, ISRU has been achieved by the time of Children of a Dead Earth; after all, no materials are being brought from Earth. But ISRU for military expeditions seems like a key factor; the ability to recover usable supplies from hostile territory seems like a critical part of forward logistics. This will be the responsibility of the logistics fleets, coming hours or days behind the combat spacecraft, and part of their biggest job will be to find some way of extracting usable propellant - and thus delta-V for the combat fleet. Methane and Hydrogen are easy enough to come by; hydrogen can be electrolyzed from water, carbon can be found pretty much anywhere (including human exhalation), and between them various chemical processes such as the Sabatier reaction can be used to produce the desired reactants. And water can be found a number of places. Other options are to harvest methane directly from a body that contains it, principally Titan, or the atmosphere of Neptune. What fuels can be extracted easily, and whether or not mobile logistics bases can be defended in the face of aggression, seems to be a major factor in determining the flow of an interplanetary war. Other fuels may be harder to come by. Deuterium can be produced in a nuclear reactor, and possibly combined with regular hydrogen to produce hydrogen deuteride; whether or not this reactor is feasible to lug around the solar system to produce HD fuel is in my mind a big factor in determining whether or not HD fuel is viable as a primary fuel source for a fleet. Thoughts on ISRU in Children of a Dead Earth? |
|
|
|
Post by beta on Oct 4, 2016 18:57:50 GMT
Remember that most of these solar bodies you are talking about are already colonized .. heavily in many cases (200 million people on Mars for example).
So, rather than landing in someone's "backyard" and starting to pump methane, you would more likely create some sort of deal to be supplied your resource of choice. Taking resources by force would be another option, but that opens an entirely new problem of the solar bodies not being just pretty backgrounds and having potentially hostile or friendly elements (or both) that can and will affect your interactions with them.
|
|
acatalepsy
Junior Member
Not Currently In Space
Posts: 97
|
Post by acatalepsy on Oct 4, 2016 19:24:21 GMT
Remember that most of these solar bodies you are talking about are already colonized .. heavily in many cases (200 million people on Mars for example). I think the issue with that is that no enemy is going to leave ISRU infrastructure intact for you to use if they can help it, and with months or even years of warning, they generally can help it. And with potentially years before reinforcements arrive, if you want to be able to rely on ISRU, you need to bring your own. I think the question is really whether there's that level of stability to combat that bringing in processing is a better alternative than just bringing a tanker. |
|
|
|
Post by pokington on Oct 4, 2016 19:28:51 GMT
I think the issue with that is that no enemy is going to leave ISRU infrastructure intact for you to use if they can help it, and with months or even years of warning, they generally can help it. And with potentially years before reinforcements arrive, if you want to be able to rely on ISRU, you need to bring your own. I think the question is really whether there's that level of stability to combat that bringing in processing is a better alternative than just bringing a tanker. On some level, it depends on what's cheaper. On the other, if you lose the fight, your tankers and/or refining equipment are now property of the enemy. |
|
acatalepsy
Junior Member
Not Currently In Space
Posts: 97
|
Post by acatalepsy on Oct 4, 2016 19:50:21 GMT
On some level, it depends on what's cheaper. On the other, if you lose the fight, your tankers and/or refining equipment are now property of the enemy. Well, tankers would be able to at least abort the orbit and maneuver for friendly space; not fun, but they're not going to be captured. In some ways this gets into the heart of a problem of CoaDE; spacecraft in CoaDE exist largely to fight each other. Whether or not it's even viable for defending spacecraft to simply decline an engagement - or whether a hostile fleet taking up orbit over a world can force its surrender, or whether or not those defending spacecraft will be forced to defend vital space installations - shipyards, habitats, skyhooks, etc - are very unanswered. CoaDE assumes that you have two limits - credits, and mass, and that you can't go over either. But is that a good approximation? What does an "extended campaign" in hostile territory entail? More directly technically - do you think it's possible to produce deuterium (for fusion, and more importantly for our purposes hydrogen deuteride, which is amazing stuff for NTR propellant) on site? Given how nuclear reactor happy these spacecraft are, it seems possible, but I don't know what that would look like. |
|
|
|
Post by Autochton on Oct 4, 2016 20:46:23 GMT
I think the issue with that is that no enemy is going to leave ISRU infrastructure intact for you to use if they can help it, and with months or even years of warning, they generally can help it. That sounds like a level of burnt earth that is... somewhat counterproductive. Most of the products needed as fleet consumables are going to also be needed for civilian infrastructure, things like fuel and remass, victuals, water, air, etc. People are going to have a real low sense of humor about their military messing with those. Beltalowda owkwa, beltalowda ereluf, kopeng. |
|
|
|
Post by beta on Oct 4, 2016 20:55:58 GMT
Scorched earth policy for a war that is undeclared. Might be hard to swing that one.
|
|
acatalepsy
Junior Member
Not Currently In Space
Posts: 97
|
Post by acatalepsy on Oct 4, 2016 21:14:58 GMT
That sounds like a level of burnt earth that is... somewhat counterproductive. Most of the products needed as fleet consumables are going to also be needed for civilian infrastructure, things like fuel and remass, victuals, water, air, etc. People are going to have a real low sense of humor about their military messing with those. Scorched earth policy for a war that is undeclared. Might be hard to swing that one. What undeclared war? Like, if you have combat spacecraft slinging nuclear missiles at each other, it's on, and if your unofficial official policy is "war crimes are okay as long as we win" and "lets plan on raining nuclear death on our enemies until they unconditionally surrender and make ourselves lords of the solar system for all time", you have to figure that your opponent is not going to be keen on giving you any advantage, even if it hurts a great deal. At the very least, you cannot rely on such, because if you do and it turns out your enemy is in fact willing to play scorched earth, you are, in a word, screwed. So you need a plan B, and that plan be can be bringing enough infrastructure to start living off the land, or have home sending sufficient tankers and reinforcements to continue combat operations in the face of opposition. |
|
|
|
Post by RA2lover on Oct 5, 2016 2:45:13 GMT
You still need to figure out where you're going to extract resources from. Asteroids are far enough apart to make transportation of resources between them unfeasible in military timescales, and not every asteroid is going to have everything necessary.
|
|
|
|
Post by boomertiro on Oct 5, 2016 3:01:48 GMT
But a good chunk of the campaign is undeclared war. Though there is a difference between the narrative of the campaign and the possible realities, and the truth is any technology that can exist should exist since that's the real point behind CoaDE anyway. Full scale war and every form of not really war with the smaller powers involved for the sake of being able to justify any scenario.
Honestly what's stopping powers from intercepting comets? Comets could give huge advantages when caught by the right people at the right time. There are entire worlds of possibilities not quite being taken advantage of.
|
|
|
|
Post by aetreus on Oct 5, 2016 6:17:13 GMT
Deuterium isn't uncommon, it makes up about 0.02% of the hydrogen here on earth, and occurs at a similar rate on comets. There's less of it in the gas giants or the sun, but the other terrestrial planets have decent concentrations as well. Processing the thousands of tons of water(easily accessible sources are mostly water) isn't going to be super cheap, but if there's a big market I don't think that deuterium would rank among the most expensive or rare materials.
|
|
|
|
Post by argonbalt on Oct 5, 2016 16:11:59 GMT
Can ISRU be used in aerobraking? Like for example, an attacking fleet aerobrakes into orbit around Uranus, then utilising a ram scoop picks up methane from the atmosphere, while also slowing down. Would this be effective? I can see this as a huge boost for the current model of ideal Methane for fighting/Hydrogen for moving model of ship design. Like for instance(depending on the efficiency and engines available) the following situation occurs:  1 A ship inserts into the Uranus sphere, 2 It uses Hydrogen for the main trip 3 It Aerobrakes and switches out the H for CH4 colleting it with a ram scoop 4 It switches to CH4 NTR and moves out of close orbit to fight 5 fighting I see this as an interesting work around for the engine debate, though it could be improved by several major adjustments in the design: A) A universal fuel tank rated to both hold hydrogen and Methane B) A sabre like conjoined engine that can use both H and CH4 as propellants, or switch between them. This system would eliminate the need to hold drop tanks at all as the ideal fuel is waiting there for pick up, likewise the disadvantage of the extra secondary engine weight is balanced out by not needing to carry the heavy propellant. |
|
|
|
Post by beta on Oct 5, 2016 17:24:41 GMT
The number of orbits you would have to make would likely be much higher than 1 to get an appreciable amount of reaction mass.
|
|
|
|
Post by argonbalt on Oct 5, 2016 17:56:58 GMT
Please to not take the serious science diagram too seriously.
|
|
|
|
Post by blothorn on Oct 5, 2016 20:10:08 GMT
Note that aerobraking is usually done in very high atmosphere--if you dip deep you will lose too much velocity to get back out. Very thin atmosphere (the accessible portions of which are superheated plasma due to the passage of a spacecraft at very high velocity) does not seem promising for large-scale collection.
|
|
