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Post by newageofpower on Feb 13, 2017 0:47:06 GMT
So please, do some calculations before you get on your high horse. Nah, my horse is plenty comfy, and I've done interplanetary orbital transfers with worse accelerations (some of my first MPD attempts come to mind). You'd never build the thing in a deep Hill Sphere, which, by definition, is almost certainly under surveillance/observation. Duh. Leaving parking orbit from an orbital shipyard around some miniscule, godforsaken asteroid is perfectly reasonable with that kind of acceleration.
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Post by bdcarrillo on Feb 13, 2017 4:25:23 GMT
Well I think we now see that some level of stealth is feasible, and flinging cargo containers or unmanned cargo ships are viable as well.
I think we really need background information on the sensors used in game to arrive at any real conclusion on how hard it would be to detect the hypothetical hydrogen steamer.
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Post by shiolle on Feb 13, 2017 5:41:59 GMT
Nah, my horse is plenty comfy, and I've done interplanetary orbital transfers with worse accelerations (some of my first MPD attempts come to mind). You'd never build the thing in a deep Hill Sphere, which, by definition, is almost certainly under surveillance/observation. Duh. Leaving parking orbit from an orbital shipyard around some miniscule, godforsaken asteroid is perfectly reasonable with that kind of acceleration. So we agree then that the original mission described in the article you linked is impossible? I doubt your freighters had only 6km/s of delta-v at the same time. And now, since you've got such a comfy horse, could you please follow your own advice and give me a new design that accounts for the new fuel requirements. That godforsaken asteroid becomes the center of attention the moment you start building something there. "Why are so many transports going to that rock?" That's the question all intelligence analysts are going to ask. Remember that these 'stealth' ships stand out against any body in the solar system, including that godforsaken rock. If we can detect a 0.1% dimming in the spectrum of a star, I'm sure we can detect the dimming caused by 2.4 km long ship passing in front of an asteroid. So, they are not that hard to detect on either end of their journey and placing them around a remote asteroid is not going to help you. I still don't think these ships are superior to a plain civilian freighter loaded with the same weapons payload for the same nasty surprise. Especially given the pains one needs to go through to construct and maintain them.
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Post by newageofpower on Feb 13, 2017 6:09:19 GMT
So we agree then that the original mission described in the article you linked is impossible? No, we do not agree. That godforsaken asteroid becomes the center of attention the moment you start building something there. "Why are so many transports going to that rock?" That's the question all intelligence analysts are going to ask. Remember that these 'stealth' ships stand out against any body in the solar system, including that godforsaken rock. To be honest, this differs based on what tech levels we assume. CoADE implies that we have sub-nanometer precision for mass produced parts from anywhere between micrograms and kilotons; if we can assume extremely flexible industrial technology with low minimum intensity thresholds, then producing a Hydrogen Steamer from a godforsaken asteroid need not require shipments, whether stealthed or not. Of course, that would enable the cheap manufacture of precision sensors... Hm. I may have to change this bit. Obviously the background body transit detection problem exists (and was acknowledged in the original link), but if we suppose that no single faction has control over more than a minority of critical Hill Spheres, and that sensor coverage is limited to controlled zones, then the probability of any sensor seeing the steamer transit a body is very, very low; probably within an order of magnitude of sensor bugs. It is only when the Steamer is (relatively) close to both a background body and said sensor that detection becomes probable rather than possible.
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Post by shiolle on Feb 13, 2017 7:29:04 GMT
The ship in that article is designed around a specific mission. If it cannot do a Hohmann transfer, you need a different ship. I actually made this steamer ship in CoaDE to test things, but now I need to mod the campaign to model the mission too, and I had some problems with that. To be honest, this differs based on what tech levels we assume. CoADE implies that we have sub-nanometer precision for mass produced parts from anywhere between micrograms and kilotons; if we can assume extremely flexible industrial technology with low minimum intensity thresholds, then producing a Hydrogen Steamer from a godforsaken asteroid need not require shipments, whether stealthed or not. Of course, that would enable the cheap manufacture of precision sensors... Hm. I may have to change this bit. Well, if I understand you correctly the shipyard is not stealthy, nor will ISRU operation be stealthy. So it doesn't matter whether you use one mission to deploy all the infrastructure or make regular shipments. Obviously the background body transit detection problem exists (and was acknowledged in the original link), but if we suppose that no single faction has control over more than a minority of critical Hill Spheres, and that sensor coverage is limited to controlled zones, then the probability of any sensor seeing the steamer transit a body is very, very low; probably within an order of magnitude of sensor bugs. It is only when the Steamer is (relatively) close to both a background body and said sensor that detection becomes probable rather than possible. I would say this problem was glossed over in the original article. The steamer is orbiting that body. It will cross the disc of the asteroid of the planet on every orbit from most angles. Why can't a telescope around Earth observe, say, a Martian trojan asteroid? With three telescopes: one in orbit of Earth, one at Earth-Sun L4 and one at L5 you won't be able to select an orbit that wouldn't cross the disc from the point of view of all three. The same is true when the ship approaches Earth, and it becomes a worse problem for the stealth ship by a few orders of magnitude.
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Post by The Astronomer on Feb 13, 2017 7:45:49 GMT
The ship in that article is designed around a specific mission. If it cannot do a Hohmann transfer, you need a different ship. I actually made this steamer ship in CoaDE to test things, but now I need to mod the campaign to model the mission too, and I had some problems with that. I'd like to invite you to our team
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Post by Enderminion on Feb 13, 2017 12:31:37 GMT
If my hypothectical space empire were to find a steamer I would test a nuclear weapon nearby (within kill radius) and claim I never saw it, thus reducing your investment to nothing.
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Post by newageofpower on Feb 13, 2017 15:57:29 GMT
Well, if I understand you correctly the shipyard is not stealthy, nor will ISRU operation be stealthy. So it doesn't matter whether you use one mission to deploy all the infrastructure or make regular shipments. Obviously the background body transit detection problem exists (and was acknowledged in the original link), but if we suppose that no single faction has control over more than a minority of critical Hill Spheres, and that sensor coverage is limited to controlled zones, then the probability of any sensor seeing the steamer transit a body is very, very low; probably within an order of magnitude of sensor bugs. It is only when the Steamer is (relatively) close to both a background body and said sensor that detection becomes probable rather than possible. I would say this problem was glossed over in the original article. The steamer is orbiting that body. It will cross the disc of the asteroid of the planet on every orbit from most angles. Why can't a telescope around Earth observe, say, a Martian trojan asteroid? With three telescopes: one in orbit of Earth, one at Earth-Sun L4 and one at L5 you won't be able to select an orbit that wouldn't cross the disc from the point of view of all three. The same is true when the ship approaches Earth, and it becomes a worse problem for the stealth ship by a few orders of magnitude. Firstly, it is clear that we have differing views on any potential future political situation. In my mind, a CoADE like future will be filled with many independent colonist groups, each attempting to create their own utopian society. As a result, there are countless miniature polities around countless minor bodies, all generating industrial heat, many with their own shipyard complexes. While stealth is complicated in such a situation, this also creates vast amounts of sensor noise. Secondly, an orbital construction site need not pass in 'front' of an given astronomical objct and Earth; given usage of Langrage points a steamer's construction site could very well sit on the opposite side of a body vs Earth. Next, an out-of-plane trajectory can massively reduce chances of sensor occlusion against objects in the Solar System, to the point where it becomes negligible. Such manouvers have their own issues, but further enhance stealth. If my hypothectical space empire were to find a steamer I would test a nuclear weapon nearby (within kill radius) and claim I never saw it, thus reducing your investment to nothing. That is actually a good response. Of course, this might escalate into open warfare, but better open war than a bunch of stealthships ready to unload into your capital.
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Post by theholyinquisition on Feb 13, 2017 15:57:59 GMT
Of course, that would enable the cheap manufacture of precision sensors... Hm. I may have to change this bit. ... and that sensor coverage is limited to controlled zones... Considering the recent trend towards cube- and nano-sats, and the very stealth tech that the hydrogen steamer uses, massive networks of stealth sensors becomes a possibility.
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Post by Easy on Feb 13, 2017 16:26:54 GMT
Of course, that would enable the cheap manufacture of precision sensors... Hm. I may have to change this bit. ... and that sensor coverage is limited to controlled zones... Considering the recent trend towards cube- and nano-sats, and the very stealth tech that the hydrogen steamer uses, massive networks of stealth sensors becomes a possibility. As sensors and data sets expand exponentially we rely more on algorithms and computers to filter out the noise and unimportant information. Which means you could detect the stealth ship and track it, but misinterpret and no human will ever consider or even be aware. Consider Pearl Harbour where the Japanese attack squadrons were detected on radar and not given enough attention or alarm by the operator. Even September 11, 2001 where hijacking procedures were in place and trained by personal. But when it happened the controllers were slow to implement the emergency procedures. The stealthship might be detected in transit by a sensor, the sensor throws a notification logged by the computer and it goes into the box of "that was weird" that a human will never review. Even if a human does review it is just another anomaly among thousands and has no more significance. Because how would you really know it wasn't some random space junk or a glitch.
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Post by ross128 on Feb 13, 2017 17:32:17 GMT
The main problem I see with the much-vaunted "hydrogen steamer" is that it's not a practical rocket. Although the article claims 8km/s of exhaust velocity (with no math to back it up), I find it extremely unlikely that such a velocity can actually be achieved without a correspondingly high exhaust temperature. They claim to solve this problem by using an extremely large nozzle to give the gas room to expand and cool before leaving the craft, but all that achieves is giving you a white-hot nozzle the same size as what your exhaust plume would have been.
After all, expanding and cooling is exactly what the gas would have done *after* leaving the nozzle anyway. Covering the necessary expansion volume with the nozzle only shifts the problem from a 3000K exhaust plume to a 3000K nozzle, one way or another you're going to have to radiate that heat eventually. It stands to reason that either the hydrogen steamer isn't actually as stealthy as advertised during a burn, or its exhaust velocity isn't nearly as high as advertised.
And that's besides the fact that a significant factor in detection is time. Even with the best stealth imaginable the question usually isn't *if* you get detected, but *when*. If you're going to need several months of burning to initiate a transfer and several more months of burning to complete an insertion, that's a huge window where you can get caught up in an asteroid-monitoring sweep while your engines are on.
And after all that, even if it's lucky enough to evade detection for all the years it will take to get to its destination, the war might be over by the time it arrives because the side with conventional ships has already attacked and won.
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Post by shiolle on Feb 13, 2017 18:10:26 GMT
Firstly, it is clear that we have differing views on any potential future political situation. In my mind, a CoADE like future will be filled with many independent colonist groups, each attempting to create their own utopian society. As a result, there are countless miniature polities around countless minor bodies, all generating industrial heat, many with their own shipyard complexes. While stealth is complicated in such a situation, this also creates vast amounts of sensor noise. Secondly, an orbital construction site need not pass in 'front' of an given astronomical objct and Earth; given usage of Langrage points a steamer's construction site could very well sit on the opposite side of a body vs Earth. I agree that a hydrogen steamer is least vulnerable during transit, that's why my arguments were focused around detecting it before or at launch or at its destination. I also agree that out of plane trajectories will make it even less vulnerable in transit, but they require more delta-v and more time still to perform those maneuvers. I think that if the Solar System is as colonized as you imagine, Lagrange points are actually the worst places to hide anything and many of them will see a significant traffic. Unlike the infinite number of similar trajectories there are only so many of these points. I would like to remind you how this discussion progressed: - The departure is not stealthy.
- It can be.
- The acceleration is too small.
- So we will use asteroids to build the stealth ships.
- But the asteroids make detecting those ships easier and building the shipyard will attract attention.
- We will use IRSU and advanced manufacturing method to get rid of transport ships.
- But that can't be stealthy and stealth ships will still occulude the asteroid.
- We will use Lagrange points.
And we get back to needing regular transport ships because there are no free natural resources at Lagrange points. Also, the relative vulnerability of the hydrogen steamer during the long months while it performs its maneuvers around Earth still remains the elephant in the room. A separate note on small societies. Actually, I think such environment makes detecting secret military installations easier. There can't bee too many of those small societies you cannot physically keep tabs on them because establishing space habitats requires significant initial investment. There will probably at most a few thousands of those. Each of that societies need to communicate and trade (because they are small by definition and cannot build everything they need). So, any industrial level heat signature that does little to no communication, serviced by the government without much publicity, or have disproportionate production capacity compared to what they sell, is worth investigating. The stealthship might be detected in transit by a sensor, the sensor throws a notification logged by the computer and it goes into the box of "that was weird" that a human will never review. Even if a human does review it is just another anomaly among thousands and has no more significance. Because how would you really know it wasn't some random space junk or a glitch. "That was weird" does not have to go through unreliable human. We are not in the forties. Anomaly verification can be automated too until the proof of something being there that wants to hide is definitive. I think you underestimate the capabilities of big data analysis. Humanity only begins to grasp what is possible; we collect a lot of data but no one is using it to full potential, not even the dreaded NSA. Does that mean that every stealth ship will be detected at once? No, I don't think so. Does that mean that you can rely on a fleet of stealth ships (crewed ships if we believe the article about hydrogen steamer) to launch an unstoppable first strike? I don't think you can either.
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Post by Enderminion on Feb 13, 2017 19:23:37 GMT
If my hypothectical space empire were to find a steamer I would test a nuclear weapon nearby (within kill radius) and claim I never saw it, thus reducing your investment to nothing. That is actually a good response. Of course, this might escalate into open warfare, but better open war than a bunch of stealthships ready to unload into your capital. Why you can't prove I knew the steamer was there?
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Post by shiolle on Feb 13, 2017 20:15:08 GMT
The main problem I see with the much-vaunted "hydrogen steamer" is that it's not a practical rocket. Although the article claims 8km/s of exhaust velocity (with no math to back it up), I find it extremely unlikely that such a velocity can actually be achieved without a correspondingly high exhaust temperature. They claim to solve this problem by using an extremely large nozzle to give the gas room to expand and cool before leaving the craft, but all that achieves is giving you a white-hot nozzle the same size as what your exhaust plume would have been. After all, expanding and cooling is exactly what the gas would have done *after* leaving the nozzle anyway. Covering the necessary expansion volume with the nozzle only shifts the problem from a 3000K exhaust plume to a 3000K nozzle, one way or another you're going to have to radiate that heat eventually. It stands to reason that either the hydrogen steamer isn't actually as stealthy as advertised during a burn, or its exhaust velocity isn't nearly as high as advertised. And that's besides the fact that a significant factor in detection is time. Even with the best stealth imaginable the question usually isn't *if* you get detected, but *when*. If you're going to need several months of burning to initiate a transfer and several more months of burning to complete an insertion, that's a huge window where you can get caught up in an asteroid-monitoring sweep while your engines are on. And after all that, even if it's lucky enough to evade detection for all the years it will take to get to its destination, the war might be over by the time it arrives because the side with conventional ships has already attacked and won. I agree with this, and that is what I referred to when I said previously that there is something fishy going on with the cooling system in the ship. Yet, I still need to get around to doing these calculations. Just a few points which I can present now for your consideration: - The ship relies on cooling by evaporating hydrogen. This hydrogen needs to be pumped through the whole ship. If you don't your bubbles of boiling hydrogen won't get anywhere, they will remain where they originated spreading heat around and creating hot spots you want to avoid. I very much doubt that it takes only two kw to move all that hydrogen around through piping and gas separators and provide power for the crew module and on-board systems like the author claims.
- I don't understand where the author gets that 8km/s of exhaust velocity, he just says that by heating hydrogen to 3000K exhaust velocity can reach 8km/s. If you were wondering, you can find the formula for exhaust velocity here (equation 1.22). We don't know all the variables though, like pressure in the furnace. However, it is quite obvious that the engine is 100% efficient in the article (I mean the lenses and the furnace). All sunlight that strikes the lenses get into the furnace. There are no internal reflection and no heating of the lenses. All energy that got into the furnace is used o heat hydrogen. The walls don't store a single watt. I guess that the author figured that all the boiled hydrogen that was used to cool the components of the system will get dumped into the furnace anyway and then...
- Well, as you correctly point out the second law of thermodynamics says heat cannot be destroyed, only moved around. So if the hydrogen exhaust is cooled to 22K, all the heat is moved to the nozzle and since the nozzle is cooled it gets dumped into the remaining hydrogen. The problem is clear now: since your hydrogen reserve is dwindling and the amount of heat you need to store is ever increasing at some point you will have all your hydrogen boiled off, but you still haven't spent it all for thrust and your ship is getting above 22K since you no longer have anything colder than that. The former has to occur before the latter or you will break thermodynamics, but how much hydrogen you will have spent for thrust by then is worth calculating. And don't forget the heat from other sources like on-board nuclear reactor and habitat is stored into the hydrogen as well.
In other words, the whole concept can be rephrased as "the ship uses its remaining propellant as a heat sink". There is nothing more to it.
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Post by Easy on Feb 13, 2017 21:11:12 GMT
The main problem I see with the much-vaunted "hydrogen steamer" is that it's not a practical rocket. Although the article claims 8km/s of exhaust velocity (with no math to back it up), I find it extremely unlikely that such a velocity can actually be achieved without a correspondingly high exhaust temperature. They claim to solve this problem by using an extremely large nozzle to give the gas room to expand and cool before leaving the craft, but all that achieves is giving you a white-hot nozzle the same size as what your exhaust plume would have been. After all, expanding and cooling is exactly what the gas would have done *after* leaving the nozzle anyway. Covering the necessary expansion volume with the nozzle only shifts the problem from a 3000K exhaust plume to a 3000K nozzle, one way or another you're going to have to radiate that heat eventually. It stands to reason that either the hydrogen steamer isn't actually as stealthy as advertised during a burn, or its exhaust velocity isn't nearly as high as advertised. And that's besides the fact that a significant factor in detection is time. Even with the best stealth imaginable the question usually isn't *if* you get detected, but *when*. If you're going to need several months of burning to initiate a transfer and several more months of burning to complete an insertion, that's a huge window where you can get caught up in an asteroid-monitoring sweep while your engines are on. And after all that, even if it's lucky enough to evade detection for all the years it will take to get to its destination, the war might be over by the time it arrives because the side with conventional ships has already attacked and won. I agree with this, and that is what I referred to when I said previously that there is something fishy going on with the cooling system in the ship. Yet, I still need to get around to doing these calculations. Just a few points which I can present now for your consideration: - The ship relies on cooling by evaporating hydrogen. This hydrogen needs to be pumped through the whole ship. If you don't your bubbles of boiling hydrogen won't get anywhere, they will remain where they originated spreading heat around and creating hot spots you want to avoid. I very much doubt that it takes only two kw to move all that hydrogen around through piping and gas separators and provide power for the crew module and on-board systems like the author claims.
- I don't understand where the author gets that 8km/s of exhaust velocity, he just says that by heating hydrogen to 3000K exhaust velocity can reach 8km/s. If you were wondering, you can find the formula for exhaust velocity here (equation 1.22). We don't know all the variables though, like pressure in the furnace. However, it is quite obvious that the engine is 100% efficient in the article (I mean the lenses and the furnace). All sunlight that strikes the lenses get into the furnace. There are no internal reflection and no heating of the lenses. All energy that got into the furnace is used o heat hydrogen. The walls don't store a single watt. I guess that the author figured that all the boiled hydrogen that was used to cool the components of the system will get dumped into the furnace anyway and then...
- Well, as you correctly point out the second law of thermodynamics says heat cannot be destroyed, only moved around. So if the hydrogen exhaust is cooled to 22K, all the heat is moved to the nozzle and since the nozzle is cooled it gets dumped into the remaining hydrogen. The problem is clear now: since your hydrogen reserve is dwindling and the amount of heat you need to store is ever increasing at some point you will have all your hydrogen boiled off, but you still haven't spent it all for thrust and your ship is getting above 22K since you no longer have anything colder than that. The former has to occur before the latter or you will break thermodynamics, but how much hydrogen you will have spent for thrust by then is worth calculating. And don't forget the heat from other sources like on-board nuclear reactor and habitat is stored into the hydrogen as well.
In other words, the whole concept can be rephrased as "the ship uses its remaining propellant as a heat sink". There is nothing more to it. 1. You are correct the cooling system is nontrivial and must be powered by a pumping system, the entire hull is similar in complexity to a cooled rocket nozzle. The ship is cooled by the transition from liquid to gas. 2. The heat source is irrelevant and the Fresnel lens unnecessary. A nuclear heatsource could be substituted, assuming it can handle the high temperature. 3. The rocket nozzle is isobaric in operation. Much like a CO2 or Air Tank will get very cold when discharged quickly. The nozzle doesn't need to accept anything but incidental radiant heat during the process. The nozzle and engine must be insulated from the rest of the craft and actively cooled externally for obvious reasons.
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