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Post by Enderminion on Jun 25, 2017 17:14:23 GMT
NSWRs FTW
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Post by bigbombr on Jun 25, 2017 17:27:35 GMT
Rocketry is already risky enough without turning your spaceship in a nucleair bomb as soon as someone sneezes on it. Performance is impressive, but cost and safety are problematic. If you truly wish to make large scale space travel routine, spaceflight has to become both cheap and safe.
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Post by Enderminion on Jun 25, 2017 17:32:52 GMT
Rocketry is already risky enough without turning your spaceship in a nuclear bomb as soon as someone sneezes on it. Performance is impressive, but cost and safety are problematic. If you truly wish to make large scale space travel routine, spaceflight has to become both cheap and safe. life's too short to worry about that
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Post by princesskibble on Jun 25, 2017 19:06:56 GMT
I'm a chemical rocket girl lol :3 They do everything, and if you have propellant depot infrastructure, they go everywhere! No expensive radiation toxic powerplants or enormous solar panels needed! Getting to orbit is expensive though, and they take forever to get anywhere. Laserlaunch or lofstromloops to get to LEO, laserthermal or resistojets to get out of the gravity well, and MPDT's for inter body travel. You need more thrust than a resistojet to get out of the gravity well, otherwise your stuck spiraling thru a deadly band of radiation! I think no matter what, Hohmann orbits are going to be used for interplanetary travel for a long time. Nobody wants to be stuck on an orbit careening out of the solar system! With propellant depots that makes efficient but theoretical engines like MPDTs superfluous. We have a hundred years of experience with chemical rockets <3 Its like terraforming - by the time we have the technology to do something like that, we don't need it!
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Post by bigbombr on Jun 25, 2017 19:23:16 GMT
Getting to orbit is expensive though, and they take forever to get anywhere. Laserlaunch or lofstromloops to get to LEO, laserthermal or resistojets to get out of the gravity well, and MPDT's for inter body travel. You need more thrust than a resistojet to get out of the gravity well, otherwise your stuck spiraling thru a deadly band of radiation! I think no matter what, Hohmann orbits are going to be used for interplanetary travel for a long time. Nobody wants to be stuck on an orbit careening out of the solar system! With propellant depots that makes efficient but theoretical engines like MPDTs superfluous. We have a hundred years of experience with chemical rockets <3 Its like terraforming - by the time we have the technology to do something like that, we don't need it! MPDT's are not theoretical. And terraforming is not only hard, it's simply a less efficient use of mass than O'Neill cilinders. Spaceships are expensive, so you want them to make their trips quickly, so you can earn back your investment swiftly. You'd also want to limit the radiation exposure of your crew and passengers. People also prefer being stuck in tin cans for as short an amount of time as possible. Therefore, there are economic, health and comfort reasons for using high specific impulse drives (like MPDT's or Hall effect thrusters). And resistojets might not have the thrust to take off from the surface of the Earth, they have plenty of thrust to get out of a gravity well if you give them sufficient power. A 1 GW methane resistojet can have more than 3.41 MN of thrust.
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Post by bigbombr on Jun 25, 2017 19:23:48 GMT
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Post by EshaNas on Jun 25, 2017 22:40:08 GMT
You need more thrust than a resistojet to get out of the gravity well, otherwise your stuck spiraling thru a deadly band of radiation! I think no matter what, Hohmann orbits are going to be used for interplanetary travel for a long time. Nobody wants to be stuck on an orbit careening out of the solar system! With propellant depots that makes efficient but theoretical engines like MPDTs superfluous. We have a hundred years of experience with chemical rockets <3 Its like terraforming - by the time we have the technology to do something like that, we don't need it! MPDT's are not theoretical. And terraforming is not only hard, it's simply a less efficient use of mass than O'Neill cilinders. Spaceships are expensive, so you want them to make their trips quickly, so you can earn back your investment swiftly. You'd also want to limit the radiation exposure of your crew and passengers. People also prefer being stuck in tin cans for as short an amount of time as possible. Therefore, there are economic, health and comfort reasons for using high specific impulse drives (like MPDT's or Hall effect thrusters). And resistojets might not have the thrust to take off from the surface of the Earth, they have plenty of thrust to get out of a gravity well if you give them sufficient power. A 1 GW methane resistojet can have more than 3.41 MN of thrust. So you recognize that people don't want to be stuck in tin cans...and then say that it's more efficient in the long term on a thread of making humanity multiplanetary for people to live their whole lives in floating tin cans. Maybe some would prefer that, but I'm sure enough would be 'dirtside' to not care about the 'inefficiency'. Definitions like 'hard', 'efficient', and 'expensive' also change drastically with levels of spatial infrastructure, advances in technology, and even levels of government. A hyper-libertarian society chugging around with corporate or even personal rockets most likely wouldn't see terraformed worlds, but a mixed-economy hyperpower or even a collectivist union might at least try with their collective resources and capabilities, even just to the 'Okay, we can walk around without gear for a few thousand years and have a few standing million kilometers of water and a heavy ad-hoc ozone and Co2 atmosphere to help with radiation and heating' point, with further improvement thereof down the road if possible in the case of Mars or even just turning some ice-moons like Callisto or Enceladus into massive water-balls. But I think in the end that the major problem isn't even anything to do once we're in space. The main problem is getting to space in the first place, again and again and again. We can't blast antimatter or nuclear fire out of our lifters off Florida or Guiana, we're stuck with chemical reactions for that. And the best we have for that is theoretical metastable metallic hydrogen and some variants thereof. And let's hope the universe is so nice that such things could ever be exploitable.... This doesn't bar more 'stationary' infrastructure such as laser launches or launch loops or even magnetic fountains (though Earth so far prohibits Terran-based space elevators - lucky Luna and Mars!), of course, but if we're talking about doing things ASAP those things still require far more investment and maintenance than various disposable, partially reusable or fully reusable lifters. Getting to space constantly and efficiently and with numerous options for a myriad of roles is what's needed, thereof, nearly anything works with what we have now, if applied numerously enough, from nuclear to chemical to solar to antimatter.
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Post by bigbombr on Jun 26, 2017 3:13:19 GMT
So you recognize that people don't want to be stuck in tin cans...and then say that it's more efficient in the long term on a thread of making humanity multiplanetary for people to live their whole lives in floating tin cans. Maybe some would prefer that, but I'm sure enough would be 'dirtside' to not care about the 'inefficiency'. Definitions like 'hard', 'efficient', and 'expensive' also change drastically with levels of spatial infrastructure, advances in technology, and even levels of government. A hyper-libertarian society chugging around with corporate or even personal rockets most likely wouldn't see terraformed worlds, but a mixed-economy hyperpower or even a collectivist union might at least try with their collective resources and capabilities, even just to the 'Okay, we can walk around without gear for a few thousand years and have a few standing million kilometers of water and a heavy ad-hoc ozone and Co2 atmosphere to help with radiation and heating' point, with further improvement thereof down the road if possible in the case of Mars or even just turning some ice-moons like Callisto or Enceladus into massive water-balls. But I think in the end that the major problem isn't even anything to do once we're in space. The main problem is getting to space in the first place, again and again and again. We can't blast antimatter or nuclear fire out of our lifters off Florida or Guiana, we're stuck with chemical reactions for that. And the best we have for that is theoretical metastable metallic hydrogen and some variants thereof. And let's hope the universe is so nice that such things could ever be exploitable.... This doesn't bar more 'stationary' infrastructure such as laser launches or launch loops or even magnetic fountains (though Earth so far prohibits Terran-based space elevators - lucky Luna and Mars!), of course, but if we're talking about doing things ASAP those things still require far more investment and maintenance than various disposable, partially reusable or fully reusable lifters. Getting to space constantly and efficiently and with numerous options for a myriad of roles is what's needed, thereof, nearly anything works with what we have now, if applied numerously enough, from nuclear to chemical to solar to antimatter. 1) O'Neill cilinders are much more pleasant than the interior of a spaceship. Gravity can be 1g or whatever desired, there is space for farming/parks, ... Hardly tin cans. 2) I didn't argue that terraforming would be too hard to be possible. I argued that it takes orders of magnitude more effort for orders of magnitude less livable area. It would also take several orders of magnitude longer. 3) Twin stage (partially) reusable rockets like SpaceX are an impressive step in the right direction, and a good start. If you want any kind of settlement further out than the moon, they are suboptimal. Lofstromloop and laserlaunch require vast investments (+/- 10% of the annual budget of the US military) but building a self sufficient Mars colony would be an even more massive investment. Also building the advanced launch infrastructure actually lowers the total cost of establishing a self sufficient Mars colony. 4) Laserlaunch can be build in parts (beam convergence) and can be used for a variety of purposes. Cheap acces to LEO, hypersonic intercontinental travel, the foundation of a lasernet, ...
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Post by apophys on Jun 27, 2017 11:46:07 GMT
Zubrin, for instance, knows that the math on the VASIMR is solid, but because NASA doesn't have nuclear power plants on hand to churn out 10 MW, we're not going to Mars in 30 days and until NASA churns out capable nuclear tech all money into VASIMR is basically wasted, in his words, a 'hoax'. From the website of someone who worked on developing an MPD: "So then why is the Air Force developing these engines when they can't do anything? Because the military isn't as short sighted as people like to think. The top brass understand that it sometimes takes decades to develop a useful system. If we don't start now we'll never have them when the power systems are finally available." - www.waynesthisandthat.com/mpd.htmThe SAFE-400 space reactor is 100 kWe and 512 kg. That's about 300 times the mass of a minmaxed CoaDE equivalent (and better power density than stock reactors, lmao). Expect space reactor tech to get better over time. There are also some nuclear submarines which are 'light', I think my criteria was under 10,000 tones for total tonnage, but those reactors are well, for submarines, not spaceships, and conversion might not be worth the hassle. And because they're often military, numbers on the reactors themselves are hard to come by. The NR-1 apparently clocked out 144 kilowatts, the French K48 around 48 megawatts, and the American? S2C around 1.8 megawatts. Other subs might have 'small' nuclear reactors but their total tonnage conceals the tonnage of the reactors themselves. The S9W on the current USS Virginia submarine (7800 ton surface displacement) produces 40,000 shaft horsepower, which converts to ~29.8 MWe. I didn't find its mass, but it shouldn't be more than the S8W on Ohio-class submarines, which is 2750 tons. That is ~18 times heavier than an equivalent 300 SAFE-400 reactors; submarines have different considerations than spacecraft.
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rgm79
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Post by rgm79 on May 24, 2018 6:09:31 GMT
dV is king and NTRs have more. But when we start to produce hydrogen from ice we will see that we hawe 8 tons of oxigen per every ton of hydrogen. Chemical trusters will use this oxygen too, but with NTR you forced to drope it (life support can not consume this ammount of oxigen - adult human need only 1 kg per day). Optimal oxigen to fuel ratio for LOX/LH2 is 6 not 8. But let use 8 ratio and Isp = 4 km/s instead of 4.4 km/s with optimal ratio. To have dV 4 km/s (enough to go from Mars to LMO and more then enough to go from Moon to EML point) with chemical trusters we need 1.7 tons of LOX/LOH2 per ton of craft dry mass. And with NTR with ISP = 9 km/s only 0.56 tons of oxygen per ton of dry mass. But to produce this 0.56 tons of hydrogen we waste 4.48 tons of oxigen. Then in case with LOX/LH2 and dV = 4 km/s we can fuel almost 3 times bigger ship than in case with NTR for equal fuel plant output. At least for cargo missions LOX/LH2 and LOX/CH4 will be more usefull than "NERVA-type" TNR. I know that Musk go to use LOX/LCH4 on-Mars production, but with LOX/LH2 calculations much simplier.
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Post by ironclad6 on May 31, 2018 22:09:49 GMT
IMHO we think about this process all wrong. People think of going to space as being about lebensraum when in fact there's none to be had, not simply anyhow. What there is in our solar system are various energy resources such as the Jupiter plasma torus and the charged particle output of The Sun itself. We won't be an multiplanetary species of any significance until we start harnessing these energy sources, even on a miniscule level. As I see it we don't get anywhere meaningful in the process until we master fusion power. Once that happens we can build MPDT with serious thrust output.
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Post by bigbombr on Jun 1, 2018 6:08:52 GMT
IMHO we think about this process all wrong. People think of going to space as being about lebensraum when in fact there's none to be had, not simply anyhow. What there is in our solar system are various energy resources such as the Jupiter plasma torus and the charged particle output of The Sun itself. We won't be an multiplanetary species of any significance until we start harnessing these energy sources, even on a miniscule level. As I see it we don't get anywhere meaningful in the process until we master fusion power. Once that happens we can build MPDT with serious thrust output. I'm skeptical of the power-to-mass ratio of fusion reactors and fusion drives. Solar electric might give better acceleration.
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rgm79
New Member
Posts: 15
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Post by rgm79 on Jun 2, 2018 13:54:01 GMT
IMHO we think about this process all wrong. People think of going to space as being about lebensraum when in fact there's none to be had, not simply anyhow. What there is in our solar system are various energy resources such as the Jupiter plasma torus and the charged particle output of The Sun itself. We won't be an multiplanetary species of any significance until we start harnessing these energy sources, even on a miniscule level. As I see it we don't get anywhere meaningful in the process until we master fusion power. Once that happens we can build MPDT with serious thrust output. I'm skeptical of the power-to-mass ratio of fusion reactors and fusion drives. Solar electric might give better acceleration. You fusion-povered ship will have better trust-to-weight if you remove fusion reactor from it
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Post by ironclad6 on Jun 3, 2018 3:03:56 GMT
I'm not saying fusion power is a foregone conclusion. I'm only saying that nothing short of fusion power can make you a multi planetary species.
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rgm79
New Member
Posts: 15
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Post by rgm79 on Jun 3, 2018 3:17:45 GMT
I'm not saying fusion power is a foregone conclusion. I'm only saying that nothing short of fusion power can make you a multi planetary species. We already fusion power on Sun. BTW, charged particles in solar wind is not good solution for solar power - sun emite more energy in form of light.
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