Hard Light Productions Forums
Off-Topic Discussion => General Discussion => Topic started by: Kosh on January 26, 2008, 07:01:19 am
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Is there anyway to turn plasma into a useful energy source (other than the good old steam engine technique)?
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There are no energy sources. It's all just conversion from one form of energy into work. I don't know where you took the steam engine thingy, but even in steam engine, the steam is definitely not used for the primary energy storage.
AS far as plasma as "energy source" is concerned, I can only think of fusion, and that requires pretty specific kinds of plasma - it needs either deuterium-tritium mix, helium-3 plasma, or some other fusion-eligible materials in rather high concentrations to work properly. The only reason plasma is involved in this process, though, is that to achieve fusion, the electrons around the nuclei need to come off so the nuclei can hit each other freely. It's not plasma specifically that is required for fusion; fusion just requires high enough start-up energy before the nuclei hit each other forcefully enough to initiate fusion reactions.
Of course, if you throw a magnetically contained plasma ball at someone, he or she will definitely consider it as a source of energy as far as the damage caused by it is concerned... Same as batteries can be viewed as "sources" of energy for cars, cell phones, laptops and so on... even if it's just storage (ie. conversion of electrical charge to chemical bond energy and back again) from physical perspective.
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There are no energy sources. It's all just conversion from one form of energy into work.
That's kind of what I meant. How can you convert plasma (massive amount s of heat energy) into work (something usable)? What I meant with the steam engine thing is that even in nuclear power plants, all we really do is use the heat to boil water, so it's still just a glorified steam engine.
The thing is that fusion reactions creates enormous amounts of heat and some designs use plasma, so is there a better way to turn all that heat energy into work than boiling water?
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There are no energy sources. It's all just conversion from one form of energy into work.
That's kind of what I meant. How can you convert plasma (massive amount s of heat energy) into work (something usable)? What I meant with the steam engine thing is that even in nuclear power plants, all we really do is use the heat to boil water, so it's still just a glorified steam engine.
The thing is that fusion reactions creates enormous amounts of heat and some designs use plasma, so is there a better way to turn all that heat energy into work than boiling water?
There are ways.
You can use it to heat another substance, which can then be circulated in a heat exchanger that can be found in pretty much all electric power plants based on producing heat, be it with burning, nuclear power, concentrating solar radiation with mirrors etc. Of course this is the glorified steam engine you speak of, but what isn't then. It's a good way, but with fusion reactor the temperature tends to be a problem of some extent, more so than on fission based nuclear reactors.
To deal with extreme temperature, which normal matter obviously wouldn't hold, fusion reactors that are known to work for some time use a torus-shaped magnetic field to contain the plasma where the fusion actually happens, to separate it from physical contact with the reactor walls. Of course the radiation will heat the inner walls, but that can be dealt with, if enough energy is transferred away from the core. Heat exchanger does exactly that - it cools the reactor core and heats up itself, it's pressure increases and you got yourself thermal energy from the fusion.
If you want to avoid the steam engine altogether, another possibility in case of fusion is that you can use induction to capture the kinetic energy of the charged particles coming from the fusion (mainly alpha particles, aka. Helium.4 nuclei). After all, movement of charged particles is current, right? You just need to make sure that the particles are guided to same direction via static magnetic fields, and all is fine and dandy - they will cause a current to induce to nearby coils.
Partially, you could also possibly use some kind of layer of photoelectric cells to try and capture the gamma rays from the reaction, but the problem with that is that you need a really thick stack of the cells due to high penetration of gamma rays.
Of course, if at some point the integrity problems are solved, you could basically build a frakking four-stroke internal fusion engine that replaces spark plugs with, say, a laser and the fuel injection system would spray a small cloud of plasma into a chamber, where it would be contained in the middle of the chamber... Then, bang the laser heats the plasma sufficiently to start a fusion reaction, the plasma heats up a lot, expands, pushes the cylinder down. Exhaust would consist of helium; the "only" problem would be the stray neutrons making the engine block and other components radioactive on slow or not-so-slow rate, depending on what kind of reaction was used.
Of course, seeing how four-stroke engines are most definitely not amongst the most thermally efficient devices, if there actually were a need to convert energy from fusion directly to kinetic energy, a stirling engine would be more viable solution.
By the way, it's a common misconception that plasma must be really hot and fiery and melt everything it touches instantly. It doesn't really do this because in most applications, plasma is not really that dense. But to achieve fusion, the plasma needs to be heated to really high temperatures to offset the lack of pressure - you can't very well compress 15 000 000 Celcius-degree plasma mechanically. Magnetic compression is a possibility, but it takes a lot of energy in itself. Thus as far as I know, the fusion reactors currently designed will use greater temperature than in, say, Sun's core, to replace the missing pressure element that is present on natural fusion reactors, stars, where the massive gravity well makes the static pressure pretty much uncomprehensible on the core.
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thanks. By the way, how do you know so much about this? Are you a physics major?
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thanks. By the way, how do you know so much about this? Are you a physics major?
I knew this all the way back to high school. I've always read a lot and more importantly, I have a knack of actually remembering stuff that interests me, even if I read it once or twice only. Fusion reactor is actually a very simple contraption in theory - just like nuclear bombs; it's the technological limitations that make it so hard to accomplish...
But, I do indeed study physics as well. :p
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Would it also be possible to use the plasma from a fusion reactor as a source of thrust?
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Turn it into a weapon, use it to enslave a race, put said race on treadmills with threat of said weapon. Attach treadmills to generators. Don'' use more energy than is produced on "examples"
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Is there anyway to turn plasma into a useful energy source (other than the good old steam engine technique)?
yes... duh...
here
(http://www.egielda.com.pl/images/art/cache/dc16e9146b1fdb770afd2a8947c07b86.jpg)
here
(http://www.fightingtigersofveda.com/nurgledude2.JPG)
and of course...
here
(http://rdo.unirep.ru/Descent2/weapons/PLASMA.GIF)
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That looks ALOT like the gattling gun in pax imperia... :wtf:
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If you're talking about the last thing, you can't call yourself a real gamer if you have never seen that. :D
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and even if you don't know, you should be able to infer from the rest of the post. :p
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lol i agree with CP...
anyone who considers himself a freespace fan should know what the last gun is ;)
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I never played Descent and I still consider myself a FreeSpace fan.
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Would it also be possible to use the plasma from a fusion reactor as a source of thrust?
i dont think the impulse would be that high. mass would be low too so you wouldnt get much thrust. high mass of propellant and high specific impulse (velocity of propellant) = a **** load of thrust.
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High mass of propellant translates also into high mass of the ship which translate into extremely costly - and ultimately slow - flying gas cans.
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To be more exact, high specific impulse != high mass of propellant, by definition of the impulse:
I = dp = dm*dv
in which dp is change of momentum (aka impulse) that the ship (dry weight, without propellant) gains when it uses all it's fuel, dm is the mass of propellant used and dv is the ejection velocity gained by the propellant, in relation to the ship.
To have good specific impulse, a space ship designer can choose either huge flying gas can, or they can increase the ejection velocity. Both affect the impulse of the ship in a linear way - if you double the amount of fuel, the specific impulse doubles. If you double the ejection velocity, impulse doubles. Do both, the impulse quadruples.
Obviously the increased ejection velocity is more cost effective, since
A: the ship needs less fuel to be capable of travels made by corresponding ships with smaller ejection velocity and more fuel
B: the reduced amount of fuel means that the ship is easier to construct, and it can have more storage space and payload for it's size, since the fuel and fuel tank structures don't require as much volume and mass.
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So with regards to my previous question, is that a yes?
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that all depends on the velocity of your plasma, and how much you can throw
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I'd say it's highly unadvisable to run the fusion on the rear of your ship so fast that it produces meaningful amounts of resulting nuclei to be used as a direct propellant.
I mean, yes, it could possibly work to a degree - but your ship better have some ruddy good radiation shielding. The mass loss in single fusion reaction from, say, deuterium+tritium -> helium + neutron is negligible, so within reasonable error bars you could say that when you insert a kilogram of fusable plasma into your engine, and assumign it fully fuses and is released as a propellant... you still have only about one kilogram of propellant to be used, but the energy released in the reaction would be ginormous, and it would probably result in your ship's rear section vaporizing (which, admittedly, can cause significant amount of thrust but I suspect it wouldn't be very pleasant ride, especially if it's not a one-way-ticket).
Also, a lot of the energy is released as gamma radiation from fusion, not to mention neutrons. You can't direct neutrons with magnetic fields (at least very easily...), and gamma rays just burst to every random direction from the reaction, so that's a significant energy loss that you can't convert into propulsion.
A better solution - EVEN with losses in thermal exchange - would be to contain the fusion-plasma in the reactor, trap most of the gammas into radiation shielding, which causes the reactor - including the shielding - to heat up and the thermal energy can be used to expand suitabe propellant to large volume and to be propelled backwards that way. This has the advantage of taking care some of the cooling of the reactor as well - at least while there's any propellant left. The propellant used could be liquid hydrogen, nitrogen or perhaps some inert gas like Xenon, Neon etc. In this scenario, certainly the fusion waste helium can be added into the mix, but you would still need a separate mass of propellant, the stuff coming from fusion is not really sufficient to offer a long term propellant source.
Of course, if the system could use helium, you technically *could* replenish your propellant storage slowly by converting hydrogen isotopes into helium, but you would need to run the reactor in some kind of full-power-idle mode a long time to get any significant amoutns of inert propellant (helium) and what more, since you need to get the fusion materials from somewhere anyway, it just doesn't pay off. :blah:
Another choice (more like what we seem to have in FS2 by the way) is to use the fusion reactor quite like any "normal" fusion reactor hooked to power grid, and use the energy into either propelling ions (or, fully ionized gas aka. plasma) - with electric field.
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A better solution - EVEN with losses in thermal exchange - would be to contain the fusion-plasma in the reactor, trap most of the gammas into radiation shielding, which causes the reactor - including the shielding - to heat up and the thermal energy can be used to expand suitabe propellant to large volume and to be propelled backwards that way. This has the advantage of taking care some of the cooling of the reactor as well - at least while there's any propellant left. The propellant used could be liquid hydrogen, nitrogen or perhaps some inert gas like Xenon, Neon etc. In this scenario, certainly the fusion waste helium can be added into the mix, but you would still need a separate mass of propellant, the stuff coming from fusion is not really sufficient to offer a long term propellant source.
So about how much thrust could something like that (or any of the other suggestioned designs) make?
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As Herra Tohtori said... That depends on the amount of fuel ejected and on the exit velocity of the said ejected fuel. As neither are known it is rather difficult to estimate it.
EDIT... With quick google search...
http://www.projectrho.com/rocket/index.html
http://www.projectrho.com/rocket/rocket3c.html
Dunno how 'good source' that is but at least but...
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So about how much thrust could something like that (or any of the other suggestioned designs) make?
Oh brother...
I'm gonna mostly ignore the neutron flux, because I assume you don't have a way to redirect them neutrons towards the rear of your ship - an easy task with alpha particles because of their +2e charge (damn, this starts to sound like an RPG :p), all it takes is a magnetic field... neutral particles won't change their direction in mag field, so the neutrinos from the reaction would travel on pretty much linear trajectories, and assuming your fusion chamber is still mostly concealed by the ship, the ship's structure would be equally or almost equally hit by them -> no notable change of momentum from them.
Okay then... Assuming you're using deuterium-tritium fusion fuel mix, the resulting helium nuclei (alpha particles) will have roughly 3.5 MeV energy (source, about what kind of nuclei were observed coming from fusion going on in JET tokamak reactor running a 1.5 MW fusion reaction (http://www.iop.org/EJ/abstract/0741-3335/34/13/027/)).
3.5 MeV is 5.60761762e10^-13 Joules of kinetic energy on each helium nuclei produced. From this it's easy to calculate the velocity of the nuclei - that is
E(k) = ½ m v^2
v^2 = 2 E(k) / m
v = Sqrt (2 E(k) / m)
since the mass of alpha particle is 6.644656e10^-27 kg, just throw them into the equation to see that the velocity is
v =~12991758.6 m/s, which is a heck of a lot of speed. Just to check if it's accurate, compare it to speed of light - approximately 300,000,000 m/s. The velocity of the alpha nuclei seems to be about 4% of speed of light, which is thankful because now it's unnecessary to use relativistic equations for defining momentums and stuff - for the accuracy we require, anyway.
Okay, now we have the (average) velocity of alpha nuclei, and we're going to divert their vector towards the rear of the ship, so that effectively the ship gains the same momentum as each alpha nuclei, but forwards.
Now the momentum of a single alpha nuclei seems to be about
p = m*v =~ 8.633e-20 kgm/s
And every reaction releases one of these critters. Okay then, using chemistry terms, if we have one mole of deuterium nuclei (not molecules!) and one mole of tritium nuclei, we end up with one mole of helium nuclei, assuming the fusion is perfect (which isn't gonna happen but since we're looking for upper limits, best case scenario, it's OK).
Deuterium's atomic weight is 2u, tritium's is 3u, helium's is 4u (and the neutron that goes away is 1u, but nevermind that now). Roughly. There are some mass loss, but on this scale, it's not all that notable anyway, so I'm gonna blatantly ignore it aside from saying that actually helium+neutron weighs a little less than deuterium+tritium, and that's it. Helpfully, the atomic mass unit is configured so that when the atomic weight is 1 u, one mole contains one gram of the matter.
So, when the engine consumes grand total of 5 grams of deuterium-tritium mix (in proper ratios), it gives us 4 grams of helium to use as propellant.
Now then... the one mole of helium weighs (about) 4 grams, as was determined. One mole contains 6.0221415e23 particles (Avogadro's number), which means we're gonna multiply the momentum with this... multiplier number... to determine the momentum that the ship can at best gain from using grand total of 5 grams of fusion fuel:
p = 6.0221415e23 * 8.633e-20 kgm/s = 51989.1475695 kgm/s
which feels like a lot of momentum, but what it essentially means is that with 5 grams of fuel, you will manage to make a 52 ton ship travel at a whopping one metre per second, in the time it takes for the reactor to consume the 5 grams of detrimix fuel...
To put it in thrust terms (or force);
F = dp/dt
which means that if the fusion reactor can consume 5 grams of fuel in, say, 60 seconds, the thrust from it would be
F = 52000 kgm/s / 60 s = 866.7 N
If the reactor can use the mentioned 5 grams of fuel in 1 second, the maximum thrust would be 52 kN.
And seeing how utterly incredible amounts of energy are released, the achieved momentum/thrust/acceleration ratio is not really mind-bogglingly good. Also when you think of 52 ton space ship, you should be looking at something about the size of a good-sized airliner (like Airbus A320, or perhaps Boeing 757) as a reference to size, and compare to existing chemical rocket engines - Apollo-type service module engine produced 98kN thrust.
And I reserve the very viable possibility that something went wrong in the calculations.
As a final analysis, it's obvious that as far as propellant consumption is considered, this kind of drive is rather efficient, but propellant consumption is not all in all. In this case, fusionable isotopes are not as abundant as normal hydrogen in space, so where you gonna get all those precious grams of detrimix fuel?
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As a final analysis, it's obvious that as far as propellant consumption is considered, this kind of drive is rather efficient, but propellant consumption is not all in all. In this case, fusionable isotopes are not as abundant as normal hydrogen in space, so where you gonna get all those precious grams of detrimix fuel?
So the only reason that this hasn't been done is that there isn't enough fuel? I'm assuming all these ideas have been around for a long time so I would hope fuel shortages would be the only thing holding this up........
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No, the reason is that it isn't technically or energetically feasible.
I once did some calculations on how energy consumption (ie. power requirement), propellant consumption, ejection velocity and momentum are connected. In the end the equation is really simple - the faster you eject the propellant, the more energy it consumes in the ship's reference frame - remember, double the ejection velocity, double the momentum, BUT quadruple the amount of energy consumed to accomplish the relative velocity between ejected propellant and the ship.
That's also why it takes obscene amounts of energy to propel anything to 4% speed of light. And energy consumption is also important when space ships are considered... or rather, if there's sufficient amount of fuel/propellant, it's the cooling that becomes problem rather than power levels.
Also, the main reason no one even thinks of doing this in their right mind is that right now, we don't even have self-sustaining, energy-outputting fusion reactors. They need to be maintained with constant energy input that is more than the reaction itself yields. Probably situation will change as ITER and further in future DEMO become active, but right now fusion hasn't even been accomplished in huge research facilities - much less in any kind of vehicle, not to mention a space ship in which light weight is kinda priority. Also, radiation shielding can't be accomplished without a lot of mass aboard, so it's kinda so-so whether or not a nuclear reactor on board a manned space ship would be a blessing or curse.
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I never played Descent and I'am still consider myself a FreeSpace fan.
then i've got news for you.......... you're not a fan.
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I never played Descent and I'am still consider myself a FreeSpace fan.
then i've got news for you.......... you're not a fan.
Who are you to decide that? :doubt:
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Probably situation will change as ITER and further in future DEMO become active,
What is so different about their designs to change this?
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Mostly the fact that they will be the first two fusion reactors designed to offer positive energy output from the get-go. Thus far, the research has been pretty much concentrated on getting the fusion happen in the first place, in a controlled manner, then increase the energy output and reduce the energy consumption.
JET-tokamak reactor has in some tests managed to produce more energy output than input, but only for really short periods of time. ITER will be bigger, stronger and better and hopefully will be able to keep the energy output consistently and meaningfully bigger than the energy used tto keep the thing going on. DEMO will be a, well, demo of a commercially viable tokamak fusion reactor.
Basically it's pretty much like comparing previous attempts on powered flight to Wright brothers' first Flyer. The biggest difference between them are the fact that Flyer had a sufficiently lightweight and powerful engine, whereas the previous ones didn't. Also, Lilienthal, Bernoulli et al had done a lot of work that the Wrights used to make their flyer aerodynamically viable flyer... and the result was that the Flyer flied, when previous attempts had failed.
Similarly, the basic idea on JET, ITER and DEMO is the same - toroidal chamber with magnetic coils keeping the plasma in the middle. Now it's just making the process more streamlined, less energy-consuming while increasing the volume of the reactors to increase power capacity.
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I don't think the JET or other tokamak designs are a good source to estimate how a fusion engine would function.
Namely, the engine has a huge advantage, namely, that it can simply eject the spent plasma; so you don't have to hold the whole thing in place, you can have a strong current/stream (movement) in the plasma that could also help its handling.
However, that's the lesser source of miscalculation: in the Tokamak designs, it's not an aim to further energize the particles in the reactor...quite the opposite. The missing mass has become a huge load of energy - unlike the power plant designs, here we don't just absorb/radiate it all over the place if we can help it. We want to convert that energy to kinetic energy of the propellant.
Other calculation - namely the ones on project Rho - have shown a lot bigger specific impulse with these kind of engines:
"Deuterium-Tritium Fusion rockets use the fusion reaction D + T ⇒ 4He + n. If you add up the mass of the particles you start with, and subtract the mass of the particles you end with, you can easily calculate the mass that was converted into energy. In this case, we start with one Deuteron with a mass of 2.013553 and one atom of Tritium with a mass of 3.015500, giving us a starting mass of 5.029053. We end with one atom of Helium-4 with a mass of 4.001506 and one neutron with a mass of 1.008665, giving us an ending mass of 5.010171. Subtracting the two, we discover that a mass of 0.018882 has been coverted into energy. We convert that into the fraction of fuel that is transformed into energy by dividing it by the starting mass: Ep = 0.018882 / 5.029053 = 0.00375.
Plugging that into our equation Ve = sqrt(2 * 0.00375) = 0.0866 = 8.7% c. "
(http://www.projectrho.com/rocket/fusion.gif)
That's almost 3 times your specific impulse, but that's also the theoretical limit.
I also find the couple of gramms / second consuming engines somewhat unlikely, though your hypothesis based on the Tokamaks and therefore the current limits of magnetic engineering may more than apply. (I think the open bottle nature of a rocket is what would make a big difference here).
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I don't think the JET or other tokamak designs are a good source to estimate how a fusion engine would function.
Namely, the engine has a huge advantage, namely, that it can simply eject the spent plasma; so you don't have to hold the whole thing in place, you can have a strong current/stream (movement) in the plasma that could also help its handling.
Ah, but then problem becomes - how to contain the deuterium-tritium plasma that is yet to be fused, and how to let the fast charged alpha particles escape to generate thrust?
The problem with fusion is that in an uniform temperature/pressure plasma cloud (with sufficient energy levels to cross the Coulomb barrier), fusion reactions happen pretty much uniformly as well, which increases the temperature of the plasma, propelling newly formed alpha particles everywhere inside the plasma, trying to expand the plasma cloud's volume, but while there still are also deuterium and tritium in the mix, you don't really want them to escape as well, as it would seriously weaken the efficiency of the engine.
The answer could possibly be to use some kind of pulse fusion technology - not using a continuous fusion, but instead alternating between confining magnetic field and "guiding" magnetic field to guide the expanding cloud of positive ions backwards. Pour a few micrograms of plasma into confining magnetic field, light it up with lasers, let it fuse (which increases it's temperature), then switch to guiding magnetic fields, which releases the ions from confinement and turns the expansion of plasma into propulsion.
With sufficiently large frequency, the pulses would feel more like steady humming on the ship.
However, that's the lesser source of miscalculation: in the Tokamak designs, it's not an aim to further energize the particles in the reactor...quite the opposite. The missing mass has become a huge load of energy - unlike the power plant designs, here we don't just absorb/radiate it all over the place if we can help it. We want to convert that energy to kinetic energy of the propellant.
Yes, but since the reaction itself that I used in the example is the same, it means that the alpha particles from similar reaction would have (approximately) the same kinetic energy from the reaction.
Other calculation - namely the ones on project Rho - have shown a lot bigger specific impulse with these kind of engines:
"Deuterium-Tritium Fusion rockets use the fusion reaction D + T ⇒ 4He + n. If you add up the mass of the particles you start with, and subtract the mass of the particles you end with, you can easily calculate the mass that was converted into energy. In this case, we start with one Deuteron with a mass of 2.013553 and one atom of Tritium with a mass of 3.015500, giving us a starting mass of 5.029053. We end with one atom of Helium-4 with a mass of 4.001506 and one neutron with a mass of 1.008665, giving us an ending mass of 5.010171. Subtracting the two, we discover that a mass of 0.018882 has been coverted into energy. We convert that into the fraction of fuel that is transformed into energy by dividing it by the starting mass: Ep = 0.018882 / 5.029053 = 0.00375.
Plugging that into our equation Ve = sqrt(2 * 0.00375) = 0.0866 = 8.7% c. "
(http://www.projectrho.com/rocket/fusion.gif)
That's almost 3 times your specific impulse, but that's also the theoretical limit.
I also find the couple of gramms / second consuming engines somewhat unlikely, though your hypothesis based on the Tokamaks and therefore the current limits of magnetic engineering may more than apply. (I think the open bottle nature of a rocket is what would make a big difference here).
Now that is interesting, my thanks for more accurate data. :)
To be honest I'm a bit surprized that I got to at least approximately same magnitude of achieved impulse compared with the calculations of that mentioned group, which are much more likely way more accurate. The relative accuracy of my calculations surprizes me, especially since I used very crude approximations and mostly just picked an estimate of the kinetic energy/velocity of alpha particles from fusion, based on the first source I could find that seemed reliable.
In guesstimation physics, I consider it a relatively good achievement if the results are on the same magnitude (in this context, same exponent of ten) with more accurately calculated, actual physics (either theoretical or experimentally measured values)...
And, as said, even with three times the specific impulse (and three times the thrust), it would still mean consuming 5 grams of deuterium-tritium mix in a second to achieve thrust of 150 kN (or something like that anyway). As a theoretical maximum. A bit more than the amount of thrust from Pratt&Whitney J58 with it's 142 kN thrust (the engines used in SR-71 Blackbird).
Now, as I stated before, as you increase the ejection velocity and reduce the mass of propellant, the amount of work increases exponentially. Seeing how the mentioned J58 engine looks like this with afterburners on...
(http://upload.wikimedia.org/wikipedia/commons/6/60/J58_AfterburnerT.jpeg)
Glows pretty nice and warm, right? Well, the energy released in the chemical reactions is much much less than what is released in fusion of five grams deuterium-tritium, and releasing that amount of energy in a second would result in pretty brightly glowing end point of the rocket. Of course a lot of the energy would go into the plasma expansion thrusters as kinetic energy, but even so, it would make the plasma itself glow terribly brightly, not only on gamma ray wave lengths but also infra-red and visible light - which could have serious adverse effects on the rear end of the space ship.
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If you're talking about the last thing, you can't call yourself a real gamer if you have never seen that. :D
No i've seen it, i just recognized the similarity now tho
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i figure the hardest part of rocket science is keeping your engine from melting. :D
i think fission + ion is the way to go for now. by the time our magnetic technology reaches a level to make fusion viable, other propulsion technologies may become feasible, such as accelerating the interstellar medium. you could probably also use magnetics to contain hotter chemical reactions than could be achieved by most materials and cooling approaches used today.
forcefields are good for technology :D
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Holy ****. Can someone translate all this technobabble for your average sub-gymnasium scholar :eek2: :eek2:
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Fusion = hawt. :p
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Holy ****. Can someone translate all this technobabble for your average sub-gymnasium scholar :eek2: :eek2:
Yeah, there's so much technobabble in this thread you'd think it was dialog from a star trek episode.
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Actually, Herra and Flaser have been doing a very good job of condensing extremely complicated material into layman's terms. It is very difficult to appreciate just how hard it is to achieve a controlled fusion reaction without going into obscene detail. You haven't even begun to see the technobabble yet. Try taking a course in plasma engineering. Just one. For a semester. It'll make your head spin, you'll never use anything you learn in it, but man, what a rush!
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Holy ****. Can someone translate all this technobabble for your average sub-gymnasium scholar :eek2: :eek2:
Yeah, there's so much technobabble in this thread you'd think it was dialog from a star trek episode.
unlike in startrek, theres actually math in the technobabble
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I never played Descent and I'am still consider myself a FreeSpace fan.
then i've got news for you.......... you're not a fan.
Who are you to decide that? :doubt:
... a better and more experienced and respected fan than you...
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:rolleyes:
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None of you fans could provide sufficient cooling to fusion powered flame war. Hopefully this one can:
(http://www.kids-online.net/learn/click/details/fan.jpg)
:p
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I never played Descent and I'am still consider myself a FreeSpace fan.
then i've got news for you.......... you're not a fan.
Who are you to decide that? :doubt:
... a better and more experienced and respected fan than you...
The logic here eludes me. Does this mean that if a person has never played Flatout, he can't claim to be a Colin McRae Rally fan?
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Guys, let's try to keep to the physics and not trying practical applications of exothermic reactions? ;)
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practical applications of exothermic reactions
:ha:
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i figure the hardest part of rocket science is keeping your engine from melting. :D
i think fission + ion is the way to go for now. by the time our magnetic technology reaches a level to make fusion viable, other propulsion technologies may become feasible, such as accelerating the interstellar medium. you could probably also use magnetics to contain hotter chemical reactions than could be achieved by most materials and cooling approaches used today.
forcefields are good for technology :D
(http://img145.imageshack.us/img145/5393/atomicrocketme4.jpg)
I guess you haven't seen one of the VASMIR designs, have you?
That's a fission engine, that replaces the reaction chamber with a fission reactor. Simply put, you cool a conventional block of fissioning material with hydrogen and use the excited matter as propulsion.
Once again: every serious sci-fi geek/enthusiast should read project rho:
http://www.projectrho.com/rocket/index.html
It's THE REFERENCE, in laymen rocket/spaceship design; and happens to be 100% scientifically accurate and damn good read at the same time.
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i was reading about that engine yesterday actually. if it has gears does it have a clutch too? :D
anyway that was essentially what i was talking about. the list of theoretical ion/plasma engines is actually quite long, vasmir is just one among many. up till now most ion engines have a limit on the output of their power source and therefore also a limit on the size of your engine, so to speak. more power such as that from a nuclear reactor, would allow for ion engines to produce more thrust, run more efficiently/longer or both (or neither :D ).
not that you can plug a 10kw engine into a 100kw reactor and expect it to perform 10 times better. in all likelihood all you would do is fry your engine. but better space reactors, means more energy, means you can power more powerful engines. there are many theoretical drives that require much larger power supplies to operate than are currently available. im sure many engine concepts are still being tested in labs because their waiting for a better power plant to fly it with.
i recall visiting projectrho many times before, pretty cool site. i was skimming through looking for engines which make use of the interstellar medium, not necessarily "burning" it or storing it as fuel. but engines that can accelerate it through magnetic means and thus produce tiny thrust over the course of several decades without the trouble of carrying propellant on board. projectrho seems to be void of information on such an engine (probably because its too far off from convention).
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i was reading about that engine yesterday actually. if it has gears does it have a clutch too? :D
anyway that was essentially what i was talking about. the list of theoretical ion/plasma engines is actually quite long, vasmir is just one among many. up till now most ion engines have a limit on the output of their power source and therefore also a limit on the size of your engine, so to speak. more power such as that from a nuclear reactor, would allow for ion engines to produce more thrust, run more efficiently/longer or both (or neither :D ).
not that you can plug a 10kw engine into a 100kw reactor and expect it to perform 10 times better. in all likelihood all you would do is fry your engine. but better space reactors, means more energy, means you can power more powerful engines. there are many theoretical drives that require much larger power supplies to operate than are currently available. im sure many engine concepts are still being tested in labs because their waiting for a better power plant to fly it with.
i recall visiting projectrho many times before, pretty cool site. i was skimming through looking for engines which make use of the interstellar medium, not necessarily "burning" it or storing it as fuel. but engines that can accelerate it through magnetic means and thus produce tiny thrust over the course of several decades without the trouble of carrying propellant on board. projectrho seems to be void of information on such an engine (probably because its too far off from convention).
Project Rho mainly focuses on rocket designs that fulfill a high delta-v requirement. It's also a giant shrine to Stanislaw Lem and Robert Heinlein, both of whom proposed the first realistic nuclear rockets.
You got one thing wrong though: ion engines do have propellants, they typically use noble gases. They have very high specific impulse compared to other existing engine designs. Although their thrust is very low, so they can't act against a strong gravity field (high delta-v requirement); but once you're in orbit, you're halfway to anywhere, so you can simply accelerate perpendicularly to whatever grav well you're sitting in.
Once there, and once you actually want to stretch your legs, you need to be very prudent with your propellant. Hence, why NASA and everybody else is so interested in these ion engine designs.
If you're looking for pure propellantless designs I recommend the following designs:
-The Solar Sail is the oldest, and probably still our best bet for an interstellar mission (although it would take decades, the craft would reach .3 c, or a 1/3 of lightspeed which is nothing to scoff at).
http://en.wikipedia.org/wiki/Solar_sail
-Magnetic Sails are also another good propulsion, though their propulsion power drops a lot sharper outside the solar system than solar sails, while insystem they're a lot stronger.
http://en.wikipedia.org/wiki/Magnetic_sail
Nuclear engines, while not suited for interstellar missions (no propellant using engines is), produce the rare combination of being capable of both high specific impulse, and high thrust.
The reason why many are enamored with the design is, that these thing would be actually capable of lifting off Earth, going to another a planet, landing there, and once again lifting off. No other design can fill the insanely high delta-v requirement of such a mission.
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i knew that ion drives used propellant. its just the energy to drive said propellant is provided by a power system, and the output of that system has a positive effect on engine performance (or at least to the point where the mass of the system makes scaling up the power of the engine pointless). its just my last paragraph was thrown out of context (as far as that goes it belongs in another post all together). i was really trying to dig up the physics behind concepts such as the bussard ramjet with that one.
magnetic and solar sails are interesting as well. it actually seems absurd that were not using them already. solar sails would allow much longer duration missions, multiple missions, all with the expenditure of a single spacecraft. thats actually common practice. no mission has ever had its plug pulled simply because all the goals were met. if theres something more they can do with the craft, nasa is certainly gonna do it. why launch 3 probes when you can go 3 places with one probe?
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solar sails would allow much longer duration missions, multiple missions, all with the expenditure of a single spacecraft.
I guess it is because there is no real willingness to make such missions happen. Invading other countries is more important than making sure some of our species gets off this rock.
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Well, if you think about it, it will be a "stars or bust" situation to humanity at some point. Meaning that at some point, we need to either lie down and die, or leave for a new solar system.
Even before that, Earth will grow too hot - Mars and the moons of Jupiter would offer some refuge for some time, but eventually Sun will die and that'll be the story of humanity, unless interstellar travel is developed. The stage where Earth will be rendered uninhabitable (oceans vaporize into the atmosphere) will happen as "little" as 0.5-1 billion years in the future. At that point, Mars will have pretty pleasant climate as far as temperatures are considered, but the atmospheric pressure would still be a big problem. Moons of Jupiter and possibly Titan of Saturn will be the last sanctuaries for life in solar system. Of course, living in Jupiter's radiation belts would be... interesting, to say the least. :shaking:
But the gist of it is that in 4-5 billion years, sun will eventually expand to red giant and then either slowly wither away or blow it's outer parts into space as a planetary nebula. AT that point at least we need to have those colonization ships at ready - although preferably sending a lot of them away during longer period of time would be smarter than making them go at the same time as one huge rag tag fleet. All that about putting all the eggs in the same basket beer to the same bag and so forth, you know... Perhaps groups of five to ten ships would deal with the travel time better than single ships, as far as psychological, social and cultural effects of generations long space travel are considered.
As to how actually construct these hundreds or even thousands of ships for the humanity (even in lessened numbers from present), I would recommend carving tunnels, living quarters, storage space, fuel tanks, facilities to repair or manufacture any part needed in the ship's tech from raw materials, hangar for maintenance ships, fighter planes (who's gonna get into outer space without a fighter complement?! :D) and of course transport ships to move from ship to ship in each group, a BIG greenhouse to make food with, in asteroids of sufficient integrity... and then slap some kind of engines on it's surface, as well as radiators for the reactors needed to offer energy for high pressure natrium lamps needed for the greenhouse(s).
Basically, a Rama of sorts, but possibly without the centrifugal gravity.
Meh, I'm rambling again. But it's strangely comforting that at some day, humanity will either have to at least try and get away from solar system or lie down and die. And knowing humanity, they will at least try, which will IMHO be the greatest adventure of humanity whether or not it fails or succeeds and to what extent. Who know's, perhaps a ship will reach a new habitable world... and they're gonna call it "Kobol"... ;7 :drevil:
It's just a shame we won't be there to see it. :(
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Well, if you think about it, it will be a "stars or bust" situation to humanity at some point. Meaning that at some point, we need to either lie down and die, or leave for a new solar system.
I'm not willing to wait until the sun turns into a red giant. We can at least explore our solar system now. We have the technology. Propulsion? for long term missions a solar sail can work. Gravity? Simulated through rotating sections. Life support? Submarines can stay submerged for very long periods of time, why not use that kind of technology? Long term energy source? Until fusion becomes viable, we're stuck with fission. At least the waste can be dumped in space. So what's stopping us? I guess it just isn't "cool" anymore. The Apollo program proved that if we really want to extend our reach beyond low earth orbit, we can.
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Radiation is kinda big obstacle. Well probably... As there have been very few manned missions that have gone further out into the space than just into the orbit its still kinda difficult to say.
Any mission that sticks close to the Earth is relatively well protected but if you go for prolonged period outside the protective EM field of the Earth you will be exposed to cosmic and - more importantly - solar radiation. Ofcourse assuming the ship is big enough you probably could power EM field generator strong enough to keep the crew safe or then plate the ship with lead panels... But that doesnt exactly help with the heat and weight problems of the said ship.
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But that doesnt exactly help with the heat and weight problems of the said ship.
Heat and weight in space don't really mean that much.
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But that doesnt exactly help with the heat and weight problems of the said ship.
Heat and weight in space don't really mean that much.
Yes, they do.
Heat, matters a lot, because you don't want to melt your ship with excess heat, and thus if your ship's equipment produces heat (which they do), you need some way to remove the heat from your ship. And in space the only way to do that is radiate it to space, and that means you need radiators on the outside of your ship. On the other hand, you will want to insulate the living quarters (and sensitive equipment that must be kept at constant temperature to work properly) of your ship as well as possible, because you will not want to waste any more energy than necessary to try and either cool them or heat them.
So, the thing is - if your ship produces enough excess heat to require a radiator, or possibly an array of them, that brings us to another if these important issues - weight. Or rather, mass.
You will want your spaceship to have as little mass as possible and as much payload in relation to the fuelled weight of the ship as possible. This is because reduced mass improves acceleration and it means that you can manage same kind of velocity changes with less fuel - or, bigger velocity changes with same amount of fuel.
This means that you can travel from, say, Earth to Mars using either less fuel or less time with a ship with reduced mass.
On the other hand, regarding human physiology, weight is an important thing to have as well. In case you didn't know, long term exposure to weightless conditions on the orbit has some serious adverse effects on the bone density and muscle mass of astronauts - that's because both bones and muscles (and ligaments as well) are adapted to take some amount of constant abuse, develope microfractures and minuscule tears, and while repairing them they maintain the tissue and even strengthen it when the abuse increases, which is why you feel sore after exercising, but in the end you'll get stronger, faster and more resilient to damage as your muscles and tendons get stronger and more durable, and your bones do the same.
Weightlessness removes most of the abuse that human body needs to maintain it's integrity. As a result, astronauts need a lot of active exercising to apply artificial abuse to themselves, because on casual life on zero-g they wouldn't get enough of it. Of course this has an impact on their productivity if they need to do anything else than sit and monitor the ship.
On even interplanetary travel, some kind of artificial gravity would be very much appreciated in the long term because it could keep the travellers able to, you know, stand on their own legs withotu breaking their femurs under their own weight. :blah:
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[edit] Drat, Herra beat me to it! [/edit]
Yeah, they do. Weight especially is a big deal. Ignoring for a moment the horrendous problem of getting something that massive into orbit in the first place, then you need enough thrust to move it around. Even our next-gen engines that are just now coming into use will be severely taxed by "lead shielding."
Heat dissipation is another big one because you are completely dependent on radiant heat exchange. Convection and conduction just don't exist up there. You need much higher thermal differentials with radiant heat exchange to get the same Q-dot you'd get with the other two modes. Again, you can't afford to have something really massive up there, so your heat dissipation system needs to be really light-weight and efficient. Close in to the Sun (like where we are) it is a very challenging problem because you have so much heat coming in from the Sun, but even in shadow you still have to deal with heat released from your own equipment and people.
As far as space radiation (the cancer causing kind) is concerned, from what I've read, if the Apollo guys had been unlucky and been outside the van Allan belts during a solar flare, they very would very likely have died. At the very least they would have gotten very sick. There is no protection comparable to the double combo of the Earth's thick atmosphere and magnetic field. The problem with setting up a comparable magnetic field aboard ship (aside from power considerations) is that it will not protect from all directions uniformly, and from some directions (north and south) it will not protect at all. Electrostatic fields will only protect against particles of one charge or the other.
Honestly, the most promising idea I've heard so far involves strengthening humans themselves against the damage radiation can do. I read an article just the other day about some guy at Rice who has been playing around with a nano-tube based drug that seems to be affording a good deal of resistance to radiation damage to mice. http://www.sciencedaily.com/releases/2008/01/080128084415.htm (http://www.sciencedaily.com/releases/2008/01/080128084415.htm)
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On even interplanetary travel, some kind of artificial gravity would be very much appreciated in the long term because it could keep the travellers able to, you know, stand on their own legs withotu breaking their femurs under their own weight. :blah:
Artifical gravity would be unecessary because space travellers aren't subjected to the stresses of gravity in the first place. The Russians have kept a guy in space for over a year. You can live fine in zero-G; the hard part is returning back to Earth.
As you said, it would be nice to have gravity during long voyages, but by the time we're talking about "even interplanetary travel" and artificial gravity, we'll have the technology to more easily solve the problem with biology. With use of growth factors, we could "force" the body to maintain muscle and bone mass in zero G.
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Heh, just insert the self-repair DNA code from Deinococcus badiodurans (http://en.wikipedia.org/wiki/Deinococcus_radiodurans) into human genome so that it actually works, and you got yourselves a space human!
By the way, if I recall correctly Van Allen belts are actually the areas of space where the charged particles (protons and electrons, mostly) guided by Earth's magnetic field end up being held - they need to go somewhere and since they are averted from Earth, they go there to hang, and during a flare/protuberance a lot more particles are released from the sun, and thus the concentration of the energetic particles in the Van Allen belts increases as well.
So I believe it's the other way round - had the astrounauts been in the Van Allen belt areas during a time when the particle winds from solar eruption reached Earth, then there would've been a lot of big trouble. But they wouldn't have had time to get cancer, they would have caught some serious radiation poisoning and ended up covering the insides of their ship with bloody vomit and diarrhoea.
A pleasant mental image indeed. :shaking:
->Mustang19 - yeah, it's not a problem during the journey, but unless the astronauts are going to spend the remainder of their life up there, the journey itself would pretty much just suck all the way since they would need to dedicate a lot of mission time and effort onto exercises, whereas if there was an artificial gravity section, just moving about would offer a large portion of the exercise they needed.
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Re: Van Allen Belts, I don't think I was making myself clear. I didn't mean outside versus inside the belts themselves, more like what side of the belts the astronauts would have been on. Being inside the actual Van Allen Belts is not a good idea whether or not there is a flare because, as you say, that's where the charged particles end up getting trapped. I may have been wrong in thinking this, but I was more thinking of the belts as defining the limit of Earth's magnetic field's influence. As long as you are between the Earth and the belts, you should be fairly well protected. Beyond those belts, the only shielding you get is what you take with you.
I could be wrong about the range of Earth's magnetic influence more or less ending at the Van Allen Belts. It just makes sense to me if that's where the charged particles end up, beyond that point you aren't safe anymore. If the Apollo astronauts had just been in open space during a flare, I don't know if the flux would have poisoned them to the point of death then and there or not.
The point I was trying to make is that in any interplanetary expedition or even just trying to get to the moon, you may as well be naked for all the protection our current technology affords.
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Our best bet is Gliese 581 c. First extrasolar planet with atmoshpere ever discovered.
Although one year is only 13 days (yes, 13 days for a full circle around the sun), temparature is estimated to -3 to +40 °C. Nice and comfy.
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I'd be more worried about flare time, personally. At .073 AU from its sun, Gilese 581c is going to get a ****storm of x-rays at close range whenever the star flares. And it will flare. Gilese 581 is classified as a variable (HO Librae) based on past observations. As a general rule, red dwarfs have significant oscillations in their output. They aren't very bright to begin with, so oscillations that wouldn't be a big deal in a brighter, hotter star (like, say, the Sun) become more significant.
I'm not saying you couldn't make it work, but you'll weigh a bit more than twice what you are used to, and your primary will be rather punchy.
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As you said, it would be nice to have gravity during long voyages, but by the time we're talking about "even interplanetary travel" and artificial gravity, we'll have the technology to more easily solve the problem with biology. With use of growth factors, we could "force" the body to maintain muscle and bone mass in zero G
Yeah, we can turn into Shivans!
Heat dissipation is another big one because you are completely dependent on radiant heat exchange.
I thought the other guy was talking about ambient heat :p
Surely there must be a better way to protect against radiation (ambient radiation, as well as radiation from your own reactor(s), solar flares, etc) than just piling on the lead.
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There isn't.
At least, where gamma/röntgen radiation are concerned. Mass is the only thing that stops that stuff... no, "stops" is the wrong word, even mass only absorbs a percentage of gamma radiation, some will always statistically get through the thickest wall of lead you could imagine.
Mind you, any kind of mass works just fine, it's the amount of mass that is important... or rather, the density of the matter and the thickness of the "wall". Lead is commonly used radiation shielding material because it's conveniently dense and thus you don't need to stack it as thick as, say, concrete, steel or water. In a case of space ship, the best bet is to have the ship big enough to work as radiation shielding and have a natural "shelter" zone in the middle. Alternatively, it could be possible to only shield one part of the ship to work as a shelte, or shield the whole ship sufficiently so that it's safe to hang out anywhere during the fiercest radiation conditions imaginable.
Obviously, the problem with first method is the general scope. The second method is possibly the most sensible. Both of these solutions require a sufficient warning time to evacuate the crew to the shelter before intense radiation conditions. The third one doesn't have these problems, but instead it means that the mass/payload ratio of the ship will reduce dramatically.
Particle radiation is easier to stop completely than electromagnetic ionizing radiation, but even that requires rather thick walls on the space ship or radiation shelter. Or a magnetic field strong enough - perhaps it would be possible to actually use the coils of tokamak fusion reactor to generate a strong external magnetic field, which would guide the brunt of particle radiation to the poles of the ship.
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At least, where gamma/röntgen radiation are concerned. Mass is the only thing that stops that stuff... no, "stops" is the wrong word, even mass only absorbs a percentage of gamma radiation, some will always statistically get through the thickest wall of lead you could imagine.
So it doesn't respond to any sort of electromagnetic fields or anything?
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I seem to recall some experimentation around gravity and a magnetised super-conductor, apparently, by spinning the superconductor, it's possible to influence gravity in centre of the unit, sort of like the London Moment in electromagnetic fields.
Of course, the downside to this is that the cure is probably less healthy than the problem....
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if youre using water as a propellant, it might be feasible to stick the living quarters in the middle of the propellant tank. 12 feet of water is enough to keep you safe from material which would probably kill you in a couple minute of exposure. and for interstellar flight youd definately need that much propellant. hell drill out the core of pluto or other ice dwarves, strap a few nuclear-water rockets to it and use that as a space craft (just dont fly too close tot he sun or you will turn into a comet). you can probibly use crushed ice as fuel quite effectively.
i dont think you would need full duration gravity for interstellar travel as a generation ship. sence a good many generations would exist never knowing gravity. when you get close enough to a habitable planet (within a couple hundred years travel), you could just induce a spin on the ship, slowly building up to the g level of the planet youre colonizing. in the hollowed out ice dwarf scenario, there would probibly be enough gravity inside to allow you to walk around on the inside walls.
genetic engineering will almost certainly be a plus. not only will you need to adjust youre dna to space flight, you would also have to re-adjust it to your destination at some point in flight. in the process you might actually become a zero g race, as the people who reach another star may simpley be so used to it that the thought of living on a planet would be alien. at that point it might be better off for humans to stay spaceborne and not land on anything with more gs than you could get off of with a vehicle the size of a vw beetle.
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Yeah, and water has the advantage of being the second most common molecule in the universe... It's also easier to store great masses of it, much easier than hydrogen, which is very light even in liquid form and requires a really low temperature or high pressure to stay liquid.
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if youre using water as a propellant, it might be feasible to stick the living quarters in the middle of the propellant tank. 12 feet of water is enough to keep you safe from material which would probably kill you in a couple minute of exposure. and for interstellar flight youd definately need that much propellant. hell drill out the core of pluto or other ice dwarves, strap a few nuclear-water rockets to it and use that as a space craft (just dont fly too close tot he sun or you will turn into a comet). you can probibly use crushed ice as fuel quite effectively.
i dont think you would need full duration gravity for interstellar travel as a generation ship. sence a good many generations would exist never knowing gravity. when you get close enough to a habitable planet (within a couple hundred years travel), you could just induce a spin on the ship, slowly building up to the g level of the planet youre colonizing. in the hollowed out ice dwarf scenario, there would probibly be enough gravity inside to allow you to walk around on the inside walls.
genetic engineering will almost certainly be a plus. not only will you need to adjust youre dna to space flight, you would also have to re-adjust it to your destination at some point in flight. in the process you might actually become a zero g race, as the people who reach another star may simpley be so used to it that the thought of living on a planet would be alien. at that point it might be better off for humans to stay spaceborne and not land on anything with more gs than you could get off of with a vehicle the size of a vw beetle.
There's just one problem: no embryo will develop into a human without gravity.
Even if for just a specific part of the term, the mother (or the artificial womb) will have to be in gravity or its semblance.
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Why?
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Apparently cell structures and even some types of individual cells demand a gravity vector to develop properly. Mind you, any kind of weight can do, be it caused by gravitational acceleration or centripetal acceleration.
Interestingly, roaches apparently grow faster, stronger and tougher (http://en.rian.ru/science/20080117/97179313.html) in weightless conditions... :shaking: :nervous:
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Kewl :yes:
Go russia.
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You won't think it's kewl when them space roaches escape the Russian research facilities and spread a deadly zombie virus all over the world!
Grrr. Argghh.
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think a roach could survive re-entry?
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Well, better than your average Joe Astronaut for sure.
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i meant minus space vehicle, flick the thing retrograde and watch it burn up :D
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Hmm...
They would probably survive the lack of pressure and oxygen for long enough, but the re-entry heat is a problem for them. Unless they are flicked hard enough that they gain the pro-grade vector's opposite and fall right out of sky. That, they would probably survive - they can take some serious acceleration, so put a bunch of roaches on a barrel and the barrel on a coil gun that accelerates the bucket onto reverse orbital velocity, or close enough. Then them roachys would just plummet down from the sky. And as freaky as it sounds, some probably would survive the treatment.
But re-entry at orbital velocities... no. Just no.