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Toshiba, which designs a small nuclear reactor named 4S (for "Super Safe, Small, & Simple"),
The 4S is a sodium-cooled fast spectrum reactor -- a low-pressure, self-cooling reactor. It will generate power for 30 years before refueling
Toshiba, which designs a new 10-megawatt nuclear reactor costs about $ 25 million
Pay the operating costs, estimated at 10 cents a kilowatt-hour
. There are no complicated control rods to move through the core to control the flow of neutrons that sustain the chain reaction; instead, the reactor uses reflector panels around the edge of the core. If the panels are removed, the density of neutrons becomes too low to sustain the chain reaction.
Designers chose sodium so they could run the reactor about 200 degrees hotter than most power reactors, but still keep the coolant depressurized.
It will use uranium enriched to 20 percent and generate power for 30 years before needing to be disposed of and replaced.
This special 'you don't need to do anything to keep it going safely' feature of the reactor is to be found in the way that the operating system has been reduced to the simplest possible level. For example, the primary coolant pump which transports the heat generated in the nuclear fuel is a component installed inside the reactor vessel. What is more, it uses liquid sodium as the coolant, which means it can use an electromagnetic pump with no moving parts. That is one reason why it can continue operating for as long as 30 years. The heat of sodium, primary coolant, is transferred through a heat exchanger to a secondary coolant, and that heat exchanger is also inbuilt inside the reactor vessel.
One more unique feature of this reactor is that there are no control rods for controlling the nuclear reaction, though existing medium- and large-sized reactors have control rods. In place of the control rod, an annular reflector which is used for reflecting the neutrons produced by nuclear fission so they can be used efficiently, moves up and down inside the reactor vessel, controlling the nuclear reaction over the long term, over the short term, as well as moment by moment.
For a space power system, high reliability and low specific weight and volume are driving requirements. Efficiency is important to the extent that it influences system weight and low efficiency places extreme requirements on the energy source. Liquid metal MHD is a passive energy conversion process and thereby minimizes the number of rotating components. A liquid metal cooled fast reactor provides the heat source for the liquid metal MHD working fluid, while retaining a relatively compact core configuration for this range of powers. The power system studied is based on a two phase flow liquid metal MHD generator with lithium as the electrodynamic fluid and helium as the thermodynamic fluid.
Chazbro
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You leave out one of the most CRUCIAL issues for any space reactor it's Mass. I'm not sure what figures you have been looking at, but a brief Googling of the subject led me to a Los Almos paper about a reactor similar to the one you are discussing. It produces 50-MW electric but masses 250 Metric tons. This gives a power to weight ratio of 200W/Kg. Good, but hardly spectacular, and there was no indication that this reactor was desigend for space use, with the heavy and bulky radiators necessary. I'm curious as to what figures you are looking at that make you so happy.
Another issue is the use of MHD as a means of power conversion. MagnetoHydroDynamics is still in it infancy and typicaly has a much lower efficency typicaly only 10-20%, much lower than that of a turbine. However a MHD system may weigh less then a turbine, making it more attractive for a space based system.
He who refuses to do arithmetic is doomed to talk nonsense.
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Efficency is NOT important, what is important is that the total plant mass be low as possible per-watt. The USAF ponderd a reactor (the SP-100) with only 5% conversion efficency, but with 100kWe it still would have only weighed 5-6MT. It would have had no moving parts at all beyond the reaction control mechanism.
So let me get this straight...
The reactor uses liquid sodium as the primary coolant, but then passes the heat off through an exchanger to liquid lithium which is passed through an MHD loop, and finally passes off the remaining heat to Helium to spin a turbine and finally dump the core heat.
That sounds like an awfully complicated reactor for space use... three kinds of coolant? Two heat exchangers? Two MHD pumps, a helium Brayton cycle pump(s), and a turbine/generator to boot? That is really bending over backwards to keep the core output down, isn't it? The core output isn't as important either, given that the specific power of the core scales somewhat.
Too much complexity for too little bennefit... we need simpler reactors, with only one or two coolant loops, which operate at high temperatures to minimize radiator mass/size. Using MHD for electrical generation is an interesting factor that I didn't know was headed for "prime time," but the low-temperature helium loop is a real problem. Skip the Helium, and skip the Lithium too unless Sodium doesn't work in MHD converters very well.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Try googlig the Toshiba S4 reactor. It only produces 10MW and doesn't weigh anywhere near 250 MT. But its a safe bet that any megawatt class reactor is going to be heavy. Power/Mass density issues will just have to handled through ongoing R & D. As for complicated, any Nuclear reactor that actually EXISTS will, in fact be complicated I can pretty much asure you of that. Thats one of the advantages of actually having to deal with them first hand instead of only reading about them. I Understand their complexity. I guess any reactor that actually EXISTS will be far more complex than a reactor technology that doesn't----I concede that point!
Chazbro
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"Power/Mass density issues will just have to handled through ongoing R & D. As for complicated, any Nuclear reactor that actually EXISTS will, in fact be complicated I can pretty much asure you of that. Thats one of the advantages of actually having to deal with them first hand instead of only reading about them. I Understand their complexity."
Yeah, uh huh. You effortlessly ignore the point that myself and Mr. Stanley have tried to educate you about, which is a space power plant (the whole plant, including core, converters, radiators, shielding, etc) must generate much more power per kilogram than any small reactor ever has if it is to operate an engine like VASIMR really effectively.
Chazbro, in your deep wisdom about nuclear power plants, do you not understand the concept of a conceptual heat engine? The Carnot cycle and whatnot? I am sure you have, and myself and Mr. Stanley know about it and a bit of thermodynamics with our chem/phys background... in any case, the higher the temperature you can operate your reactor, the more power it can produce per-pound for a comparable thermal wattage, thanks to smaller radiators and/or more efficent conversion.
The problem with contemporary nuclear reactors like you want to employ, like the Toshiba 4S here, is that they don't operate at a very high temperature, with this on imparticular only operating at 550C and the final Helium loop will undoubtably operate at much lower temperature. In fact, most space reactors constructed and proposed to date operate at higher temperatures still, 1100-1400C or higher, and they still aren't hot enough.
At temperatures still higher, you could perhaps improve the specific power of the plant, but this is really getting close to the limit for practical solid-core plants. Right now, really "good" plants still don't produce enough power per-mass to run a VASIMR engine by a factor of several times over... anyway, the point being, that contemporary solid-core reactors are not going to be able to attain much higher temperatures, so there isn't going to be an R&D breakthrough that radically improves this specific power for a "traditional" plant arrangement.
We are running up against the limits of what practical materials can withstand, and there isn't going to be a magic bullet that keeps the core from melting... so what do you do? Let it melt, and presto, gas-core nuclear reactors. Improvements to solid core power plants aren't ever going to make it really effective at powering a VASIMR rocket without either trading payload or trip time simply because you can't drive them hot enough.
As far as complexity goes, its a matter of failure modes and mass: the more stuff you have to add to the plant to make it operate, the less and less efficent (watts per kilo) its going to be. A simple power plant should be easier to avoid the infamous "weight creep."
This power plant also needs to be able to operate for about twenty years, most of it non-stop, with no maintenance whatsoever. None. No overhauls, no refueling, no nothing... This is the second reason why the plant must be extremely reliable - more reliable then a submarine's or this Toshiba reactor - either through massive redundancy or lack of failure modes. You know all about failure modes, being a professional engineer don't you? Well, if we add massive redundancy, that will severely impact the specific power, so therefore the reactor must have a minimum of failure modes.
So, the plant must be simple and robust. A complicated plant is just unacceptable, and thats all there is to it.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Welcome Chazbro38,
You seem to have an interest in nuclear power and have done some research on some current earth based systems. I would like you to help out with the newmars wiki provided you stick to objective facts you researched (i.e. earth based nuclear reactors) and do not speculate too wildly about the performance these reactors would have in space based propulsion systems.
The goal of the wiki is to try to present material in as non an opinionated form as possible. When there is a large group of people that have a particular view we can present that information as a view and not as fact. What I suggest that you do for earth base systems is perhaps create a page for each earth based reactor you find interesting. Some key numbers will be the power the reactor produces, the weight of the reactor, the efficiency of the reactor, the volume of the reactor and how hot the reactor operates at.
As for applications to space technology I hope you would listen to GCNReveneger. He is a highly intelligent and educated person that takes a deep interest in space exploration. Although you may not always agree with him you could learn a lot from him. He is currently doing his PHD in chemistry.
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these are really intresting topics in here, but i wouild like to put some of my input in here too...
when your in space, lots of the standard rules wont apply. Temperature is a big factor of reactors, from cooling to heating... in the reactor section of a ship there usually wont be the whole living quarters and everything under a controled temperature environment.
if your doing long range travel like say mars (crazy i know lol) you would want multiple power systems. its like with cars, you could just get a lemon even if it is hand built to exact specs, there is always that thing that could go wrong. Not even just talking about the things that could go wrong with the system, but what about using multiple power sources for driving the VASIMR enigne?
Sure you might add lots of weight to the ship... but then all that means is that it drives like a train instead of a bus. so what when its not made for high manuvering?
there are lots of factors when dealing with non-stationary powerplants. just some food for thought.
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Having multiple powerplants for safety would be really nice, but smaller reactors generate less power per-pound then their larger counterparts, since the reactor vessel has a greater surface area per-volume, since the plumbing would be much more complicated, and since you must have duplicate control systems which will not weigh much different reguardless of size.
The power-per-pound is absolutely critical for a high-power electric propulsion system like VASIMR, where the mass of the powerplant is one of the two "make or break" factors that make it practical or impractical. The power plant will be throughly tested at full power before leaving orbit I am sure, so given how difficult it will be to make a high-performance VASIMR ship, the small safety tradeoff is probobly acceptable. It isn't a difference between train versus bus, its a difference if fission-electric/VASIMR is worth the trouble or not.
I imagine that a pair of nuclear plants, despite being smaller, will likly cost more then one large plant too. Since we will have a heavy lift rocket available to launch parts for a VASIMR ship, the extra mass of the larger plant should not be a problem.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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ok i just did some research on the VASMIR project. Chang-Diaz said that on 200 mega watts a 20 Metric Ton shuttle can reach mars in roughly 39 days...
There has to be a way to increase the over all productivity of this meathod so even if it is using the same ammount of power, it will put out more propultion than this design.
Does anyone know where they have a schematic of this engine? I would love to take a look at it and see what could be done to make it more reasonable...
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ok i just did some research on the VASMIR project. Chang-Diaz said that on 200 mega watts a 20 Metric Ton shuttle can reach mars in roughly 39 days...
There has to be a way to increase the over all productivity of this meathod so even if it is using the same ammount of power, it will put out more propultion than this design.
Does anyone know where they have a schematic of this engine? I would love to take a look at it and see what could be done to make it more reasonable...
I think 39 days is very fast for a trip to mars and I am surprised it only took 200 MW. I am curious what the fastest trip time possible would be if a solid core reactor was used. So I take it that it is impossible to build a 200 mega watt space based solid core nuclear reactor including radiators and everything else for under 20 Tons. Does mars direct use a 20 ton nuclear reactor? What output does it have? 5 mega watts?
Also something important is missing in that figure. How much of that 20 tons is propellant mass?
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ok i just did some research on the VASMIR project. Chang-Diaz said that on 200 mega watts a 20 Metric Ton shuttle can reach mars in roughly 39 days...
There has to be a way to increase the over all productivity of this meathod so even if it is using the same ammount of power, it will put out more propultion than this design.
Does anyone know where they have a schematic of this engine? I would love to take a look at it and see what could be done to make it more reasonable...
I think 39 days is very fast for a trip to mars and I am surprised it only took 200 MW. I am curious what the fastest trip time possible would be if a solid core reactor was used. So I take it that it is impossible to build a 200 mega watt space based solid core nuclear reactor including radiators and everything else for under 20 Tons. Does mars direct use a 20 ton nuclear reactor? What output does it have? 5 mega watts?
Also something important is missing in that figure. How much of that 20 tons is propellant mass?
that 20 metric tons is total... so add more weight and add more time...
personally i believe there are ways to get those engines working with lots less power. you still need to figure fuel for the propultion, the actual ship its self, and everything else... logically that means there has to be multiple engines working at the same time, and thus more weight... so all that means is that we need a better power source and a different technology.
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ok i just did some research on the VASMIR project. Chang-Diaz said that on 200 mega watts a 20 Metric Ton shuttle can reach mars in roughly 39 days...
There has to be a way to increase the over all productivity of this meathod so even if it is using the same ammount of power, it will put out more propultion than this design.
Does anyone know where they have a schematic of this engine? I would love to take a look at it and see what could be done to make it more reasonable...
I think 39 days is very fast for a trip to mars and I am surprised it only took 200 MW. I am curious what the fastest trip time possible would be if a solid core reactor was used. So I take it that it is impossible to build a 200 mega watt space based solid core nuclear reactor including radiators and everything else for under 20 Tons. Does mars direct use a 20 ton nuclear reactor? What output does it have? 5 mega watts?
Also something important is missing in that figure. How much of that 20 tons is propellant mass?
that 20 metric tons is total... so add more weight and add more time...
personally i believe there are ways to get those engines working with lots less power. you still need to figure fuel for the propultion, the actual ship its self, and everything else... logically that means there has to be multiple engines working at the same time, and thus more weight... so all that means is that we need a better power source and a different technology.
I always thought that electric propulsion engines were very efficient in converting energy to velocity. So I don’t think you are going to make big performance gaines by improving the efficiency. It is a good point though that area the crew lives in will probably be 20 tons, add onto that the mass of the propellant radiators and nuclear reactors, the vasmir engine as well as any other parts of the ship and I think that we are talking terawatts of power and not megawatts. Looks like is going to be one big darn expensive ship, perhaps costing as much as it would cost to build an Orion. On the plus side I think that a vasmim ship would have a longer lifespan and use cheaper fuel then an Orion powered ship.
That and the fact that VASMIR would be usefull at lower speeds for cargo and probes.
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do we have any researchers e-mail adresses? I would love to contact them and give them some input with current studies and research of my own.
I am positive there are ways to make the VASMIR engine almost twice as productive. either by using less power or by using the same ammount but getting more thrust out of it.
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do we have any researchers e-mail adresses? I would love to contact them and give them some input with current studies and research of my own.
I am positive there are ways to make the VASMIR engine almost twice as productive. either by using less power or by using the same ammount but getting more thrust out of it.
Well that could be true given the tradeoff between energy efficiency and fuel efficiency. Anyway from the numbers you gave you could calculate the thrust since you know the payload energy output and travel time. Once you know the trust they gave you could check to see if that thrust is optimal for the travel time. I would think that they would of gave an optimal number to make there research look better but I look forward to you results.
When you calculate those results we will find a place for it in the new mars wiki:
http://www.newmars.com/wiki/index.php/VASIMR
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20MT doesn't make any sense except as the payload mass, since whatever reactor/vasimr combination will obviously weigh far more then this.
There is a theoretical maximum limit for the efficency of a VASIMR engine, Dragoneye: look at this from a pure physics point of view, that when every single watt of electricity is converted into momentum, then you can't change the engine to produce any more because there is no more energy available. When every bit of electrical energy is changed into motion energy, you have reached 100% efficiency, and no more improvement is possible, so you would have to trade fuel efficency for thrust like other engines.
You can probobly improve the efficiency of a VASIMR engine a little bit with improve technology, but I doubt that you can build on its already good efficiency much. You are not going to be able to make VASIMR much better by trying to reduce its energy consumption.
Considering the rather small payload (only 20MT?) I bet that Diaz wants to use a very large solid-core nuclear power plant, but I am puzzled by his extremely large 200MW figure. Maybe he means that such a power plant would require that much thermal energy? If so, and this heat could be 5-10% converted to electricity, that would give you 10-20MW of electricity (a much more reasonable figure).
A gas-core power plant that produces 200MW of electricity was postulated at the University of Florida, but given its extremely high performance, it does not make sense that the VASIMR ship could not carry more payload. I bet that Diaz is referring to a solid-core reactor and its thermal output.
The best way to make a VASIMR ship more practical is to figure out where you can reduce the mass of the engine, and probobly employ a reactor with high-temperature thermal/electric converter of some sort.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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i agree that the figure seems weird, but look at the time frame... 20 MT in 39 days... thats fast as hell! on average we are looking at reducing travel times with that engine from 7 months roughly to about 4.... so figure 20mt x 4 and you have roughly 80mt to play with.
as far as me thinking out loud (or typing) about the engine being able to be much more efficient, i was thinking about using the engine in a rerun process to creat a higher potential than its able to do right now...
we know how the engine works but here is a run through so i can explain where the rerunning would work on it..
propellant of Helium runs through the magnetic component turning it into plasma, and then the energy wanting to escape runs out the back as exhaust basicly like on a plane...
well a rerun design would take the plasma state and use that to help aid the magnets to convert the gas into plasma (like taking fire to creat fire) and run it through as exhaust still..
i could be completely wrong, but then again it never hurts to think out side the box
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You are talking about a regenerative VASIMR engine, trying to use the plasma exhaust to generate electricity to offset the engines' high electricity requirements, right?
That will do you no good, since the plasma exhaust will slow down when you pass it through the coil to make electricity, and when that happens the fuel efficency suffers.
Back to the basic physics of rocket propulsion... for a given amount of power, the fuel efficency and the thrust are inversely related, so that even if you had an engine with that used every single watt of power to push your propellant, you will either have to choose between thrust and efficency or simply get more power.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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ok, so say you give up some thrust for saving power. i would say its worth it because then that means it takes less of a powerplant to create power that is offset at a specific out put efficiency level...
what about a reactor system that holds and uses plasma power to power the magnets? there are always ways to do things differently...
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ok, so say you give up some thrust for saving power. i would say its worth it because then that means it takes less of a powerplant to create power that is offset at a specific out put efficiency level...
what about a reactor system that holds and uses plasma power to power the magnets? there are always ways to do things differently...
If you give up thrust to save power the trip is going to take longer. In terms of people the faster we travel the better. In terms of cargo there will be an optimal economic travel time based on many things including: the time value of money, the price to get mass to LEO, the amount of times the engine can be reused, and how the engine depreciates with respect to time.
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i agree, but still with even say... a 2 month advance ment in the ammount of time it will take to get there, along with the almost permanent long distance ship, the cost affectiveness of it since all it will need to refuel is helium (for the rough 20 years of the Fusion reactor onboard) it will be worth it to go with something a little more well rounded...
good points
-faster
-reusable
-inexpensive to opperate
-and simplicity of opperation
the draw backs are
-Expensive initial cost
-space assembled
-assembly time
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It sounds like you are talking about a Helium-fusion tyle reactor to power the VASIMR engine.
That would of course be really great, but we don't even know if it is practical to build a portable fusion reactor, and would be without a doubt many decades away.
In the mean time, we are stuck with fission reactors to provide power for a VASIMR engine, and feeding it with Hydrogen to improve its fuel efficency.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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It sounds like you are talking about a Helium-fusion tyle reactor to power the VASIMR engine.
That would of course be really great, but we don't even know if it is practical to build a portable fusion reactor, and would be without a doubt many decades away.
In the mean time, we are stuck with fission reactors to provide power for a VASIMR engine, and feeding it with Hydrogen to improve its fuel efficency.
yea i have been doing alot of reading on doing it with H4 and then using N to keep it cooled down enough. it should work fine out side earths atmosphere with no direct light contact from sun or something like that to make it overheat...
be back on later i have to go to Job #2
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