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Captain
Join Date: Jun 2012
Posts: 622
# 41
08-16-2012, 02:50 AM
Quote:
Originally Posted by lilchibiclari View Post
The thing is, whatever you are venting as exhaust has to have been carried on your spacecraft in a tank. Cooling a nuclear reactor via water evaporation will require about one kilogram of water per kilowatt-hour of energy (the energy required to heat water from freezing to boiling and then boil it away is about 3/4 of a kilowatt hour per kilogram). Thus, a megawatt-class reactor will require about a ton of cooling water PER HOUR. Every six weeks of flight time will thus require about one thousand tons of cooling water--which is problematic when you consider that a spacecraft that would be using a one megawatt reactor would have a total non-fuel mass of only a few hundred tons to begin with--a heavier ship would demand an even bigger, hotter reactor. (Please note also that there are VERY few possible coolant materials that would carry away significantly more heat per kilogram than water while also being relatively safe for humans, and all of those cost quite a bit of money if you want to exhaust hundreds of tons of them per flight.)


Redundancy is good, but it adds bulk and mass, and when you are paying US$1000 or more per kilogram launched from Earth's surface to orbit, you want to make everything as lightweight as possible. A single 1-megawatt reactor weighs less than two 500-kilowatt reactors, since you don't have to double the mass of every component in order to double the power output. Likewise, in Star Trek, having several warp cores working together would take up more space and mass (and more labor to operate and maintain) than a single large one, which means that the more efficient plan is to have the main warp core and a smaller emergency one so that the ship isn't stranded if the main one fails. Note that in Star Trek, the only Federation ships to have more than two warp cores are the ones made to separate into multiple warp-capable sections, such as the Prometheus.
Can't they use liquid nitrogen as a coolant for the nuclear reactor or just have the reactor expose to space since it is what -300c? wouldn't that be enough? Ya prometheus is the only ship known to have more then one warp core which is a good idea to have a backup but I guess since sub communication can travel faster than warp speeds at great distance too maybe there is know need.
Captain
Join Date: Jun 2012
Posts: 1,893
# 42
08-16-2012, 03:19 AM
Quote:
Originally Posted by raj011 View Post
Can't they use liquid nitrogen as a coolant for the nuclear reactor or just have the reactor expose to space since it is what -300c? wouldn't that be enough? Ya prometheus is the only ship known to have more then one warp core which is a good idea to have a backup but I guess since sub communication can travel faster than warp speeds at great distance too maybe there is know need.
You haven't been paying attention, have you...

Liquid nitrogen idea: That's essentially limited fuel, as you can't cool the nitrogen down effectively enough.

Exposure to space: Space is cold because there is little matter to transfer heat. Therefore, you have little matter to target for the reactor heat transfer. That's why the radiation and infrared ideas were mentioned in above posts.
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Dalo Lorn
DaloLorn, StarCraft 2 Roleplayer and proud of it.
Captain
Join Date: Jun 2012
Posts: 622
# 43
08-16-2012, 03:26 AM
Quote:
Originally Posted by dalolorn View Post
You haven't been paying attention, have you...

Liquid nitrogen idea: That's essentially limited fuel, as you can't cool the nitrogen down effectively enough.

Exposure to space: Space is cold because there is little matter to transfer heat. Therefore, you have little matter to target for the reactor heat transfer. That's why the radiation and infrared ideas were mentioned in above posts.
Actually I have been and do remember what you have said. Just thought of other ideas for the cooling problem.

Anyway back on topic, lilchibiclarim, dalolorn has mentioned that they can use infra red to cool the reactor and material which transfer the heat outside.
Commander
Join Date: Jun 2012
Posts: 341
# 44
08-16-2012, 03:31 AM
Quote:
Originally Posted by lilchibiclari View Post
The thing is, whatever you are venting as exhaust has to have been carried on your spacecraft in a tank. Cooling a nuclear reactor via water evaporation will require about one kilogram of water per kilowatt-hour of energy (the energy required to heat water from freezing to boiling and then boil it away is about 3/4 of a kilowatt hour per kilogram). Thus, a megawatt-class reactor will require about a ton of cooling water PER HOUR. Every six weeks of flight time will thus require about one thousand tons of cooling water--which is problematic when you consider that a spacecraft that would be using a one megawatt reactor would have a total non-fuel mass of only a few hundred tons to begin with--a heavier ship would demand an even bigger, hotter reactor. (Please note also that there are VERY few possible coolant materials that would carry away significantly more heat per kilogram than water while also being relatively safe for humans, and all of those cost quite a bit of money if you want to exhaust hundreds of tons of them per flight.)
LENR device or similar can be cooled with less, and does not require water. gases. salts, even just the heat to drive a stirling engine to drive the generator could be used. there are no losses in a closed system. you're think of a standard BWR or PWR, neither would be of practical use. they require to much space, technical expertise and are inherently unsafe. the VASIMR engine can use a wide variety of gases. and would require much much less reaction mass than conventional rockets of any kind.

Quote:
Originally Posted by lilchibiclari View Post
Redundancy is good, but it adds bulk and mass, and when you are paying US$1000 or more per kilogram launched from Earth's surface to orbit, you want to make everything as lightweight as possible. A single 1-megawatt reactor weighs less than two 500-kilowatt reactors, since you don't have to double the mass of every component in order to double the power output. Likewise, in Star Trek, having several warp cores working together would take up more space and mass (and more labor to operate and maintain) than a single large one, which means that the more efficient plan is to have the main warp core and a smaller emergency one so that the ship isn't stranded if the main one fails. Note that in Star Trek, the only Federation ships to have more than two warp cores are the ones made to separate into multiple warp-capable sections, such as the Prometheus.
reactor yes, LENR device no. they are much smaller by far. 2 at least, engines and life support separated. and this craft would not be built on earth, parts would be flown up and it would be built in orbit. the most practical method as attempting to build something to travel to mars with live cargo would require a much stronger structure with greater overall weight than building it in orbit. impractical to build an manned interplanetary craft on earth.

modular construction, each launched by rockets available at present, assembled in orbit. this also brings down the cost of developing a new rocket that could handle all the weight if the entire thing was launched from earth as well as the aforementioned weight savings from not requiring the craft to resist the high G of an earth based launch.

just the oxygen, nitrogen, food supplies, heaters, CO2 scrubbers, living/sleeping/exercise areas alone would take up a great deal of weight and space. then there's the lander, vehicles...this is by no means a small project. the craft itself would never touch ground. would not be built or designed to do so, yet more weight savings.

it also more than likely would not be anything like the pretty smooth hulled ships seen in star trek and most sci-fi. modules tacked together with scaffolding, engines at one end and access tubes running between different modules. rounder than most of the girder builds in sci-fi as well. since having the center and the ends closer reduces any rotational stresses from the decel flip (minor true) or emergency maneuvering.

whole design does depend on LENR or similar device to produce power. though, improvements in piezoelectronics increasing the conversion rate would allow standard steady state nuclear batteries to perform the task as well. requiring no cooling so all in all possibly much lighter as there's no generator either.
Rihannsu
Join Date: Jun 2012
Posts: 3,176
# 45
08-16-2012, 03:43 AM
Quote:
Originally Posted by deadspacex64 View Post
reactor yes, LENR device no. they are much smaller by far. 2 at least, engines and life support separated. and this craft would not be built on earth, parts would be flown up and it would be built in orbit.
NASA seems to explore the possibilities of LENR-driven one-stage space planes, though. So you'd possibly launch into orbit with that vessel, refuel in orbit to get the necessary reaction mass, then use the same vessel for interplanetary travel.

At least in theory, this should be possible with LENR technology. But I guess that would need a few decades of development.
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Captain
Join Date: Jun 2012
Posts: 1,893
# 46
08-16-2012, 06:02 AM
Quote:
Originally Posted by raj011 View Post
Actually I have been and do remember what you have said. Just thought of other ideas for the cooling problem.

Anyway back on topic, lilchibiclarim, dalolorn has mentioned that they can use infra red to cool the reactor and material which transfer the heat outside.
I merely reminded you of the idea, which was mentioned in an above post.
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Oh, lovely, I can't even requote the Douglas Adams quote I used to have here I WANT IT BACK!!!!
Dalo Lorn
DaloLorn, StarCraft 2 Roleplayer and proud of it.
Captain
Join Date: Jun 2012
Posts: 622
# 47
08-17-2012, 03:12 AM
Quote:
Originally Posted by sophlogimo View Post
NASA seems to explore the possibilities of LENR-driven one-stage space planes, though. So you'd possibly launch into orbit with that vessel, refuel in orbit to get the necessary reaction mass, then use the same vessel for interplanetary travel.

At least in theory, this should be possible with LENR technology. But I guess that would need a few decades of development.
Has anyone else built a LNER reactor other than Rossi? who apparently is taking order already!
Captain
Join Date: Jun 2012
Posts: 735
# 48
08-18-2012, 01:18 AM
Quote:
Originally Posted by raj011 View Post
Can't they use liquid nitrogen as a coolant for the nuclear reactor or just have the reactor expose to space since it is what -300c? wouldn't that be enough?
Assuming that you are using any form of gas expansion cycle (e.g. Stirling, Brayton, or Rankine cycles) for converting your reactor energy into electricity or propulsion (i.e. reactor --> heat --> gas --> turbine/piston/rocket), then you are almost certainly going to want to run the engine as hot as possible (at LEAST 1200 C if not more), because gas expansion is fundamentally more efficient the greater the difference between maximum and minimum temperatures within the power cycle. Water absorbs a LOT more energy to heat up and boil than just about any non-toxic material in existence--a whopping FOUR TIMES as much energy per kilogram per degree Celsius as liquid nitrogen. Liquid nitrogen is thus only useful as a coolant if you need your coldest temperature to be colder than liquid water--otherwise you will get more cooling from using water.

Quote:
Originally Posted by deadspacex64 View Post
LENR device or similar can be cooled with less, and does not require water. gases. salts, even just the heat to drive a stirling engine to drive the generator could be used. there are no losses in a closed system. you're think of a standard BWR or PWR, neither would be of practical use. they require to much space, technical expertise and are inherently unsafe.

reactor yes, LENR device no. they are much smaller by far. 2 at least, engines and life support separated. and this craft would not be built on earth, parts would be flown up and it would be built in orbit. the most practical method as attempting to build something to travel to mars with live cargo would require a much stronger structure with greater overall weight than building it in orbit. impractical to build an manned interplanetary craft on earth.
Yes, but two 1-megawatt LENR systems would still be heavier than one 2-megawatt LENR system, simply because there are components of the system that do not scale up in direct proportion to power output. Stuff like the physical housing, mountings, and connectors will not necessarily be twice as massive when you double the power output, just as a 400 horsepower automotive engine is less massive than two 200 horsepower engines. Thus, if you want your system to be as lightweight as possible, you still get a lighter system mass by using a single large power supply instead of multiple smaller ones.


Quote:
just the oxygen, nitrogen, food supplies, heaters, CO2 scrubbers, living/sleeping/exercise areas alone would take up a great deal of weight and space. then there's the lander, vehicles...this is by no means a small project. the craft itself would never touch ground. would not be built or designed to do so, yet more weight savings.
Studies for near-term interplanetary missions have estimated non-propellant mass in the range of 200-1,000 tonnes. (For comparison, the Space Shuttle Orbiter has a non-propellant mass of 80 tonnes plus up to 25 tonnes carried in the payload bay, while the current configuration of the International Space Station masses 450 tonnes.)

Current NASA Mars Mission Design Reference Architecture Document: http://www.nasa.gov/pdf/373665main_NASA-SP-2009-566.pdf
Captain
Join Date: Jun 2012
Posts: 622
# 49
08-18-2012, 05:49 PM
has NASA or any other company or person experimented with LENR technology?
Rihannsu
Join Date: Jun 2012
Posts: 12,736
# 50
08-18-2012, 08:53 PM
LENR is still in the theoretical stage.
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