Thrust to weight ratio

[Sisyphus]

Did you read post #20?

[Zolar V]

yea i read it and i understand what you are trying to convey. i agree with what you are saying, i was just having a thought. there is so much energy potential within a nuclear fission reaction, that it seems odd we cannot increase energy output and decrease size.

[insane_alien]

the smaller it is, the less energy is available.

 

nuclear power does have pretty high energy density but it is FINITE.

 

a bell206 helicopter has a power to mass ratio of 420W/kg if we take sysiphus's example mass then you need 42GW of power to keep this afloat.

 

naval reactors are nowhere near this scale. aircraft carriers may approach 300MW but they won't be operating at that ALL the time. and this isn't counting redundant systems which you WILL need. otherwise you will crash the first time there is a propblem.

 

even commercial reactors don't go this high. and they're several stories and the rest of the steam plant requires a lot of space too. and since they tend to be around 1GWe then you are going to need at LEAST 42 of them. propbably more like 60 to account for redundancy and maintenance and refuelling. and the cooling plant is going to be ENORMOUS.

 

the power plants alone would cost trillions and probably weigh more than the pretty small 100Mkg of the nimitz class.

 

this isn't even factoring in the extreme problems of the air currents around this. you're going to be moving a crapload of air to make lift. this will create high winds, downdrafts, turbulence and all things that make landings extremely dodgy.

 

you can make an airfield with greater capacity for a few million. heck, you can get an aircraft carrier for a few hundred(of its not state of the art military spec)million. but this thing is likely to cost more than all global economies combined and require a whole new generation of groundbased breeder reactors to generate the fuel required to keep this thing in the air.

 

and all this is just for one measly little strip.

[Zolar V]

but it would be a really really cool little measly airstrip.. IN AIR.

[insane_alien]

unfortunately, coolness doess not translate into practicalness or cost effectiveness.

[Zolar V]

not nessasarily, if i were to go out on a limb here and think about possible usefull applications. I would have to think that this would be a good concept on another plantet that has a bit less gravity and little to no landmass on the planets surface. imagine Stargate Atlantis but the city in air instead of the water, due to the practicality of having it off the ground/water.

thinking of a reason why, maybe the craft has multiple stories and has multiple docking bays for planitary vehicles. the reason why it would have planitary vehicles is because there are more than one floating islands.

but thats just another thought.

You know in another 100 or 200 years we will have a need for some things similar to these..... just saying..

[insane_alien]

if there's no landmass then why not just have it floating on the oceans then? there really isn't a useful scenario for this.

 

also, in the case of the low land area planet, where are you going to get the fissionables to fuel your monstrosity?

 

nuclear reactors do regularly need to be refueled, either that or they require super high enrichment with would require a very large ground based isotope separation facility.

[Cap'n Refsmmat]

I don't see how having airports in midair will help anything. You still need airports on the ground to board planes to get up to the airports in the air.

[insane_alien]

nah, you just land the airport at an airport airport.

[npts2020]

insane_alien; It has been 30 years since I was doing the same job as ydoaPs but IIRC the power of a reactor on a carrier is closer to 1 or 2 MW than 300. (might be classified info but the Navy never made me sign any kind of long-term nondisclosure agreement)

[insane_alien]

http://en.wikipedia.org/wiki/A4W_reactor

 

says 104MWe for a naval reactor. so that would be about 300MW thermal.

 

EDIT: i imagine a lot of the earlier ones focused more on the production of steam from pure heat rather than converting it to electricity though. but on all the nuclear carriers the shaft power is in several hundred megawatts which certainly does mean the reactors were of that sort of magnitude in power, just maybe not producing that much electricity which would be relatively small.

[npts2020]

says 104MWe for a naval reactor. so that would be about 300MW thermal.

 

EDIT: i imagine a lot of the earlier ones focused more on the production of steam from pure heat rather than converting it to electricity though. but on all the nuclear carriers the shaft power is in several hundred megawatts which certainly does mean the reactors were of that sort of magnitude in power, just maybe not producing that much electricity which would be relatively small.

 

I may be mistakenly recalling the service generator (electrical) output rather than reactor's total output of energy. Like I say it has been a long time since I really had to think about it.

[michel123456]

Nuclear reactor need a huge amount of water for cooling purpose, otherwise they simply melt. That's the reason why all nuclear plants are positionned near rivers or upon ships/ submarines.

[ydoaPs]

Nuclear reactor need a huge amount of water for cooling purpose, otherwise they simply melt. That's the reason why all nuclear plants are positionned near rivers or upon ships/ submarines.

 

Not exactly. The cooling towers(or ocean for ships and submarines) are used as a heat sink in the steam system. The cooling of the reactor is done by generating steam in the secondary system.

 

 

A nuclear propulsion system for a spacecraft wouldn't need that. The primary system could heat the gasses directly and expel them through a nozzle.

[insane_alien]

and for the waste heat that gets absorbed by the ship, well, thats what the radiators are for.

[ydoaPs]

and for the waste heat that gets absorbed by the ship, well, thats what the radiators are for.

 

It's not exactly waste heat if you use it to warm the ship!

[michel123456]

A space elevator maybe?

http://en.wikipedia.org/wiki/Space_elevator