but is there a way to generator megwatts of energy from nuclear reactors that are lighter and compact. I swear that nasa has built and experimented on a nuclear reactor with an ion engine that is more compact? But still this does not explain why in the mean time they cant use a current nuclear reactor with the VASIMR engine for further testing.

A lot of the nuclear material once housed in warheads is being repurposed for nuclear power plants. Several US nuclear power plants are using fuel rods that were once aimed at them in the head of a missile housed in Russia.

The question isn't really whether it's POSSIBLE but whether it's practical.... or politically convenient.... and again... governments get paranoid when they hear "nuclear"...

Well Dr franklin chang diaz, the leader behind the VASIMR has gone on record of stating to get to Mars in a month or 2 you will need a Nuclear reactor to power the engine. At least they are still going ahead to put the engine on the ISS.

1. Cooling in space is a nightmare.
2. Getting the stuff into orbit is expensive and dangerous. Because rocket launchs sometimes go wrong. It's rocket science, after all.
3. NASA seems to work on LENR-based power sources, which are apparently much more promising.

1) Cooling in space is a nightmare! you are joking right!?
2) Expensive yes, how is it more dangerous?, they will most likely construct the thing and the rest of the ship in space.
3) LENR based power sources? unfortunately i don't know what that means.

no, it isn't.

just need power, lots of it. various nethods could be used as have been noted that aren't the standard reactor types. LENR is essentially a nuclear thermal battery. unstable as of yet, and they're still not sure why or exactly how it works. they do know it can have thermal runaway explosions. it's potential once they get it sorted is enormous.

it's also quite scary for corporations that deal in energy resources the world over...it can be made simply (one high school does it annually) with non restricted materials. (palladium, deuterium) it still has a ways to go however. nice thing is if there was an accident at launch using a LENR power source, no worries.

Okay, tell me: How do you cool a spacecraft? I am not an expert, but without any medium to transport the heat to, it seems rather complicated to get rid of unwanted waste heat. Of which you will have lots with any type of nuclear reactor, fission, fusion, LENR, antimatter, or otherwise.

That is not a very good description. It seems to be a way of using a clean nuclear reaction (beta-decay) as power source. In essence, it seems as if it could allow fusion-rocket level specific impulse with no radiation and no dangerous waste.

"Enormous" indeed.

heat is radiated from all surfaces into space unless that surface is facing the sun and being heated. space is not the insulator, not the same as a vacuum bottle. if it was planets would never have cooled >.> nor would the apollo 13 astronauts risked being frozen to death due to heat losses. the capsules were actually designed with those losses in mind...heaters and the electronics themselves covered the losses. impressive engineering balancing act for the era, among many.

old bad sci-fi claimed space was a perfect insulator. in space objects radiate heat, as the surrounding vacuum is considered cold. the transfer is by radiation, not conduction or convection. from hot to cold.

and thermal is more accurate than anything else, short form. that's all it does is produce heat. that's all any nuclear reaction does in varying degrees (at least what we use from it). we use the heat produced. so at present, it's a thermal battery. it will have a finite life span (hence the battery part) and produces an abundance of heat.

once the kinks are worked out you'll most likely see them wrapped in gases or liquids that will be heated to drive generators. cooled, then fed back to the LENR device for reheating.

But heat is radiated only at a certain pace, right? Once the energy density of the reactor in the spaceship is too high, the available radiation surface should not be able to keep up. Only question: What speed is it allowed to be?

(Besides, the sun is a problem, too, as it is rarely absent in our solar system...)

Well, put this way, any nuclear reactor is a battery.