The Last Post Game!!!!

[Swatopluk]

The nuclear thermal rocket sounds more interesting.

Last _{and feasible} Post

Most sci-fi before the actual moon landing took it as a given that something like that would be used.

Last Post

[Sibling Zono (anon1mat0)]

The problem is that it's heavy (plus the nuclear thing), yet radioisotope thermoelectric generators coupled with ion propulsion are more likely to be used.

Last _{perhaps for my comet ship} Post

[Swatopluk]

But those nuclide batteries are not very powerful. The largest on space probes have just 500W output. The ones the Soviets used to power lighthouses contained up to 100 kg radioactive material in order to have sufficient output.

Last Post

[Sibling Zono (anon1mat0)]

I know, thermocouples aren't particularly efficient and not much research seems to be placed on power production.

Last _{more in accuracy as those are used to measure temperature changes} Post

[Swatopluk]

Even at 100% efficiency their main area of use would still be longterm low-yield power output. The same could be said of the ion drive of course but imo the basic minimum output to make it worthwile would still be quite high and thus require a large amount of amassed radioactive material to start. The economies of scale would set in at a rather high level. In other words an ion driven vessel/object has to be either extremly light with a high intensity power source or very big with a constant low intensity. Not fully fitting analogy: ultra fast ships tend to be either minute or extremly big. There are few very fast medium sized ships. Both tpyes use different power sources (e.g.gas turbines on race boats and nuclear reactors on aircraft carriers). It's not feasible to build a nuclear reactor for a small boat or to build a mega-PS gas turbine.

Last Post

[Aphos]

Last _{to infinity and beyond} Post

[Sibling Zono (anon1mat0)]

But in space you can have a significant temperature differential between the reactor and outer space, and if the thermocouples could take advantage of such differential they yield would be significantly greater.

Last _{still not enough electricity to run something like a VASIMR} Post

[Swatopluk]

As I said, even 100% efficiency with these low specific yield devices would not make them feasible at the sizes we can currently consider for the spacecraft.
Projects for fast interstellar probes usullay think about either mini-devices of less than a kg or huge behemoths (talking the size of oil tankers or more here).
The former would not have engines of their own but be driven by e.g. laser batteries on the moon. They could only do a fly-by at relativistic speed in the targeted solar systems because there would be no way to decelerate them.

last Post

[Sibling Zono (anon1mat0)]

Last _{how small can you make a 2MW generator?} Post

[Swatopluk]

Depends on how long you want it to run. Laser with pulses in that range can be built to fit into a matchbox.

Last _{but the pulses are very short} Post

[Sibling Zono (anon1mat0)]

Can you get a laser efficient enough to send a ship to Mars or the jovian moons?

Last Post

[Swatopluk]

For small probes it would already be sufficient but for larger ones, I think, we are not yet far enough. In any case the laser would have to be outside the atmosphere, which again poses the question of energy supply.

Last Post

[Aphos]

Last _{spacetime continuum} Post

[Swatopluk]

No chance to tap into Zero-point energy

Last Post

[Sibling Zono (anon1mat0)]

You can use large solar panels in orbit to power the death ray laser.

Last _{somehow the other approaches sound more feasible at this point} Post