I would leave to fly these

[Kerbol Macrosystems]

https://en.wikipedia.org/wiki/Project_Pluto

Project Pluto - if a nuclear reactor and a ram jet had a baby.  Take all the water out of a nuclear reactor and change the geometry of the fuel cells.  Air goes in the ram scoops, passes over the nuclear fuel rods to heat up, and creates thrust out the back.  If developed to fruition would be able to fly for months at a time.

https://en.wikipedia.org/wiki/Fission-fragment_rocket

Like a NERVA, but without the hydrogen.  You let the core heat up until it begins to vaporize and become a plasma.  Plasma is ejected from the rocket like an ion engine.  Depending on the geometry the ISP can get on the order of 100,000 s or 1,000,000 s.

[nosirrbro]

I personally wouldn't recommend flying anything that is spitting out nuclear waste or gas that has been in direct contact with a supercritical sample of uranium/plutonium.

[TimePeriod]

Radiation shielding.

Lead.

Rocket.

Plane.

No.

[sardia]

9 minutes ago, TimePeriod said:

Radiation shielding.

Lead.

Rocket.

Plane.

No.

You can save a ton of weight if you leave out the lead shielding. Or have it unmanned.  

[p1t1o]

To be fair, if you remove generous payload of nuclear warheads, that will probably save you fair amount of weight for use as you see fit

I <HEART> project Pluto

I wouldn't want you flying anywhere near my house though...

[wumpus]

[note: this is only about the fission rocket.  Don't make a nuclear plane.  Note that after the plane dropped the bombs the plane was expected to "buzz Russia" and spread nuclear waste.  It was as much a destructive weapon (ok, to much less a degree) than the bombs it contained.  You don't want one taking off, flying, or landing near you.]

If you can hold fission in a magnetic bottle like that, I'd assume you can do the same to fusion.  On the other hand, tokamaks *do* work to some degree (they just can't get net positive energy for any economic value of "net positive), so the basic idea may be possible with our present understanding of fusion.  I just really, really, don't believe this is going to be ready for prime time any time soon.

Note the shielding shouldn't be that big a deal.  And you hardly need lead, water works just as well https://what-if.xkcd.com/29/ .  In a normal rocket, the fuel tanks would work fine, but with enormous ISPs you will probably want an asteroid or something lodged in between the engine and the living quarters as shielding.  Hopefully this time the engineers will be on the right side of the "firewall".

 

Edited April 19, 2016 by wumpus
specified which I was responding to.

[Snark]

Moving to the science forum, since this is about the actual science/engineering involved rather than playing in-game.

[Kerbol Macrosystems]

I was thinking of these as in-game mods.  I guess the near-future tech already offers some parts with huge ISP, but Project Pluto is a little unique.  It's a fuel-less engine that generates a ton of heat, so it can never slow down without overheating.  Plus if you don't play with deadly re-entry then shielding is not a problem 

[PB666]

5 minutes ago, Snark said:

Moving to the science forum, since this is about the actual science/engineering involved rather than playing in-game.

If you want to call it science, we actually are moving from functional systems, to untried space systems, to barely practical high energy input system to something that has 7000 ISP but with so little mass and thrust you would be better off with solar panels and an ion drive.

A small fraction of the last few days posting.
  Accelerated proton decay engine using higgs boson or X-Y bosons.
  Wapping things with 100GW of lasers enough to obliterate them and then 60,000g of forces. (this being proposed by notable folks that have cash to try) 
  Strings hanging from space. Carbyne makes it all the more credible.
  Space fountains of magnetically charged particles.
  Microwave resonance chamber thruster.

Its not exactly like we are here wanting for more impractical systems.

  but, OK.