If Nuclear Lightbulbs Are So Awesome Why Has No One Built and Flown One?

[Spacescifi]

 

Seriously folks. I enjoy spaceflight because it is like the ultimate physical challenge for mankind, but I think in a lotta ways we hold ourselves back.

I am not about colonization like Zubrin, I just would like the ability to visit and come back in one piece.

 

Tech to that end is all I want. 

 

So nuclear lightbulbs.... why are they not flying?

Is it...

A: Powers that be are:

 

B: Nuclear lightbulbs do not work as well as advertised.

C: Too much of:

D: A combo of all three.

C: Something else.

 

Really, I do not care if is an SSTO or not, would a nuclear lightbulb offer any advantages in space? In atmosphere it can potentally if is boosted to ramjet speeds first with boosters. With said ramjet, and closed cycle nuclear heating of the air before being expelled.

 

What do you say to this?

Edited December 15, 2019 by Spacescifi

[magnemoe]

Multiple problems. Its not something you would ever use on an probe, its an engine for larger ships who we have none as they would be too expensive to build.

Very hard to test on earth, and as you need an large ship to use it it has been no need to test it.

other systems like z-pinch fusion are much easier to develop, as each experiment don't leave an meltdown area. 

Its kind of nerva^2, yes it has more trust an better ISP but difficulty of testing is way way higher. 

[wumpus]

36 minutes ago, magnemoe said:

Multiple problems. Its not something you would ever use on an probe, its an engine for larger ships who we have none as they would be too expensive to build.

And that's enough of a reason.

Since 1972 no human (thus nothing but probes) has left LEO.  Without any ships going outside of LEO, there's no reason to build an interplanetary engine (although NASA did build a NTR).

I'm also not sure what's so great about it.  It sounds far more dangerous to develop (see recent Russian missile disaster), while yielding barely any Isp gains over existing NTR designs (which also have political benefits from being grandfathered in by NASA as "man rated").

For probes and other non-crewed vehicles, there is always ion propulsion.

[Bill Phil]

It’s at a low TRL. That and nuclear power isn’t necessarily politically viable for space exploration - and space exploration is heavily tied to politics (as much as we don’t like it, it’s still true). 

We also have no true reason to build large ships.

One thing we only recently discovered is just how seriously the USAF was considering developing Project Orion nuclear pulse propulsion vehicles - not for exploration of course, but that would have likely occurred as a side effect. The argument the higher ups in the DoD used against it wasn’t that it wouldn’t work, but that they had no way of knowing that they even needed to push thousands of tonnes around in high energy trajectories and if they ever did, by that time other options might be available. By all indications it looked like they didn’t need it anytime soon. So they didn’t do it.

But it was a lot closer than we usually think.

Meanwhile gas core rockets are far more complex and suffer the same issues as Project Orion - it’s too big.

[kerbiloid]

Spoiler

Because it's heavy and takes too many nuclear physicists to change the lightbulb.

 

[KerikBalm]

12 hours ago, Spacescifi said:

closed cycle nuclear heating of the air before being expelled.

I'm not sure that works so easily. The heating is done by EM radiation through the quartz. Hydrogen propellant would need to be doped with a compound to more efficiently absorb the "hard" UV radiation (liquid hydrogen would be rather transparent to this hard UV). I think you might need something similar with intake air. But a doping compound to mix in small amounts with air still would save a lot

10 hours ago, wumpus said:

yielding barely any Isp gains over existing NTR designs

The only build designs get around 800s, the lightbulb designs could get 1500-3000 sec, that's double to triple existing designs. If solid core NTR is worth it vs chemical, then closed cycle gas core would be worth it over solid core. 

Granted the upper Isp limits of a solid pebble bed reactor are higher, if you use halfnium-tantalum carbide allows for the pebble shells... in which case the fission fuel is molten, but contained in a solid sphere.

I'd say the reason they haven't been used is the same reason NERVA has never been used

[sevenperforce]

How many rocket scientists does it take to change a nuclear lightbulb?

Spoiler

Ask the physicists; the rocket scientists are too scared to try.