Why aren't we using nuclear thermal rockets?

[DDE]

1 hour ago, Green Baron said:

The released reactor cores of the Rorsats form a radiation belt in a debris orbit at 950 km (search Rorsat NaK drops).

I do recall the hypothesis, but everything I’ve scooped up doesn’t mention radiation (with one Space.com columnist shrugging as to whether the droplets are rad); so it’s a nasty case of debris generation, not directly related to the type of powerplant.

On a tangential note, 24Na has a half-life of 15 hours. The Wiki specifically notes this via-a-vis NaK coolant. Unfortunately, it’s a beta emitter, so it should be able to energize a belt.

Edited December 20, 2018 by DDE

[Green Baron]

Uranium 235 radiates, it halfs every 700 million years or so. It belongs to the most poisonous materials known. The drops are coolant liquids from the satellites. Furthermore it is unknown if, when and how the satellites leak fuel or other hazardous material, or what happens in case of collisions. They are a life threatening heritage for a long time, if they can't be cleaned up. And they are in a region where "unexpected debris events" are very likely.

https://www.researchgate.net/publication/2353432_Effects_of_the_rorsat_NaK_drops_on_the_long_term_evolution_of_the_space_debris_population

https://www.sciencedirect.com/science/article/pii/S0094576505000834

https://www.space.com/6322-nuclear-powered-soviet-satellite-acts.html

---------------

The point above was: a single part out of a collection of 10, which together sum up to 1% of the fission material in the satellite's core, was lethal on contact. Pick it up and take it home and the person will die an unaesthetic death, probably causing sicknesses like cancer in others. And for a normal human it is impossible to tell on sight. "Look ma, i found a satellite part !" could be an obituary for a whole family and more.

Launching a rocket with a larger reactor would bear the considerable risk of dropping that stuff back to earth, potentially killing people immediately and others later or rendering an area uninhabitable. And there is no need right now to take that risk, which brings us back to the original question. In the future (decades from now) it is likely that there will be much more efficient methods (am thinking of possible fusion). Until then we may actually have work to do for people in space, or on other bodies.

[kerbiloid]

That's why I've bought this thing 30 years ago and from time to time use it just for fun,

Spoiler

Of course it's only gamma, but it's beta than nothing.

P.S.
It can beep.

Edited December 20, 2018 by kerbiloid

[DDE]

7 minutes ago, kerbiloid said:

Of course it's only gamma, but it's beta than nothing.

Betas are fine. You can actually feel the burn. 

37 minutes ago, Green Baron said:

It belongs to the most poisonous materials known.

It doesn’t. It’s merely as chemically poisonous as lead, which makes the alpha-ray damage (requiring ingestion) utterly negligible.

39 minutes ago, Green Baron said:

They are a life threatening heritage for a long time

They aren’t, not yet, seeing as how debris events can’t deorbit them and there are no manned flights in MEO.

42 minutes ago, Green Baron said:

Pick it up and take it home and the person will die an unaesthetic death, probably causing sicknesses like cancer in others. And for a normal human it is impossible to tell on sight. "Look ma, i found a satellite part !" could be an obituary for a whole family and more.

That’s a quick trip towards a Darwin award. Random poorly supervised radiation sources are exactly one of the reasons I was told to stay away from any odd object, trefoil or not. There are tens of thousands of industrial and medical gamma emitters, not to mention hundreds of full-sized RTGs, unaccounted for.

44 minutes ago, Green Baron said:

.Launching a rocket with a larger reactor would bear the considerable risk of dropping that stuff back to earth, potentially killing people immediately and others later or rendering an area uninhabitable.

Oh, please. An unstarted reactor presents no radiation hazard; one built to last would probably survive the booster explosion and lithobraking, RTG casings certainly do.

[kerbiloid]

People should build an orbital station to store the spent radiation sources and call it Death Star.

[Green Baron]

43 minutes ago, DDE said:

It doesn’t. It’s merely as chemically poisonous as lead, which makes the alpha-ray damage (requiring ingestion) utterly negligible.

Yes, it does. You are apparently unaware of the risk of enriched u 235. A brief contact can and does cause death. You don't fall immediately, which doesn't make things better.

https://www.ncbi.nlm.nih.gov/books/NBK158798/

Quote

They aren’t, not yet, seeing as how debris events can’t deorbit them and there are no manned flights in MEO.

Yes they are, read the links i posted.

Quote

That’s a quick trip towards a Darwin award. Random poorly supervised radiation sources are exactly one of the reasons I was told to stay away from any odd object, trefoil or not. There are tens of thousands of industrial and medical gamma emitters, not to mention hundreds of full-sized RTGs, unaccounted for.

But normally not as poisonous as reactor fuel and contaminated coolant. People actually die from contact and inhalation. Cesium from medical stuff for example is still not good and can when longer in contact with cause cancer, but it is by far not as bad as the above.

Quote

Oh, please. An unstarted reactor presents no radiation hazard; one built to last would probably survive the booster explosion and lithobraking, RTG casings certainly do.

That is ... nonsense. An intact reactor only presents a potential hazard. A broken one .. look at Tchernobyl and Fukishima. As i said, people actually do die. And if it breaks in the atmosphere (don't tell me it survives intact, it simply did not and will not in the future) or on impact you'll have a big and lasting mess.

Edited December 20, 2018 by Green Baron

[DDE]

34 minutes ago, kerbiloid said:

People should build an orbital station to store the spent radiation sources and call it Death Star.

Storing it on the Moon is a great idea.

[kerbiloid]

3 minutes ago, DDE said:

Storing it on the Moon is a great idea.

On the Moon you have to land it. It can crash. Orbital station has much weaker speed requirements on approaching.

Edited December 20, 2018 by kerbiloid

[tater]

The guys at Marshall are near enough on a new design that with some funding they could fly one in short order.

We should of course ignore the Luddites and use NTRs. The designs I have seen could have the launch vehicle explode during liftoff, and they could pick the reactor up off the bottom of the ocean afterwards and reuse it.

[Ozymandias_the_Goat]

On 10/12/2012 at 1:37 AM, doggie015 said:

Nuclear FISSION is rather unsafe, however there is more than one way to use nuclear energy...

If you can make a fusion reactor small enough to fit in a rocket engine then you have a very safe alternative. Fusion uses less fuel in the reactor, the waste is not a problem as all the fuel is converted into energy, at most you can only have enough fuel for a few milliseconds of operation at a time in the reactor, if the core is breached it stops producing heat in less time than it takes for you to blink, and it runs on Hydrogen, already widely used in space travel!

At the same time, we have a long way to go before we even produce a functional terrestrial fusion reactor, so it’s not as if a fusion reactor is a near future technology. 

On 10/12/2012 at 12:04 AM, Qumefox said:

No, the real danger with an NTR engine is a craft failure at high altitude/sub orbital.. or in an unstable orbit that will eventually decay and have the engine re-enter and land in a populated area.

I’m not sure if a failure at high altitude would be catastrophic, at least not in the manner that you describe. An NTR stage, as you said, would be solely an upper stage, which probably would not even be fired until the ship is in orbit. I suppose that you might be thinking of something like a second-stage failure, in which case the payload would crash before reaching orbit. However, consider that all space agencies intentionally plot launch paths over unpopulated areas. Indeed, if an NTR launched from the KSC was to have a catastrophic second stage failure, it would either crash into the Atlantic Ocean, or be traveling so fast the reentru forces would destroy it before it could deal any damage. Plus most of the world has very low population density, so the odds of an NTR hitting a population center is essentially zero. The only people who would be at risk are the crew of the vehicle but this is why cargo and crew should launch separately. 

[kerbiloid]

4 minutes ago, Ozymandias_the_Goat said:

forces would destroy it before it could deal any damage

Isn't this destruction exactly that danger?

[Ozymandias_the_Goat]

24 minutes ago, tater said:

The guys at Marshall are near enough on a new design that with some funding they could fly one in short order.

We should of course ignore the Luddites and use NTRs. The designs I have seen could have the launch vehicle explode during liftoff, and they could pick the reactor up off the bottom of the ocean afterwards and reuse it.

Exactly! The risks of using an NTR are really the same as with any rocket engine. Space travel is simply dangerous, there is no way around that...yet. The entire fear of NTRs is simply the irrational fear of nuclear technology.

5 minutes ago, kerbiloid said:

Isn't this destruction exactly that danger?

 

But to respond to your question, isn’t the amount of radiation produced by an NTR failure rather small? If it disiopated over a large area, namely an unpopulated one, the fallout would be rather minimal? And anyway, second stage failures are relatively rare, and the vehicle is at greatest risk during the first stage burn. And as @tater said, failure of the first stage would still allow reactor recovery.

Edited December 20, 2018 by Ozymandias_the_Goat

[kerbiloid]

6 minutes ago, Ozymandias_the_Goat said:

isn’t the amount of radiation produced by an NTR failure rather small?

I guess, not the radiation of the running reactor is the main danger, but the radioactives from the destroyed one.

[Green Baron]

12 minutes ago, Ozymandias_the_Goat said:

Exactly! The risks of using an NTR are really the same as with any rocket engine. Space travel is simply dangerous, there is no way around that...yet. The entire fear of NTRs is simply the irrational fear of nuclear technology.

Experience tells the contrary, people rather ignore risks than logically calculate them. There is no irrationality connected to existing nuclear failures, in contrary there is an irrational hope in "it'll go out good and if not we'll keep it under the carpet" connected to these failures. I spare you the sources for that claim. While the small kilo reactors might survive a launch failure, they will (probably) not survive an uncontrolled reentry, and finally spread their contents on impact or when dissipating in the atmosphere(*). The coolant mentioned above was the basis for Kessler's theorem. While chances that things hit population may be low (not zero, that is the ignore part :-), see Chinese rocket launches, even an astray rocket from Baikonur could fall on a nearby city and one from Florida could reenter over Europe or Africa), there is no need to take it.

Sure, fusion is not there in the next 20years, but maybe in 50 ...

(*) radioactivity has been measured by planes after uncontrolled reentries of Rorsat reactors. So they do not survive, "fortunately" most of them fell in the ocean.

Edited December 20, 2018 by Green Baron

[DDE]

38 minutes ago, Green Baron said:

Yes, it does. You are apparently unaware of the risk of enriched u 235. A brief contact can and does cause death

https://www.ncbi.nlm.nih.gov/books/NBK158798/

Your link is broken.

Furthermore, since uranium is a very weak alpha emitter (a corollary of a long half-life) there’s no imaginable mechanism for it to act as the Sudden Death Factor. Tritium fusion fuel is far, far worse on that front, BTW.

38 minutes ago, Green Baron said:

That is ... nonsense. An intact reactor only presents a potential hazard.

An unactivated reactor pile with the neutron absorbers in place is a just an arrangement of large quantities of very weakly radioactive materials. Except for the flimsy NaK reactor held together by metal straps - apparently the Soviets expected a neat RUD and burnup in the upper atmosphere - reactors tend to be very robust.

Edited December 20, 2018 by DDE

[kerbiloid]

Kosmos-954 was 4 t heavy
vs
Canada is 9 mln km² large

And how much emotions that small reactor has caused.

(Btw Canada didn't catch it, so Kosmos:Canada 1:0)

[Bill Phil]

41 minutes ago, DDE said:

Storing it on the Moon is a great idea.

Yeah but then the Moon gets sent careening through interstellar space.

[Green Baron]

6 minutes ago, DDE said:

Your link is broken.

https://www.ncbi.nlm.nih.gov/books/NBK158798/

Quote

... Sudden Death Factor ...

Yep, cancer and cellular decay take some time ...

Quote

An unactivated reactor pile with the neutron absorbers in place is a just an arrangement of large quantities of very weakly radioactive materials. Except for the flimsy NaK reactor held together by metal straps - apparently the Soviets expected a neat RUD and burnup in the upper atmosphere - reactors tend to be very robust.

That is what i criticize. The filling is not very weakly but highly radioactive. And it is not the stopped reactor in quiet conditions but the broken impacted parts of it. And the Soviet expectations obviously where incorrect. The reactors broke up in the atmosphere and spit their contents over >10.000 square miles.

Edited December 20, 2018 by Green Baron

[kerbiloid]

Spoiler

If put them on the prograde side of the Moon, we can do an almost eternal retrorocket and make Moon close again.

 

[DDE]

6 minutes ago, Green Baron said:

Sure, fusion is not there in the next 20years, but maybe in 50 ...

It will likey never catch on in space propulsion. I’ve never seen anyone conclusively show it has an advantage in specific power once you factor in the dry mass of the powerplant.

[tater]

3 minutes ago, Green Baron said:

Experience tells the contrary, people rather ignore risks than logically calculate them. There is no irrationality connected to existing nuclear failures, in contrary there is an irrational hope in "it'll go out good and if not we'll keep it under the carpet" connected to these failures. I spare you the sources for that claim. While the small kilo reactors might survive a launch failure, they will (probably) not survive an uncontrolled reentry, and finally spread their contents on impact or when dissipating in the atmosphere(*). The coolant mentioned above was the basis for Kessler's theorem. While chances that things hit population may be low (not zero, that is the ignore part :-), see Chinese rocket launches, even an astray rocket from Baikonur could fall on a nearby city and one from Florida could reenter over Europe or Africa), there is no need to take it.

Sure, fusion is not there in the next 20years, but maybe in 50 ...

(*) radioactivity has been measured by planes after uncontrolled reentries of Rorsat reactors. So they do not survive, "fortunately" most of them fell in the ocean.

This is flat out wrong for modern designs. I'm about as worried about the NASA NTR guys causing a nuclear disaster as I am about being hit on the head by debris from ISS. It's a complete non-issue for serious designs by people who aren't idiots---I have no opinion on NTR designs by, say, the Chinese, but the NASA designs would literally survive orbital reentry (the thermal stresses are lower than operating as an NTR). I'd in fact be fine with a nuclear launch vehicle (a hybrid air-breather has been proposed that looks pretty cool, it is reusable---in space, it never comes back to Earth.).

[Green Baron]

15 minutes ago, tater said:

This is flat out wrong for modern designs. I'm about as worried about the NASA NTR guys causing a nuclear disaster as I am about being hit on the head by debris from ISS. It's a complete non-issue for serious designs by people who aren't idiots---I have no opinion on NTR designs by, say, the Chinese, but the NASA designs would literally survive orbital reentry (the thermal stresses are lower than operating as an NTR). I'd in fact be fine with a nuclear launch vehicle (a hybrid air-breather has been proposed that looks pretty cool, it is reusable---in space, it never comes back to Earth.).

Before you continue with "idiots" and so (lets stay friendly), the reactors that did reenter did not survive, despite claims of being able to, so this is incorrect. A more compact RTG might. If you have infos on larger reactors, that may be the time to post them, but i doubt there are any except claims.

@tater: This article says that the risk of contamination of an RTG during a launch failure can not be excluded. So there you go. Will you take back the "idiot" ?

Edited December 20, 2018 by Green Baron

[kerbiloid]

5 minutes ago, DDE said:

It will likey never catch on in space propulsion. I’ve never seen anyone conclusively show it has an advantage in specific power once you factor in the dry mass of the powerplant.

It has advantage in fuel. There is deuterium everywhere in the water.
And its ISP is higher.
It produces less radioactive wastes. It potentially has much less problems with criticality if say the reactor is induced by the lasers or magnetic field.

 

[DDE]

14 minutes ago, Green Baron said:

https://www.ncbi.nlm.nih.gov/books/NBK158798/

Yep, cancer and cellular decay take some time ...

That is what i criticize. The filling is not very weakly but highly radioactive. And it is not the stopped reactor in quiet conditions but the broken impacted parts of it. And the Soviet expectations obviously where incorrect. The reactors broke up in the atmosphere and spit their contents over >10.000 square miles.

Aha, so we’re not talking about the easily observable ARS effects, but the ever-so-elusive and understudied long-term effects of low-level exposures, ones nearly impossible to extract from background cancer rates.

Or perhaps they don’t even exist and a little radiation actually improves health, as argued by proponents of radiation homeostasis.

As to the Buk reactor, spreading the debris around was lart of the plan; preferably the debris would have been spread around globally. The most basic counter to pollution is dilution, remember? Tall smokestacks, dumping sewage in large bodies of water...

4 minutes ago, Green Baron said:

despite claims of being able to, so this is incorrect

Well, it wasn’t an NTR. I have repeatedly shown you that Buk-5 was built far more flimsily and used a different mitigation strategy.

After the ‘954 incident, the reactor was equipped with an additional fuel rod ejection system to guarantee RUD in the upper atmosphere.

13 minutes ago, tater said:

I have no opinion on NTR designs by, say, the Chinese

Honest question: do they even have them?

Edited December 20, 2018 by DDE

[sh1pman]

24 minutes ago, DDE said:

Tritium fusion fuel is far, far worse on that front, BTW.

Only if you inhale/ingest it. And then it's metabolized and released by your body fairly quickly. I work with tritium a lot (well, used to work a lot, now using cheaper and safer alternative). If it's contained, even in plastic, it's harmless.