Excellent. It's way past time.

NTP research never should have been stopped in the first place.

(Edited to correct typo)

Awesome. We've wasted too much time. Nuclear Rocketry is the path to a bright future for all the people of earth.

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Given our track record with junk in orbit it could be a positively glowing future here in a century as it all falls back down.

Nuclear rockets are only deployed in trajectories that do not intersect with any planet.

Sure. Until they get caught in the Kessler belt we are busy building.

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Please explain how an object on a trajectory that does not intersect with any planet gets caught in a Kessler belt.

Well we have to get it all up there first and we dont have teleporters.

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They stopped it because of an accident that caused super criticality, a massive radiation release.

Material, and nuclear science wasn't quite up to the task 50 years ago.

Spez, the deaths were a separate incident.

Got a reference? I think the early 1960s JSLAMM engine may have been canceled for that but the late 60s early 70s NERVA space test was axed by the Nixon Administration as part of budget cuts and descoping of the Saturn replacement down to just the shuttle/LEO. https://en.m.wikipedia.org/wiki/NERVA

One idea would be to use reusable 1st booster rockets like the ones space x uses to reduce the amount of debris left in space.

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I'm unaware of any such accident with NERVA NTRs, but very much open to correction. Might you provide a reference?

Looks like the deaths were from a separate incident, but here's a link I found.

https://youtu.be/db97RSlALYw

That incident was in 1958. NERVA didn't start seeing budget cuts until 1969 when Nixon got in, over a decade later. It seems unlikely there was any connection.

Fresh nuclear fuel isn't very dangerous. It's only after it's been used for a bit that it gets full of nasty isotopes.

So the simple answer is to launch the reactor cold and only activate it once safely in orbit.

That.. sort of sounds like the plot to an alternate history novel I read years ago, not the actual history.

Right. Fresh fuel isn't dangerous. /s

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If it fails, how big of an explosion are we talkin here?

Does anyone know how large these would be compared to a civilian energy reactor? When these come up, there’s always a debate about the risk of a catastrophic failure spewing radioactive material in unpredictable ways. But I’ve never been clear on what the scope of the disaster would be. Is it way more radioactive material or far less (and even that spread more thinly)? How uninhabitable is how much area for how long from a nuclear disaster on the way to space?

A worse case disaster, I mean. It sounds like for a Mars trip, we wouldn’t be using these engines until far enough in space. But let’s say this tech becomes routine. Maybe the Congressman for wherever these engines get made has a meeting with the contractor’s lobbyist and decides NASA needs to buy more engines. And then 💥kaboom💥.

They LIE as soon they open their dirty mouth. NASA scam of the Earth

What is blud waffling about

Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:

|Fewer Letters|More Letters| |-------|---------|---| |LEO|Low Earth Orbit (180-2000km)| | |Law Enforcement Officer (most often mentioned during transport operations)| |NERVA|Nuclear Engine for Rocket Vehicle Application (proposed engine design)| |NTP|Nuclear Thermal Propulsion| | |Network Time Protocol| |NTR|Nuclear Thermal Rocket| |RTG|Radioisotope Thermoelectric Generator|

^(5 acronyms in this thread; )^(the most compressed thread commented on today)^( has 12 acronyms.)
^([Thread #8482 for this sub, first seen 25th Jan 2023, 13:17]) ^[FAQ] ^([Full list]) ^[Contact] ^([Source code])

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He's more or less right. In its pure form it's as much dangerous from its heavy metal qualities as it is from radiation, hence the person holding this 90% pure plutonium puck wearing gloves.

Yeah, that photo doesn't tell me much about the relative dangers. I get that it's fairly safe in a puck as an alpha emitter, but that's not really the danger we are discussing, is it?

Referring to the earlier comments, I think it is what we're discussing - the pure "unburned" form being relatively safe.

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>Nuclear rockets are only deployed in trajectories that do not intersect with any planet.

unless there is a launch failure or Newton to pound thrust conversion error...

That was one of the plot points of "Voyage" by Stephen Baxter.

Just uranium. Like, what is found naturally all over the place.

Relatively short burn times. Thus only a small radioactive inventory of fission products.

A test was done back in the day. Equivalent to a few tons of TNT.

Yup. That was the one. The engine killed a few characters off after an accident during a test.

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I'm willing to take that risk.

The main issue is the radiation emitted during the blast. That has a higher lethal radius compared to the explosion. But still, somewhat managable.

No reason to launch anything significantly radioactive. It's the waste you have to worry about, the fission fuel itself is (comparatively) safe. It has to be, if it were seriously radioactive it wouldn't still exist after almost 5 billion years in the ground.

Still not exactly *safe*, but so long as you stay well away from critical mass the heavy metal poisoning will probably do more damage than the radiation.

And I think I recall hearing that NASA is moving strongly away from using legacy pre-physics units for anything, in large part because it opens the door to stupid conversion errors like that, and someone inevitably walks through.

I think a big issue was simply that using an NTP on Earth is a really, really bad idea - I seem to recall hearing of an idea from that era of flying one over the USSR to essentially carpet-dirty-bomb them into submission.

And off Earth... we haven't had any national interest in doing that. The moon race was good cold-war propaganda and ritualized combat... bringing nukes into it was exactly what we were trying to avoid. Going to other planet's though? Where's the profit, power, or security in that? Especially after determining that the moon was just a big dead rock we were nowhere close to being ready to usefully colonize, and photos from the 1965 Mariner mission established that Mars was probably the same.

Yeah, the long-term dreams are inspirational - but it's likely to be generations before anything except mostly-automated asteroid mining (which was completely out of reach at the time) will be able to turn a profit, and colonialism is all about getting rich. Not having your great-grandkids get rich, assuming they can even maintain a position to cash out on your investment rather than someone else's grandkids being the ones to do so.

Please don't send one into space. It could fail and cause a LOT of sad.

> Does anyone know how large these would be compared to a civilian energy reactor?

Tiny. A civilian energy reactor has to implement two heat exchange systems -- one for transferring heat from the core, and one for heating water to steam to turn turbines and then condense it again.

For NTP there are no circular heat exchanges, and no turbines. It's just a hot core in your reaction chamber, which heats the hydrogen you squirt on it, and the hot hydrogen gas escapes out the rocket nozzle.

The smallest critical mass of plutonium is about four inches across. In theory that's all you need in the reaction chamber, but in practice you will also want cladding so that your hydrogen reaction mass erodes the cladding and not the plutonium (else you'll be squirting plutonium out the rocket nozzle along with your hydrogen), and a bisecting neutron reflector shutter or something so you can turn the core on and off.

So, maybe something about twelve inches across? Still much smaller than a civilian power reactor.

Pretty sure they stopped it because Soviet and American diplomats agreed that would ease international tensions, without really understanding what they were talking about.

First of all, I'm an opponent of nuclear power here on earth.

But I'm absolutely for nuclear propulsion in space. These rockets can be made safe, the thing to be concerned about is the waste product. Prior to launch, the fuel can be encased safely as was done with the Apollo RTGs. So even the explosion of a fully fueled rocket on the pad will not be a problem. The engine is then only activated once safely in space.

There is no reason by have any panic reaction just because it has the word nuclear in it.

If it fails to reach orbit for any reason then it will most certainly intersect with at least one planet.

I still don't see fission powered jets at a commercial airport any time soon.

Maybe on Mars, in fact a fission rocket would good for 2nd stage payloads to the outer planets.

The future is fusion, and probably won't be any nuclear powered craft until then.

I mean nuclear fuel is typically comprised of uranium-235 and uranium-238, both of which occur naturally and can be found in low levels within all rock, soil, and water. Soil for example contains about 12 milligrams of uranium per kilogram on average.

A typical space-based fission reactor contains abut 30 kg of uranium. If a rocket blew up halfway through the launch and scattered that perfectly over a radius of say 50km, and it was all absorbed by just the top 1cm of soil, that would amount to an additional 0.3 milligrams of uranium per kilogram of soil.

Of course, if it spread over a smaller area the concentration would be higher, but it would have to be a pretty small area for there to be enough to matter, so it's not likely to be a major hazard in the grand scheme of things.

 

In practice it's more likely that the fuel rods would remain largely or entirely intact and end up at the bottom of the ocean somewhere. The ocean contains approximately 4 billion tonnes of uranium, so even if the fuel rods were gradually eroded, they'd quickly be diluted into irrelevance.

Now, there are some ways that it might be possible for someone to be exposed to a dangerous quantity - for example, say something like a gram of uranium being chipped off and somehow ingested by someone, my point is more that it's not going to be a widespread ecological disaster.

Whereas in the case of a disaster like Chernobyl, there were a lot of nasty isotopes present in the partially spent fuel rods, most notably iodine-131, caesium-134, caesium-137 and strontium-90. These isotopes are tens of millions of times radioactive than uranium-235 or uranium-238, so even the most miniscule quantities are dangerous.

I'd also point out that we already regularly launch other dangerous substances on rockets. Hydrazine for example has comparable toxicity per milligram to uranium, and large satellites are regularly launched with literal tonnes of that onboard.

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