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Why aren't we using nuclear thermal rockets?

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Nuclear energy is contentious and complex, both from a technical and people (human nature) perspective. It's unfortunate that people eagerly fit themselves into the Pro or Anti camps.

Fissile material is hard enough to keep contained in dedicated containment vessels on the ground. A couple of major incidents provide evidence of this. So it's not something you want on a rocket, since rockets have a tendency to go wrong. There is ample evidence of that. Only a few days ago SpaceX had a minor incident.

Besides, as others have pointed out, high Isp NERVAs are not needed for missions to Mars. What is needed is MONEY.

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You all assume they are not used... NASA may be open about everything they do, but the government launches plenty of stuff no one knows about :)

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Look what damage made green guys in Germany

I looked and see no damage done by green guys.

I do however see Germany is frontrunner in renewable energy.

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You all assume they are not used... NASA may be open about everything they do, but the government launches plenty of stuff no one knows about :)

Your response indicates a certain optimism about how easy it is to hide something expressly designed to get hot in an enormous insulator floating above enormous arrays of sensors designed specifically to detect just that. For a nuclear reactor to enter space without anyone becoming aware of it would require the sort of global conspiracy that wouldn't need it.

I think more than just the general consensus against nuclear engines, we don't have any pressing reason to use them. Most nuclear engines are designed around sustained thrust at a significant rate, and we don't launch anything heavy enough far enough away to justify the hassle.

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above all else id say political reasons. the fact a contrey will be using nuclear power of any kind makes people un easy, especially civilians who dont understand it. even with nuclear power plants, some contries are hard up to try and get nuclear power because of world sanction.

the reason we dont use them are more because of people, and less because of the item themselves.

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Humans are not launching nuclear thermal rockets because humans have yet to create and implement, on large scales, reliable closed ecosystems that can support humans, or machines, indefinitely without expensive maintenance and resupply missions. It is a sadly overlooked issue in space travel, I think. The politics are really a distraction.

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Other than a manned mars mission (which we don't have the budget/technology for anyway) what would nuclear thermal rockets be used for?

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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!

I think you need to look up what a NERVA is and how it works..

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Moderator Comment: Excellent and interesting thread, but it's not really about Kerbals. It would be more suited in 'The Science Labs', thread moved. Thanks.

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One of the major issues with NTRs is restriction on weapons-grade material; to make a reactor small but powerful enough to be useful in space, you need fuel more highly refined than most nuclear weapon cores. Plus there's the pretty big problem where no rocket big enough to launch one and a reasonable payload for it has existed for 40 years.

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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!

from what i know a fusion reactor efficiency is directly proportional to it's size, so it would be impossible to use that tecnology for a rocket engine.

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I was amused by the guy who said it was strange how people are too eager to go into pro and anti camps.

And how he said '...a few major incedents show...' when the only major incedents I can think of [Chernobyl, Three-Mile Island, Windscale] were all results of gross incompetence, human error, and bad design - which are three things we no longer have problems with because of those incedents. if anyone can be trusted not to let incompetence, human error and bad design get in the way of a mission, it's space agencies.

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Space reactors can't really be compared to land based power plants in that manner, for a number of reasons.

One of the major lessons learnt from those incidents was the need for proper containment, in these case meaning 3+ metres of reinforced concrete; something which clearly can't be used on a spaceborne reactor. The same is true for most other safety improvements, like redundant cooling system or most automatic shutdown systems; and then there's the fact that a land-based power plant is unlikely to have to handle re-entry, something which has happened to actual space-based reactors three times already, and would have had serious consequences with the higher powered reactor needed for an NTR.

The reactor itself also wouldn't be particularly comparable to a power station either, due to the massive power density required; it would be better compared to the reactors on submarines, which have a habit of failing spectacularly and fatally.

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it would be better compared to the reactors on submarines, which have a habit of failing spectacularly and fatally.

There are several fatal flaws in this logic. Most of them have to do with comparing US aerospace design and construction principles with cold war era soviet military doctrine and principles. Specifically the cold war soviet nuclear submarines you listed. Soviet doctrine of the era was to make as many as possible, as fast and cheaply as possible. Safety was never a high priority for them. Certainly not nearly as high as it is in the US, for something involving the space program.

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You can't really say that the US track record is much better than the former Soviet Union. Both the american and soviet military had many nuclear incidents during the cold war:

http://en.wikipedia.org/wiki/List_of_military_nuclear_accidents

The problem with nuclear engines is what happens in the case of a launcher failure. Rockets are much less reliable than aircraft, and statistically, given enough launches, there will be failures.

April 21, 1964 – Indian Ocean – Launch failure of a RTG powered satellite

A U.S. Transit-5BN-3 nuclear-powered navigational satellite failed to reach orbital velocity and began falling back down at 150,000 feet (46 km) above the Indian Ocean.[34] The satellite's SNAP-9a generator contained 17 kCi (630 TBq)[35] of 238Pu (2.1 pounds), which at least partially burned upon reentry.[36][37][38][39] Increased levels of 238Pu were first documented in the stratosphere four months later. Indeed NASA (in the 1995 Cassini FEIS)[35] indicated that the SNAP-9a plutonium release was nearly double the 9000Ci added by all the atmospheric weapons tests to that date.[40][41] The United States Atomic Energy Commission reported a resulting threefold increase in global 238Pu fallout.[42][43] All subsequent Transit satellites were fitted with solar panels; RTG's were designed to remain contained during re-entry.

Edited by Nibb31

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I was amused by the guy who said it was strange how people are too eager to go into pro and anti camps.

And how he said '...a few major incedents show...' when the only major incedents I can think of [Chernobyl, Three-Mile Island, Windscale] were all results of gross incompetence, human error, and bad design - which are three things we no longer have problems with because of those incedents. if anyone can be trusted not to let incompetence, human error and bad design get in the way of a mission, it's space agencies.

I think the Japanease would beg to differ with your assessment.

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There are several fatal flaws in this logic. Most of them have to do with comparing US aerospace design and construction principles with cold war era soviet military doctrine and principles.

Why do you assume we're talking about the US here? Look around you; what countries do you think would actually launch one of these things? The three major candidates are Russia, China and the US, all pushing forward in both space and nuclear power.

The US is clearly a no-go for this tech, due to typical nuclear hysteria.

China are very optimistic about nuclear power, just look at the rate they're building plants (26 right now); but even in their vaguest predictions they have no aims in space beyond simply going to the Moon, rendering the technology essentially a waste of money.

Russia are also very optimistic about nuclear power, they're planning on building eleven in the near future, and are also moving forward rapidly in space, thanks to all of the oil money that's been rolling in for the past decade, and they have big plans; they are the only nation with real Mars plan, for example. They're also the nation with eleven reactors identical to the one at Chernobyl still running, the one building insanely vulnerable floating power plants, and the one that's already splattered a country with lethally radioactive debris from a de-orbiting nuclear reactor.

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Loss of political support and cancellation

The Rover/NERVA program accumulated 17 hours of operating time with 6 hours above 2000 K. Although the engine, turbine and liquid hydrogen tank were never physically assembled together, the NERVA was deemed ready to design into a working vehicle by NASA, creating a small political crisis in Congress because of the danger a Mars exploration program presented to the national budget. Clinton P. Anderson, the New Mexico senator who had protected the program, had become severely ill. Lyndon B. Johnson, another powerful advocate of human space exploration, had decided not to run for a second term and was considerably weakened. NASA program funding was somewhat reduced by Congress for the 1969 budget, and the incoming Nixon administration reduced it still further for 1970, shutting down the Saturn rocket production line and cancelling Apollo missions after Apollo 17. Without the Saturn S-N rocket to carry the NERVA to orbit, Los Alamos continued the Rover Program for a few more years with Pewee and the Nuclear Furnace, but it was disbanded by 1972.

The most serious injury during testing was a hydrogen explosion in which two employees sustained foot and ear drum injuries. At one point in 1965 the liquid hydrogen storage at Test Cell #2 during a Los Alamos Scientific Laboratory Test was accidentally allowed to run dry; the core overheated and ejected on to the floor of the Nevada desert. Test Site personnel waited 3 weeks and then walked out and collected the pieces without mishap. The nuclear waste from the damaged core was spread across the desert and was collected by an Army group as a decontamination exercise.

[edit]In the space program

NASA plans for NERVA included a visit to Mars by 1978 and a permanent lunar base by 1981. NERVA rockets would be used for nuclear "tugs" designed to take payloads from Low Earth Orbit to larger orbits as a component of the later-named Space Transportation System, resupply several space stations in various orbits around the Earth and Moon, and support a permanent lunar base. The NERVA rocket would also be a nuclear-powered upper stage for the Saturn rocket (the Saturn S-N), which would allow the upgraded Saturn to launch much larger payloads of up to 340,000 pounds to Low Earth Orbit.

NERVA rockets had progressed rapidly to the point where they could run for hours, limited in run time by the size of the liquid hydrogen propellant tanks at the Jackass Flats test site. They also climbed in power density. The larger NERVA I rocket gradually gave way to the smaller NERVA II rocket in mission plans as efficiency increased and thrust-to-weight ratios grew, and the KIWI gradually gave way at Los Alamos to the smaller Pewee and Pewee 2 as funding was cut to lower and lower levels by Congress and the Nixon administration.

The RIFT vehicle consisted of a Saturn S-IC first stage, an SII stage and an S-N (Saturn-Nuclear) third stage. The Space Nuclear Propulsion Office planned to build ten RIFT vehicles, six for ground tests and four for flight tests, but RIFT was delayed after 1966 as NERVA became a political proxy in the debate over a Mars mission. The nuclear Saturn C-5 would carry two to three times more payload into space than the chemical version, enough to easily loft 340,000 pound space stations and replenish orbital propellant depots. Wernher von Braun also proposed a manned Mars mission using NERVA and a spinning donut-shaped spacecraft to simulate gravity. Many of the NASA plans for Mars in the 1960s and early 1970s used the NERVA rocket specifically, see list of manned Mars mission plans in the 20th century.

The Mars mission became NERVA's downfall.[2] Members of Congress in both political parties judged that a manned mission to Mars would be a tacit commitment for the United States to decades more of the expensive Space Race. Manned Mars missions were enabled by nuclear rockets; therefore, if NERVA could be discontinued the Space Race might wind down and the budget would be saved. Each year the RIFT was delayed and the goals for NERVA were set higher. Ultimately, RIFT was never authorized, and although NERVA had many successful tests and powerful Congressional backing, it never left the ground.

In conclusion: In the Early 1970s, Nixon saw the NERVA project as a gateway to a manned Mars station, which he also saw as ending up costing a LOT of money. Remember in the early 70s we were still in the Cold War with the Soviets, so anything we would try to do, the Soviets would (shortly thereafter, and pretending it was their idea all along) also do the same thing.

So, Nixon didn't want to get into a spending match with the Soviets, to see who could blow the most money on their space program.

It's too bad, too, because this could be seen as the end of manned exploration in space. I think XKCD said it best, "Ok, so Spirit and Opportunity are pretty awesome. And Kepler. And New Horizons, Cassini, Spirit and Opportunity, Curiosity, TiME, and Project M. But c'mon, if the Earth were a basketball, in 40 years no human's been more than half an inch from the surface."

moon_landing.png

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REASONS FOR NO NUCLEAR ROCKET ENGINES: rember these things THE END OF WW2 nuclear bomb COLD WAR russia threatened us with nukes.

REASONS FOR IT:about a tiny one or a big one will blow up

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REASONS FOR NO NUCLEAR ROCKET ENGINES: rember these things THE END OF WW2 nuclear bomb COLD WAR russia threatened us with nukes.

REASONS FOR IT:about a tiny one or a big one will blow up

There is a difference between a Nuclear Fission and Nuclear Detonation.

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I think the Japanease would beg to differ with your assessment.

Fukishima had a certain amount of hubris involved in it too. Just pull up the wiki page on the accident and you can see several instances of TEPCO being warned and ignoring those warnings (ignored a Tsunami study that highlighted the plant's vulnerabilities to seawater, this was dismissed as unrealistic, as well as the IAEA telling them that a 7.0 quake posed serious risks to the plant) and TEPCO falsifying records.

There is sufficient reason to doubt that the plant would have melted down if TEPCO had taken heed of those warnings.

Also, compare Fukishima with Tokai both plants are on the coast of Japan. Both plants were hit with similar Tsunami waves. However, because Tokai took the Tsunami warnings seriously, they were increasing the size of the dike around the plant and were about to ride out the waves.

Edited by Tauge

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I think you understood my point whilst assuming that I was making a different one. Or something...

That's exactly what I meant. Hubris, incompetence, greed, and sheer stupidity. Humans a prone to it, and nuclear power can be such a pain-in-the-ass when it comes to making mistakes, that it's wise to plan against human idiocy. A lot more than we do for say, airplanes. As for space agencies being somehow immune to bad design, error, and incompetence, (as the person I quoted asserted) that's equally absurd. NASA whelped a probe once by human-error and bad design, by completely mucking-up metric-to-imperial conversions. And Hubble was definitely a case of bad design and error (I'm not bashing the telescope here; the thing is fantastic), which just goes to show mistakes happen, even at the best of times when you're extra vigilant. Add a bit of corporate greed and complacency to the mix, and you have a recipe for things to go very wrong.

My point is, that most of the time, we can afford for something to go wrong some of the time. Civil aviation is a wonderfully safe enterprise, where things go right almost all the time, and when they go wrong...okay, some people die, but on the whole not that many when you consider how many people get moved-about in the same time frame. When nuclear power plants go wrong, they can go very, very, very wrong in the worst cases (analogous in this case to the plane crashing into a mountain, say; rare, but happens). We've learned from our mistakes, sure, but we're still human. That means we need to be hyper-vigilant, and more so when these toys are in the hands of people with profit motives that want to squeeze their margins for all they're worth.

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In short : don't give torch stupid person or he burn his house down (and entire neighborhood) instead illuminate it's interior :P.

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IMO eventually the human race will figure out how to use nuclear power and everything without any risks but like so many things all we can do is wait.

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IMO eventually the human race will figure out how to use nuclear power and everything without any risks but like so many things all we can do is wait.

We know how to handle it safely, but some people get ignorant. It's people that are the problem, not the nuclear reactors. :P

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