Finally! This is one of the few fission uses I'm genuinely excited about. Nuclear-thermal just makes so much sense for in-space propulsion of large vessels compared to chemical rockets.
I think the obvious concern would be failure scenarios. There will always be failures in space technology. As space expands exponentially (as it is likely to do so in the future), failures will become relatively regular. So the obvious question would be what would happen if a nuclear rocket, with reaction in process, crashed to Earth. Or even if it broke up in the atmosphere.
Nuclear weapons testing was mostly designed to maximize power output by burning up as much fissile material as possible in one big explosion. Conversely, it was meant to minimize fallout. A broken nuclear reactor (no nuclear explosion) would be the opposite: lots and lots of fallout (broken reactor bits) scattered over a wide area. The radioactivity from a broken nuclear rocket could be more dangerous than that from a great many bombs.
Reactors that have not yet been started do not contain that much radioactivity actually, nuclear detonation creates a lot of gunk during the energetic phase due to neutron activation and similar processes.
Also you can presumably shield reactors to survive reentry or even ship the fuel in multiple such reentry proof containers. And of course longer term build these in space, given nuclear propulsion is basically in space only anyway given its characteristics.
One solution would be have a kill-switch that detonates the reactor fuel as a nuclear bomb (assuming it could be configured in such a way; this is probably more difficult than I imagine). There would be major political problems with this approach though, as you're then shooting nuclear missiles.
Even as a layman in these things, I know that a nuclear reactor is far, far from a nuclear bomb and isn't easily made one. You can't 'configure' a reactor to become a bomb.
A better way would just be shielding, make sure it stays in 1 piece through reentry and impact. And still doesn't leak radiation then.
Can’t we just send up the propulsion system and the fuel separately? So like, ya, either could fail, but one is just some fancy equipment being g destroyed and the other is…unert uranium or plutonium coming down, needing to be cleaned up but not in a particular dangerous mode. Then once in orbit and the risk of crashing into earth is much less, put them together, fire up the reactor and go?
Nuclear testing got to carefully select locations to minimize harm, uncontrolled reentry of nuclear rockets has significantly less control.
It’s not the 99 rockets falling into the ocean shortly after launch that are problematic, it’s the 1 that almost works but then lands in the city we should be concerned with.
We might see more obvious direct human impact from debris landed in cities, but nuclear debris falling into the ocean or land that isn't densely populated by humans still has plenty of bad side effects.
Sealed fuel capsule at the bottom of the ocean should not be a big deal - ideally you would fish it out and re-launch it. This has already been done with an RTG before.
It already happened with Kosmos 954 and will probably happen again soon: ~20 other satellites had been sent in space with the same tech. Kosmos crashed away from (human) life centers but that was a huge stroke of luck. Research area was 100k+ km2.
Launches are less to be feared because they are oriented toward sea and the most critical moment are the first minutes. The device discussed is intended to travel away from earth so as you noted it won’t be dangerous after it quit orbit.
Disclaimer: not skilled in any related field, just a consumer of space science popularization videos for newbies.
Not soon. Most of these other rorsat reactors have been put in a parking/disposal orbit where they'll last a long time (I forgot how long bit I think it was in the order of thousands of years)
I'm kinda surprised the soviets even thought of the environment in that way.
Because it largely is? It ends up on the sea bed, covered in sediment, then eventually recycled into the Earth’s mantle some millions of years from now. It doesn’t enter the biosphere.
Abyssal zones of the ocean are only populated by creatures that feed on hydrothermal vents, or dead creatures falling down from the surface. But the mid pacific has no hydrothermal vents and the surface is a dead zone due to human activity. So there is no source of food for life to exist here, and outside of the occasional whale fall it is truly dead.
Terrifying, didn’t know there’s a second patch on the south. The census map in my parent post show this area populated by “predators” but not much zooplankton, so not sure what lives there. There’s also probably a bunch of debris from nuclear tests in this region.
>As space expands exponentially (as it is likely to do so in the future), failures will become relatively regular.
Or it could go the way of the airline industry where failures become less regular as the industry develops ways of systematically reducing them.
Also, nuclear rockets should probably be launched to earth orbit in pieces, separately, so that if any one launch fails it won’t create a nuclear accident in the biosphere. Then assemble and power up the nuclear rocket as far away from earth as possible.
The solution to this is to build it in the moon from moon rocks and send it by maglev trains. Full scale spaceships can be 3D printed in parts, assembled on-orbit, and Dragon/Starliner class rowboats can be used to board it.
Longer term - definitely thats the way to go. But first we need to build all this infrastructure & nuclear termal propulsion might be already necessary to get there.
>As space expands exponentially (as it is likely to do so in the future), failures will become relatively regular.
It's possible that reliability/safety will improve as fast as the launch cadence does, in which case we could see the accident rate staying flat or decreasing.
Yes, you can have the reactor offline, with control rods inserted for launch. Then when you reach the requisite altitude, withdraw the control rods and start up the reactor. In the event of a launch accident and potential destruction of the reactor, the enriched uranium fuel would be a chemical hazard (uranium is a heavy metal like lead), but only a mild radiation hazard (since there are no high-gamma fission products, and the uranium has undergone heavy purification prior to fuel fabrication).
I think this is the default for any launch of reactors from Earth - launch inert, possibly in pieces and ideally in re-entry proof capsules so you prevent contamination and can re-launch after a failure.
I assume here you mean to denote by "space" the number of human spacecraft, and not the negative pressure contribution in the cosmological stress-energy tensor. In that case, why should it be likely to expand exponentially in the future?
From across the pond it feels like American millennials and Gen-Z have already declared their country to be a failed state.
How much can a nation progress if its youth is pessimistic about everything? It doesn't matter whether the pessimism is based on actual problems (healthcare, housing prices etc.) or learned through terminally online reddit/twitter consumption.
It’s amazing reading this knowing a billionaire squandered that brand name after pouring billions into acquiring it. I hope when the smoldering ruins are auctioned at the bankruptcy proceedings jack gets to buy it back and uses it for his decentralized network.
If we're talking about the contents on TikTok, there's probably a very good reason why the ultimate owner of TikTok, the Chinese government, wants that kind of content to be the majority sentiment on the platform.
The US declared war on the concept of terrorism in 2001, directly invaded two nations as part of that effort, and overthrew multiple governments before ultimately abandoning the war and handing a broken Afghanistan back to the Taliban in 2021.
We did an excellent job of making sure the war was fought on foreign soil and largely stayed out of our daily life back home, but we definitely were at war.
(I'm focusing on the US here, but there were quite a few other major conflicts and military coups around the world during the same time)
Well, you could make the argument that during the 2000-2020s the US was at war with undeveloped countries that definitely had no chance of dethroning the US technologically; this is different because China is in a position to do just that.
For sure there are differences in the enemy if you consider us already at war with China and/or Russia. It's my personal opinion that WWIII kicked off the day Russia's navy left port and circled around Europe to get to the Mediterranean (Dec 2021), but we haven't technically declared war yet.
Its worth noting that Afghanistan may be less developed technologically but they have now successfully fended off invasions from both the Soviet Union and the US. Never underestimate your enemy in war, especially if you're Goliath invading David's home.
Hot war in outer spaces is should do. War is fine so long 1.(selfishly) it won't kill me, 2. it has no chance of ending the humanity, and 3. the sites devastated can recover.
Colonial wars in the asteroid belt and beyond. Interstellar wars. Maybe the first FTL drive could be on an autonomous space torpedo, and that could be lore explanation for the shape of warp nacelles in this timeline.
As wacky as this all sounds it's definitely not the worst possible outcome. Megalomaniacs ruling over tribes, kingdoms and nation states have been throwing their people into bloody wars since the dawn of time.
If America and China are dead set on having another dick measuring contest, we're all much better off if they do it with drones halfway between here and the moon, instead of near earthbound population centers. By all means let's make outer space the future of war, as far away from humans as possible.
That should also help with the post battle debris situation - most lunar orbits are inherently unstable, so any debris should auto clean in a relatively short while, unlike with many important Earth orbits where stuff might stay up for millenia due atmospheric drag being just too low.
It's almost intuitive if you consider the distance from Bangor to LA is pretty much the same distance as Madrid to Moscow. Think of the diversity between Madrid and Moscow. Bangor to LA won't take you through an equal amount of diverse cultures, the US is a single country after all, but the diversity is certainly there.
Not that intuitive, as the country has a language in common and one can simply drive from Bangor to LA without any local government asking questions. I have the impression cultural differences spring more from the economic and educational ones, unlike Madrid and Moscow, which have very long histories that are almost completely disconnected for most of that time.
It's funny because it's this, turning inward and waging war on ourselves after there wasn't an obvious enemy anymore that's responsible for the decline the upstream comment was talking about. Post WWII through the 90s saw massive increases in global standard of living, 2020's the west has gone back to religious squabbles over absurd ideological things. Watchmen had a similar idea.
Post WWII understood how terrible war was. Post 90s those that experienced it in mass were going extinct. We forgot what fascism did to the past and too many are embracing it again.
The people making these aren't any good at building houses.
The lack of housing is, IMO, a failure of government — material costs for homes are surprisingly low compared to everything else — but even then, housing policy is a different department to the space stuff.
>The lack of housing is, IMO, a failure of government
Lack of housing is a "feature", not a bug, as it enriches the housing owning class and makes it more difficult for "undesirable" people to move in with NIMBYs.
Then take some from the bombs used to kill people. It's a false dichotomy to say if we spend anything on space we can't spend anything on problems on Earth.
Aw man, forget all that noise. Bring back "Project Orion"*, baby!
If we're not gettin' out our (NASA-approved) Huarache sandals, "waxing down" our pusher plate, and surfing "the pocket" of those sweet nuclear detonations in the near future, then, I'm afraid our species is utterly consigned to the category of "posers"!!
See, Kilgore knew how to put this kind of (heavier) ordnance to good use:
I loved hearing this called “the Devil’s pogo stick” once.
There were some paper studies showing that a thermonuclear version could theoretically work and reach speeds up to 10% the speed of light, which would be the Centauri system in a bit over 45 years. Of course you would have to slow down too which probably adds another few years.
If this can be theoretically done with technology contemporary with the Summer of Love, it really does make the Fermi paradox seem like something real.
For this new initiative, I can see 2 big differences. On one hand they will use medium enriched uranium (up to 20%), while the original program used highly enriched one (85%), so it's going to be more challenging to extract as much power from a compact reactor. On the other hand, in 2023 we have computers and nuclear reactor simulation software that was not available in 1960, so that could provide a huge advantage.
The biggest challenge I see is how to power down the engine. You can't simply flip a switch a turn off a nuclear reactor. You can stick in all the control rods, and the fission stops in less than a second, but the fission products will continue to generate heat for a few hours, initially at about 10% of the full reactor power. During this cool-down period, you will use the same coolant (hydrogen) as during normal operation, but you won't get the same exhaust velocity. With a traditional chemical rocket you don't have this problem. If you get a specific impulse of 450 s, you always get that. If a nuclear thermal rocket can get 900 s running at full throttle, but it goes down to 100 seconds in cool down mode, the main advantage might not be so great after all.
I think the internal temperature might get high enough to melt things ? You could have a separate cooling system, but that will add more complexity and mass.
Yes, but the liquid fluoride thorium reactor does not get anywhere close to the temperature you need for a nuclear thermal rocket. It might get close to 1000 ℃, but you need about 2200 ℃ to get the 900 seconds specific impulse that makes nuclear thermal rockets so appealing. At that temperature that liquid salt has long vaporized.
Well that's the most obvious way to put FUD out there.
It might be a good time to review the number of failed launches on crew rated rockets (the safety requirements on which are roughly equivalent to the requirements for carrying nuclear material). Particularly ones which led to a loss of crew, as those would correspond most closely to a possible nuclear material release.
It's far less scary, but alas not as convenient for FUD.
Depending on the design, failure during launch can be anywhere from "meh" to "basically high-altitude Chernobyl" — random actinide decay products (and plutonium fuel) are bad, unreacted uranium fuel is mostly a heavy metal hazard rather than a radiation hazard.
(Could be worse, but the Orion drive is currently illegal by treaty and hopefully nobody is dumb enough to use that in Earth's ionosphere anyway).
The nuclear payload could be treated similar to humans, with eject systems and soft landing built in.
The fuel will only be needed for a lighter craft in deep space. Getting it up with a high reliability rocket (like Falcon 9) significantly decreases risk.
> The nuclear payload could be treated similar to humans, with eject systems and soft landing built in.
In principle yes — even just on the grounds that enriched fuel is expensive — but it's a hard thing to prove in advance, hence all the times humans died in a space mission one way or another.
There have only been 5 instances resulting in 19 fatalities. None were when exiting the atmosphere. 2 were the flawed Space Shuttle on return. Only one other was a flight system, on an experimental craft.
"Meh" is a casual response that means "this does not matter much". I don't know that it's proper English by any means, but it is certainly a common colloquialism. A cursory search suggests that it's imported from yiddish.
It's not an uncommon expression. I searched the term in a chat room my friends (of varying professional backgrounds) have used over the past 5 years. There were about 200 instances of us using the word.
Please refrain from being nasty to people going out of their way to answer your question. Any longtime English speaker is qualified to make observations about what is happening in their linguistic community. They went the extra mile to quantify it for you (in a community other than HN, in direct response to your question). You are free to choose how much weight you assign to their observation, and it's fine if it differs from your experience, but it's uncalled for to ask "what they're smoking."
I remember learning that when they started testing atomic bombs (I think?) the nuclear debris in the air spread basically throughout the whole united states and the government tried to keep quiet about it. Something similar will probably happen here if they mess up with the launch.
I remember that video; the long story short was that a manufacturer of films for photography noticed that their films had spots on them, they initially thought it was defects, but because they had samples prior to testing, they saw an uptick.
But maybe I remember wrong.
Edit: the video in question is [1] and the conpany was Kodak.
The thing to remember about that is that we can measure tiny amounts of radiation very cheaply, and tiny amounts are harmless. In fact we are bathed in a constant, but tiny, background level of radiation all the time. Thousands of nuclear weapons were tested all across the world, in the United States, in the Soviet Union, on Pacific Islands, etc, etc. The radiation from that certainly caused a small uptick in the background level of radiation, but it hasn’t actually harmed people.
The main reason that the US was secretive about it was that nuclear weapons were a secret, not because there was a shameful health problem to hide.
Incidentally, the best way to reduce your exposure to radiation is to move away from the mountains and go live at the beach. Mountains are mostly made of granite, and granite always contains small amounts of uranium and thorium which decay to radon gas. Also, live as far away from coal power plants as possible, those things are horrifying.
Background radiation may be unlikely to give an individual cancer whilst still causing cancer across a population. It just isn't possible to attribute the cause. Surely the same is true of fallout from testing and estimates would back that up. It may not be something we worry about as individuals. But it is something that nasa should worry about.
"""There have been 2,121 tests done since the first in July 1945, involving 2,476 nuclear devices. As of 1993, worldwide, 520 atmospheric nuclear explosions (including 8 underwater) have been conducted with a total yield of 545 megaton (Mt): 217 Mt from pure fission and 328 Mt from bombs using fusion, while the estimated number of underground nuclear tests conducted in the period from 1957 to 1992 is 1,352 explosions with a total yield of 90 Mt.[1]"""
Depends on the details; in water, too close to ground water, near ground level and breaching the surface (Operation Plumbbob), and I don't have numbers for those.
But still, thousands of bombs were in fact tested, and the context here is testing a reactor that won't be on Earth at all via a diversion into "we can detect really small levels of radiation".
Background radiation is categorically different than ingesting/inhaling radioactive substances with the latter many orders of magnitude more dangerous.
The claim, nuclear testing related increases in radiation exposure not being relevant for public health is probably false. There are only very few studies with dubious reliability. The lifetime increase due to that nuclear testing is estimated to be 4.4 Millisieverts. It would have risen continuously with more surface tests, which got abolished accordingly.
The idea, beaches were a sanctum against radiation is wrong again. Sand is ground down mountains in case you wondered. Some are highly radioactive. But of course, UV light is harmful radiation as well.
We eat bananas all of the time. Bananas are delicious and nutritious, and they are known for containing lots of potassium. Well, some of that potassium is radioactive! It’s not very much radioactivity though. It is an amount which is easily measured, but which is not harmful enough to make eating bananas dangerous. This is true even though the potassium will be used to strengthen your bones and teeth. It will also be distributed to your muscles, red blood cells, skin, etc, etc.
Reusability helps with long term reliability. You would probably want to avoid launching nuclear material on a new rocket, but a human rated rocket like Falcon 9 would be totally fine.
Well look at the number of missions with RTGs on board and you don't have to imagine, nuclear powered probes and satelites are not unheard of. The soviets also had an entire series of fission powered spy sats way back.
> Once it reaches a safe orbit, the reactor will be turned on.
Fission reactors aren't appreciably more radioactive than rocks you can dig out of the ground until you turn them on. This is something that wouldn't be brought online until the riskiest part of the launch has past.
Uranium that has not been in a reactor is almost nonradioactive and inert. It only gets spicy after you let it go critical for a while, and fission products accumulate.
Any reasonable nuclear-powered craft would not start up the reactor until it's already in a nice, safe, high orbit.
What failed rocket launches? That hasn’t happened in a long while. SpaceX just surpassed their 100th consecutive first-stage launch without any failure. Boosters are super reliable these days.
I'm no engineer, but it sure seems to me like you could either split things up into multiple launches, or potentially manufacture the fuel in orbit, no?
Falcon 9 has had more than 200 consecutive successful flights in a row. That is more than double the next most successful, Delta II with 100 in a row.
It also has well over 100 successful landings in a row, while the next closest rocket has 0. (Rocket, not capsule or shuttle, which are all still far lower)
The basic idea is straightforward: A nuclear reactor rapidly heats up a propellant, probably liquid hydrogen, and then this gas expands and is passed out a nozzle, creating thrust. But engineering all of this for in-space propulsion is challenging, and then there is the regulatory difficulty of building a nuclear reactor and safely launching it into space.
Can anyone give a eli5 explanation of what makes this better than a conventional rocket? There still needs to b some mass ejected obviously. Is it that nuclear heat is able to make it go faster and provide more reactive force than burning it? What does the analysis look like?
It's the high temperature and the lower exhaust molecular weight.
Specific impulse (Isp) is how much force you get from each mass unit of propellant you exhaust. So an engine with Isp = 300 gives 300lbs force for every pound of exhaust gas mass.
IIRC, Isp scales as the inverse square root of exhaust molecular weight. So a pure (molecular) hydrogen exhaust would have a molecular weight of 2. A pure H2/O2 engine would have an exhaust of H2O (assume it's running at stochiometric H2/O2 ratio to simplify things), or an average molecular weight of 18.
For everything else being equal (temperature, pressure, etc.), the H2 Isp would be sqrt(18/2), about 3x the H2/O2 Isp. That's mainly why rocketeers would like nuclear engines, more oomf from a given mass of propellant. It's also (conceptually) simpler because you only need to handle one propellant vs. two or more for conventional liquid fuel combustion.
It's more complex, of course. If the reactor is really hot, it can partially dissociate H2 into atomic hydrogen, lowering the exhaust molecular weight still more. But dissociation is an energetically expensive process, so there's bound to be a tradeoff between energy consumed by dissociation vs. increased Isp. I've no clue how that would work out.
The real limiting issue tends to be materials in the reactor - at some point, every known material is a liquid or a gas and the reactor stops being an ongoing concern.
Usually reactors run cooler by several orders of magnitude, as this is referred to as a ‘meltdown’ and people get snippy about the releases of radiation and expensive cleanup crews, etc.
Space is more forgiving and has fewer HOA types, so they can go closer to the limits - but it’s still the same underlying issue.
Yeah, the materials issues dominate design basics. They've looked at HfC and HfCN as nuclear engine materials (m.p. ~3950°C), pretty exotic.
I feel like if designers would drop their effort to wring out the last increment of Isp from nuke engines and reduce temperatures to ~2000°C, it would give faster development. There are many materials that can live in 2000° hydrogen for >100K hours.
There's an old Rand study that showed H2 would give an Isp >1100 at 1 atm chamber pressure (!), temp ~2000°C, exhaust pressure 10e-4 atm. Seems worth exploring.
Part of the issue I suspect why reasonable isn’t being considered is that I don’t expect anyone to have a reason to really use them right now regardless - all the nuclear propulsion designs have a high ‘fixed’ weight cost in the reactor, so would only make sense overall in a ‘hundreds of tons to Uranus ASAP’ type situation, where the overall weight for thrust can be lower due to the better fuel efficiency.
So far we thankfully haven’t had a reason to really need to do that right now.
And if we’re doing theoretical designs, why not make it ‘interesting’?
On a side note, if we’re considering crazy ideas - my favorite is the one that makes Project Orion seem clean!
The propellant is important for its bulk (some mass to shoot out the back) and it's energy.
In a chemical rocket, the propellant provides both the bulk and the energy. As it happens, there isn't that much energy in chemical propellants per kg, but the rest of the engine is light enough that these things can fly to orbit.
In a nuclear rocket, the energy comes from a nuclear reaction and the gaseous fuel only provides the bulk. This is way more efficient. But such rockets likely cannot achieve orbit on their own because the whole set up is too heavy.
In an Ion jet, the energy comes from (usually) solar power and the gaseous fuel provides the bulk. These are even weaker because of the limited instantaneous power that can be generated to feed it, but they are very efficient in how much thrust they can provide per propellent weight. Some versions (like arcjet) are a combination chemical rocket/Ion jet.
Almost definitely not. If there's enough material to collect in a realistically short timeframe, there's enough drag to bring the craft back into the atmosphere.
Also you'd be fighting conservation of momentum - if the material you gather isn't going your speed and direction, you lose some of your speed and direction to pick it up. Given how fast anything has to go to reach orbit (about 17000mph for low Earth orbit) and escape velocity is about 41% higher, that speed difference would be a major problem.
For atmospheric flight the closest thing is a jet engine which is "air breathing", i.e. requires air to run and works in part by sucking air in, using some of the Oxygen in it for combustion, and shoving the extra air out the back. This gives them much higher efficiency than chemical rocket engines, as they don't have to carry their own oxidizer or the mass to eject for propulsion - but only works because the air is dense enough where they operate. Which is not true for space flight. Commercial jets typically fly a bit under the speed of sound in air which is 767mph. Of course supersonic air craft exist - I think mach 5 is achievable by some military jets - but that's still a fraction of orbital velocity. Anyhow running in the atmosphere means jets don't "scoop up air" in any sense but rather just use it immediately - so any lost momentum can be immediately countered by the engine.
Another direction to think about it - a simple model for air resistance says that air resistance increases with the square of your velocity (and with the density of air, which exponentially decays with height though also depends on temperature. I think the height wins out though.
Not sure if the equation works at extremely high altitude. But certainly this favors using air at lower altitudes and probably also lower speeds
A rocket functions by ejecting mass out the back at high speed. By conservation of momentum, the rocket then accelerates.
You want to optimize for velocity gain (also known as delta-v) per unit mass of propellant. So the question is, should you eject something heavier at lower speed, or something lighter at high speed? Which is more efficient?
If you write out the equation for a rocket ejecting some propellant at some velocity, apply conservation of momentum, and solve for the ratio of delta-v to propellant mass (just a bit of high school physics), it turns out that a higher exhaust velocity makes a more efficient rocket.
As a sibling post points out, if you compare water vapor with hydrogen at the same temperature, hydrogen will have the higher velocity. Chemical rockets usually produce water and/or carbon dioxide, which are bigger molecules and therefore less efficient propellants than hydrogen. So if you have a way to heat hydrogen to the same kinds of temperatures you get in rocket exhaust — say, in a nuclear reactor — that’ll make a more efficient rocket.
There are of course considerations other than pure efficiency. Our most efficient rockets, ion engines, are indeed crazy efficient, but their thrust is measured in milli-newtons or newtons. They can’t be used to lift things off earth. They also use propellants like krypton and xenon, presumably because they’re easier to store than hydrogen.
The temperature of a gas is proportional to the average kinetic energy of its particles. So if you compare (e.g.) water vapor to hydrogen at the same temperature, the hydrogen molecules are moving faster.
A hydrogen+oxygen chemical rocket propels H₂O, while a nuclear thermal rocket can use the lightest propellant (H₂) because the heat comes from elsewhere.
Assume that total propellant mass is a constant (limited by the launch vehicle) and temperature is a constant (because melting the rocket would be bad.)
With constant mass, you increase the total momentum by increasing the exhaust velocity. With constant temperature, you increase the exhaust velocity by making the molecules smaller.
"Is it that nuclear heat is able to make it go faster and provide more reactive force than burning it?"
Yes, that is mostly it. Just compare the explosion from some hydrogen with a nuclear bomb. It is all about energy for mass in space, because all the fuel you have, you have to bring up into space, which needs more fuel, so need more fuel to bring that fuel up ... nuclear could help with that mass ratio a lot. And I like the concept in theory - as long as none of them explodes halfway up to space.
This is not the same. It's nuclear electric propulsion, not nuclear thermal propulsion. A nuclear reactor generates electricity and that electricity drives an ion thruster. The specific impulse is astounding (7000 seconds vs 450 seconds for the best chemical rockets), but the thrust is absolutely wimpy (15 Newtons, vs 250 kilo-Newtons for the US NERVA nuclear thermal rocket engine).
The reason communications with the Voyager 1/2 twin probes have lasted for like 45 years:
Voyager 2 is equipped with three Multihundred-Watt radioisotope thermoelectric generators (MHW RTG). Each RTG includes 24 pressed plutonium oxide spheres, and provided enough heat to generate approximately 157 W of electrical power at launch.
I would much prefer the US to focus on space based nuclear reactors, both for surface and for in space propulsion for electric transport. Much better reward.
That’s an odd thing to say. Almost as if you’re in favour of nuclear for nuclear’s sake? Plenty of people have reasonable reservations about use of nuclear, not least the social /political ones of where to store waste that are still mostly unsolved. Blasting fission cores into space on rockets with fairly high failure rates in absolute terms seems like a fairly fine balance to strike?
Probably depends on your risk profile. Do we find new ways to safely generate energy using nuclear, or slowly cook ourselves alive on the planet's surface?
Or to put it another way, at what point should we throw a Hail Mary in the energy demand game?
People here tend to run to extremes when they disagree with something. I am not here to detail out every individual practical application for nuclear energy; I am also not here to say where it should be avoided. Something something naysayers have a problem for every solution.
There is and has been a anti-nuclear sentiment when it comes to energy written in media for quite a few years and seeing that sentiment be turned around is positive. I am convinced(and it's just an opinion) the negative portrayal of nuclear energy is directly related to the financial influence that oil and other energies have over many sectors of the economy and government.
You don't need to store nuclear waste, since you can burn it up in some fuel cycles. Essentially all the problems of nuclear power on the ground are political issues -- entrenched interests, weapons proliferation, and so forth -- not technological ones like safer reactors and nuclear waste.
That really does hand wave away a lot of important details. Those problems on the ground are the reason I am generally not pro nuclear… not because intrinsically I think it’s a bad idea to split atoms.
So you think nuclear powered cars are a good idea?
„ In all cases, however, the primary safety issue would be the car's survivability (well the reactor) during a crash. Any serious crash could result in a very serious miniature nuclear contamination disaster. Not ideal to say the least, especially considering the number of serious crashes each year. Not to mention the need to protect nuclear fuel from abuse by potential terrorists.“
> Wernher von Braun, the German engineer who defected to the United States after World War II, recognized the potential of nuclear thermal propulsion even before his Saturn V rocket landed humans on the Moon with chemical propulsion
> German engineer
Why does von Braun get such a pass from his Nazi past? Because he was useful?
Yeah, I think a lot of people would say that one's actions post-war are worth some weight in the equation, and culturally this person was positioned so as to not only make a big positive contribution in that quite separate context as far as values go, but a contribution which was also part of "our side" of a pitched cultural battle which is still raging. So like, how Nazi could you still be, in that actions-speaking sense.
Plus, people-controversy is a topic that's actively avoided in writing for a lot of audiences, especially if it invites fault-spreading, like if it's going to end up as a big whataboutism-fest.
Difficult topic in its way. Including of course the WW2-and-prior way involving terrible aspects like forced labor working under him, etc. So, less of a defense of a person here and more of a guess about rationale in authorship.
There won't be any fission products in the fuel if the chemical launcher fails to take the nuclear payload to orbit. The reactor activates for the first time after the initial orbital launch. The virgin fission fuel is less radiotoxic than RTG fuel.
>The reactor activates for the first time after the initial orbital launch.
So they're going to launch an untested reactor into orbit without even turning it on first? Getting a reactor up and running is hard enough on the ground. I would expect any reactor to have had thousands of hours of testing and tweaking before being placed on the launch pad; that is the process for military boats and we have 60 years of experience in that environment.
These aren't intended to be powerful complex designs like what the navy uses. They're going to be small, simple and low power with as few moving parts as possible. Probably passively cooled, and having just enough plumbing such that propellant is only heated up when the only way for it to go is out the nozzle.
After all, waste heat is much harder to get rid of in space than here on Earth.
For reference, other space nuclear reactor designs NASA has looked into have been in the lower kilowatts in terms of power output.
Space stuff doesn't yet need the power output relative to size of a modern military reactor, the bigger concern is being reliable and providing stable long term power.
