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Nuclear Rockets Moving Along
AKAImBatman writes "Bruce Behrhorst of NuclearSpace.com recently stumbled across a new engine from everyone's favorite Jet Engine maker, Pratt & Whitney. Unlike P&W's previous engines, however, this engine is not a jet, and is powered by Nuclear Fission.
It seems that P&W has responded to the need for Mars transportation by inventing the first commercially viable nuclear thermal rocket. They have heavily improved upon the NERVA NRX design from the 60's, and have even solved the graphite ablation problem! With this new engine, it seems that an inexpensive trip to Mars is now firmly within our grasp. Will we rise to the challenge?"
This design is significantly different from the NRX. For one, they didn't attempt to build the most powerful reactor in the universe. For another, they took advantage of LHOx afterburners. With both of those design choices in mind, they were then able to use a titanium shell to act as the heat sink for the reactor. Not only does it not ablate, but the titanium will melt and scram the reactor long before the reactor itself experiences meltdown.
:-)
In other words, this is an extremely safe reactor design.
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It means they can run the engine and not wear it down from friction. Or at least not wear it down at a rate that is greater than the projected lifecycle of the engine. Having only STFA (Skimmed), I don't know if they are intended for single or multiple use.
Gravitation? What do you mean? Lack of on the surface? Or lack of gravity in space. Either way, we've solved this problem.
Uninhabitable surface? In what sense? No, I won't go strolling on Mars in my jockeys, but it's not that bad once you have a spacesuit on.
You have two hands and one brain, so always code twice as much as you think!
I suspect few people realize we've launched nuclear materials into space on many occasions. IIRC, the Pioneer probes are nuclear-powered.
Who knows? We may even have had some of those probes fail to launch properly, in which case the nuclear material had no major ill effects. (That I'm aware of, anyway.)
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A nuclear explosion has to push against something, in this case a graphite pusher which would theoretically erode too quickly.
s ion
More info on nuclear propulsion efforts
http://en.wikipedia.org/wiki/Nuclear_pulse_propul
Well, you could always RTFA. Here:
BB: Is there a 'fail safe' operation in the event the reactor core must
be shut down exiting a planetary 'gravity well' or on approach to a
'gravity well' ?
RJ: There are several features that we have adapted and evolved into the
current 'TRITON' design to handle risk mitigation for the Uranium
Dioxide (UO_2 ) fuel element core in a Nuclear Thermal Rocket (NTR).
We have approached this by providing an integrated, robust design the
uses dual turbopumps (turbopumps provide coolant flow to the reactor in
propulsion mode).
In thrust mode where you have high power operation, is where this
concern has been typically addressed.
The safety features that have been taken into account for risk reduction
entail constant supply of reactor coolant by using dual turbopumps. This
means turbopumps with their moving parts like bearings, shafts, turbines
etc. may cavitate and over speed, if for some reason one of the
turbopumps showed signs of malfunction or not operating within
appropriate parameters, you could effectively shutdown or bypass the
offending turbopump and still have coolant flow going to the reactor.
This is one of the key features for propulsion mode operation to make
sure coolant is available to ?flush; the reactor if it needs to be shut
down when it has gotten to the full thermal power level. In power mode
it's [core] sitting at an idling power-level so the amount of time for
the reactor to over-heat if starved of coolant (i.e. He/Xe gas) is
extremely negligible because you are running the reactor core at nearly
half the maximum temperatures the core is design for. So, if in the
event of something like let's say, a minor leak in the radiator during
power-mode operation, you can do a shut-down of the reactor from a very
moderate control state without over-heating the reactor core. Other
failure mode mitigation would be to have a segmented radiator design, or
have a coolant purge circuit in the design, or actually split the
coolant circuit to provide redundancy. We also have several valve
arrangements so that in the event of leakage in idle power mode you
could shut a section of the radiator down; the temperature of the
reactor is so low it would cool down on its own. This works to our favor
in the ?TRITON? design because the CERMET core materials have high
maximum operating temperatures since it's designed for exit temperatures
near 2,700-K in the propulsion mode.
Another feature is the nature of going to a fast spectrum reactor. It
allows issues such as criticality and impact immersion (e.g. wet sand or
salt water) to immediately be mitigated because of the reactor neutron
flux levels and the use of only a reflector and no moderator to
thermalize a bulk of the neutrons. Essentially it helps to 'poison' the
internal nature of the reactor so in the worst case event at launch, if
the reactor were to end up in sand or saltwater it will keep it from
resorting to a super-critical state. If it shuts down after a brief
period of operation, like for some reason and I had to shut it down
during an early phase of a human Mars mission, the 'burn-up' (fission
product build-up) is so low. Even if I run it for only 5 minutes or, 10
minutes I'd have built up only a minuscule amount that could barely be
measured with regards to build-up of fission products in the core. So if
it did for some reason re-enter the earth?s atmosphere, the radiation
levels are only slightly higher than typical naturally occurring levels.
Now, you would have to methodically go through a full risk analysis, or
a whole mission point-to-point to define the 'What if scenarios' along
the mission's plan to properly build in aborts for all the most probable
failure modes.
For example, one 'What if scenarios' would look at the failure modes for
an orbit capture high-thrust burn at a planet Mars or for Lunar
transport. In essence, an inve
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Did you read the article? It has 15000 pounds of thrust, at nominal output. Totally useless for ground-orbit missions. It is designed to fly from orbit here to orbit somewhere interesting.
"I do not agree with what you say, but I will defend to the death your right to say it"
Not to sound paranoid, but when the reactor overheats and falls off where does it go?
Launch profiles are designed so that everything falls into the ocean. NASA has aborted quite a few launches, and has never dropped anything on people's heads. China on the other hand...
What happens if the reactor falls off over a populated area?
Well, since it's not supposed to be activated until the craft is already outside of the atmosphere, I suppose someone gets a bump on the head. Even if we assume that the reactor overheated, the titanium shell will melt down and scram the reactor before the reactor itself melts down. It should be nice and cool (and still wrapped in titanium shielding) by the time it hits the water.
Say the reactor falls off on the way to mars. Unless there is a shift in the momentum of the ship or the reactor it'll just melt down beside the ship. Then imagine the case where the ship can separate itself from the reactor. Now how do they get back?
The mission profile suggests three engines. Unless there's a critical failure in all three, a modified flight path could be developed.
While this is probably an improvement, I'd hardly consider it safe.
Consider a chemical rocket on the way to Mars. What happens if the tanks explode? That's right, you've got no way back. Even the failure of one engine could spell doom for the mission. This engine is more powerful, and FAR safer than any chemical engine. Even if the tanks leaked on the way, fuel could still be scooped from Mar's atmosphere. No chemical rocket can make that claim.
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Very simply put, the NERVA engines ran so hot that the Graphite used to transfer the heat from the reactor into the exhaust would flake off and end up in the exhaust. The problem is that while the hydrogen exhaust cannot be made radioactive, the graphite can. So you'd get little specs of radioactive graphite raining down behind you. It wasn't so much graphite as to be a major concern, but many of us would rather not exhaust anything radioactive if we can help it.
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I call troll. The picture you linked to was the INTENTIONAL destruction of a NERVA engine. Why would they do that? To test if safety procedure were working, and gauge issues with fallout. You'll note from TFA, that this engine has even more safety features, such as a titanium shell that would prevent catastrophic spread of materials. Also, it wouldn't even be activated in the atmosphere.
And before you whine about "we don't know", go do some reading about launch accidents involving nuclear materials.
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RTFA
It's for propulsion in Space not for getting into orbit. You can put the powersource in containers that survive being blown up, and fit them to the engines in orbit.
Did you bother checking the track record of nuclear material that has already rained down? Seems the US has done a fairly good job containing such materials. (That is, right after they figured out that it might be a good idea to do so. :-))
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I think many people were aware that the Cassini probe contained nuclear material. Remember the protests by the hippy/environmentalist/potsmoking/liberal/Democrat s/JohnKerrySupporters before it was launched?
This is why we don't launch over populated land masses, like the Russians did (and do). I believe there were some radioactive elements on board the Shuttles, but when it all falls deep in the ocean it's as bad. OK, not as bad for the human population. That said, don't forget it did spew a great deal of rocket fuel which is really nasty stuff. Solid rocket fuel, once lit, will not extinguish, even underwater. Again, though, we plan for these things in launching and mitigate their risks. There will be nuclear power in space in future systems. Right now there's too much baggage to make it viable anyway. Nuclear creates a lot of heat which makes heat dissipation a dominating reason to not use it with current technology.
Was not NERVA somehow proscribed by the NTB?
You're confusing NERVA with Orion. The NTB is about nuclear explosives, which neither the NERVA or Triton engines use. In fact, the Triton engine is really nothing more than your average, power generating reactor. It's primary difference from NERVA is that they're not trying to build the most powerful reactor in the universe.
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No, but tritium is.
Been there, done that, realised it wasn't the smartest idea ever.
If you Read the article they say that if the engine does a castatrophic failure, the amount of nuclear material released is on the order of a few curries.
Unlike say the millions of curries now currently in storage as waste.
i thought once I was found, but it was only a dream.
Well, yeah...
You're more right than you (may) know. I served on a nuclear sub, as a reactor operator. In the two years of schooling we get, there's much emphasis on rote memorization as well as understanding. One list we had to memorize is "negative public consequences if there were an accident", one of them being "negative public reaction to the naval nuclear program". We were operating in secret. We were taught that a major part of the reason that the naval nuclear program even still exists is because it's never (ever) had an actual accident. ("Accident" being a strict government policy-defined term.) The only reason we can get away with six nuclear reactors bobbing up and down in San Diego's bay right at this moment is because people really honestly don't know they're there. They're not in the news, they have a low physical profile. "Well yeah", nuclear subs have been operating in secret.
If aspiration is a virtue, achievement cannot be a vice.
Preach it brother! When I start talking to enviro-fundamentalists about this, at some point in the argument, I wave my hands and grind it to a stop and say:
"Let's be totally clear. You realize we're talking about zero emissions here. ZERO...FRICKING...EMISSIONS? As in no CO2 or CO, no more ozone alerts, no more FRICKING SMOG? Let's just be totally clear about this. Starting with the fact that, again, we're talking about ZERO FRICKING EMISSIONS how many waste and storage problems can we budget for? Given the fact that the global warming problem is FRICKING SOLVED, how do we proceed in this argument?"
This usually stops the fundies in their tracks. Of course, I realize that most of the pollution actually comes from automobiles, but that's where the hydrogen car becomes useful, rather than just a political football to be bounced around.
If your bitterest enemies are people who hack the heads off civilians, then I would say you're doing something right.
The Tory reactor was DESIGNED to spread as much radiation as possible over populated areas. This was considered a "bonus" by the military, as they could keep wreaking destruction even after the bombs were dropped. In short, the design was a little sadistic.
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I think if I were an astronaut, I'd be more worried about the solar radiation than the rocket's radiation.
Shielding a nuclear reactor has been done over and over again (in power plants, submarines and aircraft carriers). Me thinks they're getting pretty good at it.
The magnitude of damage when something goes wrong (ignoring the statistical chances, if Murphy's law doesn't alert this to you, Chernobyl and 3 Mile Island should)
Millions of people have died from Coal power. Less than 100 have died from Nuclear power. Here's an event that makes Chernobyl look like a walk in the park:
The Great Smog
Now sit and think for a moment which technology is more dangerous. The one we've embraced (coal) that we know is killing millions, or the one we've shunned (nuclear) which has killed very few, even in the worst disaster in history?
The unwanted side effect of wide spread use of nuclear power: nuclear proliferation.
Not such a big deal when the reactor is on its way to Mars. And since the materials are U235 before the engines are activated, it will be pretty hard for "terrorists" to obtain any plutonium from them.
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Low Profile?
You seem to think that subs are the only nuclear powered vessels. What about Aircraft Carriers (CVN), Cruisers(CGN) and Destroyers(DLGN). All surface ships.
I was a MM on the USS Arkansas where I spent majority of my time down in the bowels of the ship working on reactor 1.
Sorry, teleporters just kill you and then make a copy. A perfect, soul-less copy.
VASMIR seems like a far more generally useful form of space propulsion. The basic premise is the use of radio and magnetic fields to accelerate propellants. Its also inline with the general plan for societal advancement. It is rooted in many of the same technology we'd use to build Fusion reactors, relying upon superconductors, magnetofluid-dyanmics and plasmas. It was derived from plasma manipulation techniques discovered in fusion experiments.
Whereas a nuclear rocket will aid one given form of space travel: moving to mars and back, VASIMR systems are useful from launch to interplanetary, using extremely dynamic engines which consume virtually neglidgible reaction mass (aka fuel). They do, however, require a power source, which could well some nuclear variety, particularly for takeoff. VASIMR's fuel is hydrogen, which is a) readily available anywhere in the galaxy (including mars) and b) the most effective radiation shield we know.
This guy said one nuclear engine should cost about $1 Bil to produce. ITER is estimating $10 Billion for the first working Fusion power plant and will indirectly aid useful space travel more than a nuclear rocket. The ITER project aims to create a 500MW sustainable power plant. Compare this to JET, our current Tokamaka, which bursted at a world record 16MW. Yes, this is an apples to oranges comparison.
We need to stop dumping cash at quick easy bandaids to solve the next problem and begin evaluating our long term priorities as a society. We are wasting money on a hydrogen economy which will make coal plants burn the fuel our current cars would be burning anyways. We are wasting money building nuclear rockets. There is an energy crisis at hand and a environmental problem looming. We need reknewable resources. If we're going to be dumping billions in to space flight again, we might as well research two things which will go hand in hand.
Harness plasma. Make fusion go. Learn how to D-T react, and then get D-D reactions as fast as possible. Miniaturize.
Nuclear subs can remain submerged almost indefinitely. They are also quieter than diesel subs (although diesel boats are very, very quiet when running on batteries, they're very, very noisy when running on their engines)
Logistics is a lot easier when you don't need to fuel the boat...just its crew.
Why yes, I AM a rocket scientist!
There's a huge, huge difference between newly minted RTG generators being launched on a one-way trip, and a nuclear thermal rocket on a two-way trip.
c id ents
RTGs are incredibly simple devices; they simply generate heat in an enclosed container. No moving parts are needed. The heat moves across a junction in metals to a radiator; a heat differential across a junction in metals can generate power. The simple design allows most of the work to focus on how to seal the radioactive material so that it does the least damage in the event of an accident (instead of having to focus mainly on how to stop an accident from occurring). Also, the quantity of material used in RTGs is typically far, far lower.
Nuclear thermal rockets are full pressurized gas reactors. They involve all of the effects of vorticity and other hard to simulate phenomina in an incredibly high pressure/high temperature environment that is hard enough to control in a conventional rocket. Such an environment is worse than it initially sounds, because of several factors: 1) Radiation weakens the crystalline structure of reactor materials, and 2) The chemical composition of the fuel rods is constantly changing. Conventional rockets are already somewhat complex beasts (read about how the SSMEs work, for example); this will make SSMEs look like cheap toys.
Nuclear reactors are not as safe as most people assume; I recommend people read this as a primer:
http://en.wikipedia.org/wiki/List_of_nuclear_ac
An explosion in earth's atmosphere on a return trip (i.e., with lots of decay products) would be the absolute worst kind of nuclear accident physically possible. Even on the initial trip out of the atmosphere, however, it would be a Chazhma-bay level disaster.
Honestly, I don't want to see the effect that this would have on our still-recovering ground-based nuclear power industry (a much simpler task, and yet one we still have a lot of trouble with). That's my primary concern. People are already scared enough of nuclear power as it is; we don't need a nuclear disaster to occur in as publicly-visible location as "right over everyone's heads". It'd kill the industry.
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Ya need to know that sub-critical nuclear fuel is never going to produce a mushroom cloud. Producing a runaway nuclear reaction is extremely difficult. You'd require the right isotope of uranium, first. Then you'd need two sub-critial lumps separated enough so the radiation engendered by their proximity wouldn't simply vaporize the engine before a chain reaction could take off. The two-sub-critical masses have to be brought into close proximity quickly, usually by firing the masses into each other with two high-explosive devices; picture a tube with HE on each end, with a uranium "shell" on each charge. You'd fire both shotgun shells down the tube to meet each other. The temperature and the radiation caused by their increasing proximity tries to vaporize the assemblage, but the sheer speed at which they collide enables the neutron levels to increase to a the point where a runaway chain reaction released enough energy to raise the temp to a few million degrees. Boom.
If a nuke Challenger went down, the LH2 used as propellant would ignite with the O2 from the air, and you'd get a big boom. Not as much as the Challenger with it's perfect blend of LOX and LH2, but it'd be pretty big, as booms go. But the reactor would simply fall like a radioactive Geo Metro. No boom. Wrong isotopes, no way to go critical.
There are no more CGNs or DLGNs in service.
http://www.ornl.gov/info/ornlreview/rev26-34/text/ colmain.html
m d= Retrieve&db=PubMed&list_uids=3600052&dopt=Abstract
136 rem/person/year is the estimated radiation dose from coal in America. We're talking about a Chazhma bay or a Chernobyl occurring - tens to hundreds of rem in *hours*. In 1986, civilians around Chernobyl received 8.6 million rem/person/year:
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?c
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Project Pluto - what a concept. I can't think of a more outright crazy manifestation of the Cold War.
Here's an excellent article over at Astonautix:
http://www.astronautix.com/lvs/slam.htm
Once again: I didn't say PWR! I explicitly mentioned that in the last post, and you still didn't catch on. How many times am I going to have to mention this? I said that it's a pressurized reactor; and it *IS*. It has pressurized, hot hydrogen. That makes it a *pressurized reactor*. It doesn't make it a PWR, but it makes it a pressurized reactor.
... is exactly like comparing the safety of a modern diesel engine to that of a 19th century locomotive engine ... a 19th century locomotive engine wouldn't render hundreds of square miles inhospitable for hundreds of years if it blew up at the wrong time. Serious consequences merit serious precautions
...
c id ents
> there is no working fluid passing through the reactor
There is hot pressurized hydrogen passing through cladded channels right in the middle of the fuel rods.
>
> look at the statistics for the number of people killing in non-nuclear boiler explosions
Most nuclear power plants (not all) generate their power through... you guessed it, boilers running turbines.
> Then look at the number of people killed by coal emissions
Don't get me wrong; I support nuclear power over coal power. Just because I have concerns that the technology is not yet ready for building a *rocket* (something that we already have a lot of trouble with - and for good reason, it's a huge challenge!) doesn't mean I don't like nuclear power.
Combining two "in development" technologies, one of which has major consequences and a huge, huge public backlash against the nuclear power industry if it fails, is not something that should be rushed. One of the main reasons I have a problem with this is because of the consequences it would have to the future of nuclear power development.
> If you use official figures
First off, I think you need to look at the totality of nuclear power accidents:
http://en.wikipedia.org/wiki/List_of_nuclear_ac
Please read the whole thing before you respond. Most people have no clue just how many, and how extensive, nuclear accidents have occurred - and not just in the past.
Secondly, the main impact of Chernobyl was not the deaths (although your numbers are a bit odd; if you only count direct deaths, you get a number around 48; if you include radiation-induced thyroid cancer, you get around 1,800, most of which were exposed immediately after the fact; there are also 600 people who have returned to the dead zone, who are undoubtedly going to die young). The main impact of Chernobyl is how large of a region it ruined, and the impact of it on nuclear power worldwide. As for the area ruined, you can look at a map:
http://home.eunet.no/~lyngar/lions/chrnbyl1.jpg
That's 28,000 square kilometers >5 curies/km^2, 10,500 km^2 >15 curies/km^2, etc. The economic loss from this is truly staggering. To date, 375,000 people have been relocated.
Now, Chernobyl happened to be about as poorly timed as possible (the fuel rods needed to be changed soon, and it was a full-sized nuclear reactor), so is a poor analogy. Nonetheless, even a Chazhma-bay style disaster (meltdown right after fuelling) would be way too much. It'd doom the nuclear power industry. Heck, even a non-meltdown accident on such a craft would be disastrous for the nuclear power industry - look at the relatively minor accident at 3 mile island, for example (far from our nation's worst, but it got publicity).
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Risk is a very technical term. I work for NASA, and we calculate risks all the time. Your definition above is incomplete.
The key to understanding risk is that you have to multiply the probability an event happening by the negative effects of the event. So, there's a relatively high risk of you having a fender-bender in your lifetime, but the potential downside is only a few thousand dollars.
Compare that to the very small, but non-zero, chance of a nuclear meltdown occuring. Even with today's technologies, that number is not vanishingly small. Multiply that number by the economic damage that a real nuclear accident would cause, and you have a fairly high dollar amount. I am not a nuclear engineer, so I won't hazard a guess as to how much this would be.
Any highly coupled, highly complex system will have accidents eventually. Unless the new reactor designs are not highly coupled and highly complex, then there will, eventually, be an accident. Just look at Three Mile Island, where several problems happened at the same time, causing the readouts to be confusing to the engineers. Unless and until a nuclear reactor is a simple and uncoupled system, we shouldn't be using them. As soon as a design can simplify the system, we should be going all out. I believe that so-called "pebble-bed" reactors are a good start, but I don't know enough about them to comment, sorry.
I think Gas Core is the way to go. As the article mentions, a solid core reactor engine is expected to have a specific impulse of only 800-900 seconds, compared with 1500-2000 for a Gas Core engine of the closed loop type (no radioactive emissions). This translates into heavy lifting capability. As the article says, the solid core engine weighs to much it is only useful for vehicles already in orbit, so it would have to be lifted up in pieces by other ships. For really grand-scale work, like putting factories and hotels into space and hauling significant loads to Mars in a reasonable time, we need the big kahuna lifting power of a gaseous core engine.
Here is a highly detailed 12-part article that discusses a Saturn-V size gas core rocket that would lift a payload of 1000 TONS from the ground to orbit and return with an equal payload to a powered landing. Skip the first 5 parts (author's justification of why to build it) if just want to know how it works.
It's pretty safe to say that the likelihood of a nuclear reactor crushing into a critical configuration despite the normal measures taken to keep it "off" (neutron-absorbing control rods inserted, etc) is vanishingly small. In that you are correct.
In a gun design you only need to move one mass. This only appears to be feasible with U-235. Faulty thinking; the temperature and radiation (which turns the bomb core into high-pressure gas and pushes it apart again) are caused by the reaction; they are not separate from it.One point you appear to be missing is that the nuclear reaction takes a certain amount of time; neutrons are not infinitely fast, nuclei do not fission instantaneously, the exponential change rate of the reaction (whether growth or decay) is controlled by the composition of the material and its geometry. The geometry controls whether a splitting atom has a > 1 or < 1 probability of causing another fission. If the probability is >>1, you've got an explosion in progress; if it is < .5, you've got a lump.
The goal of the bomb designer is to turn the sub-critical mass into a prompt-supercritical mass before a chain reaction can begin and take the mass apart again; to this end they design implosion mechanisms and neutron generators to make everything happen when desired and not a microsecond before. The goal of the reactor designer is to make certain that the chain reaction is always under control. We can see that this isn't overly difficult; even Three Mile Island had a nicely-controlled reaction (its problem was lack of coolant), and only the Russians appear to have been careless enough to have a major incident (and without any containment building either, tsk tsk).
Sustainability and energy independence essay