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?"

Comments

Not quite

[DarkHand]

Too bad the public fear of anything with the word 'nuclear' in it will grind this project to a halt. :(

Re:Not quite

[EvilCowzGoMoo]

I don't think 'nuclear' alone will ground the rocket. It will however be the scapegoat for any little problem that may arise.

Re:Not quite

[Anonymous Coward]

It'll just have be renamed to the "Super fun happy propulsion device"

Re:Not quite

[Paster Of Muppets]

New
Untried
CLever
Economically
Acheivable
Rocket

Re:Not quite

[Short Circuit]

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.)

Re:Not quite

[Kingpin]

Why should I not fear radioactive material in the atmosphere? Given the track record of shuttles, launchers and what have we - there's obviously a non-negligible chance of accidents happening. In case of such an accident, radioactive debris will fall down, radioactive rain could happen?

So, why should I not be worried? Please enlighten me.

Re:Not quite

[AKAImBatman]

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. :-))

Re:Not quite

[Surt]

The saddest part is that he mis-pronounces it on purpose to _gain_ votes.

Re:Not quite

[Control Group]

As a rule, I don't reply to AC's.

But damn, that's the best "in Soviet Russia" joke I've ever seen on here, and it didn't say anything about Soviet Russia.

And if you'll just provide a billing address, I'll send you an invoice for post-nasal soda removal from my keyboard.

Re:Not quite

[Rei]

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.

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_acc id ents

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.

Re:Not quite

[Catbeller]

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.

Re:Not quite

[NardofDoom]

People were all up in arms about Cassini's launch because it had the largest RTG ever launched. They were afraid that it would break up on launch and spread plutonium all over the planet.

Unfortunately, they ignored the fact that coal burning power plants put more radioactive material into the air every minute than was in the Cassini probe, and that the plutonium wouldn't atomize. It would sink like a rock into the muck at the bottom of the ocean, just like the dozen or so nuclear subs that have been lost. And it would pose no threat to life on Earth.

Nuclear and radiation are buzzwords that freak out people that don't understand. I'm radioactive right now. Should I be buried in a Nevada salt mine or shot into the sun?

Re:Not quite

[OrangeTide]

Well the shuttle program was originally designed to shuttle cargo and people to an Earth orbit space station. Then from the space station you could go to the Moon, Mars, whatever. If you could safely transport a nuke rocket to Earth orbit and launch and return to a space station (ISS?), then I would think the risk would be much lower. Assuming you were able to fling an old nuke rocket away from the earth when you no longer wanted it. Rather than letting it sink into the atmosphere and burn up.

Re:Not quite

[NardofDoom]

The only way we'd accomplish that is with subliminable messages. Maybe we could put them on the Internets.

Phew!

[grub]

and have even solved the graphite ablation problem

I was just lamenting over the seemingly unsolvable graphite ablation problem!

Re:Phew!

[spellraiser]

Yeah, but why did it take so long? It's not exactly rocket science, now is it?

Oh wait ...

Re:Phew!

[AKAImBatman]

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.

Re:No chance...

[Morgahastu]

So Nuclear subs have been operating in secret?

Re:No chance...

[AKAImBatman]

That's why it's up to you, me, slashdot, and anyone else who cares about space travel, to make it clear to the public that "Nuclear" is not a dirty word. Odd as it may sound, two thirds of Americans are currently in favor of nuclear power! If we can keep that number rising, perhaps the public will finally ditch their ridiculous fear!

Re:Mars?

[hoggoth]

> Perhaps they should solve other problems of being able to visit Mars such as its gravitation and the fact that the surface is quite uninhabitable.

Last I heard, both Earth orbit and the Moon are quite uninhabitable, yet we've visited both of those.

Nuclear subs

[SimonShine]

So Nuclear subs have been operating in secret? Well, yeah...

Re:Nuclear subs

[lousyd]

So Nuclear subs have been operating in secret?

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.

Re:Nuclear subs

[Holi]

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.

Re:No chance...

[Pxtl]

Nuclear is only okay on things that are designed to kill people. Didn't you get the memo?

when will people learn our focus should be energy?

[Anonymous Coward]

Exploration of mars should be second on our list of things to do in the US. Number one should be to have a clear goal on replacing oil as the main source of energy within, say 10 years. Then the US government can shift it energy policy from war to something that benefits us and the world. Why can't we say, ok, first, lets get this urgent problem behind us, and then focus on the next big thing.

Re:Indeed.

[AKAImBatman]

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. :-)

Safety Question

[higgins]

This isn't meant as a panicky "omg! nucular!" question. But we have seen a few space craft blow up spectacularly. Now, I assume the designers are bright enough that these engines could not actually produce a nuclear explosion, but wouldn't a conventional explosion at high altitude run a high risk of scattering nuclear material all over the place? Is there a good reason I shouldn't be worried about that?

Re:Safety Question

[Reducer2001]

There already was a spacecraft/satelitte that had a nuclear device in that "blew up" in space. The only thing that remained was the nuclear material, still perfectly stored in it's container. I'm sorry for not having a source to back to this up, but I'm at work. Here's a ton of info about this stuff.

Re:Safety Question

[honestmonkey]

This engine is not designed (as far as I can tell, I didn't actually read the entire article or anything radical like that) for use in the atmosphere. It would be carted up into NEO and attached to whatever ship is going to Mars. The fuel can be put in containers that would survive an accident on liftoff. All in all it's no worse a problem than any other liftoff. And it's probably one of the only realistic ways to get to Mars.

Re:Safety Question

[AKAImBatman]

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

Re:Safety Question

[WhiplashII]

The real question here is "how safe is a radiactive substance?" People often try to answer this by saying, we have done X so it isn't possible to have the reactor break, etc. (I mean, it is only for use in space, so it really shouldn't ever be near unshielded humans. Space is already a nastly place filled with radiation.) But everyone knows that humans aren't perfect, we can't forsee everything, etc. So, if the thing blows up and dumps radioactive stuff all over, what happens?

Well, first of all note that the Earth we live on is radioactive. We are constantly subjected to a high dose of radiation, and our bodies are relatively immune to it. In the scenario you mentioned where the radioactive substance is spread across a wide area like a continent, its contribution to the radioactivity levels is dwarfed by Earth's natural radiation. The real problem is concentration, for example if the stuff does not burn up but comes down as small chunks. Each small chunk can hurt or kill a person, depending on the size of the chunk and its level of radioactivity. The object in question would hurt you if you were exposed to it directly (like it fell on your house), but wouldn't kill you right out. You would get sick, go to the hospital and be treated. Your neighbors wouldn't get sick, but would be evacuated (and probably lose their house as well).

Summary: A worst case event could hurt or kill a couple dozen people, just like a normal rocket launch.

Hopeless

[Ford Prefect]

What's wrong with Project Orion? ;-)

I mean, if we're going to go to Mars, we might as well do it properly - even if it does end up filling the atmosphere with radioactive fallout...

Re:No chance...

[Anonymous Coward]

Odd as it may sound, two thirds of Americans are currently in favor of nuclear power!

Most Americans are in favor of garbage dumps too as long as it's not in their back yard and their taxes don't increase.

Re:Mars?

[NardofDoom]

With all due respect, you have your head up your ass.

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.

Re:No chance...

[gobbo]

I, like many of those in your two-thirds 'statistic,' am not afraid of fission. I'm afraid of idiots who don't know what to do with the products of fission, but take on the job anyway and truck it to some underground facility. I'm afraid of a for-profit utility that cuts corners. I'm afraid of backroom legistlation that looks the other way for the "Mr. Burns" in your town. In other words, the social risks need to be considered, for they are as significant as any technical issue. No different from building a dam upstream; do you want them to bid on the job based on cut-rate concrete? In this issue, the risks are potentially very large and long-lasting, and technology simply isn't enough.

So the fear isn't ridiculous; what's ridiculous is looking at the problem like a technocrat.

Re:Wooooooo Hooooooo!!!!!

[wamatt]

A nuclear explosion has to push against something, in this case a graphite pusher which would theoretically erode too quickly.

More info on nuclear propulsion efforts

http://en.wikipedia.org/wiki/Nuclear_pulse_propuls ion

Re: Silly public hysteria

[dpbsmith]

It's too bad that silly public hysteria when they started filling the atmosphere with radioactive fallout in the 1950s doomed such projects (at least until those who remember the 1950s die off).

We coulda had Project Orion. We coulda sea-level canal across Nicaragua excavated by peaceful nuclear blasts. We coulda had electricity too cheap to meter.

All spoiled, spoiled I tell you. Just on account of a few dead sheep, some irradiated Japanese sailors, a few U.S. soldiers with cancer, a little bit of fogged film (cardboard cartons made from fallout-tainted woodpulp), and a few "Sunshine Units"-worth of strontium-90 in the milk. And some problems working the bugs out of Windscale, Detroit Fermi, Browns Ferry, Three Mile Island, and Chernobyl.

Re:Public Buy In

[CrimsonAvenger]

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.

You're kidding, right?

[Omega697]

With this new engine, it seems that an inexpensive trip to Mars is now firmly within our grasp. Will we rise to the challenge?

There are so many other things standing in our way before we get to Mars, it's not even funny. Do you seriously think that we only need a good rocket to get to Mars? There's no way any trip to Mars in the next 50 years will be considered "inexpensive".

Re:safe

[AKAImBatman]

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.

Re:No chance...

[danila]

The fear is ridiculous because nuclear plants have an excellent track records, because modern designs are inherently safe, because nuclear waste is compact and relatively easy to store. You counter this with some generic arguments about "cutting corners". Yeah, I am not afraid of building libraries per se, but rather of idiots who build them using a lot of asbestos and poor materials so that they make every reader sick and then eventually collapse, burying hundreds of people underneath the ruins. So let's not build libraries, right?

You completely fail to grasp the real picture, as if you don't understand a definition of risk. Let me clarify - risk is not that the sky is falling, it's that there is a certain measurable uncertanty over the sky's future position, which we must take into account.

In real world the risks related to nuclear energy are small. Contrary to what you and your alarmist friends may believe, building a new nuclear reactor doesn't mean a Chernobyl and Hiroshima combined for everyone in 1000 km radius.

P.S. If you think only technocrats know basic math and are rational, that's rather sad.

Re:No chance...

[mwood]

Except for all those contaminated fish. I have photos. (Not secret or amateur stuff either; this was published in the Time-Life Science Library decades ago.)

It's "okay" to do nuke stuff underwater because the people who shout the loudest *think* it not harmful, just as above-water nuke stuff is evil because the same people *think* it is evil.

Nuclear policy is probably one of the best arguments for keeping the common man away from the levers of government, alas. We know less than we should about cleaning up power reactor accidents, for example, not because nobody bothered to wonder about it, but because Congress got wind of the SPERT trials and realized they'd never survive the public finding out that we were deliberately making experimental reactors fail in order to understand how to deal with the real thing. (Not to say that we know a lot about cleaning up the mess from coal-fired plants, waste from manufacturing photovoltaic cells, etc. either....)

Environmental concerns just ignored?

[RealProgrammer]

>public fear of anything with the word 'nuclear' in it

We can't start polluting space with all of that radiation. It'll kill all the trees!

(For those of you who went to American public schools, a) space is a big place and b) it's pretty well irradiated already by all those pesky stars. There are no trees in space.)

Re: Silly public hysteria

[Control Group]

Please do not lump Project Orion and the Nicaraguan Canal together with nuclear power generation.

Nuclear power generation is self-contained, and only problematic in case of catastrophic failure. The other two are problematic when functioning as designed. Associating the three is precisely what has prevented the use of nuclear power generation.

You of course scare-monger by mentioning nuclear power plant failures, but you'll notice that the world has (shock!) survived just fine. While the death toll from an event like Chernobyl is certainly tragic, there are risks associated with developing any technology. Beyond which, I have the sneaking suspicion that more people have died from the effects of air pollution caused by fossil-fuel power generation than have died due to nuclear reactor failure by orders of magnitude.

I also suspect (based on broad stereotyping, admittedly, so feel free to tell me I'm wrong) that you also buy into global warming as a result of mankind's CO2 production, in which case the death toll from fossil fuel plants will be yet more orders of magnitude higher than would be caused by the occasional nuclear plant failure.

Weirdly apropos

[caveat]

discovery wings is at the moment running a show on Project Pluto, the government's project to develop a nuclear-powered ramjet in the 50s/60s. the research got up to successfully running the full-scale Tory-IIC 500Mw prototype for 5 minutes at 35,000lbs thrust. i realize a ramjet design is different from a thermal rocket design, but does anybody know why 'they' can't use the basic design of the tory reactor, homogenous uranium/beryllium oxide fuel tubes, at the heart of the rocket engine? seems an ideal situation, theres no graphite to ablate and AFAIK the oxide ceramics stand up pretty well to hydrogen.

Re:No chance...

[mwood]

Okay, so what *should* we do with the products of fission? Recycling is not allowed, since this yields a bit of plutonium which automatically causes all nations to start building bombs. You don't want to store it. "Use it" or "throw it away" seem to be the only options. Should we wave a magic wand and make it disappear?

Re:Nuclear Test Ban treaty implications

[AKAImBatman]

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.

Wrong risk

[MemeRot]

The risk I worry about isn't Chernobyl. It's waste products that have been stored in metal barrels for decades. This country has an abysmal record on safely disposing toxic waste products of all kinds, and there STILL is not a single site working site for permanent disposal of nuclear waste (which will change with Yucca mountain I know). Too bad many experts say that Yucca mountain is seismically unstable....

The problem with nuclear energy is a false economy. How much expense will running Yucca mountain for the next 10,000 years rack up? How much of its running expenses are currently subsidized by the federal government? That offsets any advantages nuclear fission has in my opinion.

Fusion obviously has none of those problems, and research into it is drastically underfunded. If the government funded a research program on 1/10 the scale of the Manhattan project into fusion I'm convinced it would become a viable power source and overshadow any of the other alternative energy sources being talked about.

our focus should be freedom

[npongratz]

Are you serious??? You want the United States to focus on one scientific goal? You are saying, in effect, that even though there are well over 290 million people in the US, each and every citizen should be forced by the government to be focused solely on what you think is the Right Thing(tm). Give me a break!

The US is still (ostensibly) a free market, capitalist country. Each citizen and industry is free to pursue their own interests. And yes, that even includes interests that might not fit perfectly into narrow-minded people's ideas of what is Best For The Country(tm).

Thanks to visionaries pursuing their unique interests in a free market economy, non-conformists have made leaps of creativity and ingenuity that have created some of the most helpful technologies used around the world. Don't ruin it for the rest of us with your command-and-control utopia.

Re:Why does it have to be a rocket?

[0123456]

"Can't we make an airplane engine from this reactor?"

Been there, done that, realised it wasn't the smartest idea ever.

Not quite... accurate

[Mulletproof]

You simplify this too much. The public tends to fear nuclear power because very specific groups spin nuclear power as the evil demonic force opposed to mother nature. These same groups often use nuclear power as fear-leverage in politics. "Gasp! They want to open up more evil nuclear powerplants and refineries that pollute and readioactivate! Don't vote for them or your child wil grow up with 5 arms! Nuclear waste spill across the highways and nich impreganable underground containment will leak into the ground water, killing us all in several thousand years assuming our technology doesn't advance whatsoever from this point forward. Fear teh nuk3z!"

It's simple to say the public fears it. It's important to know who is driving that fear.

coal is 1ppm - 10ppm Uranium, some bomb grade

[puzzled]

Burning coal puts 25 tons of bomb grade Uranium into the air every year and I forget the exact amount of U238. The U238 gets hit by high energy neutrons from cosmic ray impacts and changes into ... Plutonium.

Launching a little dab of Uranium under highly controlled conditions doesn't seem like such a big deal when you know this fact.

Bah!

[ljavelin]

Note that the engineering term "intrinsically safe" has a substantially different meaning than "inherently safe". Although the terms are used interchangably by some, those who live by the "law of milspecs" never confuse the two.

In any case, it'd be wise for P&W to rename it something other than a nuclear engineer. That's dumb marketing. Hell, they don't call the Army's M1 tank the "nuclear tank", despite its use of depleted uranium.

And anyhow, many jet engine parts use radioactive materials for hardness and during the manufacturing process. This is not news.

VASIMR

[LordMyren]

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.

Re:No chance...

[purfledspruce]

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.

Re:Don't dismiss the fear...

[Ba3r]

As I said I am all for nuclear power; as I realize the statistics are in favor of it over other sources of energy. In my parent post my aim was to prevent people, such as yourself, from stubbornly denouncing the counter-arguments (and their derived fears) against nuclear power, as you did.

Now, just to be patronizing and make sure you understand I will repeat: I am for nuclear power, because statistically it is Safer, and I think that most uses of nuclear power will not lead to proliferation.

HOWEVER, the fears mentioned are not completly illegitamite, and it is essential we understand them to convice people otherwise.

Sure, coal power is far more deadly to society as a whole, but people (think they) understand how coal works and how it kills people (suffocation, burning, crushing, carcinogens). People aren't as familiar with nuclear power, and the idea that so little can be so powerful gives them the willies.

The second point I find far more persuasive against nuclear power. If nuclear power is used in more industries, and more often, then it is invariably exposed (both in terms of concepts and engineering, and raw materials) to more people. The more people it is exposed too, the less secure it is and more possible (statistically!) that one of those people might not be worthy of entrusting with such powerful concepts/materials. Whether or not the nuclear power will be sent to Mars, silently glide 300m below the water off the Siberian coastline, or power an office building, the more widespread it is, the greater the potential that someone who wants to abuse it will get access.

Since you so drastically misunderstood my post, I will yet again, since I am still frustrated, emphasize that I am For nuclear power and I Agree with the rational, and obvious conculsions you felt necessary to post but I understand that others are not aware of this, and you stubbornly denouncing them as ignorant and blasting out facts will Not quell their fears. You must Understand those fears, especially the legitimate points of those fears, and then maybe you won't copy and paste your canned "Now sit and think for a moment which technology is more dangerous" response, which is part of the reason We pro-nuclear power people never get anywhere. phew!

Please stop spreading misinformation

[Engineer-Poet]

The misconceptions in the parent are legion, and I can only address a few.

... 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.

Bombs typically use spherical shells, not separate lumps. To be critical, each splitting atom has to emit neutrons which have a probability of splitting ~=1 other atoms. To be prompt supercritical requires the prompt neutrons to have probability of splitting >1 other atoms (there are also delayed neutrons from the fission products; if I understand correctly, these usually take too long to be significant in a bomb explosion). It doesn't matter how you arrange the fissionables so that they're sub-critical until you want them otherwise, anything will do.

The two-sub-critical masses have to be brought into close proximity quickly

Which depends on the spontaneous fission rate of the material you're using. U-235 is low enough that you can just fire a slug into a sub-critical tube and it's very likely that nothing will happen until after they've finished coming together (half-life of 700 million years means low fission rate). Pu-239 requires a rapid spherical implosion (24,000 year half-life) and higher isotopes of Pu will drive the requirements even harder (or cut the likelihood of a successful "boom" even lower).

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.

You'd fire both shotgun shells down the tube to meet each other.

In a gun design you only need to move one mass. This only appears to be feasible with U-235.

The temperature and the radiation caused by their increasing proximity tries to vaporize the assemblage

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).