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Nuclear Booster Rockets
Logic Bomb writes: "According to the New Scientist, NASA would like to explore replacing its chemical-based booster rockets with nuclear versions. Engineers think it could be the first step towards major reductions in launch costs that would eventually lead to widespread public access to space. NASA is aware that such a project faces massive PR difficulties. As a non-expert member of the public, I can verify that. :-)"
> they need a powerful reactor. They energy
> density must be far higher than the reactors
> currently in use. There was a project in the
> 1960'ies, and they came to the conclusion that
> they need a 2000-3000 times higher energy
> density.
THIS IS COMPLETELY FALSE. I am shouting because you are absolutely nuts. The power densities (energy density is *not* the right term) of NERVA reactors that were actually built and tested in the '60s are *multiple* orders of magnitude higher than power reactors used for electricity production. Ballpark: 1000 times higher! They have existing designs which are powerful enough to be useful for upper stages right now. Primary booster designs are about one more order of magnitude larger and perfectly feasible.
> they need a conventional booster for
> the first 30000 feet...
Not if they simply provide the ram rocket (that's the correct term for the design which the article describes) with oxidizer and integral combustors for early acceleration. Then the hybrid design would be chemically powered at lift off, but nuclear powered the rest of the way. It need not use a separate booster, but could be a an SSTO (single-stage-
to-orbit).
> the reactor must
> withstand an explosion of the conventional
> booster
This isn't very difficult for the designs which are likely to be tried. Early graphite designs would break up and release radioactivity easily, but it sounds (from the uranium dioxide reference) like they will be making the fuel elements from a tungsten-UO2 cermet. This stuff is *really* hard, dense and tough. You would be surprised at how little a chemical explosion might do to it.
Furthermore, it is important to understand that nuclear fuel is only *very slightly* radioactive until the reactor is powered up and fission products are produced. A wrecked *fresh* core below 30 000 feet represents a near-zero hazard.
> they must convince the public that
> the radioactive traces that are released in
> the upper atmosphere are negligable.
This is going to be a political problem, not a scientific problem. It is important to understand that the thickness of the atmosphere makes a *really* good radiation shield. Radionuclides in the stratosphere may be released and emit gamma rays, but almost *none* of the gammas will reach the ground. You should realize that there are something like 7 (metric) tons of air over every square meter between you and the stratosphere!
Stratospheric fallout is perhaps hundreds of times less threatening to the environment than tropospheric fallout. There's no rain up there. In the troposphere, rainout is the primary means that radioactivity will reach the ground - in a few days. But with no rainout, finely-divided stratospheric fallout remains aloft - and on the preferable side of that 7t/sq.m shield - for months. Fission products are mostly short lived, and a tremendous amount of decay occurs before they will reach the ground.
Furthermore, the amounts normally released are likely to be very small - because of that tungsten-UO2 cermet again. The UO2 particles in the cermet will do a tremendous job of retaining fission products, and the fuel elements should be cladded with plain tungsten or a similar metal or alloy.
-- Mike Greaves
I'm scared of radiation because it does horrible things. It caused Braniac's head to grow and he couldn't even find a toupee after all his hair fell out. It made Dr. Octopus turn evil. It ruined Mr. Fantastic's sex life and made the Thing the fondest desire of all women everywhere. It was even responsible for the spider that bit Peter Parker and ruined his self-centered little life. Worst of all, it created the incredible Hulk, who is still roaming around the southwest wreaking havoc at great expense to the taxpayers.
Given this history, I think its perfectly reasonable to be scared of Nuclear anything, and especially of what will happen when a Nuclear Reactor is exposed to cosmic rays above the stratosphere. We JUST DON'T KNOW what will happen under these conditions!
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-- Slashdot sucks.
(Disclaimer: this comes from an advocate of nuclear power. Add the appropriate block of salt.)
I've often wondered if your average anti-nuclear activist actually understands the physics involved. I'm not flaming, I'm genuinely curious. Through the media, I've seen many protests over the most trivial and safe use of nuclear technology (the Cassini launch comes to mind) but in all those news reports I've never seen an activist give a solid technical reason why they oppose nuclear power. Is that subtle filtering on the part of the media, or are these people genuinely clueless?
That's absurd! Thousands of people die every year from toxic coal waste (a good amount of which is released into the air, despite a complex filtering system).
Very, very true, and I thank you for bringing it up. In fact, less than a thousand kilometers from where I live, there's one of the world's worst coal-related toxin sites. Do a search for "Cape Breton tar ponds" in any search engine and you'll find tons of news reports on this problem.
The Sierra Club has put together a horrifying report on this site. By an astonishing coincedence, this place also has the highest cancer rate in Canada. Hmm.
And this is Canada, supposedly a bastion of environmental friendliness. Can any of you imagine what the situation might be like in countries where the local government doesn't care at all about the environment and doesn't have to be accountable to citizen's health concerns?
I'll be the first to admit that nuclear isn't a perfect solution, but stories like the Sydney tar ponds are what make me realize just how much more horrible fossil fuels can be. Nuclear waste may be more dangerous per mass unit, but at least there's a lot less of it.
Because stupid people can't get the images of mushroom clouds and Chernobyl stuff out of their heads. Just like when someone hears you work with computers, they think you're an expert with anything that contains wires.
"That's Tron. He fights for the Users."
It's sad that even the term nuclear had been so villified in the United States. Environmentalist groups did their best to kill American nuclear power in the 70's and 80's - unwittingly allowing for more and more pollution from smog-emitting coal plants and inefficient natural gas plants. Good luck on NASA pushing nuclear rockets through - look at the trouble they had with the Cassini probe.
Considering that in 1993 then Vice President Al Gore killed both the lithium breeder and fuel pellet nuclear designs after tests showed them to be excellent energy producers and perfectly safe against radiation release, it's clear that the American attitude to anything with "nuclear" in the title is based off irrational fears and half-truths.
Breaking through this ignorance barrier is going to harder for NASA than sending a man to the Moon...
The biggest real issue is whether the reactor contents could be adequately contained during a worst case accident. If this is possible, and I suspect it is, there is no real danger associated with this technology.
OTOH, the biggest practical issue is whether anti-nuclear hysteria will stop this thing because of the neglible amount of radiation produced at high altitudes when it fires. I am sure that too many people are happier with the amounts of CO2, toxic gases and (at higher altitudes) ozone depletion that is caused by current rocketry than they would be with the pospect of any tiny amount of the dreaded r a d i a t i o n products released into the stratosphere. Perhaps they fear mutation in the UFO's ;-)
Certainly in the US, where most people are innumerate and don't know physics, and Europe, where too many people are ecophobes, this will be the biggest problem.
The only good weather is bad weather.
Let's look at some of the claims in the article:
"Nuclear systems give you a chance to reduce your mass and so your overall costs to orbit," Adams says.
This is a missile-builder talking. He's clearly obsessed with one particular engineering measure of "goodness", which is called "ISP". There has been any amount of research in the last twenty to thirty years that shows that maximizing ISP does not necessarily reduce costs. If NASA's current rockets were operating at the lower end of what you can do with chemical engines then he might be correct, but they are in fact several orders of magnitude off.
Nuclear propulsion could allow single-stage rockets to reach orbit - cutting the need for expendable boosters and allowing what he calls "airline-like" access to space.
Chemical propulsion allows single-stage to orbit, if you do it correctly. In fact, NASA has already built several rockets capable of single-stage to orbit operation, but they just haven't used them that way. The second stage of the Saturn V was one of them. Launched by itself, it would have been capable of making orbit with a small payload. It had the necessary ratio of fuel to total mass.
It would also be lighter and be able to lift a bigger fraction of its starting mass into orbit - perhaps as much as 45 per cent. "With existing systems, it's more like 10 per cent," he says.
This is true, but it DOES NOT MATTER. The 90% of the mass that doesn't make it to orbit is fuel. Fuel is very cheap. The current Space Shuttle uses something like $20 million dollars of fuel to get to orbit (and the vast majority of that is the solid rockets, not the hydrogen). The total cost of a Shuttle mission is more like $1000 million. Even if you could make the fuel free it wouldn't make the shuttle any cheaper.
What is important to cheap access to space is to make the vehicles *totally* reusable, like an airliner, not throw-away like a missile. The Shuttle is partially reusable, but it still throws away a huge amount of itself each flight, and has to be totally refurbished -- a process that takes months. Space flight won't be cheap until you can fly, come back down, fill-her-up, and fly again the next day.
Even if that means that 98% of what you leave the ground with is fuel it doesn't matter until you've got total costs down to well under a tenth of what they are today, and maybe closer to a hundredth.
If you're interested in this then I highly recommend that you go and read what the Space Access Society has been writing about this stuff for more than five years now.
Okay, lets assume you didn't say Africa and actually picked a place with low (or zero) population, rather then people you just didn't care about - its still risky. First, if it explodes on take off, we're probably not too bad off, but its no fun - remember that volcano a bit back, that resulted in a cold summer? That spread ash over the sky world wide. This explosion wouldn't even be close, but it could still spread the nuclear fuel over a fairly wide area, and some of it could reach the first world (especially if we made our launch site the middle of the Nevada desert or something).
Second is the nastier possibility - high atmosphere fuck-up. These are more rare, like the Ariane 5 prototype and, to a lesser extent, the Challenger (the challenger didn't get that high). There, the ship has made it a long distance and is no longer near the launch site, and could be over civilization. Also, the high atmosphere explosion means that it will take much longer to land, giving the fallout time to spread worldwide. In that case, it doesn't matter where on earth you are, you're still gene-fucked.
Of course, I don't know how much they're using, how risky it is, how bad things could be if it went up exactly. This is simply explaining people's fears. Personally, I'm all for this tech, I think its important to the future of humanity, and could finally get us into orbit. Still, the enviro's are right, this is risky as hell, and even the best rockets have been known to blow up, so I'm not sure if I want this going on.
Based on the limited and informal associations I have with nuclear engineers, most US citizens became afraid of Nuclear power right around the time of the Three Mile Island accident. The feeling I generally get is that the majority of Slashdot doesn't remember three mile island.
Back in the 70's and 80's, Nuclear power was considered the clean solution to all of our energy problems. And they were considered increadibly safe. Until one melted down. Most Americans seem to remember Murphy's Law ("Everything that can go wrong, will go wrong"), and as such, prefer to err on the side of safety. Furthermore, there _is_ a problem with disposing of Nuclear waste. That stuff doesn't just disappear.
In response to a comment I saw earlier about how the first use for nuclear power being a weapon. That really doesn't apply. We detonated the first atomic weapons back in the 1940's. Our Nuclear Power industry was booming in the 60's and 70's. It died in the 80's. People didn't just wake up and realize that this same technology had intentionally killed thousands. No, they were more afraid that it might _unintentionally_ kill thousands more.
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