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Comment: Re:Radiation shielding not feasible (Score 4, Informative) 374

by Soralin (#46343927) Attached to: Report: Space Elevators Are Feasible

Simple solution for the Van Allen belts: remove them.

https://en.wikipedia.org/wiki/...

High Voltage Orbiting Long Tether, or HiVOLT, is a concept proposed by Russian physicist V.V. Danilov and further refined by Robert P. Hoyt and Robert L. Forward for draining and removing the radiation fields of the Van Allen radiation belts[29] that surround the Earth.[30] A proposed configuration consists of a system of five 100 km long conducting tethers deployed from satellites, and charged to a large voltage. This would cause charged particles that encounter the tethers to have their pitch angle changed, thus over time dissolving the Van Allen belts. Hoyt and Forward's company, Tethers Unlimited, performed a preliminary analysis simulation, and produced a chart depicting a theoretical radiation flux reduction,[31] to less than 1% of current levels within two months[32] using the HiVOLT System.

If you're going to be building a space elevator, getting rid of the Van Allen belts is a relatively easy task in comparison.

Comment: Re:Logic! (Score 1) 776

A major flaw in your argument here: Uranium isn't very radioactive. Fuel pellets for nuclear reactors, that have not yet been used, you can handle with your hands without much in the way of problems (heavy metal poisoning, like with a block of lead, would be far more significant than any radiation here). On the other hand, once they've been through a reactor, you don't want to be anywhere near them.

The major source of radioactivity comes from the fission products. Heavy atoms need to be more neutron-rich to be stable, and lighter atoms are stable with a more even ratio of protons and neutrons. So when you split a heavy atom, you generally end up with a couple of lighter atoms which are far too neutron-rich to be stable, and which fairly rapidly decay into other things, producing and radiating away energy in the process (i.e. radiation).

That's where all of the lasting radioactivity comes from, after the reactor has been turned off. Uranium has far too long a half-life, billions of years, or hundreds of millions of years, for the main couple of isotopes, to have much effect on the amount of radioactivity. (generally, the longer the half-life, the less radiation, since a long half-life means less decay events per period of time. The candle that burns half as long burns twice as bright, or something like that. Isotopes that decay over a period of years for example, would produce approximately 8-9 orders of magnitude more radiation.)

Comment: Re:Government waste (Score 1) 257

by Soralin (#45056919) Attached to: Boston Dynamics Wildcat Can Gallop — No Strings Attached

If you want a small nuclear power source, you can go with a polonium-210 RTG. polonium-210 generates about 140KW/Kg, and has a half-life of around 138 days. And it decays by alpha radiation, so it doesn't need much radiation shielding. It's been used before, such as in soviet lunar rovers, Lunokhod, although as a heat source, rather than a power source.

Although, given that you have to create all of that polonium, transmuting it in tiny quantities, it's going to be a bit expensive. All of the logistics to keep it fueled with gasoline would likely still be cheaper, and so you could produce a lot more of them. And that's not even mentioning the obvious concerns about a machine running around full of polonium.

Comment: Re:They also want to allow private cyberwar... (Score 2) 443

That is only true if you define "stealing" to include depriving the original owner of the use of their property. Which almost nobody does.

"almost nobody" seems to include the US legal system: Dowling v. United States (1985) http://en.wikipedia.org/wiki/Dowling_v._United_States_(1985)

http://en.wikipedia.org/wiki/Copyright_infringement#.22Theft.22

Copyright holders frequently refer to copyright infringement as theft. In copyright law, infringement does not refer to theft of physical objects that take away the owner's possession, but an instance where a person exercises one of the exclusive rights of the copyright holder without authorization.[6] Courts have distinguished between copyright infringement and theft holding. For instance, in the United States Supreme Court case Dowling v. United States (1985), bootleg phonorecords did not constitute stolen property. Instead, "interference with copyright does not easily equate with theft, conversion, or fraud. The Copyright Act even employs a separate term of art to define one who misappropriates a copyright: '[...] an infringer of the copyright.'" The court said that in the case of copyright infringement, the province guaranteed to the copyright holder by copyright law—certain exclusive rights—is invaded, but no control, physical or otherwise, is taken over the copyright, nor is the copyright holder wholly deprived of using the copyrighted work or exercising the exclusive rights held.[1]

Not to mention that in moral terms, it is the same damn thing as conventional theft. But hey, let's focus on technicalities of language. Nobody (except the industry people themselves, or those taking their paychecks such as legislators), is going to say that the tactics proposed by the media industry are reasonable or morally acceptable. But the fact that they are dicks about making their point does not diminish the validity of their point that piracy is not ok.

In moral terms, theft and copying are not the same thing. Taking a loaf of bread from you, or watching how you made a loaf of bread, and then going home and doing the same thing myself, are not morally equivalent. Even if you say two different things are both wrong, it's incorrect to assume from that, that they're necessarily the same wrong, in type or degree.

Comment: Re:How do RTGs work? (Score 1) 134

by Soralin (#42621267) Attached to: China's Nuclear Rover Will Sample the Moon

It looks like that's what they're doing though in some capacity, basically running most of it during the day on solar power, and then just using a small RTG to keep it warm enough that it doesn't freeze to death during the night, and possibly keep communications and stuff like that running.

Just because it's a machine doesn't necessarily mean that all of its components can survive -170C temperatures.

And even Curiosity doesn't do work at night, it uses a smaller RTG than needed to power all it's components, and charges up batteries at night for operations during the day. Pu-238 is a bit hard to come by (and expensive) in large quantities, so you do what you can to limit the size of an RTG.

Comment: Re:Wouldn't They See That in the Endocrine System? (Score 1) 252

by Soralin (#42609423) Attached to: Researchers Study Mystery of the Toddler Who Won't Grow

Sort of offtopic but I'm a little disappointed that this unfortunate affliction for this person is being spun as a possible "fountain of eternal youth" in the article. Come on, people. We should be working to better understand this so we can help people

Yeah, it's a bit blatant on that point, but saving the lives of 100,000 people every day wouldn't be helping people? A cure for aging would save more lives than a cure for everything else combined.

Comment: Re:Not very useful the way it's worded. (Score 1) 205

by Soralin (#42600231) Attached to: Nuclear Rocket Petition On White House Website

Ouch, yeah, I know ion drives are low thrust, but that takes quite a bit longer than I was thinking, and I didn't calculate exactly how long that would end up taking. (Although I get about half that time with those figures, 11 months for low Earth orbit->mars transfer. But slowing down at the far end even would be tricky and time consuming as well.)

Something that might be useful for moving cargo around, but yeah, not quite that suitable for manned missions unless you can bump up the thrust by a huge amount, which would require a lot of efficiency.

Well let's see, It's about 3.8 km/s from LEO to mars transfer orbit. and 6.1 km/s from low Earth orbit to low Mars orbit, if you're not areobreaking. For low earth -> low mars orbit, at 20000s (196 km/s exhaust velocity), that would take a mass ratio of around 1.0316, or around 2.37 tons of propellent for a 75 ton dry mass rocket. At 800s (7.84 km/s ), that would take a mass ratio of around 2.177, or around 88.3 tons of propellent for a 75 ton dry mass rocket. If you can areobrake at the mars end, and only need the low earth -> mars transfer costs, those numbers would drop to 1.47t and 46.8t.

So, you'd more than a 25t difference to account for propellent costs. If you're starting with a base 75t ship in both cases, If you can airbrake at the far end, it's at least 45t extra for NERVA, bringing it up to around 120t. If you have to slow down with rockets, it's more like an 86t difference, bringing it up to around 161t. And those are just for hoemann transfer orbits, minimum delta-v, maximum time.

So there's some potential there, if you can toss on an extra 30t of power production and engines (over and above the NERVA reactor mass, since I assumed a 75t dry mass for each so that would already be included for both), and get the thrust output up an extra order of magnitude. With something like http://en.wikipedia.org/wiki/Dual-Stage_4-Grid (only one I could find near 20k isp), 100N would take about 10MW (Ouch). According to http://en.wikipedia.org/wiki/Solar_panels_on_spacecraft You can get 300W/kg solar arrays, meaning you could get 10MW using about 33.3t (10MW at around Earth orbit side at least). That's almost practically viable (There would probably be extra mass in support structures and such, but in space, and under mm/s^2 scale acceleration, it wouldn't be under much stress) And you could save a bit of travel time in the middle part by adding extra propellent to do something a bit faster than a strict hoemann transfer orbit, with that much power, a bit of extra propellent can go a long way.

Comment: Not very useful the way it's worded. (Score 5, Interesting) 205

by Soralin (#42578603) Attached to: Nuclear Rocket Petition On White House Website

Nuclear Thermal Rockets can have a higher efficiency than than conventional chemical rockets, but it's not as much as you might think. There's a limitation that to have a higher exhaust velocity in a thermal rocket, the exhaust needs to be hotter. And it can only be so much hotter before your reactor starts becoming molten rather than a solid. Which means that efficiency tops out at a bit less than double the exhaust velocity of conventional rockets.

Now, that's still useful, if you can get enough thrust to get up off of the planet (and to overcome the weight of the reactor in the process), then you might be able to lift quite a bit more into orbit. Except the petition is for an NTR that would only operate in space. And in space, where you don't really have to worry about the amount of thrust, and your speed is limited by your fuel and your exhaust velocity, things like ion drives can reach efficiencies an order of magnitude higher, or more. Which means, an NTR in space only wouldn't be as useful, compared to nuclear-electric or solar-electric propulsion.

I suppose an NTR not used for Earth surface to orbit might still be useful in landing or taking off from other objects. Really, that's where its strength would be, if you can get it to have high enough thrust, then it would be useful for getting things into orbit and back, as a surface-to-orbit ship. But as far as orbit-to-orbit ships go, ion drives and other electric propulsion can get a lot more speed out of the same tank of propellant.

Comment: Re:yeah, except for the true part (Score 3, Insightful) 305

by Soralin (#40427609) Attached to: Cyanide-Producing GM Grass Linked To Texas Cattle Deaths

OK, You tell me the procedure for mating a cucumber with a salmon.

http://en.wikipedia.org/wiki/Endogenous_retrovirus
http://en.wikipedia.org/wiki/Horizontal_gene_transfer

Virus infects salmon, new virus being produced ends up incorporating part of salmon DNA, virus gets passed to cucumber, virus inserts salmon DNA into cucumber and it ends up incorporated into it's genome, new offspring has genetic material from both cucumber and salmon. In practice, there may have to be a number of intermediaries there, but that's the idea, and it's 100% natural, and has happened numerous times before, and the results of such can be seen in the DNA of a number of living things.

We have a equal opportunity Calculus class -- it's fully integrated.

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