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Submission + - SpaceX sets target date for next launch: February 24th

Rei writes: After some consternation about the pacing of Falcon 9 upgrades, SpaceX has announced that it plans to launch again from Cape Canaveral with a target date of February 24th. While the primary mission will be to place the SES-9 communications satellite in orbit, this will also mark their fourth attempt to land the first stage on an autonomous drone ship, after their last launch touched down softly but fell over when one leg failed to latch. SpaceX is working to significantly accelerate the rate of production and launches — they are reportedly moving the factory from 6-8 cores produced per year to 18 at present, and expect to reach 30 by the end of the year. After the upcoming launch, they expect to launch one rocket every two to three weeks.

Comment Re:virtual mars better than a virtual fantasy worl (Score 1) 32

Why not combine the two? Use their virtual environment as a frontend for a collaborative colony-building simulation (with our "best knowledge" data on the likely distribution of minerals and such incorporated), everything from mining, refining, production, goods transportation, installation/assembly, etc. People could contribute modules that accomplish tasks, with varying levels of design maturity (everything from stub modules that simply take a given set of inputs and yield a certain set of outputs, to actual nuts-and-bolts level of detail systems with rigid-body physics models and CFD chemistry calculations, all the way to real-world tested systems), along with code controlling how individual systems behave in different circumstances. All components would have defined realistic wear and tear over time / various consumables. The ultimate goal for participants would of course be a setup where every module is highly defined, down to the level of nuts and bolts, and every individual component in them can be manufactured by some other system on the planet, in a manner such that the net throughput is sufficient to produce all of hardware required to keep all systems operational plus enough to keep the associated humans alive and comfortable - while having the net mass that would have to be shipped to Mars as low as possible.

It wouldn't be something your "average gamer" would get involved in, I'm picturing something more for engineering students, active/retired engineers, etc, with some funds set aside for real-world testing of the more mature systems. You could generate interest by making clear that systems developed in the environment that reach a sufficient maturity state (passing real-world testing and showing a valuable service to future colonists) would be slated for actual deployment to Mars when the opportunity presents itself.

Detailed 3d environments aren't really a critical aspect of that for some systems (such as refining). But for others, such as transport, they're a critical part of the picture. Even for things like mining, having a good grasp of the types of environments that particular minerals occur in would be quite important - does X occur in this area on hard to access cliff faces, surrounded by dune fields, deep in craters, etc? How can we get it out of there and get it back to where we need it? How can we position each component so as to minimize transport requirements to all others (since one won't find all mineral deposits in the same location)? Etc.

Comment Re:Minecraft version (Score 1) 32

Oh geez, if any group ever wants to hack a website "for the lolz", they should totally hack NASA's server for this service and insert some ancient ruins or a monolith or something. ;) The prank would hit twice - first by the people thinking it was proof of aliens, and then when NASA corrected it, people thinking it's a coverup ;)

Comment Re: Batteries just don't store enough energy... (Score 1) 253

Also, there's a lot of diversity in terms of aircraft electrification that one can take, it's not an all-or-nothing thing. There's lots of different proposals for varying degrees - for example, high bypass with electric turbofans, using onboard electricity to spin the compressor so that you don't have to have a turbine, and so forth.

Comment Re: Batteries just don't store enough energy... (Score 5, Insightful) 253

Yes. Also, you can't ignore comparative efficiencies of engines. Or engine mass to weight ratios. Or the length of time to market, and the expected level of battery change during that time period. Or side benefits (for example, the ability to have small, very light engines was made use of in one NASA experiment that placed numerous small engines along a wing, causing an effect that created drastically more lift at low speeds and allowing for a much shorter takeoff distance).

And beyond that, you can't ignore economics. Having reduced range but getting your fuel at a fraction of a cost may ultimately prove to be more desirable. It's a very complex issue that one can't just make all-encompassing statements based on a single figure like "energy density of batteries vs. energy density of fuel".

Anyway, this is hardly Elon's first time to mention it. Years ago he mentioned that he wants to be the first person to have an electric plane break the sound barrier. If there's anything one can say about Elon, it's that he sure doesn't set the bar low...

Comment Re:Icebergs float on glaciers (Score 5, Informative) 40

No, it does not form "one huge crystal". Nitrogen ices at these temperatures have little structural integrity. It was well known before we got to Pluto that if we saw any sort of relevant topography, we'd know immediately that it was from water ice, as nitrogen ices are so weak that they'd just flow slack over time.

Comment Re:Icebergs float on glaciers (Score 5, Informative) 40

Nitrogen ices at these temperatures, while crystalline, have rather low viscosity. If you put weight on them, they slowly diffuse around it until the object either sinks or is buoyantly balanced out. The latter happens in the case of water ice.

Also, it's worth noting that it's not pure nitrogen ices, it's a nitrogen-carbon monoxide-methane eutectic. Nitrogen is the most common component, however. Also, there are multiple crystal phases that can be taken, depending on the conditions. Nitrogen ices are most famous for having some rather "explosive" phase transitions between different states.

Comment Re:sunfire / in my stellerator / makes me... happy (Score 1) 98

Fast neutron cross scattering sections in the couple MeV range barely vary over more than the range of 1-10 barns

1-10 barns is, of course, by definition, an order of magnitude. There is a massive difference between 10 barns and 1 barn. Tenfold, to be precise. ;)

More to the point, you can't just combine all cross sections like that. The energy imparted from an elastic collision isn't the same as from an inelastic collsiion, which isn't the same as an (n, gamma), and so forth. Elastic collisions are particularly low energy, particularly the higher Z the target. Taking them out of the equation yields much greater differences between materials in the range of a couple MeV. The upper end of the neutron energies are "somewhat" similar (up to about one order of magnitude), but down below 6 or 7 MeV or so there's quite a few orders of magnitude difference.

Likewise, total cross sections have no bearing on the accumulation of impurities in the material. The particular cross sections are relevant not only in terms of reaction rate, but also what sort of impurities you tend to accumulate and what effect they have on the properties of the material. Which of course varies greatly depending on what exactly they are.

Integration of annealing cycles into blanket design is not brought up enough in some design studies, but is a consideration to help

It's not a side issue, it's a fundamental issue to the design of a material designed for high temperature operation under a high neutron flux.

Blanket design is extremely constrained by tritium breeder ratio to ensure more tritium is produced than used, which squeezes volume allowed to be used by coolant, ... but they have much lower neutron flux to worry about. Gen 4 reactor designs are in the 500-1000 C temperature range, exceeding in some cases what is thought reasonable for fusion blanket design. ... Blanket replacement is considerably more complex than fuel replacement in a fission reactor

Perhaps they've been heading in a different direction since I was last reading on the topic, but I was under the impression that a prime blanket material under consideration was FLiBe. Which operates in a temperature range of 459-1430C, and is its own coolant. That doesn't change what the first wall has to tolerate, but as for the blanket itself, you have no "structural properties" to maintain, and cooling is only limited by the speed that you can cycle it.

The last paper I read on the subject also suggested that for breeding purposes one needs not only beryllium (they were reporting really poor results with high-Z multipliers), but the optimum ratio (to my surprise) worked out to be significantly more beryllium than lithium. So building structural elements out of beryllium serves double purpose, you don't have the excuse of "I need to use steel because it's cheaper" - you need the beryllium either way. It's strong, low density, similar melting point to steel, but retains strength better with heat, and highly thermally conductive. Beryllium swelling from helium accumulation stops at 750C+ as helium release occurs. So pairing a beryllium first wall with a FLiBe-based blanket seems like a very appropriate option.

Please don't get me wrong, I'm not at all disputing the great amount of engineering work left to do. I'm just more optimistic that appropriate solutions will be found. Perhaps I'm just naive in that regard ;)

Comment Re:sunfire / in my stellerator / makes me... happy (Score 1) 98

So on average the fission reactor material only has about 10% of its atoms displaced over the lifetime, while the fusion reactor would have, on average, every atom displaced hundreds of times over the lifetime.

How can you make generalized statements like that? Cross sections vary by many orders of magnitude Fission reactors are generally made of steel, which is hardly setting any records in terms of low cross sections. The smaller the reactor, the less material you have to replace, and the more expensive the material you can use. And being "displaced" is not a fundamental universal material property effect, it depends on how the material responds to radiation damage, which varies greatly. Generally materials respond better at high temperatures (annealing), and fusion reactors operate of course at far higher temperatures than fission reactors.

I have trouble seeing how one would consider neutrons per square meter to matter more than neutrons per MeV. Because neutrons determine what you're going to have to replace, and energy determines how much money you get from selling the power to pay for said maintenance. You can spread it over a broad area and do infrequent replacements, or have it confined to a tight area and do frequent replacements, the same amount of material is effected. Some degree of downtime for maintenance is normal in power plants - even "high availablility" fission plans still only get ~85% uptime.

Comment Re:sunfire / in my stellerator / makes me... happy (Score 1) 98

Hmm, thought... and honestly, I haven't kept up on fusion designs as much as I should have... but has there been any look into ionic liquids as a liquid diverter concept? In particular I'm thinking lithium or beryllium salts. They're vacuum-compatible, they should resist sputtering, they're basically part of your breeding blanket that you need already... just large amounts, flowing, and exposed. Do you know if there's been any work on this?

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