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Comment Re:Really? (Score 1) 179

Reprocessing fission waste has proved expensive, difficulyt and prone to accidents and leaks everywhere that it's been tried. It's not impossible, but you end up
dealing with a mixture of hot radioactive nitric acid and insoluble radioactive sludge of unknown composition, using only remote handling. The plants all had a lot of down-time, stuck valves, corrosion problems, ....

Comment Re:Consumables (Score 1) 49

The comment is a about the general frequency of water. For Earth if you want a lot of water, Ceres or a well-chosen comet seem like the best choices at the moment, with the craters at the South pole of the Moon a bit of a long-shot. If you just need a few tons you may as well send it up from Earth. Finding water in the outer system is not a surprise, but finding so much on Mars and Ceres was a bit unexpected.

Comment Re:Mars Colonial Transporter (Score 1) 101

Nope, CH4 freezes solid at 90,7K (versus LOX boiling at 90,2K). And it becomes way too viscous as it approaches its freezing point. That doesn't mean that they can't share a common bulkhead, but it does complicate it for long-term storage (aka, Mars missions)

Fair point, but it does simplify things more than LH2+LOX would be, or even RP1+LOX if you found a way to synthesize kerosene on Mars.

Those boiling points are presumably at 1 atmosphere, but there is nothing special about that pressure. If you pressurise the LOX tank a little you can probably get them both liquid in the thermal contact at 95-100K.

The higher density, lower compressibility and higher latent heat of vapourisation of methane all make it easier to pump than LH2, saving mass and complexity.

Comment Re:Remember the NASA Wind Turbines? (Score 3, Insightful) 178

Current blades are trucked in one piece (per blade) which is impressive to see. Three of them were parked on I-5 outside of Patterson, California a few months ago. There are a lot of net videos and photos which convey the scale.

Even at the current size they can't get through many highway interchanges and local intersections. The larger ones won't be able to ship in one piece at all.

"ship" is the point. These are designs of offshore turbines. They would probably make the blades in shipyards and transport them on a barge directly to the site.

Comment Re:Capitalism (Score 3, Informative) 178

Mega installation which require mega capital which allow power companies to centralize production, control distribution, and charge consumers.

It is more efficient and less prone to failure to have distributed production with small scale wind turbines, photovoltaic, etc. on peoples' homes. But then, well, where's the profit to the established interests?

It's not more efficient. It may be more desirable for several reasons, but with wind turbines for efficiency (power produced per dollar spent) you want the big and high up. This especially applies if you are building them offshore as is proposed in this case, because buildign the base and getting there to do maintenance are high costs that depend on the number of turbines, not the power produced.

It's also not less prone to failure, at least for some definitions of failure, in that the wind is much steadier out at sea an a few hundred meters up. A professional maintenance and inspection regime also helps.

Comment Re:Check the Focus! (Score 3, Insightful) 117

Their calibration involved a reference point for one of the lasers that had to be precisely positioned. This was done by having a rigid metal bar with a polished end, covered by a very black cap with a pinhole in it. The point on the end of the bar visible through the pinhole was meant to be the reference.

Unfortunately someone scratched the end of the cap a little and no one noticed. The shiny metal in one of the scratches got picked up as the reference instead of the pinhole. As a result it was too close to the mirror by the thickness of the cap (a millimeter or so). That was enough to lead them to carefully polish the mirror to slightly the wrong shape.

They did, I believe, ignore contradictory results from another basically much less accurate method of testing the mirror, since the laser was giving consistent results and was the superior method.

Comment Re:reusability: economic case? (Score 1) 132

Falcon 9 is actually just a two stage rocket, so the second stage ends up in orbit. Recovering it would mean using fuel to deorbit and having a heat shield capable of withstanding reentry. Even just recovering the engine would be a pretty major operation.

If you wanted to avoid wasting this element then lifting it a little higher into a stable orbit (perhaps via an ion drive tug) and then making use of it for something there would make more sense.

Comment Re:Completely fabricated nonsense (Score 2) 252

Your patten also catches scientists who were being cautious and conservative to start with, so where there is uncertainty they adopt the option that gives the least radical results, the smallest anomaly, etc.

Then as the data and the methodologies improve and the uncertainties are resolved the results naturally become MORE surprising.

Comment Re:"Climate contrarians" (Score 1) 252

II'm still waiting for someone to tell me what the temperature is supposed to be.

That's fairly easy, but there are two answers:

1. If large scale exploitation of fossil fuels had not occurred in the 19th -21st centuries the global mean temperature calculated according to the Hadcrut4 methodology and averaged over a decade or so would probably have been between about 0.7 and 1.1 kelvins below the average for the last decade (ie about 287 rather than 288 Kelvins).

2. More tentative -- if agriculture had not been widespread over the last 10000 or so years, global temperature might be significantly colder as we headed down towards another ice age.

Comment Re:Again? (Score 1) 121

As the subject says -- "fuel cell" -- that means no IC engine hydrogen and oxygen (from air) produce water and electricity directly. No Carnot cycle, no moving parts. After that the drive train is electric, just like a battery car.

You can make hydrogen by electrolysis, which is not so efficient, but you can do it whereever and whenever you have cheap electricity. Alternatively if you have methane that you are allowed to burn (whether it's natural gas or from rotting sewage) you can make hydrogen pretty cheaply from it.

See also the remarks above about Audi stress-testing their tank -- the only thing that touched it was an armour-piercing round, which made a hole and no fire. A hydrogen leak is generally much LESS dangerous than a gasoline leak because it doesn't hang around at ground level and soak into things. Given half a chance it'll just diffuse away.

Comment Re:Does it have to be the whole booster? (Score 1) 118

Fair enough. You're effectively increasing the stage count by 1 (although the extra stage has no engines) so you'll need to pay the mass for the connectors between the engine stage and the fuel tank stage, and the structural elements needed to make the two stages independently handleable.

I guess the next few years will tell us which approach best suits todays materials, engines, fuels and building techniques. Should be interesting.

Comment Re:Does it have to be the whole booster? (Score 1) 118

The key element is cost/speed of turnround. The fuel tanks in a first stage may not be very expensive, but hooking up and testing new tanks will take time, and then checking the integration takes more time. SpaceX are aiming for a model where there is not much more to do that pump in fuel, a cursory visual inspection and ask the avionics to self-check. Engines would need a full inspection every so many firings. If they can pull this off it almost has to be cheaper than any model involving more reintegration.

Comment Re:Putting it in orbit would solve all these probl (Score 4, Interesting) 22

The South pole of the Moon is quite a good site. There are mountains permanently lit (for power) and crater bottoms in permanent shadow a few hundred meters away (for the telescopes). Having a large mass (like the moon) to anchor you against vibration from your own systems, light pressure, etc. and serve as a heat sink has considerable advantages.

See http://citeseerx.ist.psu.edu/v...

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