physically impossible geometries or excitation methods.

then we'll finally have the answer to "what is the sound of one hand clapping"

Homomorphic encryption is scary stuff, one could use it to make malware or drm schemes that would be, for all practical intents and purposes, impossible to reverse engineer:
http://www.kuro5hin.org/story/2010/12/15/151617/78/

FDM type 3d printers actually use around as much energy to construct things as an injection molding machine. Factoring in transport costs, they are probably a little bit better for the environment than injection molding. However, if you use a giant printer cartridge this probably changes, as they will get thrown away(seriously, who recycles cartridges anyway.

If no other body in the solar system is habitable, then make your own! Build a catapult on the moon, launch dirt to L2, and process it into a space colony. Many current space colony concepts have wall thicknesses on the order of that required to block said deadly space radiation and a sufficient ecosystem for closed loop life support.

Plus, you get the added benefit of continuous insolation and lots of space to set up solar panels(or radiators) so you can get lots of power for carrying out large industrial processes, like making more space colonies or doing various processes to keep the ecosystem running.

Now on the constant support for earth, what would you need from Earth that could not one day be made in space?

And seriously, having humanity stay on Earth till the sun burns out would be crazy.

Because then you need to engineer a microgravity drilling machine(and test it!), get it to your asteroid, de-spin your asteroid, and wrap it in elastic bands so your drill has 'gravity'. And you have to do all that before you put living quarters in. You also have the problem of moving it.

Hollowing out an asteroid is fairly complicated operation, but it's doable, just not in the near term.

Instead of hollowing the asteroid out, you could just scoop dirt off of it to make 'space sandbags.' Of course, we don't know very much about surface environment of asteroids, as of yet, there has been only one 'successful' asteroid sample return mission and it only returned a couple micron sized grains due to a sampler malfunction. As we don't have any mining devices that have been proven to work in microgravity, it might be better to scoop dirt from the Moon instead.

Of course, it might make more sense to use magnetic or electrostatic shielding to deflect said particles, they are charged after all.

He's not even using all Lego parts. And yes, there are indeed Lego propellors out there capable of generating propulsive thrust. And yes, you can even use an NXT smart brick to control a UAV.

But, worst of all it looks like he's committed one of deadliest Lego sins: irreversible modification of Lego bricks. How else are those motors staying on there?

Don't you mean an acoustic spanner, like this:
http://iopscience.iop.org/1367-2630/10/1/013018

It's been know for quite a while than one can generate a torque with soundwaves.

When the governments of the world decide it's ok for civilians to own weapon's grade uranium.

  TFA mentions that the reactor uses a 50 lb, which is about half the critical mass of uranium 235. In order for the core to maintain a fission reaction, even with the neutron shield in place, it's probably going to use weapons grade uranium.

There's been a pretty big effort to cut down on civilian usage of weapon's grade uranium(IE research reactors) and other fun fissile substances for fear of people making bombs from them.

Because NASA's running low on Plutonium and congress didn't approve the funds for NASA to make new Plutonium. It might be cheaper to retrieve this plutonium than to restart the whole plutonium production program.

NASA needs this plutonium for deep space missions. If we wanted to send a mission to a place like Europa, we'd need plutonium.

In fact the SNAP at the bottom of the ocean contains about as much plutonium as the RTG on the Curiosity rover.

While the initial 'cost' of a lithium battery is higher than the initial 'cost' of an internal combustion engine, the overall or "lifecycle" cost of a lithium battery is lower than that of an internal combustion engine.

That's pretty much the process that's been proposed by the USC contour crafting group proposed for doing rebar. Print a shell layer, drop in some modular rebar sections,then you fill up the shell with concrete so that your rebar connectors sticks out, and then repeat for the next layer. Another way to do reinforcement is to put a metal coil on your top layer and to print over it, so the coil gets embedded in the concrete. They've actually demonstrated this.

So why stop at just printing in colors? The contour crafting group has proposed putting in tiling, plumbing, electrical wiring, heaters, and strain gauges.

See this paper for more:
http://craft.usc.edu/CC/Welcome_files/resources/AIC2004-Paper.pdf

One approach to energy harvesting is to increase the efficiency of human walking and capture the energy the human would have expended walking. This has actually been demonstrated with an energy harvesting backpack. The amount of power the human should consume carrying the backpack and doing work on the generator was found to be more than the amount of power the human actually consumes.

So in other words, you still have to pay for your lunch, but you get more for your money.

see "Harvesting Energy by Improving the Economy of Human Walking," for more
http://www.sciencemag.org/content/309/5741/1686.short

Instead of throwing all that potentially valuable material into the pacific ocean, why not coral it all into one big "trash heap" and recycle it? After, it takes a lot more energy to put something into orbit than it does to move something to another orbit. At the very least, the trash heap could serve as a testing ground for space manufacturing processes.

So what happens when some wiseguy decides to mine asteroids for gold? The gold market could crash into the ground from the amount of gold flowing into the market.

As it is, gold is already more expensive per unit kilogram than the cost of launching a kilogram into space.

Cost of gold as of now: $26970.70
Cost of launching a kilogram into space:
Using the space shuttle: ~$22,000
Using a falcon 9: ~$2800

The moon's gravity well is much shallower than Earth's How much shallower you might ask? Well to get a pretty good idea, take a look at the Saturn V compared to the Apollo Lunar Module. If you want to get more technical, the mass ratio, or initial mass of rocket(w/ propellant)/final mass of rocket minus propellant of a rocket increases exponentially with the amount of delta V you need. So in other words you need 37* times "more rocket" to launch the same amount of mass to LEO from the Earth than it does from the Moon all other things being equal. * mass ratio =e^ (Delta V/ Exhaust velocity) Delta V from Lunar surface to LEO 6.4 Delta V from Earth surface to LEO 10 e^10/e^6.4= 36.5982344