Apparently moisture farmers and 'vaporators can be a real thing on Mars.

Perhaps the water is being insulated by the eddy of plastic trash in the central Pacific?

That's what bank safety deposit boxes are for. Offsite, hard to break into, more or less fireproof through sheer mass, even if the building around it burns. Ask the bank about how thick the walls are, though. Class 3 is recommended (12 inches thick concrete), with additional outside fireproofing.

> Tape isn't dead, but it's not worth it for small quantities

The cheapest LTO-6 drive on NewEgg is $1500, and Sony has the tapes for $18/TB. External hard drives are running about $35/TB. So you need ~90 TB for cost crossover on sheer data volume, not considering usability and reliability. So I would agree, with those kind of prices, you might want to *start* thinking about tape when you get to 100 TB, because 1 drive isn't very reliable. It might work for backup storage, since you can get by with a broken tape drive for however long your backup cycle is.

> That is completely self-referential.

Nope. A "bitcoin" unit is just an entry of 1.0000 in the transaction ledger known as the "block chain". The block chain is just a bunch of files listing every bitcoin transaction ever. My copy is 36 GB at the moment.

The Bitcoin Network is what makes it possible to write new transactions into the ledger in a secure way. Secure means nobody can rewrite old entries in the ledger, and everybody can verify the contents are correct. Only the person with the private cryptographic key to an address can send the balance in that address to someone else. Without the network, the ledger could not be updated, making the balances recorded there useless.

> First, a Bitcoin in of itself has no real-world value.

Neither does a UPS shipping label. It's the network of trucks and distribution centers that give the shipping token (the label) value. They are what enable moving a package from one place to another. That's a useful service, and hence people are willing to pay for the label.

Similarly, a bitcoin is merely an entry of 1.0000 units in a big distributed ledger (the block chain). It's the network of relay nodes and miners that give the bitcoin token value. They are what enable moving monetary value from one place to another. That's a useful service, and hence people are willing to pay for the tokens. Other parts of the ecosystem add more usefulness, and thus more value. Websites, wallet software, custom hardware, smartphone apps, exchanges, merchants who accept bitcoin, etc.

The transaction protocol also includes a scripting language, so you can make your money programmable. How useful is that? People have only touched the surface of what you can do with that capability.

Except the Bitcoin Network already runs at 324 Petahash/second, and each hash computation requires many floating point operations - 128 rounds of applying a complex hash function on several hundred bytes of data. Aurora competing for bitcoins won't make a significant difference in the network hash rate, it is too puny. The network already runs at ~1 million petaflops by dint of custom designed mining chips that perform the necessary calculations in hardware, massively parallel in each chip. Then you aggregate server rooms full of these chips into a mining farm.

You will need thrusters to position the big satellite in the first place (or the parts if it is assembled on site), and to counteract the Moon and Sun's tidal forces. If you can handle those, light pressure will be a small issue.

> I think a large problem is going to be space debris -

Nope. If you can build giant solar arrays in GEO, you can build small ones and attach ion thrusters to them. See the Dawn mission at Ceres and the Asteroid Redirect Mission NASA is proposing for examples. These space tugs can putter around and collect loose space debris. That however does not eliminate natural meteoroids. So your power satellite will need a maintenance program, or just accept a small amount of degradation as stuff hits it.

Solar arrays are thin, so most debris will just punch a small hole.

> The biggest unknown is the microwave link to send power to Earth.

We actually have tons of data about this, from all the GEO communications satellites, and rain fade that happens sometimes.

> The next-biggest unknown is availability of construction materials.

I was one of the people who worked on this issue while at Boeing. We found that 98% of the materials for a solar power satellite can be obtained from the Moon. A higher percentage are available if you use the Moon + Near Earth Asteroids. We didn't do the numbers for the NEO case back in the 1980's, since we had only discovered ~150 back then vs 12,500 today, and ion thrusters were not fully developed until about the year 2000. A modern study would account for both sources of materials.

We solved that problem early in the Solar Power Satellite studies at Boeing. The microwave transmitter in orbit is a phased array. The reference signal to adjust the phase is a transmitter in the center of the rectenna on the ground, powered by the rectenna. If the beam wanders off target, no reference signal, and the beam is no longer focused.

Hi Maury,

* Spectrolab rates their space solar panels for 20 years at GEO: http://www.spectrolab.com/Data.... Since they don't need to withstand weather, they can be much lighter than ground-mounted panels. 13 W/kg for a typical ground panel (not counting mounting and tracker) vs 177 W/kg for the space ones. That has implications for the energy payback time if you manufacture the panels in space.

* Your comparison of operating hours neglects that in space you have 36% higher insolation, because there is no atmospheric absorption. Therefore it takes fewer cells to produce the same output. Also the Nevada desert is an excellent location on Earth. The average location on Earth gets considerably worse hours of sunlight. Since we can't transmit power all over the Earth, cherry-picking a good location is unfair.

SpaceX couldn't get an export license then. Rockets fall under the "International Traffic in Arms Regulations" (ITAR) and need a license to export. We even had to follow those rules for the Space Station modules being built by Boeing. That's despite it being an international station occupied by lots of foreigners, Russians even.

> It does seem that the ULA has been mostly sitting on their laurels sucking at the government teat for a long while now.

Let me explain how this works. At the start of the Sea Launch program, which Boeing was a partner of, and I was working on, our program manager was an ex-Air Force officer who was a launch director from Vandenberg (where the Air Force launches polar satellites). He was a smart and competent guy, but the main reason Boeing hired him is *he knew all the right players on the Air Force side*. Another manager of mine was a former Marines officer who had done helicopter procurement.

When the people who make the buying decisions already know you, because they used to work with you, you have a much better chance than someone they never met before and have no idea how good they are, if they will get along, etc. This "revolving door" works in the other direction too, where someone in industry then goes to work in government, in the same field. The problem is you often can't find anyone else who is qualified to oversee such contracts.

> And no effective way to store it for use at night and the evenings.

I guess you haven't heard of solar thermal with storage. You concentrate sunlight with curved troughs or steerable mirrors. This is used to heat a storage material such as thermal oil or rocks. In the off-hours you use the heat to boil water, and the steam runs through a tubine-generator set like in conventional fossil plants. There haven't been a lot of thermal storage units built yet *because we don't need them yet*. For example, the 400 MW Ivanpah solar thermal plant is on the same power line as Hoover Dam. The dam serves as storage by not using water when Ivanpah is running, and saving it for night-time. Eventually you run out of existing storage capacity, and need to add more, but we are not there yet in most places.