> The government is not in the business of managing an inventory,

Tell that to the Bureau of Land Management, or the General Services Administration.

> They just don't want the public to have bitcoins.

It's a bit too late for that, given that there are 3.2 million online bitcoin wallets between just the two largest services (Coinbase.com and Blockchain.info), and about 150,000 unique bitcoin addresses are used daily ( https://blockchain.info/charts... ) Addresses are not equal to users, they hold some number of bitcoins each. Wallets hold the private keys that control addresses, and you can have multiples, but the point is lots of people already have access, and it's moving around a fair amount.

> The government could probably mine 30000 coins in thirty minutes on spare CPU power on some defense computer system.

No they can't. The combined hashing power of the bitcoin network is 1.15 million Petaflops. The top 500 supercomputers in the world have a combined power of 250 Petaflops ( http://s.top500.org/static/lis... ). Even if there are hidden NSA machines or whatever, they don't account for that big a discrepancy.

The reason the bitcoin network is so much faster is they use custom chips that do nothing but the SHA1 hash calculations used in mining. It's directly wired into the transistors, they can't be used for other math. But you can pack tens of thousands of copies of that algorithm on one chip, and mining rigs have boards with ~36 chips each, and multiple boards.

Also, the network difficulty adjusts every 50,400 coins (2016 blocks @ 25 coins per block), so if someone *could* mine that fast, the difficulty adjustment would bring it back to the normal rate (300 coins per hour) rather quickly. Lastly, that high a mining rate would be considered a "51% attack" on the network, and the rest of the network would rapidly reject the blocks and fork the history.

There are exchanges that handle that many coins daily: http://bitcoincharts.com/marke...
And three investment funds on Wall Street with more than that amount already.

All you need to do to not crash the price is arrange a private sale, or release the coins gradually. About 3800 newly created coins are generated every day, and the market absorbs that, so just keep your daily sales smaller than that, like 1000 a day or less.

The peak of $1107.92 on 30 Nov 2013 only lasted one day. That's cherry-picking your data.

One year ago today the 24-hour average price was $109.36, so at $575 we are up 425% for the past year.

The 12-month moving average is about $425, and we are comfortably above that.

I disagree. What long range plans do is identify current technical deficiencies and priorities for research and development. For example, Elon Musk has a goal to colonize Mars, and is making great progress on cheap rockets. But even cheap rockets won't be enough. You can't afford to haul everything you need to live on Mars from Earth. So you need to develop local mining and production technology. Compared to rocketry, that field is severely undeveloped. Thus knowing that Mars is a goal in 20-30 years tells you to start the research and testing *now*, so that by the time you need it, it will be ready. Therefore a plan will serve as an input to agency budgets, and highlight opportunities for private research and eventual entrepreneurs.

There are many errors in his calculations. I was part of a team that studied Solar Power Satellites when I worked at Boeing, so I think I have better data than Mr. Murphy. Let me list the ones I spotted:

* He quotes the performance gain against one of the best places on Earth (the US Mohave Desert) at 3:1. For the world as a whole, the gain is more like 7:1. Most places have much more clouds and thus less available sunlight.

* He assumes geosynchronous orbit. This is not required if you have a constellation of satellites and electronic steering of the beams (something every cell tower does today). A lower orbit allows using smaller satellites and ground receivers, closer to the cities that will use the power.

* He assumes 100 GHz transmission frequency. Generally microwave amplifiers are more efficient at lower frequencies and less subject to rain fade.

* Calls launching a large dish prohibitively difficult, while ignoring that the International Space Station demonstrated assembly of large space objects from smaller pieces.

* The study I worked on showed that 98% of the mass of a solar power satellite can be supplied from material already in space (asteroids, and the Moon). Therefore launch cost is not a major issue, provided you set up equipment to extract items like silicon and aluminum from rock.

* Space solar arrays are already 15 times lighter than terrestrial panels, because they don't need frames, seals, and glass to survive high wind and weather. If they were made in space, they would be lighter still, because they would not need to survive launch loads or include deployment mechanisms. Large space solar arrays are launched folded up to fit in the rocket.

* Radiation damage is not as severe as he assumes. Actual space solar cells use Ceria-doped cover glass for protection, and function quite well even in high radiation parts of the Van Allen belts.

* The mass delivery ratio of 100:1 he quotes is way off. Given that you are building big space solar arrays, you can attach electric thrusters to put them in position, something that modern comsats already do. Electric thrusters are about ten times more fuel efficient (although slower). With sufficient traffic to orbit, there will be an incentive to use better propulsion, reducing the ground-to-low orbit ratio by a factor of 5-10. As I mentioned before, with in-space production, you only need to launch about 2% of the satellite mass.

In total, his general method of comparing ground to space solar power is reasonable, but he misses important information and the numbers are way way off.

Give us a fancy name, and we can be a counterweight to the National Academies' reactionary reports. They assemble panels of prestigious and *old* people to review NASA's plans, and usually conclude it can't be done, because they fail to include forward-looking ideas. We need to generate reports for the future, not the past.

Dani Eder

We've barely begun. Just as an example, the amount of solar energy that passes closer than the Moon equals all the world's fossil fuel reserves every minute. How many Beowulf clusters could you run with that?

Bringing back a large (7 meter) asteroid sample in pristine condition, and sending half a ton or more back to Earth, where it can be examined by all of Earth's scientific equipment, gets you much more science than sending a probe to an asteroid. A probe has limited weight and bandwidth for instrumentation. We are still getting new science today from the Moon rocks, even after 40 years.

It also gets us technological value in learning to process the raw materials to useful products (water, hydrocarbons, oxygen, metals, radiation shielding). A few hundred tons is enough to do processing experiments. If we are ever to develop space in a big way, we have to learn to make stuff locally, instead of bringing it all from Earth.

Because of institutional and political inertia. NASA centers employ a lot of government staff plus contractor staff. None of the management want to lose jobs, and neither do the elected officials for those districts/states. So they conspire to keep things going the way they are now. SpaceX is based in Los Angeles, not Huntsville, AL, where the Space Launch System is being developed, and that upsets the way things are.

I worked on the Space Station project for Boeing, in Huntsville, and NASA went so far as to give us a free building to use in their Marshall Space Flight Center there, they wanted so badly to keep the work local. It was a truly horrid 1960's era building, but it was free, so we used it.

Fortunately for you, the project I'm working on ( http://www.seed-factory.org/ ) can solve material scarcity *and* enable us to occupy the Solar System. Self-expanding automation can grow from a small starter kit to producing what people need (building materials, agricultural equipment, utility hardware). It does so by directing part of the output to making more equipment for itself. The same starter kit idea lets you mine an asteroid, or set up on the Moon or Mars, without having to bring everything from Earth. In both cases, the leverage is huge.

> All of these places actually want dollars.

That's because their supply chain doesn't yet accept bitcoins. For a data center, I imagine their main costs are IT hardware, electricity, and staff. Once those also accept bitcoin, they don't need to use a payment processor to convert, just send the coins along to the next person.

There's a natural progression from hobbyists paying for pizza, to small online retailers taking it for socks, to larger retailers, now to satellite TV. Eventually second level suppliers will start taking it, and you begin to get a complete economy in bitcoin. But such things don't happen overnight.

> Once the mining approaches 0, people will start wanting a transaction fee to process the networks transactions.

They already collect transaction fees, but they are about 1% of miner's incomes. The real limiter is transactions/hour on the block chain. There is a 1 MB limit per block, and you can fit about 2500 transactions on average, so 15,000 per hour. This will drive up fees once the supply of transaction slots is eaten up, which in turn will drive off-chain transactions. This already happens to a limited extent. If you use your Coinbase wallet to pay a merchant that uses Coinbase as their processor, it never hits the block chain. It's just internal at Coinbase. Nothing prevents Coinbase from arranging with other processors and large merchants to do bulk transactions on the block chain, which represent many individual small customer amounts. Transaction fees to miners can then be made as small as necessary, because it's spread over many users.

Have you considered just how much energy half a million bank branches worldwide consume? Some of those bank buildings are the largest skyscrapers in the world. For a valid comparison, you need to look at total energy consumed per dollar/bitcoin transaction.

Because it's approximately true. Nominal resolution of the human eye is 1 arc-minute (1/60 of a degree), therefore a 1920 pixel wide display will subtend 32 degrees horizontally at the resolution limit. At 9 feet (108 inches), a 62 inch wide screen will subtend 32 degrees horizontally. Since screen sizes are measured on the diagonal, that equates to a 71 inch diagonal.

Human eyes are variable in resolving power, both because of their optics, density of the cones in the fovea, and brightness of the image source. Our retinas and brains also do image processing, so we can detect narrow lines, like a power line against the sky, at better resolution by interpolating eye movements (which change which cones are getting the image) and contrast enhancement.

An image with lots of narrow high contrast linear features (like text) can benefit from somewhat better pixel density, but for general colored images it does not help much.