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Comment: The last days of XOC (Score 1) 90

by Keith Henson (#47187623) Attached to: Xanadu Software Released After 54 Years In the Making

I knew the people who worked on Xanadu though not quite back to the earliest days.

The design was largely completed by the time Autodesk got out of funding it. For a while the project continued under Memex (later Filoli over trademark issues). Memex had funding problems, the core group quit, and when Memex was funded again Roger Gregory (one of the original team members) and I were brought in to try to make sense of what they had. My experience was long out of date FORTRAN and more recent assembly. The majority of the code had been written in Smalltalk and auto translated to C++ as part of the compiling process. Memory was (by current standards) insanely limited. The clever part of the code was to pack and unpack a multi dimensional tree off disk. Fan out ran to around a thousand link pointers per 8k disk block meaning three disk reads could take you to a billion unique objects. The famous log N property.

The performance critically depended on a high performance system to reclaim abandoned parts of the tree in memory and that part was not finished. (It had been designed as an Ungar-Sather moving type garbage collector and partly written but not tested.) We got it going and it ran the regression test suite. One of the last tasks was to upgrade it from the Sun compiler. The most critical inner parts of the code depended on switching tree elements around to keep the tree balanced. It used the classic c=a, a =b and a=c where a and b were links. Bjarne Stroustrup had changed the definition of overriding equal between the two compilers making this a hard bug to find. I finally found it single stepping through the assembly language representation of the code. The tools are much better now, nobody would think of writing a garbage collector from scratch. It was only 20 years ago, but it feels like a lifetime.

Comment: Re:If you're just beaming it down to earth anyways (Score 1) 230

by Keith Henson (#46850327) Attached to: How Japan Plans To Build Orbital Solar Power Stations

Let's take a crack at putting numbers on your assumptions.

Assuming power satellite people want a large market share, they will have to set the cost lower than other sources. Say 2 cents per kWh. Hydro is lower, but there isn't enough of it.

If you go into the models for calculating levelized power, then to get 2 cents per kWh, the cost of the source can't be higher than $1600/kW (6.8% discount and 20 years). Even in China nuclear reactors are about $5000/kW. Ground PV can't get close, it might hit 8-10 cents per kWh, but at that cost the concrete and steel become bigger factors than the silicon.

The rectenna, the part on earth, will cost around a billion dollars for 5 GW. That's $200/kW. I have published the details on how I estimated the cost, can quote them if you want.

I favor thermal designs as they are a lot smaller, but even with PV, it should be possible to get the cost of panels and transmitter plus labor down around $900/kW referenced to the output of the rectenna. That's assuming microwave amplifier tubes cost about the same per kW as they do in microwave ovens.

So a reasonable cost for power satellites $200 plus $900 plus $500 for the transport to GEO.

I think it's reasonable to expect power satellites to mass around 5 kg/kW.

Thus the allowed transport cost to GEO is $100/kg, or $45/lb. But that's to GEO, not LEO.

Comment: Re:Satellites have eclipses (Score 1) 230

by Keith Henson (#46850003) Attached to: How Japan Plans To Build Orbital Solar Power Stations

"The problem with space elevators (and other sky-hooks) is that if the tonnage down doesn't, over time, match the tonnage up, the orbit decays."

That's not true. Long as the cable is tight, you can lift stuff forever without anything coming down. The cable does lean a little to the east, and it saps the earth's rotation to provide the velocity at GEO. Remember there is a rigid arm from the center of the earth to the base of the elevator. If the traffic tonnage is matched, the elevator will be straight, if more is coming down, it will lean to the east.

Comment: Re:Satellites have eclipses (Score 1) 230

by Keith Henson (#46849255) Attached to: How Japan Plans To Build Orbital Solar Power Stations

Musk is right.

A reasonable economic analysis of power satellites requires about $100/kg for the cost of parts lifted to GEO.

You can't get that with rockets, not even reusable ones.

The main reason is that low exhaust velocity leads to rotten payload fractions. It's just physics, the rocket equation.

The proposed Skylon gets around 9 km/s equivalent exhaust velocity till it runs out of air, and 4.5 km/s from there up. Still too expensive by a factor of 4-5.

Leaving the oxygen out and using a 3 GW laser to heat hydrogen gives around 7.5 km/s for the last 6 km/s to orbit. The laser is hugely expensive, but run 24/7 it costs only a few tens of dollars a kg for 500,000 tons per year.

More here:


Comment: Re:Maybe not extinction... (Score 1) 608

by Keith Henson (#46843651) Attached to: Are Habitable Exoplanets Bad News For Humanity?

It's still possible, though I don't see even the excellent work of SpaceX getting us there.

It's not a sure thing that additional development of chemical rockets will do the job. If you go through the math involved, it just doesn't look good.

Space based solar power, for example, has to substantially undercut existing and projected cost per kWh in order for the investment to be worth the trouble. Depends on the numbers you use, but I make a case that the cost of lifting power satellite parts to GEO has to come down to $100/kg for SBSP to make economic sense.

It takes less than a dollar of energy to get a kg to GEO, so the physics doesn't stand in our way. But I don't think you can make a case for rockets getting down to this cost, and if you could, then the volume needed, around 10 million tons per year, just makes rocket lift look really questionable.

The problem traces back to the rotten payload fraction and that's the direct result of low exhaust velocity. However, there may be another way to skin the cat.

Skylon gets the equivalent of 9 km/s to where it runs out of air, and laser heated hydrogen will get at least 7.5 km/s for the rest of the way to orbit. From there to GEO, a hydrogen/laser stage will deliver 2/3rds of a 30 ton second stage in LEO to GEO. Running the laser full time will get three 20 ton vehicles to GEO every hour or about half a million tons per year. Scrap the vehicles at GEO and they are all payload. More details here:

Keith Henson

Comment: Re:Farming (Score 1) 737

by Keith Henson (#46741853) Attached to: Ask Slashdot: Are You Apocalypse-Useful?

When I was much younger, we raised rabbits. For years they were most of the meat the family ate.

I also did every step in making bread. Growing a patch of wheat, harvesting it, thrashing out the grain, grinding grain to flour and baking flour into bread. I can tell you it's a pain.

The most likely thing to happen that would bring down civilization would be running out of cheap energy, especially liquid hydrocarbons for transport. There are several possible ways to get around that problem. This is my proposal.

Comment: Impressed by Tim Cook (Score 1) 348

If someone reading this knows Tim, please give him my regards.

Also, if he wants to talk about the whole world going off fossil fuels to a cheap form of solar, be happy to do so. If it can't make dollar a gallon gasoline, then the idea isn't ready for prime time.

Talk I gave at Google.

A laser 33 times larger than the propulsion laser I propose.

Comment: Re:I disagree (Score 1) 221

by Keith Henson (#46351099) Attached to: South Park Game Censored On Consoles Outside North America

"The things that are done in this World in the name of [insert religion - including Buddhists ] is appalling. "

I make a case it is the other way around.

In the former world of hunter-gatherers, the nut corp would fail or the game move away. When that happened ,it was necessary to go batshit crazy with xenophobic memes and kill the neighboring tribe. The trait was selected because it promoted genetic survival. It's the underlying resource crisis that causes the appalling behavior. The memes (religions) are in the chain, but not causal.

Comment: Re:Yes, and changing that is not an option (Score 1) 115

by Keith Henson (#46291621) Attached to: French, German Leaders: Keep European Email Off US Servers

"Only true end-to-end encryption can be a solution."

I doubt even that. If NAS can't break the encryption, they put a keylogger on your computer and break the encryption that way.

One time pad is a pain in the ass for key management, but it is impossible to break and the NSA may well waste a lot of cycles trying.

Key management here is to keep the keys on your hard drive and do a military grade erase on the blocks you have used.

Sending the key on three memory sticks by different routes and xoring them together seems like it might work. Then fill the sticks several times over with junk files, or if you are really paranoid, burn them. DVDs would work for those without a lot to say.

The question is not about being paranoid, the question is: Are you paranoid enough?

Comment: Re:Quis custodiet ipsos custodes? (Latin) (Score 1) 247

by Keith Henson (#45125213) Attached to: Could Snowden Have Been Stopped In 2009?
"What if they are tapping into the NSA data for commercial gain? Selling NSA data to other businesses . . . ?"

Or using it either as a company or as individuals. Trawling all the email has got to be the best way to play the stock market ever. Those who can do this can rig the poker game that is the stock market.

Given human nature, can you imagine this *not* being done?

Comment: Re:Meh (Score 3, Interesting) 324

by Keith Henson (#44979963) Attached to: Upper Limit On Emissions Likely To Be Exceeded Within Decades
There might be a way to spend a few tens of billions and end the use of fossil fuel by making a certain kind of renewable energy less expensive than fossil fuels. We could burn several times the current consumption of oil and not create any problems if it was carbon neutral synthetic made from really inexpensive electric power.

Dollar a gallon gasoline can be made from 1-2 cent electric power. Ground solar looks like it will bottom out around 8-10 cents per kWh. Space based solar power could get down to 1/5th of that because it gets 5 times as much sunlight in GEO. That's *IF* we can get the transport cost to GEO down to $100/kg. That's about a hundred to one reduction, but looks like it could happen. Details, including some spiffy artwork, here:

Comment: Re:Takeaway: The FBI Served Up Child Porn (Score 1) 292

by Keith Henson (#44857237) Attached to: FBI Admits It Controlled Tor Servers Behind Mass Malware Attack
"and would never actually send child porn to anyone to make a case?"

They did it to Robert Thomas in the Amateur Action BBS case. Almost 20 years ago.

Charged him too. But even a jury of Sunday School teachers didn't convict on that particular charge.

Comment: Re:Sounds like John Gilmore has called it accurate (Score 1) 362

by Keith Henson (#44792491) Attached to: John Gilmore Analyzes NSA Obstruction of Crypto In IPSEC
One time pads are unbreakable if used properly.

For that you need a good random noise generator (that has not been corrupted by someone), a way to distribute the key material and relatively trivial amount of code. (XOR may be good enough.)

I don't know what is being used recently for random noise. I might want the key generator to be a dedicated hardware box with a couple of storage devices plugged into it, though for a start, a program to run on PCs might be ok.

One problem is key management. You want to delete the used part of the key store, both so you don't reuse it and to keep it from falling into the wrong hands. The obvious way would be to make up USB sticks with files of key material and delete/overwrite the used file blocks. The problem is that secure erasing of files on a USB stick is hard to do.

For casual use for unimportant matters, it might be ok. A more secure method would be to put the key files on a hard drive and use multiple overwrites to erase the used key material.

Eventually someone might make dedicated read once sticks with automatic erasure. Then you would only have to worry about physical security.

I took a fish head to the movies and I didn't have to pay. -- Fish Heads, Saturday Night Live, 1977.