Apollo Guidance Computer

Just as the history of science helps us understand and validate the science, studying the history of technology can give us a deeper understanding and richer set of tools to work with. Recently, a number of books have come out about the technology of the Apollo space program. Intrigued by the technology that inspired my youth (I was 10 when Neil Armstrong landed on the moon), I discovered that these books contain a gold mine of ideas from some of the smartest people of their time, doing a lot with a little. Two books detail one of the most important technologies relevant to my world of computers: the Apollo Guidance Computer.

The first book is “Digital Apollo – Human and Machine in Space Flight”, by David A. Mindell, The MIT Press, 2008. It covers the external aspects of the development of AGC, such as who developed it, based on what criteria, and how the developers interfaced with the astronauts and other parts of NASA. The development of a modern Human-Machine interface, how it would work with the astronauts to navigate to the moon, land on the moon, launch and rendezvouz back with the command module, return back to earth, and control the re-entry to land in the recovery zone. One of the first computers built with Integrated Chips of silicon, it used core memory and wires that ran through and around the core memory, assembled partly by experience weavers from the textile industry. Remarkably clever uses of technologies allowed the spacecraft to avoid heavy environmental control systems by programming the spacecraft to slowly rotate (“rotisserie mode”). When landing on the moon, the LM would pause during the landing and stand up to give the astronauts a view of its landing site. A crosshair grid was painted on both the outside and inside of the commander’s viewport, and Neil Armstrong aligned them by moving his head, while the AGC displayed coordinates to Buzz Aldrin that told Neil where it was going to land with respect to his aligned grid. Another case where the thickness of the windows and painted grids on both sides saved weight by not needing an extra viewing scope. Using his thumbs, Neil could move the landing point left and right, or forward and back, which instructed the AGC to fly it to that point. At the last part, the astronaut would do the final setting down, but once landed, he would have to jiggle the joystick to tell the autopilot/AGC system to take that new attitude, since the lunar surface would not be as level when landed as the AGC attitude control was trying to hold it to on the way down. This prevented the wasting of control fuel before they could shut it down as it tried to manuever while sitting there. I always wondered what the LM (or CM) pilot was the pilot of, when the commander was actually doing the flying with the hand controls. It turns out they are flying the Apollo Guidance Computer. They are punching the buttons and running the computer to do the things that are needed so that the commander can use the hand controls.

The second book is “The Apollo Guidance Computer – Architecture and Operation”, by Frank O’Brien, Springer-Praxis Publishing, 2010. This is the software book, which gives the details of the computer at a level that gave me flashbacks to my days with IBM 360 assembly language, Intel, and Motorola assembler coding. Surprisingly, the AGC was a 16-bit interruptible machine with a 3-bit opcode and 12-bit banked addressing. Not much different from the 8086 except that it was a ones-complement machine (less circuitry) and every instruction had to fit into one word. Because 3-bits only give you 8 opcodes, how did they do so much? By many clever tricks: Certain memory locations performed shifting and rotating functions when you stored a word into those locations and retrieved it. Some opcodes had address ranges which were invalid, but instead of having this cause an error, the pattern of bits was adopted as a new opcode. One opcode was a prefix that changed the meaning of the next opcode, like a shift key for a keyboard. Another opcode was a Repeat opcode that caused the next opcode to repeat multiple times based on decrementing a Count Register, which did not really exist. Since all math was integer, and the most advanced calculations needed vectors and other floating point numbers, one of the programs built into the read-only memory was an Interpreter, that allowed it to simulate a more advanced calculator. A program could execute a mixture of basic and interpeted instructions. It did all this, and it was able to pick up where it left off quickly on restart when encountering problems, thanks to its Executive program – the operating system.

The Apollo Guidance Computer lived on after Apollo, to Skylab, and is the precursor to the Space Shuttle computer. These books were well worth the effort and gave me many ideas for my current work.

Book – Discovery of the Amazon by Carvajal

Ever since I saw the Michael Wood set of documentaries called “Conquistadors“, I have been reading from translations of the original accounts and early histories of those stories. Michael Wood’s specialty is following in the footsteps of the people in the story. First I read the history of Cortes in Mexico, as told by one of his lieutenants. Then I read about the history of the Inca Empire ending with Pizarro, as told by an Incan princess after she was married to a Spaniard. Just recently I completed “Discovery of the Amazon”, by Carvajal, a friar who was part of the expedition. The 1934 edition, republished in 1970 by AMS Press, presents a number of original documents and official histories of the Indies, including two separate accounts by Carvajal.

This may be the only account of the interior of the Amazon River basin before the massive changes prior to and during colonization by the Spanish and Portugese. The story begins after Cortes’ cousin, Francisco Pizarro, takes over the Inca empire and appoints his brother Gonzalo to govern in the area of Ecuador from Quito. Stories of the River of Cinnamon and El Dorado (Golden Man) lured Gonzalo to start an expedition east into the rainforest of what turned out to be the beginning of the what is now called the Amazon River, but was then called the Maranon River. Gonzalo leads an expedition of 250 Spaniards, 2000 Indians, and horses and pigs (for food). After months of wandering, losing men and supplies, they run out of food. Gonzalo’s lieutenant and cousin, Orellano, volunteers to take the large boat they built and take about 60 men to go down the river and bring back food. Thanks to heaving flooding and swift currents, they went far downstream and eventually found food about 300 miles downstream. They realized they could not return back to Gonzalo Pizarro’s group because of the swift water, so they resolved to head downstream to the sea and return that way. Later, some accused them of desertion, but they returned and were never treated as deserters.

The wonders they saw included beautiful glazed ceramics, beautiful carvings and art work, and huge villages that extended for miles and miles down the river, with “king’s highways” leading into the interior. Chieftains who ruled for hundreds of miles, with almost a thousand miles of riverfront occupation in the middle. Maybe millions more people lived there then than live their today. The Spaniards had to go as fast as they could, stealing food along the way, fighting most of the time along the way. They ate the leather and everything they could at points. Every once in a while, a local chieftain helped them. It is an adventure story well worth the read, and you will probably think even less of the Pizarro family.

Only recently have they discovered their methods of farming in the tropics, with raised soil beds that had kitchen refuse, bones, charcoal and clay crockery broken into it, able to support much more population than today. They are starting to recreate that system of agriculture in Brazil.

From the beginning of the trip, the Spaniards heard of special female warriors, holy warriors, who covered themselves in white and led battles. They claimed to have encountered them in battle, just after they passed the Rio Negro, but noted they had all of their breasts, unlike the ancient Amazons, whose name means “no breasts”. The women lived alone, but were part of a larger domain, led by a great chief. They would take men and mate with them, but only keep the female babies, either killing the males or sending them back to their fathers.

Book – Principles of Semantic Networks edited by Sowa

As mentioned in a recent post, I received and have read the book, “Principles of Semantic Networks”, edited by John Sowa. It is comprised of a number of chapters that are expansions of technical papers by a number of researchers in the subject, as well as the transcripts of a discussion between the authors. Though they never expand the idea of the sentence past the triple, it did give me some observations and important validations of our methodologies used at my company, Datura and its Semantic-Relational Database. For example:

1. Though complex semantic meanings can be stored using many semantic triples in combination, it would be more efficient to add semantic constructs that expand on triples for exact knowledge meaning.
2. Applying semantic techniques to databases or other data structures, and vice versa, allows methods from those parts of computer science to work together.
3. Just because you can say it in a particular way doesn’t mean you should. How you say it, is important to efficiency.
4. Semantic technologies lend themselves to parallel systems.
5. Different notations can lead to different ways to represent information, but they can all be mapped to robust semantic systems.

Transit of Venus debriefing

After writing to tell you about the coming Transit of Venus, I thought I would share my photos of my success. As the time approached, the sky was cloudy and the weather report didn’t look promising. “Looks like it will be on-line”, I thought, as I found the NASA website that was broadcasting it live. As I was waiting in my windowless den in the woods, my wife came home from work to inform me that there were patches of sun getting through, so I got out my solar telescope, the Sunspotter.

Sunspotter Solar Telescope

The Sunspotter is a folded-lightpath, refracting, solar-projecting telescope that cost me $330 about 15 years ago. It’s portable, durable, takes 5 seconds to set up, and the instructions are on the outside. It’s safe to use and made for schools and you can’t fit your head in a way to get your eyes in the wrong spot. The light goes into the big lens hole on the right, bounces off the mirror on the lower left, bounces off the mirror on the lower right, bounces off the mirror on the top, and down through the secondary lens to project onto a piece of paper on the bottom, for everybody to see in a group, at the same time. Here is my camera phone picture of the projected image of the transit during the sunset:

With some photo-processing to turn it into black and white, lowering the brightness and increasing contrast, it makes a nicer photo. I could do more but that will be later. It might try the same techniques on the color version, too, now that I can see that some nice details of the sunspots and faculae (white areas) are in the images.

Enhanced Transit of Venus at Sunset, 8:32pm, June 5, 2012

The media covered the transit in many ways. One of my favorite references was how Edmond Halley had suggested that scientists should work together to get the best measurements of his predictions for the transit, in hopes of refining the calculations of the size of the solar system, particularly the Earth-Sun distance, called the Astronomical Unit (AU), since our measurements of the solar system are based on multiples of the AU, and our measurements of the distance to the stars are based on triangulations based on our movements around the sun (parallax) that give a 2 AU baseline (earth orbit diameter). Not only did they get a better value, but they laid the foundations of cooperative science, so necessary for modern science. Thanks, Halley!

The Transit of Venus, Chronometers, Captains Cook and Bligh

For those in North America, during sunset on June 5, 2012, a Transit of Venus will be underway. The Transit of Venus is an astronomical event where the planet Venus passes directly between us and the disk of the Sun, similar to the recent Annular Eclipse of the Sun. This is a rare event in human terms, that happens in “pairs”, because you get a short gap of 8 years between transits and then a long gap of 105 years between transits – so 8 years, then 105, then 8, then 105. That means you only get two chances to see it in your lifetime and only one of them is left, since the last one was 8 years ago in 2004. The next ones won’t happen again for 105 years – 2117 then in 2125. So last chance. This happens with Mercury, too, in a similar pattern, and both transits happened a few years ago. My wife and I were lucky to have seen all of them so far and hope to see this last one.

Why so rarely? That’s because the disk of the Sun in the sky is only half a degree (out of 360 degrees around) of apparent size, and the angle of Venus’ orbit is 3.39 degrees of inclination to the earth-sun plane (ecliptic), whose orbital long-axes precess, and once you combine the motions, Venus usually passes above or below the sun from our viewpoint, but occasionally spends a little in synch. Determining the exact measurements of the movement of Venus became extremely important to England’s version of the X-prize during the 1700’s, solving the problem of determining longitude at sea. This is where the rest of this blog’s title comes in – chronometers, Captain Cook, and Captain Bligh.

After losing a fleet to shipwreck, after winning a naval battle, England offered a substantial prize to whomever could solve the problem of Longitude. Latitude can be determined relatively easily, by observing the height of the North Star, or from the maximum height of the Sun and the stars as they cross the South in the sky. Longitude is more difficult and requires a comparison by time with a home reference point, Greenwich. Two methods were in competition – celestial and chronometrical. Edmund Halley, of comet fame, was the leader at the Greenwich Observatory of the celestial method, which would give ship pilots the exact timings of astronomical events to use to determine their longitude. John Harrison eventually won the prize with his Chronometer, which would keep time on a rolling ship on a long voyage through rain and heat and cold.

What does this have to do with Captains Cook and Bligh? To get exact measurements of Venus, it was decided to make exact measurements of the Transit of Venus in 1769 from widely separated locations, the Atlantic Ocean and the Pacific Ocean. This was the primary task of Captain Cook‘s first voyage of exploration to the Pacific, with Tahiti as the destination. While in Tahiti, waiting for the Transit, the valuable telescope to be used for the measurement was stolen by the natives of Tahiti. Cook was able to get it back, and was able to make his measurements. Besides the transit measurement, Cook also carred chronometers to test on his voyages.

Ok – Captain Bligh? William Bligh was on Cook’s trip to Tahiti. Later, England sent him as Captain of his own expedition to Tahiti on the ship, “HMS Bounty“, to gather specimens of the breadfruit plant, to take to the Caribbean as food for the slaves. This was the famous Mutiny on the Bounty.

Semantic Reading Ahead

I just received a used book I ordered, recommended from a Taxonomy reading list I found on Brian Seitz’s blog. The book is called “Principles of Semantic Networks”, edited by John F. Sowa, 1991. Semantic networks are branch of semantics, oriented around the semantic representation of concepts in a network graph, either directed or undirected graphs.

Other books I can recommend on networks and semantics:

Psycholinguistics, by Foss and Hakes, which discusses many concepts of brain, language, and communication, which can open up more possibilities for your semantic models.

Graphs and Applications, by Aldous and Wilson, which introduces the mathematics of networks and graphs, which is also related to polygon edges, faces, and vertices.

Data Structures Using…, by Tenenbaum and others, a series of books in several languages, introducing the basics concepts of linked lists, trees, graphs, and other data structures used in software. Choose the book using the language you are most comfortable with – Pascal, C, and C++. This was the key textbook of the early days, but the techniques that are taught are not dependent on the language’s memory constructs and can be used to mimic a memory heap or database on any language or system.

Learning Greek and Latin with my History

Many of the things I read in my historical explorations are originally written in Greek or Latin, but those weren’t the languages I learned in college. That has always kept me a step away from understanding the nuance that can be so important. A few years ago, I discovered the Loeb Classical Library. They are publishers of dual-language books from the Classical period, Green for Greek, Red for Latin. The left page is the original language, and the right page is in English. They are well annotated and you can compare the English translation to the original text, paragraph for paragraph. Luckily, my engineering studies taught me all of the Greek letters, both uppercase and lowercase, since they are used for the variables and the constants. The Loeb library has helped me learn a bit of these languages, but more than that has greatly enhanced the understanding. When Josephus discussed “Cossack” troops in Palestine, I wanted to know what the original Greek was, and I was surprised to see it was still “Cossack” starting with chi (X) in the Greek.

I need some more help from translators, though. So I recommend a great new website, http://commentingonthebible.wordpress.com oriented around a line-by-line translation of the New Testament, from both the Greek and Latin versions, starting in order of oldest (letters of Paul) to youngest. Besides learning some Greek, Latin, and the history of early Christianity, I can ask questions from the translator.

Book – “Chasing the Sea” by Tom Bissell

Just finished reading the book “Chasing the Sea” by Tom Bissell, subtitled “Lost among the Ghosts of Empire in Central Asia”. Tom tells the story of his return to Uzbekistan, five years after his short stint as a Peace Core Volunteer. His return trip is supposed to be journalistic, about the drying-up of the Aral Sea, but much of the book covers his past trip to Uzbekistan and the current trip, and the country’s past status as part of the Soviet Union and the current relations with its neighbors, such as Afghanistan, Tajikistan, Khazakstan. We see much of the country from Tom’s interaction with the people, police, Peace Corps, embassies, and most importantly, his translator and constant companion. Since there were no pictures besides the dust cover photos, his descriptions are welcome. His writing is good, but some of the analogies may become dated.

Added significance – the late events of the book take place just months before the US invasion of Afghanistan after the events of 9/11. It was published in 2003, so the author included any relevant details that might have been left out otherwise.

Super moons and annular eclipses

A week ago, we were treated with a moon that was closer (perigee) during its full moon phase than it has been in quite awhile, making a “super” full moon, with some great pictures to see here.

The partner to this extra close moon, coming on May 20, 2012,  is a moon that is farther away (apogee) during its new moon phase, on the opposite side of the elliptic orbit.  Normally, this would only be interesting to those specializing in orbital mechanics, except this new moon happens to be during a solar eclipse. The combination of solar eclipse and far-away moon gives us something less familiar – the annular solar eclipse.

Eclipse Anular by sancho_panza on flikr

The name comes from “annulus“, which means “little ring” in Latin. When the moon is farther away, its apparent size is smaller than the apparent size of the sun, so it cannot totally block the sun. You can compare the difference in a great photograph here. This difference in apparent size leaves a bright ring of sun around the apparently smaller moon.

Like any solar eclipse, where you live affects what you see. Most of the United States west of Ohio will get to see some of the eclipse in some form. Here in southeastern Michigan, we will get to see a partial, annular eclipse at sunset on Sunday night, May 20, 2012. Hope it’s not too cloudy!

A Convergence of Data Models in Semantic-Relational Databases

Reblogging:

A Convergence of Data Models in Semantic-Relational Databases

2012/05/12

One of the best things about Semantic-Relational Databases is how easy it is to map your data model to a sentence. Think about, how does all of your training for a particular data model start? To consolidate: “Start with the sentences that describe the conceptual processes, things, actions, etc … and convert them to entities, relations, objects, etc.”

Let’s survey how different models map to semantic-relational databases:

Entity-Relational Data Modeling – the entities become the nouns, subjects and objects, of the sentences. The relations become the verbs. An attribute can be considered as a relationship to a value, so the attribute or column heading become verbs, while the cell value becomes the object of the sentence. Multiple primary keys become subjects with modifiers. Multiple columns that work together become verbs or objects with modifiers.

Object Data Modeling – the primary key becomes the subject. Each field becomes a verb, and the value of each field becomes the object of the verb. Fields that are arrays or collections become verbs with modifiers.

Semantic Data Modeling, Semantic Network, or Semantic Web – this one is

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