Apollo 11 Computer System

Many people believe the computer systems of the Apollo 11 space craft are ancient and little can be learned from them. I disagree. The computer systems in the Apollo 11 were, in some regards, more advanced than the computers of the 1990s and early 2000s. There are a couple of things that lead me to that conclusion.

The first is that the computer on the both the Lunar module, “Luminary” and the command module, “Comanche” were networked wirelessly via radio frequency and also were in direct communication with the computer at the mission control, “Tranquility.” This was in July of 1969. We did not develop robust wireless networking technologies for another nearly three decades with the development of the 802.11 “Wi-Fi” protocols in 1997. Taking this a step further, even wired communication between computers was not standardized until four years later with the release of the 802.3 Ethernet standards. Needless to say the communications for the computing systems were decades ahead of their times.

The second major advancement in computers that was ahead of times was the processor itself. Though the system performed around 1000 times slower than a modern computer, it had some features that were not developed commercially in processors until the early 2000s. Among those features was the capability to run multiple threads. Threads are independent processes that can run at the same time; for example it was capable of tracking the exact location of the spacecraft using computer vision to determine the view angle of particular stars at the same time as it was calculating the firing thrust of the engines to properly align the craft for a safe landing. We did not have true multi-thread processor capabilities in home computers until around 2001 with the release of the first multi-core processor by Intel. You will also notice that I mentioned computer vision in the example. You might be surprised to realize that the computer in Luminary did live-image processing to determine the angle and location of the craft both for the lunar landing and the reentry angle to make it safely back to earth.

The third advanced feature of the computer in the Apollo spacecraft was the ability of the system to “self-heal.” During the mission, an unlikely set of circumstances caused the guidance computer to begin throwing alarms. These alarms were caused by the radar system that was tracking the module for recovery in the case of a mission abort. The program started using too much computing power at a critical phase in another thread that was helping to land the craft. The robust design of the system allowed the computer to make the decision to terminate the radar process and focus on landing the craft. Self-healing computer code and systems are still an advanced field of computer science.

I am fascinated by the excellent work done by the team at the Massachusetts Institute of Technology under the direction of Margaret Hamilton. The code was publicly released in July of 2016 and computer scientist all over the world got to see the human-ness shining through in the very complex code. There was a terrible habit of typing “WTIH” for “WITH” about 20 times in the code comments. The routine names in the code were fascinating and made it easy to picture the imaginations of the young engineers, sparked by being on the spacecraft, as they wrote code segments like “LUNAR_LANDING_GUIDANCE_EQUATIONS” and “BURN_BABY_BURN-MASTER_IGNITION_ROUTINE.” There was even apparently a problem in an early version of the code to leave extraneous data in DVTOTAL based on a comment block in the code that stated very clearly, “don’t forget to clean out leftover DVTOTAL data when GROUP 4 RESTARTS and then BURN, BABY!” It is difficult to figure out what DVTOTAL is from reading the code, but, very clearly, it is important to clear it before this routine. I am fairly certain that “BURN BABY!” means let’s get this rocket into space.

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Amateur Radio

In honor of the upcoming Amateur Radio Day celebration Saturday, June 22 in Texas County between noon and 5 p.m. in front of Pizza Express in Houston, amateur radio, its history and future, seems to be a good topic for this week.

Amateur Radio, also known as ham radio, is the use of radio frequency devices for the purpose of exchanging messages, wireless experimentation, self-training, private recreation, and emergency communication, by individuals for non-commercial purposes. The term amateur in this situation means a person who has an interest in radio electric practices with a purely personal interest and no monetary or similar reward expected from the use.

The amateur radio and satellite service is established and controlled by the International Telecommunication Union (ITU) through the Radio Regulations division. ITU regulates all the technical and operational characteristics of radio transmission, both amateur and commercial broadcasting. In order to become an amateur radio operator you must pass a series of tests to show your understanding of the concepts in electronics and the government regulations.

Over two-million people worldwide are amateur radio operators and use their transmission equipment for a variety of tasks including radio communication relays, computer networks over air-waves, and even video broadcasts. Because these radio waves can travel internationally as well as into space, the regulatory board needs to be an international board. Currently that controlling board is the International Amateur Radio Union (IARU), which is in three regions and has member associations in most countries.

My first experience with ham radio was as a teenage boy. One of my neighbors was a ham radio operator with the highest level of license. I remember him saying he could operate at 100,000 watts. He only had a 50,000 watt antenna and one night he just wanted to see what 100,000 watts would do. I remember seeing a blue glow coming off of his antenna tower that night for about ten minutes. He climbed his tower the next day to repair a cable that had melted. I remember sitting in his basement studio and watching him talk to friends in China and thinking how great it would be to become an operator myself. I still have not taken that step more than 30-years later.

I helped my neighbor set up one of the first radioteletype (RTTY) systems; he used his mechanical morse-code relay and controlled it by computer to send digital signals around the globe. The technology behind it is actually still used today for computer wireless networks, though at a much higher frequency and using transistor-based switches rather than mechanical relays. The opportunities available to amateur radio enthusiasts today are endless, and I am sure that any club member would be happy to help you get started. A great place to begin would be the Amateur Radio day coming up this weekend.

Television broadcast signals

Last week we talked about radio broadcast signals and the difference between AM and FM signals. This week I thought we could take it into talking about television broadcast signals. I am sure many of you in this area have experienced the same things that I have in recent years with broadcast television stations.  If you receive your local news via antenna rather than as a cable subscriber, there is a big difference in the quality of the TV signal since changes in 2009.

I noticed one thing which bothered me a lot; before the digital broadcast switchover in 2009, I could still get KY3 during a heavy storm. The picture had a lot of static and the sound was a little unclear, but I could still hear major weather alerts and be informed. Just recently a small tornado went through the outskirts of Edgar Springs. I heard the tornado warning and then my screen went dark. No signal, and therefore no information. The old analog stations never went completely away like this during a storm.

So what is the difference between analog and digital signals, why does the quality look so great on digital stations all the way up until they just drop off with a no-signal message? With analog it seemed that the quality degraded until you could no longer get the station, but there was never a complete cutoff. It has to do a lot with how the signals are transmitted.

The old analog broadcasts used a dual carrier technique overlaying both AM and FM signals that we talked about last week to transmit both the picture and the audio. The picture is transmitted using AM signals and the sound using FM signals. These signals are prone to noise from interference of other stations or signal bouncing off of walls, tree, and even people. The interference is what caused poor color quality, ghosting, and weak sound quality. The NTSC standard for television broadcast was adopted in 1941 and transmitted 525-lines of image data at 30-frames per second. NTSC worked well and still works today with older analog devices, like VCRs and older DVD players, but because color was not added until 1953 that standard became jokingly referred to by professionals as “Never Twice the Same Color” because of color inconsistencies between broadcast stations.

The new Advanced Television Standard Committee (ATSC) uses the same methods that store video information on DVDs or Blu-ray Discs to transmit the television signal. These methods use a digital signal consisting of a series of ones and zeros, or “on” and “off”. This new standard resulted in better quality images and sound for multiple reasons. The first is that it was designed from the ground up with things like color, surround sound audio, and text transmission taken into consideration.

The digital signal is much smaller now, allowing stations to use the same bandwidth to broadcast multiple stations, or sub-channels in addition to the main channel, using the same broadcast equipment.  Digital signals also allowed for the broadcast of the wide screen format and high definition signals. The only downfall of the digital broadcast is the inability to receive partial information from a weak signal. Digital is an all or nothing type of broadcast, as missing information in a digital signal cannot be interpreted by the receiver, causing errors and the nice “no signal” message to display on your TV.

You can think of a digital transmission as transmitting in code; if a single piece of the code is missing, it cannot be deciphered, resulting in unusable images and sound that cannot be displayed. Analog transmissions transmit the original image and sound, so if pieces are missing, the sound gets static, and the picture gets missing spots, or fuzzy. So even if the picture is clearer with digital, it is less reliable over long distances and in high noise situations like severe storms.

Radio Signals

My six-year-old son Obie was riding in the car with me Saturday night and asked a question that brought about the topic for this week. He said, “Hey, Dad, I know that FM is the radio stations, and Aux lets us listen to music from your phone, but what is the AM button for?”

Photo by Ivan Akira
FM radio carries the audio signal by 

modifying the frequency of the 

carrier wave proportionally to the 

audio signal’s amplitude. 

https://commons.wikimedia.org/
wiki/Category:CC-BY-SA-3.0

So just in case there are others out there that want to know what the AM button on your radio is for, here is a lesson on radio signals. Every radio station in the world operates on one of two different broadcast technologies. They either use amplitude modulation (AM) or frequency modulation (FM). They both use electrical current passed through a broadcast antenna to send an electrical signal through the air, but they carry, or modulate the sound wave in very different ways.

To begin to understand radio broadcast, it is first important to understand that electricity can travel through the air just like sound and light travels through the air using waves. There are two main properties to a wave. The first is the wavelength, which is inversely related to the frequency and tells the amount of distance between individual peaks in the wave. The frequency tells us how many peaks will reach us in a second. It can be thought of as how high or low a sound is, or actually determines the color of light. The second is the amplitude, or height of the wave, it can be thought of as how loud a sound is or how bright a light appears.

FM, which is the most well known radio signal, carries the sound over the air by modification of the frequency of the radio wave. As the sound wave you are broadcasting changes in pitch, the frequency of the wave changes within a given range. FM operates in a frequency range of 88-108 Megahertz (MHz), which means between 88 million and 108 million peaks of a wave hit your antenna every second. Each FM station is assigned a range of roughly 100 kilohertz (kHz), meaning the signal varies by 100 thousand waves per second. You can think of it as carrying the sound by changing the length of the wave. The FM signal will not travel as far as AM signals because of atmospheric effects on the signal.

Photo by Ivan Akira: AM radio carries 

the audio signal by modifying the amplitude

 of the carrier wave proportionally

 to the audio signal’s amplitude. 

https://commons.wikimedia.org/
wiki/Category:CC-BY-SA-3.0

AM, which is less well known, also happens to be less expensive to operate and the signals can travel much longer distances. This has to due with the longer wavelengths, which cause the signal to bounce off of the upper atmosphere, whereas FM signals pass through it. AM signals carry the sound wave by varying the amplitude, or height of the wave, in proportion to the height of the sound wave being broadcast. They operate on a much lower frequency than FM, around 540-1600 kHz which means between 540 thousand and 1.6 million waves hit your antenna in a second, roughly 100 times fewer than FM. AM stations are assigned a given frequency that never changes during their broadcast. This allows a receiver to work with a much weaker signal since it does not change, making it possible on a clear night to listen to AM radio stations as far away as northern Canada and southern Mexico.

Due to the higher sound quality of FM over AM broadcast signals, most FM stations are used to broadcast music and most AM stations are used to broadcast talk radio. So now you know what the AM button on your radio means.

Another really neat fact about AM radio is that if you tune to a weak AM station during a thunderstorm, you can hear the lightning on the radio nearly the same time as you see the flash, and it gives you an audio warning of the pending clap of thunder.