The cs.cmu.edu Coke machine was hooked up to a computer by John Zsarnay and/or Lawrence Butcher (now at Xerox PARC); essentially, the six little out-of-product lights on the pushbuttons were monitored. These would flash on for a couple seconds while a particular bottle was dispensed, and of course stay on when a column was empty. They were connected, I believe, to a terminal server machine that was programmed by Mike Kazar to keep track of the time of the last transition (short-term and long-term) for each column. He and Dave Nichols put together a simple Coke@+(TM) protocol by which any machine on the local University-grant Ethernet, and later the Internet as a whole, could probe the current status of the machine; Dave wrote the program that became the ``coke'' command, which printed out the length of time since each column had been totally empty. (The idea, you see, was to notice when a column, having gone empty, was refilled with (warm, room-temperature) Coke, because in principle you wanted to select the coldest Coke available, and thus avoid those colums that had recently been refilled.

This is a quick writeup of a lesson on how GPS (or in general, satellite based navigation) works. I’d like to thank Jasper Vos and Michel Dingen of OBS De Notenkraker for the opportunity & the very useful feedback on the lessons!
Context

10-11 year old children mostly have phones here, and almost all of them turn out to have location sharing turned on with their parents. They also use their phones while on holiday to figure out where they are.

A smattering of kids here knew that phones use satellites for precise positioning, and one or two even know about GPS. So that is good!

It also turns out there is healthy interest in discovering how it actually works.

Federalist Publisher Ben Domenech explained that children and the families who raise them are the bedrock of our communities and make our country great during Fox News “Primetime” on Wednesday.

Domenech began by pointing out that “today’s woke leftist hate many, many things: the Constitution, Donald Trump, Fox News, comedy, and, of course, you.” Domenech continued, “There was really one thing that woke socialist progressives seem to hate more than anything else,” before answering: “That’s babies.”

Domenech decried “the industrialized murder of 60 million unborn infants” and said “the left just doesn’t take their problems out on America’s kids. Their problem seems to be that there are American kids at all.”

“Radical environmentalists regard children as enemies of the climate. Corporate elites see babies as expensive competitors for the time, attention, and creativity of professional women, which they apparently feel should belong exclusively to them. Critical race theory con men suggest that babies become racist as early as three months old,” Domenech said. “Radical feminists have built their entire brand around de-prioritizing family life and shaming happy moms as sellouts to the patriarchy.”

“Progressives hate babies because they’re crying, drooling, pooping refutations of everything woke leftists believe,” Domenech continued. “Boys and girls are the answer to the left’s every argument, and the antidote to their poisonous lie.” For instance, he said, “parents learn the hard way that sex is not a social construct. Social constructs don’t pee on you while you are giving them a bath.”

Children possess many virtues and are much more than the “helpless timid victims the leftist people say they are,” and so are we, Domenech said. “That’s the left’s real problem with children.”

Children make families. Boys turn into men. Couples turn into parents, and women become “the archangels we call moms.” Just as the founders envisioned, America is a place where every child, no matter where they started, “has limitless potential and spark of divine.”

Children are also crucial for building communities. “The more attention we pay to our families, the more time we spend with other families at playdates, little league games, church picnics, school plays — children don’t just turn individuals into families, they also pull families into communities.”

“Leftism is an ideology of fear, grievance, and affected helplessness,” Domenech continued, explaining why leftism is so hostile to families. “Every year on Mother’s Day the media is filled with one article after another by childless writers defending their childlessness. … “On Father’s Day, dads have long been similarly held up as objects of correction and ridicule. These sad people protest too much, and they are not convincing anyone.”

“Kids love America, and they inspire us to make her ever more worthy of their love. Parents teach their children how to be good. The children teach their parents how to be great. Together they make America both,” Domenech concluded. “This is not something you have to do. This is something you get to do.”

Backblaze had 181,464 drives spread across four data centers on two continents. Of that number, there were 3,298 boot drives and 178,166 data drives. The boot drives consisted of 1,607 hard drives and 1,691 SSDs. This report will review the quarterly and lifetime failure rates for our data drives, and we’ll compare the failure rates of our HDD and SSD boot drives.

418. I’m a teapot.

The requested entity body is short and stout.
Tip me over and pour me out.

• A Tesla Megapack fire at the Victorian Big Battery in Southeast Australia was brought under control Monday afternoon.
• Results of the investigation will be closely watched, and could influence the way such systems are designed and built, according to Paul Christensen, a professor of electrochemistry at Newcastle University whose research focuses on lithium ion battery fires and safety.
• His recommendations include monitors within the systems, and enough space for fire crews to maneuver and aim a hose. //

Christensen also said these systems should be designed to allow space for first responders to maneuver around and aim a hose. Plenty of water should available on site, with enough hydrants installed. Containers would ideally have "dead pipes" that are capped and stick out, allowing firefighters to connect a hose, then step away and flood the container to extinguish the flames from a safe distance.

At the moment, water remains the best way to suppress a fire in any lithium ion battery energy storage system //

The Tesla Megapack fire first occurred within the 300 megawatt (450 megawatt hours) system in Geelong, Victoria starting Friday morning. More than 30 fire trucks and support vehicles and about 150 fire fighters from the CFA and local Fire Rescue Victoria responded, containing the flames so they only affected two Megapacks of the approximately 210 that make up the system. //

There have been around 40 known fires that have occurred within large-scale, lithium ion battery energy storage systems, according to Christensen's research. Those incidents, most of which occurred in the past three years, date back to 2012, and include four fires at three facilities in the U.S. in Arizona, Wisconsin and Illinois.

The story of King Canute and the tide is an apocryphal anecdote illustrating the piety or humility of King Canute the Great, recorded in the 12th century by Henry of Huntingdon.

In the story, Canute demonstrates to his flattering courtiers that he has no control over the elements (the incoming tide), explaining that secular power is vain compared to the supreme power of God. The episode is frequently alluded to in contexts where the futility of "trying to stop the tide" of an inexorable event is pointed out, but usually misrepresenting Canute as believing he had supernatural powers, when Huntingdon's story in fact relates the opposite.

Henry of Huntingdon tells the story as one of three examples of Canute's "graceful and magnificent" behaviour (outside of his bravery in warfare),[1] the other two being his arrangement of the marriage of his daughter to the later Holy Roman Emperor, and the negotiation of a reduction in tolls on the roads across Gaul to Rome at the imperial coronation of 1027.

In Huntingdon's account, Canute set his throne by the sea shore and commanded the incoming tide to halt and not wet his feet and robes. Yet "continuing to rise as usual [the tide] dashed over his feet and legs without respect to his royal person. Then the king leapt backwards, saying: 'Let all men know how empty and worthless is the power of kings, for there is none worthy of the name, but He whom heaven, earth, and sea obey by eternal laws.'" He then hung his gold crown on a crucifix, and never wore it again "to the honour of God the almighty King".[2]

Later historians repeated the story, most of them adjusting it to have Canute more clearly aware that the tides would not obey him, and staging the scene to rebuke the flattery of his courtiers.

Leap seconds are controversial things. Since the Earth does not rotate at a steady rate, over time the Earth could get ahead or behind “atomic time”. Whatever solution you propose for this, someone is going to be unhappy.

I take no position on what the best thing to do is here, except that one day I would like to do the math on the “great leap second gyroscopes” that we could mount near the poles to steady the Earth’s rotation, so we can stop talking about this. We may occasionally have to desaturate these gyroscopes with huge rockets also.

Anyhow, some new minor leap second drama is coming up, and for once we can’t blame astronomers, geologists or the International Earth Rotation Service. Imagine if they ever went on strike, by the way!

due to COVID and Trump ending the catch-and-release program, illegal crossings hit an all-time low in 2020. Then Biden sent the Bat-signal, and the cartels – who likely saw a huge drop in revenue because they were unable to get their normal quantities of drugs and people across a much less populated border – are looking to make up for a loss of revenue. So the coyotes (yes, liberals, the word is “coyote”) evangelize throughout Mexico and Central America about how easy it is to get into the United States and recruit clients they’ll eventually treat worse than animals, using them to smuggle drugs into the country, or as sex slaves, as indentured servants at illegal marijuana grows, or simply pack them so tightly into vehicles that there’s barely room to breathe.

The coyotes’ concern isn’t with ensuring that these items of inventory (that’s really what the people are to them) are breathing when they get to the United States. Dead or alive, the family owes them the money. The smuggled are expendable; if one needs to be pushed off the top of a 30′ border wall and paralyzed or killed to create a distraction, so be it. If they lose one van full of people due to a crash, well, that’s just the price of doing business. The cartels are probably more upset at the loss of the van involved since it’s an income-producing asset. If it’s regularly carting 30 people over the border, that’s $300,000 a trip. //

Wednesday’s crash was the third mass casualty vehicle accident involving illegal immigrants this year. In Imperial County, California, 13 illegal immigrants died in a fiery crash on March 1. Border Patrol sources told Fox News that coyotes jammed 25 illegal immigrants into a Ford Expedition, which has a seating capacity of eight and drove into the US through a hole that cartels had cut through a portion of an old section of border fencing:

The Save 418 Movement
We are the teapots.

Status Code 418 states that

Any attempt to brew coffee with a teapot should result in the error code "418 I'm a teapot". The resulting entity body MAY be short and stout.

-- See RFC2324 Section 2.3.2

Go to Google.com/teapot, and see for yourself.

• Galileo/GPS/BeiDou/Glonass open source monitor
• Live observer map
• Status (coverage, DOP) map

Now, as engineers, technical people or specialists in general, we hate to be told what to do exactly. We love it when you let us know what you want to achieve and when you need it, so we can get on with it and make it happen. If you also tell us why you need it, we might opine you actually don’t and there is a better way of doing it.

Just don’t tell us exactly how, because that is our job. In other words, tell us the desired outcome, relevant constraints, timeline, motivation and we’ll do our best.

Or at least that is how we like to feel about how we work. In fact we might disagree a lot with the what, the why and the when, and we can be super stubborn and difficult. But the idea remains — let us do our job, and we’ll deliver better results than when you micromanage us. //

On the flip side of the coin however.. many/most of us aren’t well equipped to pick up hints, interpret your stories as orders, or read between the lines to figure out your real meaning. Sorry. Something had to give when we learned 15000 pages of expert and arcane knowledge, and this was it.

And we might not even apologise — communicating indirectly about technical matters is asking for trouble. If you indicate vaguely what you want, you are likely to exactly not get it.

So on behalf of subject matter experts that are frankly somewhat wonky & geeky: please know we require slightly different handling than your other colleagues. Talking to us in hints and stories may be polite, but we might not pick up that you are sending us a serious message or asking us to do specific things. Do not put your important message between the lines.

When in doubt: be explicit. It will almost never hurt. Just leave us some room on the “how”.

Late July 2019, Galileo, “the European GPS” suffered from a week long outage. I’m a proud European, and I think we should have our own well-functioning navigation system, so I tried to figure out what was going on. Surely someone was monitoring this stuff in public? I come from the internet where we monitor all the things, if someone asked for it or not.

This led me on a journey to monitor Galileo, but quickly also GPS, the Russian GLONASS and Chinese BeiDou systems. Along the way, I found out out how positioning satellites really work. This also helped me understand what went wrong with Galileo, more about which later.

In this post, I want to share what I learned, firstly because it is fascinating, but secondly because it serves as documentation of what the monitoring website “galmon.eu” is actually showing.

Galmon, which we should really rename to Navmon, is a lot like the RIPE Atlas Probes, but then for space. Based on a network of volunteers literally around the world, we monitor the output of each and every navigation satellite and make the results openly available as a pretty website, JSON but also as raw data (messages). Galmon is GPL licensed open source and lives on GitHub. //

How do navigation satellites work?

Let’s imagine we launch a bunch of metronomes, musical devices that tick at a precise frequency. We’ll make them tick precisely once a second and, unlike a regular metronome, we’ll also make them tick exactly on “whole seconds”. So they emit a tick at 0 seconds past the hour, 1 second past the hour etc, one tick every second, on the second.

We put the metronomes in different orbits around the earth, so at any time, some of them are further away than others. Then, we listen to their ticks, which are conveniently transmitted over radio.

Because of the speed of light, a metronome that is 30000 km away will send out its tick on a whole second, but it will arrive with us 100 milliseconds later. A metronome that is closer to us, say 25000 km, will have its tick arrive slightly earlier. These differences are large enough that if we would put the ticks on a loudspeaker we could hear the difference.

Because we can measure the precise delay, we can tell exactly how far away each satellite is from us. In itself however, this does not help us determine our location, because we don’t know where the metronomes are! //

In two dimensions, we only need two satellites to do this, assuming we already had an accurate clock that also ticks once a second, on the second. In three dimensions, we need three satellites ticking away at us.

(Note that in the figure above, we could also be in a second position where the circles intersect - we can rule out that solution by assuming we are not actually in space ourselves).

But, at a very elementary level, this is how GNSS works: satellites tell us where they are, and they send out a ‘tick’ exactly every second (and on the second), and by timing how late that tick is in arriving at our location, we know how far away the satellite is. And by drawing some circles (actually spheres), we can discover where we are. This technique is called multilateration.

What if we don’t have an accurate clock?

We want to use GNSS to figure out where we are, even if we aren’t dragging an accurate clock with us. The speed of light means that for every nanosecond that we get our clocks wrong, our position will be off by 30 centimeters. Nanosecond accurate clocks are delicate machines that do not fit in phones.

Luckily, through some clever math, it is possible to use the satellites themselves as an accurate clock - to do so, we do need an additional satellite and a guess of the time. Such a guess could be derived by taking the average of all GNSS clocks received combined with a rough knowledge how how far away such a satellite could be. Armed with this rough guess, we might end up with:

Note that the three circles do not all cross in a single point. Because our rough clock estimate was wrong (let’s say it runs late a bit), all satellites appear to be a little bit further away than they actually are. Or in other words, all the circles are a little bit too big, causing them not to intersect in one point.

A receiver can based on this observation adjust its internal clock until all circles intersect in one point:

Once this happens, we know that the correct time has been derived.