Have you ever found out that something you remember from your youth is now gone, and you didn’t even notice? If you are a certain age, you might feel that way when I deliver the news: You haven’t been able to buy International Reply Coupons (IRCs) at a US Post Office since early 2013. By the end of 2026, you won’t be able to buy them anywhere. The age of the IRC is over.

What’s an IRC?

If that didn’t mean anything to you, you might be too young to remember, or maybe you just weren’t into shortwave listening or ham radio. Although there were other reasons to get IRCs, a radio hobby is the most likely reason a Hackday reader would have bought an IRC.

For radio purposes, here’s the problem. You’ve worked on your station for months, and one winter night, you finally pull in that rare station from Luxembourg. They’ll send you a QSL card to verify that you heard them. You only have to send them a letter telling them what time you heard them, what frequency, and some details about the program you heard. But they probably don’t want to pay the postage required to send hundreds or thousands of cards overseas.

While this is a radio-specific problem, you might find the same issue with pen pals or when trying to buy things from an overseas company.

SASE

If everyone were in the same country, the solution would be easy. Take a stamp, put it on an envelope that has your address on it, and stuff it in with the letter. Or, you could just drop a stamp or two in the letter you sent.

The problem is, US postage won’t help Radio Luxembourg. On the other hand, the effort required for you to buy postage that works in Luxembourg would have been a nightmare.

Enter the UPU

The Universal Postal Union is a UN agency that is effectively an association of post offices in 192 countries. Their charter is to facilitate mailing things worldwide.

The IRCs date back to 1906. The idea is you buy an IRC at your post office. You send it to Radio Luxembourg, or wherever. There, the mail person at the radio station could go to their post office and trade the coupon for enough local postage to send a surface letter worldwide.

Slow Death

As demand has dwindled, post offices worldwide have quit selling IRCs. As of last year, Australia still did. But Germany, Britain, the United States, and many other countries gave up on them long ago. In fact, Britain’s Royal Mail claimed that the average post office sold less than one IRC per year at the time it threw in the towel.

UPU decided to end IRCs altogether by December 31, 2026. The end of an era and, apparently, not just for radio hobbyists. It is telling that the UPU’s recent editions of IRCs had print runs of 1,000 or even 500. So they obviously weren’t selling very many.

IRCs Other Claim to Fame

If you’ve heard of these before and you aren’t interested in radio, then it might have been in economic history. Have you heard of the Ponzi scheme? It has become a generic term for any business scheme that relies on raising money from new investors to service debt owed to old investors.

However, the original Ponzi scheme dates back to 1920, when Charles Ponzi realized he could buy IRCs in a country where they were cheap and sell them for more in another country. He was happy to accept investors, of course.

The problem is that profits are thin, and the costs of acquiring and transporting large numbers of IRCs quickly swamp most potential profits. Fluctuations in currency exchange rates take the rest.

Goodbye!

So the end of the IRC marks a closed chapter for ham radio and swindling. There were probably other uses, too, that are now consumed by electronic mail, payment systems, and the like.

You have to wonder what adventures IRCs went on during their global travels. The video below shows one’s story.

Since the first V2 rocket sailed above the Kármán line back in 1944 and right up until the modern era, the trajectory of most space-bound rockets was more or less the same: after expending their propellants they would either crash into some desolate steppe or plunge into the ocean. In either event, the rocket was disposable. The important bit up top might go on to explore the stars or send a human crew off on their mission, but the booster rocket that lifted the spacecraft out of the atmosphere was always going to be sacrificed for the cause.

But in the 1970s NASA had a wild idea: what if we didn’t smash a brand-new rocket valued at millions of dollars into the ocean every time we wanted to put something in orbit? Instead, they would build a hybrid space vehicle that blended the vertical takeoff and raw power of a rocket with the capabilities of an airplane, allowing it and whatever it was carrying to make a gentle runway landing at the end of its mission. As such, the Space Shuttle was born.

With the benefit of hindsight, we now know the Shuttle wasn’t quite the spaceflight revolution that NASA had hoped for. The age of reusable rockets didn’t truly begin until 2015, when SpaceX landed the first stage of their Falcon 9. To date they’ve repeated the feat nearly 600 times, all the while increasing the reliability and speed of their operations. Today the Falcon 9 is the most prolific launch vehicle in history, and nearly every other rocket in active development is being designed to include some element of reusability.

Most recently, China demonstrated that they could recover their Long March 10B rocket by gently bringing it down into what amounts to a giant butterfly net. While it might seem a bit quaint compared to rockets that land on their tails like something out of a 1950s sci-fi movie, the idea offers considerable promise.

There and Back Again

But why did it take 70+ years before we were able to regularly refly orbital-class rockets? It’s not that there’s anything inherently complex about reusing a spent rocket. Sure, there’s a case to be made that material science improvements have made the engines robust enough for repeated use. But even if you had to rebuild the engines after each flight it would still be better than slamming the whole vehicle into the ocean. Similarly, there’s nothing particularly unique about the structure of the Falcon 9 that enables it to fly multiple times — it’s a big metal tube with tanks inside of it, just like essentially every rocket that has flown before it.

The revolutionary technology demonstrated by SpaceX in 2015 didn’t have anything to do with making their rocket go up, it was that they were able to safely bring it back without damaging or physically altering it. The Falcon 9 first stage that came back to Earth was in the same condition it was when it left the launch pad eight minutes or so earlier, albeit with empty propellant tanks and a layer of soot on the outside.

As such, most of the variability we see when comparing the reuse of past, present, and future rockets comes not from how the vehicle ascends, but how it ultimately comes to rest back down on Earth.

Splashdown is Easy, But Rough

Without question, the easiest way to recover a rocket intact is to simply slow it down before it hits the surface of the ocean using parachutes This is how all American crewed capsules, and more applicably the Space Shuttle’s Solid Rocket Boosters (SRBs), have been recovered after their flights.

But even when descending under multiple huge parachutes, splashdown isn’t exactly a gentle event. It could probably best be described as “survivable”, in that the vehicle and crew will come through the experience in one piece, but neither is likely to be terribly happy about it.

The situation of course ends up being even worse for the rocket, as its structure is going to be subjected to the brunt of the impact force. Additionally, a complex aerospace vehicle getting partially submerged in salt water is a recipe for corrosion and electrical issues, to say nothing of the thermal shock the hot engines will experience when getting dunked.

One could argue that the only reason this method of recovery worked for the Shuttle SRBs is because of their relative simplicity when compared to a liquid-fueled rocket capable of independent flight. At the risk of oversimplifying the structure of the SRB, at splashdown it was effectively a hollow tube with minimal avionics and thrust vector control (TVC) hardware that could simply be replaced before the next flight.

Still, the NASA document Solid Rocket Booster (SRB) Refurbishment Practices goes over the considerable work required to bring each booster back to flight status after coming down in the ocean. Given the challenges of refurbishing the boosters, it’s perhaps unsurprising that NASA elected to forgo their reuse on the Space Launch System despite its SRBs being largely identical to their Shuttle predecessors.

Teaching Rockets New Tricks

In the very early days, while they were still trying to reach orbit with the Falcon 1, SpaceX had actually considered a Shuttle SRB-style recovery procedure. But in the end they decided to outfit the Falcon 9 with deployable landing legs and the rest, as they say, is history.

Landing legs allow a rocket to come down on effectively any flat surface, be it a concrete pad next to the launch facility or a floating platform. But there are some fairly serious drawbacks to this approach. For one thing, the requirement for precise terminal guidance means parachutes are out of the question. The rocket needs fins, attitude thrusters, or other control surfaces to come down on the center of the pad.

It also means the rocket needs to perform a propulsive landing. That is, use its own primary engines to bring its velocity on touchdown to as close to zero as possible. This in turn requires engines that can not only restart in flight — a capability that has not traditionally been required by first stage boosters — but are able to throttle down low enough to control the rocket’s descent without simply pushing it back upwards. It’s difficult to overstate how unnatural a state of operation this is for a rocket. Indeed, it’s the antithesis of how nearly every rocket has operated since the Song Dynasty started experimenting with gunpowder in the 10th century.

Even if you can accomplish all that, the true cost of landing a rocket is in the extra mass. Although the legs will be stowed away and unused for 99.8% of the rocket’s flight time, it still has to lug all that weight uphill. If that wasn’t bad enough, there’s also the extra weight of whatever control mechanism is in place to guide the rocket’s descent trajectory as well as the propellant that needs to be kept in reserve for the landing burn.

All told, landing a rocket on legs comes with a massive payload penalty. In the case of the Falcon 9, the rocket’s maximum capacity to Low Earth Orbit (LEO) in its expendable configuration is approximately 22,800 kg (50,300 lb). But when outfitted with the hardware necessary to land, that number is reduced by nearly 25% to 17,500 kg (38,600 lb).

Dropping the Dead Weight

There was a time, not so very long ago, when critics doubted the financial viability of recovering and reusing rockets like the Falcon 9. But today, reuse has gone from theoretical to standard operating procedure. Outside of a few Old Space holdouts, it’s top of mind for every launch provider and critical for remaining competitive in a fast-moving commercial market. In November, Blue Origin even managed to land their New Glenn heavy-lift rocket on only its second flight.

So at this point the question isn’t whether or not future rockets will be reusable, but rather, what is the most efficient way to achieve that reusability?

With that in mind, it’s easy to see the appeal of China’s net recovery. While the rocket must still perform a propulsive descent — although in theory the necessary positional accuracy, and therefore the technical challenge, is somewhat reduced — it doesn’t need to have landing legs installed. This mass savings increases the vehicle’s useful payload capacity, which in turn makes it more profitable to operate. Achieving the same end goal while being easier and cheaper is an improvement in anyone’s book.

Admittedly, having the rocket come down in a huge net adds a certain amount of whimsy to the whole endeavor, but the overall logic is sound enough. It should also be said that SpaceX, for all the success they’ve had with landing their Falcon 9 on a set of deployable legs, are themselves planning on catching both the first and second stages of their next-generation Starship vehicle. Instead of a net, their goal is to pluck the rocket out of the air with a huge robotic pincer mechanism.

One is reminded of the old joke about how the Americans and Russians approached the problem of writing in space: NASA spent millions of dollars developing a pen that would work in microgravity, while their Russian counterparts simply used pencils. If China can demonstrate the ability to reuse a rocket they snagged in their net, the more elaborate methods of recovery employed by American rockets may one day look like a similarly overengineered solution.

Along with the many displays of outrage, gnashing of teeth and other displays of profound grief at the recent news that Sony will no longer manufacture physical game discs come 2028, we have also heard some voices pipe up with a variety of statements, such as that this decision makes game archiving basically impossible. Of course, the truth of the matter is that software archiving in general has become much harder already over the past decades, while game consoles are just late to the archiving-hostile party.

As an example, one merely has to contrast Sony’s PlayStation with e.g. the Valve Steam store and software by juggernauts like Adobe and Autodesk. Here the former moved after the Creative Suite (CS6) series of Photoshop and other tools fully over to the Creative Cloud (CC) subscription model, where DRM and constant rental software renewals are in order. Unlike that disc copy of CS6 Master Collection that will stay good practically forever, there’s nothing really to archive with Adobe’s CC software.

Similarly, with digital game downloads and their constant patches now put inside a heavily encrypted environment that relies on a special launcher, preserving video games has been turned into into a virtual nightmare for many years now.

Why Archive

Archiving is about accumulating historical records or materials. The scope and reason for a particular archive can differ, such as a company’s archive with financial records, an engineering department’s archive of technical references, or a museum’s archive of physical artefacts. Whatever the reason, the same goal applies: the maintaining or creating of a historical timeline that can be later referenced as needed.

An essential part of archives is to act as a primary reference source: where possible archives contain only the original documents and artefacts, making them as close to an objective source of history as possible. This is both extremely useful for a company when the tax office does a surprise inspection, but it is also for anyone who wishes to do any kind of historical research. This includes research into the development of a certain kind of software over the centuries and all types of related hardware.

Within the world of software archiving not much changes about this primary mission, except for the digital aspect that earns it the title of digital preservation. At least until fairly recently this meant mostly making copies of physical storage media and any associated physical media like documentation and manuals, but increasingly the subject of such preservation and archiving entails digital data that never was bound to or accompanied by any kind of physical media.

Such digital preservation is a big part of organizations like the Internet Archive, whose archives contain copies of software and games that might otherwise have been lost to the ages. The cases of retro enthusiasts coming across a floppy disk or CD containing some obscure game or set of drivers and uploading a copy to the Internet Archive are both numerous and an excellent example of digital preservation.

Other archives like the Video Game History Foundation (VGHF) have a more narrow focus, as their name implies. Their basic mission is no different, of course, with creating an archive that preserves history. Here the best part about digital preservation is that it makes it possible to create virtually infinite bit-perfect copies of the materials, making it incredibly easy to share and enjoy multimedia, gaming, and other content from these archives.

Digital Restrictions

Of course, if that was all that there is to be said about digital archiving and preservation then this is basically where we could conclude merrily that all is well, and that whether software is distributed digitally or on some kind of physical storage media is of no concern. In this scenario said software can be copied around to one’s heart’s content, burned to optical media and so on without restrictions, ensuring its preservation.

With distributors of software having had fits about how easy it is to copy and distribute said software since at least the 1980s, it’s little wonder that they haven’t seen fit to rely on the fact that copyright infringement is illegal, and instead sought to make it impossible to copy the data of software. This led to a wide variety of copy restriction implementations, including on floppy disks, such as Electronic Arts’ Interlock system, while Nintendo’s game cartridges mostly relied on this more obscure format to keep people from creating their own cartridges.

In the face of these hurdles, the US Library of Congress notes that, for some software, it’s not enough to have the software on some medium, but also the console or hardware to play it on.

These copy restriction mechanisms are a form of digital restrictions management (DRM), euphemistically called ‘rights management’, since DRM only removes rights. As software became decoupled from physical media by the late 90s along with multimedia content like MP3 music, alternate DRM schemes were developed that restrict copying, generally through encryption and a convoluted decryption scheme that even includes hardware-level encryption such as High-bandwidth Digital Content Protection (HDCP).

The upshot of all these copy restriction schemes is that you have to jump through many hoops to still create a copy, whether it involves breaking a floppy copying scheme, using an HDMI splitter that accidentally forgets to re-apply HDCP before sending the content off to a capture card, catching a lucky break with a leaky DVD CSS implementation, or using the analog hole to create that ‘good enough’ copy.

Nobody buys games on DVDs anymore, however. When a digital game is provided via an online store service, how can this be preserved in a digital archive? Since all of these rely on an internet-dependent DRM scheme which fails the moment there’s an issue anywhere in the chain, or if said authentication servers are turned off in N years from now, all preservation schemes here are by definition flawed or at least legally awkward.

A Digital Void

When EA created its Interlock copy restriction scheme it was likely not concerned with whether or not copies of their games would survive into the 2020s, never mind whether anyone would still be using FDDs. It does however indicate the central problem here, one that goes far beyond a black-and-white physical media vs digital-only show-off. Especially since physical media could be argued to be flawed enough that it deserved it to die.

In today’s inevitable march towards a future in which we’re all consuming content using ‘our’ Smart Terminal Devices that rely on any number of paid subscriptions to gain access to the actual content stored on the servers of our benevolent Content Overlords, what probably rankles people the most about the PlayStation physical media announcement is less the demise of physical media and more a reminder of how much has already been taken from us.

In a statement made by VGHF director Frank Cifaldi on the end of physical PlayStation discs – and the concurrent announcement of the shutdown of the PlayStation 3 and Vita online stores – this is put in the broader context of the digital void that we’re facing, in which a large part of video game history simply cannot be legally preserved.

The Legal Conundrum

Here we have to address the rather sizeable elephant in the room, in the form of copyright infringement. Here we see large groups of very nice people in friendly online communities who carefully strip any offending DRM that may even prevent the game from working, while ensuring that the freely provided bundle is kept up to date with only the best patches and anything of relevance.

Within these communities you can find entire swathes of video game history preserved for the enjoyment of connoisseurs, including tutorials, manuals, carefully curated collections mods and extensions, plus everything else that would make a professional digital archivist salivate.

But these ‘shadow archives’ are definitely illegal according to copyright law, ergo the only option available to VGHF and other organizations that are trying to stay on the light side of the law might be to wait a few decades, see which games enter the legal grey zone of ‘abandonware‘ and see whether they’ll still get hit by DMCA takedown request in 2050 for a game that ceased being offered for sale in 2026.

C’est la vie.

Pity the poor Australians. Isolated on a jagged hunk of land far from everywhere else, these industrious people have to take two-legged flights (or more) to reach a great many destinations in the northern hemisphere. It’s expensive, time consuming, and makes planning a trip a complete headache when wars break out around popular hub airports.

One airline is trying to solve this problem. The nation’s flag carrier, Qantas, has been hard at work on Project Sunrise. The goal is to run some of the longest non-stop commercial passenger flights ever, with great effort going into solving the technical and economic challenges involved.

No Stops

When travelling from Australia’s major capital cities, flights to destinations like London, the rest of Europe, or the US, all involve stopovers in intermediate airports along the way. A great many routes stop in Dubai or Qatar, while others transit through Hong Kong, Singapore, or Thailand. The need for stopovers complicates air travel for the passenger, particularly when delays cause missed connections or baggage gets lost from one flight to another. It can also just be tedious—sometimes a stopover can last 10 hours or more, which is an incredibly uncomfortable amount of time to spend in even the nicest airport. The reason behind stopovers is simple enough—the average commercial airliner just doesn’t have the fuel range to haul many hundreds of passengers from Australia to Europe in a single hop.

Qantas has been trying to improve Australia’s passenger airline links for quite some time by finding ways to eliminate these tedious stopovers entirely. Thus was born Project Sunrise, which hoped to find more direct routes between popular world cities and suitable airliners that could fly those routes without stopping.

An early 2019 test flight probed the practicality of flying from New York to Sydney in a single hop. Due to the limitations of contemporary aircraft, sacrifices were made to get the flight over the line. Where the Boeing 787-9 would normally carry up to 280 passengers, the test flight would only haul 40 to save weight, and thus save fuel. No cargo was on board, and the tanks were brimmed to ensure maximum range was available. Even then, the 16,250 km route was considered to be at 115% of the plane’s normal range, and there was only 90 minutes of contingency  when it came to fuel onboard if something went awry. Despite the challenges, the test was a success, and provided useful learnings on how to handle things like crew fatigue on a 19-hour continuous flight.

Qantas was also experimenting with practical revenue services at this time, too. In 2018, the airline had established a direct route from Perth to London, flying the Boeing 787-9 in a 236-seat configuration. Flying the 14,484-kilometer route was just within the practical range of the aircraft. It was a useful route that made travel easier for passengers departing Australia’s west coast, but far from the golden ideal of allowing direct flights to major international destinations from the major capitals of Melbourne and Sydney. The route has also since fell victim to geopolitical strife, as the Iran War shut down large swathes of airspace in early 2026. Qantas was forced to alter its flight paths, which added 30 to 45 minutes to the usual flight time—just enough to tip the route over the practical limitations of the aircraft’s range.

Future Goals

However, the crowing achievement of Project Sunrise is still yet to come. 39% of Australia’s population is concentrated in Sydney and Melbourne alone, with both capitals situated on the country’s east coast. It would be most advantageous from a business perspective for these cities to have direct links to major world destinations, and it would benefit the broadest swathe of Qantas’s customer base. Only, the problem comes back to geography, with these two capitals being over 16,000 kilometers from popular destinations like New York and London.

Qantas has risen to the challenge, regardless. The airline challenged both Boeing and Airbus to develop aircraft intended to fly routes from Sydney, Melbourne, and Brisbane, to destinations like New York, London, Cape Town, Paris, and Rio de Janeiro. This was later whittled down to a narrower focus on the Sydney to New York and Sydney to London routes. Airbus would come out victorious, with Qantas ordering twelve examples of the Airbus A350-1000ULR. The specially-configured model features an additional rear centre fuel tank and a higher maximum take-off weight in order to fly routes up to 22 hours non-stop, along with a reduced seat configuration serving just 238 passengers. The extra range makes for a huge difference compared to more conventional routes out of Australia, which often pair two flights up to 14 hours each. The extra range of the new aircraft saves passengers both hours of flight time, along with the hours normally spent sitting around on layover in a hub airport along the way.

A typical flight from Sydney to New York or Sydney to London is expected to take 19 to 22 hours. The no-stop nature of the route will enable 99% of Australians to access either destination either direct, or with one-stop—such as by flying in from another major capital on a domestic flight. The flights are expected to run with a higher-than-usual ratio of premium seats, based on the expected demand for these services.

The main thing holding back the new service is aircraft delivery. Production is underway in earnest, with the first A350-1000ULR to be delivered in April 2027. Daily non-stop flights between Sydney and London will begin from October 2027, with tickets to be on sale from February.

Aircraft cabins will be optimized to have more space and amenity to keep passengers comfortable on ultra-long-range routes.

The new Project Sunrise services will be a gamechanger for many people travelling to and from Sydney, and other Australian capitals. It will relieve a major pain point—layovers—that have become a dreaded fact of life for Australians headed far abroad. It will still perhaps be some time before Australians get more direct services to a wider range of destinations, because these new services will have to prove themselves. If the passenger numbers aren’t there, the services won’t make money, and it may not prove worth the hassle to operate these ultra-long-range routes. If, however, convenience truly is king, then there may be much greater investment in this area to link Sydney and Melbourne with more cities directly. The only losers in this case will be the hub airports across the world, which will grow just a little quieter for the loss of Aussie accents in the terminal.

A few weeks ago we published the first in a new series of articles, Know Your Food. It was born out of the realisation that most people know surprisingly little about what they eat, and to apply a bit of Hackaday curiosity to received opinion on the subject. As we put it then: “To know both how common foodstuffs should be made, as well as how they are made industrially, should be an essential for everyone” We’ll continue in that vein, with a look at organic food.

If you buy your food in a supermarket it’s likely that in the vegetable aisle you’ll be presented with a choice. On one hand you will have the normal vegetable, and on the other and usually for a slightly higher price, the organic version of the same vegetable. What’s going on?

So What Is This Organic Stuff All About?

Organic production is a system of agriculture that emphasises natural fertilisers, pesticides, and farming methods over synthetic or intensive ones. It has its roots in the first half of the 20th century, and as the decades progressed it has become an important sector of agricultural industry. I grew up steeped in organic agriculture because my grandfather was an early adherent in the years following the war, so I’ve seen it from the sharpest end. There is a lot to commend organic production for and plenty of reasons to embrace it, but with that come some problematic aspects, and even dubious claims. Here I’ll try to unpick some of that.

It’s tempting to believe that all organic production is somehow a return to a 19th century rural idyl, complete with the obligatory chickens in the farmyard. Some organic producers do take a slice of this back-to-the-land approach to their craft, but the reality of organic farming is a very modern approach to managing the ecosystem. Organic farmers are not wary of progress, and neither are they reluctant to use pesticides or other chemicals. Instead they do so according to the principles of organic agriculture, so any techniques they use are designed to be beneficial to the ecosystem, and any chemicals have a natural origin.

An important thing to understand is that the line between organic and non-organic agriculture is not sharply drawn. Crop rotation for example is long established farming practice, as are techniques such as contour ploughing in areas with soil erosion. As for fertiliser, there will be very few farming operations whose work does not include manure in some form, or who do not take advantage of nitrogen fixing crops. Pesticides such as the insecticide pyrethrum – originally derived from chrysanthemum root – or Bordeaux Mixture as a fungicide – a solution containing copper ions, so called because of its origin in French vineyards who applied lime solutions from copper containers – find uses where applicable in both organic and conventional agriculture. The important distinction lies in the organic farmers not going further than this, into synthetic amonium nitrate fertiliser for example, or glyphosate herbicide, which you might know as Roundup.

That’s the organic sales pitch, and it’s a compelling one. Now, we’ll go through the not so positive aspects, both of the movement and of the business.

Organic status is not simply conferred to produce by virtue of being organically grown. Instead it’s a legally protected designation, enforced through a system of certification performed by designated organisations. Where I grew up in the UK for example, organic certification is performed by the Soil Association. This is good because it preserves trust in organic status, but it suffers the flaw that it’s a profitable business for the certifier, and an expensive one for the producer. This in turn favours larger producers who can afford certification, and leaves the smaller producer unable to afford certification and thus unable to label their produce as organic. They can describe it as “Organically grown” of course, but they lose the cachet of the organic label. Since many small producers are by necessity organic, this affects a large number of producers if not a significant sector of the market.

Is Organic Food Really Better?

Then there is the produce itself. Is it better than the non-organic stuff? Here we enter complex territory, because the answer differs depending upon the circumstances.

In terms of what advertising people like to call “goodness”, by which I mean nutrients, vitamins and minerals, and the like, in many cases it’s difficult to make a case for the organic product being superior to the non organic one. There will be exceptions such as apples, where a typical non-organic commercial dessert apple is overwatered to the point of diluting the beneficial properties it might have in search of the elusive “crunch”. But in the more ordinary case, that organic zucchini is unlikely to have more nutritional value than its non organic equivalent. It’s important to note that the organic product will lack any pesticide residues which may be present on its non organic equivalent, however it must be remembered that pesticide residue levels in food are subject to their own stringent regulation.

In terms of flavour, yet again it’s a mixed bag. An organic product grown in as intensive a manner as can be got away with under the rules, is not likely to taste better than the equivalent. It’s difficult even to pin down what in the husbandry governs the flavour of the finished product in a scientific sense, however as someone who grew up around organic production I’d offer the view that the longer something took to produce, the better its flavour is likely to be.

The Slow Food movement champions products made in this way, usually traditionally produced foods, heritage varieties, and foods with a particular terroir. If you’re looking for better tasting food then you may not find it with a supermarket organic label, but it’s quite likely that one of those small organic producers will have what you are looking for, simply because their methods are less intensive.

Finally, if you’re looking at the benefit to the environment, it’s likely that in most cases the organic product will impose less stress on the ecosystem and the wider environment than its non organic equivalent. If that’s your concern you should also look further than the means of production and into food miles; how far did the food in front of you travel to your plate? Here in Europe the strawberry is in season from around May to September, so does it make sense to fly them from the other side of the world in January, however nice they taste?

So now I hope you have more of an idea about organic food than you did at the start of this piece. You’ll know something about its benefits and problems, and you’ll know when it’s better than its non-organic equivalent. I hope you’ll find the food you like, and if you do, I hope it’s from a small producer, they need your business. Bon appetit!

Header: MichelM10, CC0.

Local area networks (LANs) that use technologies like Ethernet and Wi-Fi are incredibly useful for letting devices talk with each other. Yet a core problem here is knowing which devices are where on the network, as anyone who has ever tried to add a network printer or network share to their system can probably attest to. Unless you happen to know the IP address of the LAN device, the port, and protocol, the target device may as well be located on the Moon without further help, such as automatic network discovery in lieu of waddling over to the device and reading the label listing its IP address.

Over the decades quite a few ways have been developed to enable such network discovery, with many of them using UDP broadcast as the first step. By broadcasting a global message on the entire LAN, any device that has an actively listening UDP socket on that particular port can parse said message and decide whether it’s feeling sociable enough to reply.

The topic of UDP broadcasting is however not as straightforward as it may sound if you’re just getting started, including the existence of many opinions on the ‘right way’. There is also a massive divide between a sprawling service discovery protocol like mDNS and a light-weight one like that one that I had to implement a few years ago for an open source project.

Network Broadcasting

The obvious advantage of a broadcast message is that a client device that seeks its protocol soul mate on the LAN doesn’t need to ping all possible IP address and subnets. Instead,  a broadcast message is designed so that all connected networking devices know that it should be forwarded to all other known devices. Thus with a single message from the client, in theory, only a single message will then neatly land at every single other connected system.

Of course, this ignores happy joy fun things such as convoluted network configurations, such as those involving overlapping Wi-Fi repeaters and subsequent routing, but in general we can assume that this is how it works. Various edge cases and fascinating complications of these will be considered in a later section.

Much of this service auto-discovery is tossed under the header of ‘zero-configuration networking‘, or zeroconf for people who don’t like typing. The best part about zeroconf is probably that there are so many standards here, ranging from DNS-SD to mDNS, UPnP, SLP and others. Perhaps unsurprisingly, one of the major issues here is that platform support here is spotty, with mDNS – despite being one of the most universal – not having much support outside of MacOS/OS X with Bonjour and Linux/BSD with Avahi.

Thus while trying to add the auto-discovery of NymphCast receivers and media servers by NymphCast clients, I found myself asking the daunting question of whether I was at risk of being about to embark on reinventing the proverbial wheel. After all, nobody wants to become the subject of an xkcd comic.

UDP Discovery Basics

As it turns out, I ought not to have been too worried, as despite looking everywhere I could find nothing along the lines of the NyanSD network service discovery (NSD) protocol that I ended up implementing and integrating into NymphCast. What I wanted after all was the most no-frills NSD possible that could be easily integrated, while working the same across just about any desktop, server and embedded platform imaginable.

All that’s needed for this is a way to create an appropriate UDP socket, and a way to either broadcast a query and receive the response, or to listen for incoming UDP packets. Here you can figure out the platform-native method for each target platform, or not reinvent the wheel and use an existing networking library for C++ like Poco. This is what I used for NyanSD, along with my ByteBauble utility to handle endianness conversions.

For the UDP server — the listening side — the procedure is fairly standard, with a regular UDP listening socket. As UDP is a connectionless protocol, there is not a lot of preamble here, just a UDP socket instance (here Poco::Net::DatagramSocket), which is bound to the target port and regularly polls for any fresh UDP packets to process. This can all be seen in the single source file for NyanSD which covers both the client and server side code.

Where things get spicy is with the client that sends the broadcast query and waits for any replies. If we were to just shove the query data into the socket along with the request to toss it over to a regular IP address, not a lot would happen. To make it into a broadcast request we need a few things:

1. Let the network subsystem know that we want to do broadcast things.
2. Create the special broadcast address for the target network interface.

With Poco the first point is easily handled by simply calling setBroadcast(true) on the UDP socket instance. For BSD sockets this sets the appropriate flag on the socket, which is essentially repeated across all OS implementations due to how prevalent the BSD socket library is.

The second point can be summarized for IPv4 as a curt ‘make it end with .255’. For example 192.168.0.255 when the client network interface’s IP address is 192.168.0.42. If there are multiple interfaces on the client system, you can go through the list one by one to broadcast on each of them before filtering out potential duplicate returns.

As for how to do broadcasting with IPv6: you don’t, as this protocol relies on multicast and special multicast receiver groups, which is another kettle of fish and of not much relevance for LANs.

Complications

If you look at the NyanSD API, it may give the impression that the query process is incredibly straightforward, with the sendQuery() function neatly returning a stack of remote systems that responded to our query. While these are definitely all the responses, it’s important to remember that NyanSD queries every single network interface. This means that the responses are likely to contain duplicates, which may even come from the loopback address when a service runs locally.

The filtering of this is captured in the NymphCast client library (libnymphcast) where the findServers() function in the main source file calls the isDuplicate() and isDuplicateName() functions, as well as the removeLoopback() function that nukes any responses that match a remote service found via a non-loopback interface. This last filtering is essential for NymphCast when e.g. using playback groups that would otherwise get confused by a stray loopback address.

Although one may think that such in-depth filtering is unnecessary if all you have is a single Wi-Fi or Ethernet interface in your system, one of the curveballs that I encountered during real-life testing was apparently related to Wi-Fi repeaters. For some reason it seems that the way that the repeaters did their broadcasting led to erroneous duplication of packets and thus multiple returns from a single system.

Depending on your exact use case and network configuration you may encounter any such issues and perhaps an exciting new one.

NyanSD Findings

Over the years that NyanSD has been used in the NymphCast project, it has proven to be one of the most reliable and probably nearly zero-fuss components. I have so far used it on Windows, various Linux distributions, FreeBSD, Haiku, Android, and the ESP32 via FreeRTOS and ESP-IDF. What this experience has proven to me most of all is that service discovery doesn’t have to be complicated.

The basic UDP protocol is simple and reliable enough that, barring a very sick LAN, there shouldn’t be any issues here. Assuming you get your filtering sorted of the responses, it’s probably the last part of a project to worry about.

One thing that I’m also very happy with in NyanSD is that there’s no set port in the protocol, like how mDNS always uses port 5353. What this means is that I can have NyanSD listen with a UDP socket on the same port as the NymphCast server’s TCP socket, which also means that different services with their own port can be targeted directly rather than every NyanSD-enabled service on the network getting blasted by every NyanSD query.

I did also do some work on a NyanSD daemon as a more central services database, but so far I have had no real need for it in a practical deployment. I guess that such a thing could be very useful if the port of a service is not set in stone, but generally that’s the one aspect of network services that tends to be boringly predictable.

When you’re driving your car, you’re probably regularly looking at the speedometer to make sure you comply with the local speed limits. The method by which it works is simple enough: the rotation of the wheels is sent mechanically via a cable to a dial on the dash, or an electronic sensor counts the rotations of the drivetrain and an electronically-controlled needle or display shows the speed.

But what about if you were in an aircraft, and the wheels had nothing to do with how fast you were going? How would you even begin to measure speed? There are two ways: there’s a convenient solution to this problem rooted in simple fluid mechanics, and a far-more-complex modern solution. Today, we’ll explore how planes and helicopters are able to figure out how fast they’re going, by the old ways and the new.

Classical Methods

A key thing most aviators want to know is how fast their aircraft is going. Specifically, it’s nice to know how fast it’s moving relative to the airstream around it, which is referred to as airspeed. This is important, because it’s the aircraft’s velocity relative to the flow, such as wind, that determines the performance of the airfoils, how much lift is generated, and whether or not the aircraft is approaching a stall condition where it might fall out of the sky.

Measuring airspeed is most commonly achieved with the use of a device called a Pitot tube. The pitot tube is a tube with a hole in one end that points directly into the airflow in the direction of travel of the aircraft.

As air flows in, it reaches a dead end and the flow slows to a stop, or stagnates, since it has nowhere to go. This allows a pressure sensor or a manometer or other device to measure the stagnation pressure at this point. The stagnation pressure measurement is related to the flowspeed of the incoming air since the kinetic energy of the flow is converted to pressure as the flow comes to a halt.

A secondary tube, pointing perpendicular to the airflow, is then used to measure the static pressure of the surrounding air, without the ram effect of the air being forced in by the aircraft’s forward motion. Then, it’s possible to calculate the velocity of the aircraft relative to the airstream by plugging the stagnation pressure and static pressure into a rearranged Bernoulli’s equation.  If the pitot tube and static tube are hooked up to electronic sensors, the airspeed can be calculated electronically, and fed to a display or digital gauge.

Alternatively, it’s possible to effectively do this “calculation” mechanically. In earlier days, static and stagnation pressure captured by each tube would be fed to a gauge. Inside, the stagnation pressure would be fed to a diaphragm which moved due to the difference relative to the static pressure which is fed into the gauge body, and the movement of the diaphragm would, via a simple mechanism, shift the needle on the gauge.

A small General Aviation aircraft might mount a single pitot tube on the aircraft, feeding the air speed instrument in the cockpit. Commercial aircraft might mount two or more for safety’s sake, in case one becomes inoperable, while large airliners may have four or even more to provide a high level of redundancy and error checking. Heaters are commonly included on pitot tubes to ensure they can be kept free of ice, which can otherwise completely block a tube and make it impossible to obtain an airspeed reading.

For pilots, not knowing how fast (or slow) the aircraft is going can be highly dangerous, as it can lead to entering unstable flight regimes such as stall. Thus, it’s imperative that the pitot tubes remain unobstructed and functional for safe flight. Many aircraft accidents have occurred because of blocked or malfunctioning pitot tubes or airspeed instruments.

The New Way

Of course, you could fuss about with pitot tubes and pressure sensors and deicing measures, but that’s all very fiddly and old hat. There is an entirely different way to figure out a plane’s speed, though it’s only been available for the last few decades. It’s as simple as throwing a GNSS receiver on the aircraft.

Yes, whether your particular poison is GPS, Baidou, GLONASS, or Galileo, any major satellite navigation system will be able to tell you the speed of your receiver. Simply measuring the change in the receiver’s position over time is enough to calculate out the speed, and any off-the-shelf receiver will present this information as standard. It’s generally not used as a primary indicator in aircraft, because it reports ground speed, not airspeed, the latter being more relevant for aviation purposes. Still, it can prove to be a useful sense check when traditional airspeed indicators are non-operative or reporting confusing data, and GNSS devices are widely used on many aircraft today.

Flying High

If you’ve ever wondered how an aircraft measures its speed as it floats through the amorphous gas cloud we call an atmosphere, now you know. Even to this day, where electronics and computer wizardry control our fanciest aircraft, airspeed measurements are still done with the same simple physics, just with some fancier sensors for help. The fundamentals haven’t changed at all. Now you know, you can always dig deeper into the many other rich applications of Bernoulli’s equation and fluid mechanics in general. Happy learning.