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Progenitor of the Weird Knife Wednesday feature column. Is “column” the right word? Anyway, apparently I also coined the Very Specific Object nomenclature now sporadically used in the 3D printing community. Yeah, that was me. This must be how Cory Doctorow feels all the time these days.

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Joined 2 years ago
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Cake day: July 20th, 2023

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  • It’s the same line of logic as when you see people post on a forum something like [img]c:\Users\Bob\Documents\My_Image.bmp[/img] and then wonder why it doesn’t work.

    “But I can see it on my computer!”

    Over the internet, the origin of all data is on someone else’s computer. All means all. And all of it needs to come down the wire to you at some point.

    You’re on the right track in one regard, though, in a roundabout way with caching: Browsers will keep local copies of media or even the entire content of webpages on disk for some period of time, and refer to those files when the page is visited again without redownloading the data. This is especially useful for images that appear in multiple places on a website, like header and logo graphics, etc.

    This can actually become a problem if an image is updated on the server’s side, but your browser is not smart enough to figure this out. It will blithely show the old image it has in its cache, which is now outdated. (If you force refresh a webpage by holding shift when you refresh or press F5 in all of the current modern browsers, you’ll get a reload while explicitly ignoring any files already in the cache and all the images and content will be fully redownloaded, and that’s how you get around this if it happens to you.)





  • The Hubble is also in a rather low Earth orbit (340-ish miles), which enables it to use magnetic brakes which allow it to ditch the excess energy from its reaction wheels into the Earth’s magnetic field so it can stop pivoting when it aims. The further away you get from the planet the less effective that becomes. The bigger your object is, the bigger your reaction mass needs to be.

    And the Hubble doesn’t inherently roast or blind innocent bystanders as it swings its point of aim across all of the intervening space between its targets. Maintaining a steady shine on one particular point on the surface is one thing, but these idiots seem to be implying that they will sell sunlight-as-a-service via some kind of subscription model to multiple customers, so they would presumably be changing targets all the time.

    The Hubble can only rotate very slowly. Per the article, 90 degrees in about fifteen minutes. Its advantage is that it only looks at targets that are very far away and hold still relative to the Earth, so there is very little parallax to worry about. If you wanted to go faster you probably can’t use the reaction wheel method that it does; you’d have to use thrusters which would consume finite fuel that’d eventually (or quickly) run out, and at that rate there’s no way you could do it as accurately. For the Hubble specifically, the amount of time it takes to get on a target is broadly irrelevant, only that it can keep itself there once it eventually achieves targeting. This would not be so with the hypothetical solar reflectors, regardless of what altitude they were flown at. And low altitude orbits would be the worst, because they’d be flying over the target’s head at tens of thousands of miles per hour in terms of ground speed and would have to rotate very quickly in order to remain even vaguely pointed in the right direction.




  • First of all, I take a bit of umbrage at the author’s constant reference to “website size” without defining what this means until you dig into the FAQ. Just blithely referring to everything as “size” is a bit misleading, since I imagine most people would immediately assume size on disk which obviously makes no sense from a web browsing perspective. And indeed, they actually mean total data transferred on a page load.

    Also, basically all this does is punish sites that use images. I run an ecommerce website (and no, I’m not telling you lunatics which one) and mine absolutely would qualify handily, except… I have to provide product images. If I didn’t, my site would technically still “work” in a broad and objective sense, but my customers would stage a riot.

    A home page load on our site is just a shade over 2 megabytes transferred, the vast majority of which is product images. You can go ahead and run an online store that actually doesn’t present your customers any products on the landing page if you want to, and let me know how that works out for you.

    I don’t use any frameworks or external libraries or jQuery or any of that kind of bullshit that has to be pulled down on page load. Everything else is a paltry (these days) 115.33 kB. I’mna go ahead and point out that this is actually less to transfer than jabroni has got on his own landing page, which is 199.31 kB. That’s code and content only for both metrics, also not including his sole image — which is his favicon, and that is for some inexplicable reason given the circumstances a 512x512 .png. (I used the Firefox network profiler to generate these numbers.)



  • That’s the main hurdle.

    Re-finding this was a pain in the ass because I didn’t save it. https://lemmy.world/post/19485246/12219336

    Editing to add some more meandering. Now this is even longer than the first one.

    In addition to surface area limitations, there’s also a pretty obvious line of sight problem in that if your satellite is positioned such that its shiny side is facing the sun, by definition it must be facing the same direction as the Earth’s currently lighted side. The further past the dusk line onto the dark side of the Earth you’re trying to hit the further you have to rotate your mirror until ultimately the surface of it is perpendicular to the incoming sunlight. This is the angle of incidence, in optical terms, and it reduces the effective reflection not only off of the mirror proportionally to the increase in angle (in a roughly geometric manner, I believe) but also where that reflected beam of light hits the ground at its oblique angle. In real terms, it will be impossible to hit any target more than a few degrees past the dusk line with any meaningful amount of energy. Insofar as this harebrained scheme could possibly hit the ground with any amount of energy at all.

    The diagram (which is surely not to scale) on these idiots’ website seems to depict a mirror in orbit around the Earth that’s about the size of Massachusetts, which is orbiting at a height that’d put it somewhere in the vicinity of the Van Allen belt, which is also a bad idea (no radio communication for you!) and would result in an orbital period of around 2.5 hours. If so, that means your mirror is whizzing over the surface at something like 14,000 MPH, and you would have some kind of line of sight to it from the ground for maybe 25% of its orbit. So even with the best will in the world and absolutely mathematically perfect rotation control it’ll only be able to remain on a surface target for about 37 minutes at most, most of which would be while it’s uselessly passing through the Earth’s shadow and is reflecting no sunlight at all, and for the remaining handful of minutes with its effective output tapering off to uselessness as it sets over the opposite horizon.

    “I’ll just position my mirrors in a geostationary orbit,” says Mr. Clever. “Then I’ll have line of sight to a big chunk of the surface and my satellite won’t move relative to it.”

    Well, the further you park your mirrors from the surface, the harder they are to aim. You can’t have it both ways. A geostationary orbit is about 22,000 miles from the surface, a distance from which even the tiniest error in alignment will result in you hitting the wrong target. You can use some middle school trig to calculate this for yourself: At a distance of 22,000 miles, an alignment error of just 0.01 degrees will result in the centerline of your beam missing the target by four miles, which in terrestrial terms is what we refer to as kind of a lot. Maintaining an alignment precision that high especially taking into account gravitational perturbation by the moon, etc., is a rather tall order. To maintain targeting precision within 223 feet, which is probably already unacceptable, you need a constant alignment precision of 0.0001 degrees, and you need to hold it there 100% of the time.

    I don’t care how big your rocket is, that’s not happening.

    All of this also assumes perfectly flat and 100% reflective surfaces on the mirrors, which never degrades or gets scuffed up or punctured by space debris. Which is also impossible.

    To recap:

    • You can’t reflect any more energy than strikes the surface area of your mirrors, end of story. The mirrors will be tiny, relative to the size of the Earth, and the Earth is huge, relative to the size of any mirror we can launch.
    • The efficacy of your mirrors diminishes geometrically with how far you must angle them relative to the direction of incoming sunlight.
    • Most of the time your mirrors will either be in the Earth’s shadow, where they are useless, or over the already illuminated side of the Earth, where they’re pointless. In easily achievable low Earth orbits, their time on target will be very short.
    • Positioning the orbits high enough to mitigate either problem will make aiming mathematically impossible, and also magnify any imperfections in focus, which are certain to be vast. That won’t work either.

    TL;DR: The whole thing won’t work.




  • Not to be a stereotypically insufferable Stallman style neckbeard about it, but the only two objectively correct answers to this question are FreeCAD for mechanical parametric things, and Blender for organic shapes or decorative models. (You can also bully Blender into doing parametric CAD work with plugins. And I guess OpenSCAD also counts, if you would rather program your models rather than model your models.)

    All of the other available commercial options are some combination of:

    • Proprietary vendor lock-in bullshit
    • Subscription model “software as a service” perpetual money sinks
    • Always online cloud services that either steal your models/make them available to anyone/probably also report you to the Feds
    • Loaded with quasi-legal licensing restrictions that prevent you from distributing or selling your own creations made with it

    Or for extra bonus points, all of the above!

    FreeCAD isn’t exactly slick and it has a rather precipitous learning curve, but it’s also basically the only viable truly free option that won’t spy on you, steal your stuff, or turn you upside down and shake you for money on a monthly basis.






  • Sedici is one of Cycle Gear’s house brands, from before they were absorbed by Revzilla. It’s the “upgrade” line to their cheap shit Bilt stuff.

    FYI, the Tusk rackless luggage will beat the shit out of your rear plastics and if you’re the type of person who likes to keep everything clean and shiny, this will annoy you. It’s also a universal one-size-fits-none situation regardless of which setup you get (the X2 or “Highland” or the regular one) so you’ll spend quite some time puzzling over how to mount it and the setup always seems janky and gimcrack. It’s also a pain in the arse to remove and put back on.

    If you can countenance it, I would highly advise just getting a set of pannier racks and doing regular luggage, either soft or hard depending on your preference. It really won’t be that much more expensive at the end of the day and it’ll piss you off a lot less.

    I have the X2 “system” on my Orion RXB. It’s awful, and I’d never do it again.