zlsa's recent activity

  1. Comment on General-purpose OS, special-purpose OS, and now: vendor-purpose OS in ~comp

    zlsa
    Link Parent
    That’s a thing in iOS. The only difference is that you need to pipe all notifications through Apple’s servers, so devices don’t need to keep connections open to dozens of servers for push...

    That’s a thing in iOS. The only difference is that you need to pipe all notifications through Apple’s servers, so devices don’t need to keep connections open to dozens of servers for push notifications. If apps could specify notification URLs, your phone would need to either poll these endpoints (using up bandwidth) or keep the connections alive (which would also use bandwidth.)

    I don’t think any app code runs when push notifications are received, but I might be wrong as I haven’t ever implemented them.

  2. Comment on SpaceX launches 58 Starlink satellites on ninth Starlink launch, including three Planet SkySats in ~space

    zlsa
    Link Parent
    For context, where I currently live, the only options for internet are satellite or a point-to-point microwave link. The latter costs nearly $300 USD/month for 5mbps up/down.

    For context, where I currently live, the only options for internet are satellite or a point-to-point microwave link. The latter costs nearly $300 USD/month for 5mbps up/down.

    3 votes
  3. Comment on Recap: SpaceX successfully launches Crew Dragon with Bob Behnken & Doug Hurley on SpX Demo-2 mission to the ISS, restoring US spaceflight for the first time in nine years in ~space

    zlsa
    (edited )
    Link Parent
    My favorite fact about the Falcon 9 is the incredible speed of the Falcon 9 first stage when it's landing back on land. The launch pad and landing pad are about 10 miles apart (~16km) by road, and...
    • Exemplary

    My favorite fact about the Falcon 9 is the incredible speed of the Falcon 9 first stage when it's landing back on land. The launch pad and landing pad are about 10 miles apart (~16km) by road, and it takes the Falcon 9 first stage about 10 minutes after its launch to land on the landing pad. If you wanted to drive from the launch pad to the landing pad and beat the Falcon 9 first stage, you would need to drive at an average speed of at least 60mph.

    So the flight starts when the booster ignites its nine engines on the ground. These engines can produce a combined total of 1.7 million pounds of thrust (~7561 kN), able to lift of about 85 elephants (or a fully-fueled Falcon 9.) Around a minute into flight, as the vehicle breaks the sound barrier, the engines are all throttled down a little bit to reduce the forces on the vehicle (remember, it's flying at supersonic speeds through the relatively thick lower atmosphere; reducing thrust just a little bit can reduce the peak aerodynamic stress levels quite noticeably.) A few seconds later, as the atmosphere thins out again, the engines throttle back up to full thrust.

    The booster passes through Mach 5 on the way up, then shuts off its nine engines and separates from the upper stage (which makes its way into orbit with the payload.) The booster immediately flips itself around and fires the engines to invert its ground path (because it's flying Mach 5 in mostly the wrong direction.)

    While casually blowing through the Kármán line (100km altitude), it orients itself engines-down; then, a few minutes later (while it's falling back through the atmosphere at several times the speed of sound), it restarts three of its engines to slow itself down. If this entry burn isn't done, the booster would burn to pieces during re-entry. (Even though it's not going anywhere near as fast as spacecraft returning from orbit, the booster isn't shielded very well, so it needs to slow down using engine power.)

    After the entry burn ends, the booster uses its grid fins to glide towards the landing pad. The Falcon 9 booster flies much like a dart; the engines are extremely heavy, like the nose of a dart; and the grid fins (at the top) are like the fletching of a dart, keeping it pointed in the right direction; unlike a dart though, the grid fins work well even supersonic and transsonic, and they're movable as well (so the onboard computer can precisely aim the Falcon 9 as it falls.)

    Then, only about 10 seconds before it would hit the ground and explode, it restarts the center engine to slow itself down. A few seconds before touchdown, it unlocks and deploys the four landing legs, constantly adjusting the engine thrust to maintain its target of zero vertical velocity at touchdown. (Since the minimum thrust of a single engine is greater than the weight of the booster, it can't hover; and therefore must perform a 'suicide burn' to land safely.) Once it touches down, the engine is shut off, the launch director says "The Falcon has landed; landing operators move to procedure 10.100," and the propellant tanks are vented one-at-a-time to reduce pressures from 50psi to a lower level.

    Which is when the car rolls onto the pad. It's been driving 65mph for the last 10 minutes, and has now broken both the local speed limit and the obvious rule of not being near rockets in flight. That's how fast rockets are.

    18 votes
  4. Comment on Small satellite launcher Virgin Orbit plans to fly its rocket for the first time this weekend in ~space

  5. Comment on Purple lightning strike during a thunderstorm in ~creative

  6. Comment on Purple lightning strike during a thunderstorm in ~creative

    zlsa
    Link Parent
    Thank you! The purple tint (and glow) was there in reality as well; my editing was mostly just brightening the shadows and increasing the contrast a little bit.

    Thank you! The purple tint (and glow) was there in reality as well; my editing was mostly just brightening the shadows and increasing the contrast a little bit.

    1 vote
  7. Comment on Purple lightning strike during a thunderstorm in ~creative

    zlsa
    Link
    Story behind this photo: I saw the thunderstorm approaching in advance, and set up the camera on a tripod pointing in the right direction. Interval shooting was used, taking photos as fast as the...

    Story behind this photo:

    I saw the thunderstorm approaching in advance, and set up the camera on a tripod pointing in the right direction. Interval shooting was used, taking photos as fast as the software allows (one photo per second.) I set the aperture as small as possible, set the exposure a tad underexposed, pressed the shutter button, and crossed my fingers.

    I got a few lightning hits, each time moving the camera a little to aim at the most recent lightning bolt. Ironically, this is the first, and best, lightning photo I got during this session.


    Some more photos from the same thunderstorm: https://flic.kr/s/aHsmNjJMRs

    Shot with Sony α6400 and Sigma DC DN 30mm f/1.4 lens.

    Camera settings: 1/3 second exposure (the other photos are within 1/3s to 1.5s or so); f/16, ISO 100.


    These photos were all edited with Pixelmator Photo on iPad. The purple glow is exactly what I saw in reality, and in the RAW file, you can clearly see that the lightning bolt itself is massively overexposed.

    Let me know if posting photographs like this on Tildes is ok!

    8 votes
  8. Comment on What are your favourite Space Games? in ~games

    zlsa
    Link
    Elite Dangerous, often described as a trucking simulator in space. The gameplay hasn't ever been particularly complex or deep, but the atmosphere and sound design is second to none, especially...

    Elite Dangerous, often described as a trucking simulator in space. The gameplay hasn't ever been particularly complex or deep, but the atmosphere and sound design is second to none, especially when playing in VR.

    Space Engine, which is less a game and more an educational tool; it procedurally generates every star in the milky way (and other galaxies besides.)

    2 votes
  9. Exhaustive Markdown test

    This is a post in ~test about Tildes! (See also: the ~tildes group.) The author is @zlsa. Oh, I almost forgot to link to the Wikipedia article on Reaction Control Systems. Click to view the hidden...

    This is a post in ~test about Tildes! (See also: the ~tildes group.) The author is @zlsa.

    Oh, I almost forgot to link to the Wikipedia article on Reaction Control Systems.

    Click to view the hidden text

    Here's all the hidden text.

    It can have markdown in it too.

    H1: This is a very long header.

    H2: This one is just as long.

    H3: Short.

    H4: How do you even tell these apart!?

    H5: come on, this is nuts
    H6: Six levels deep. You need professional help.

    Blockquotes

    let x = 42;
    
    function transmogrify(value) {
        return value * 4
    }
    

    Now, if you run transmogrify(x), you get 167 168. Removing the strikethrough is left as an exercise for the reader (that's you.)


    There's some pretty advanced stuff going on here. The cars are almost self-driving; but full autonomy is at least 3 months away, if not 6.

    • Markdown unordered list support: check.
      1. Ordered list support: check.
      2. Yep, this works.
    • And back to the unordered list, as expected.

    Mountain Height of Summit
    Mount Everest 8,848m
    K2 8,611m

    And now for some minor features:

    • I forgot a word.
    • E = mc2 and H2O

    And now for something completely different.

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    Viral pug kitsch, celiac aesthetic kickstarter small batch chicharrones. Direct trade health goth viral chia actually meh cronut chicharrones. Thundercats man bun scenester VHS. Mumblecore mixtape kickstarter chartreuse pinterest cold-pressed. Leggings retro vice tumeric distillery jean shorts flexitarian, chicharrones narwhal.

    Copper mug gluten-free pickled, you probably haven't heard of them banh mi roof party pop-up coloring book brooklyn vexillologist 3 wolf moon keytar. Enamel pin chambray tbh taiyaki cardigan tumblr cold-pressed. Yuccie activated charcoal ugh, wolf chicharrones literally trust fund aesthetic tattooed vice cornhole polaroid. Selvage XOXO sriracha tacos +1 hashtag everyday carry.

    Dummy text? More like dummy thicc text, amirite?

    A1 B1 C1 D1 E1
    FANCYPANTS AWESOMELY COMPLEX TEXT FANCYPANTS AWESOMELY COMPLEX TEXT FANCYPANTS AWESOMELY COMPLEX TEXT FANCYPANTS AWESOMELY COMPLEX TEXT FANCYPANTS AWESOMELY COMPLEX TEXT
    5 votes
  10. Comment on Stripe is silently recording your movements on its customers' websites in ~comp

    zlsa
    Link Parent
    The HN thread has a comment from a Stripe customer who saw their fraud rate go from 2% to 0.5%: Opting out of mouse tracking and similarly invasive methods of fraud detection will make things more...

    The HN thread has a comment from a Stripe customer who saw their fraud rate go from 2% to 0.5%:

    As someone who saw this first hand, Stripe’s fraud detection really works. Fraudulent transactions went down from ~2% to under 0.5% on hundreds of thousands of transactions per month. And it very likely saved our business at a very critical phase.

    Opting out of mouse tracking and similarly invasive methods of fraud detection will make things more expensive, and while you may be willing to pay more, most people won't.

    7 votes
  11. Comment on Half-Life: Alyx review (spoiler-free): The greatest VR adventure game yet—and then some in ~games

    zlsa
    Link Parent
    I've used both Link (tethered to a PC with a 5-meter USB-C cable) and Virtual Desktop (a WiFi streaming solution), and Link is far better IMO. Virtual Desktop has persistent latency issues, making...

    I've used both Link (tethered to a PC with a 5-meter USB-C cable) and Virtual Desktop (a WiFi streaming solution), and Link is far better IMO. Virtual Desktop has persistent latency issues, making your hands in-game lag behind your real-life hands, making them feel rubbery and inconsistent. (There was a very recent Virtual Desktop update to reduce motion-to-photon latency even further; however, I haven't had a chance to try this yet.)

    And yes, Quest tracking is very very good. (It uses the same fundamental system as the Oculus Rift S, just with one less camera and a different camera layout.) However, any streaming solution (including Link and Virtual Desktop) won't be as high-fidelity as playing on a dedicated PCVR headset, like a WMR headset or the Oculus Rift S. There is always some degree of additional latency and video compression artifacts. While these are easily tolerable with the Link cable, I wouldn't say the quality is equal to that of a dedicated PCVR headset.

    Also, price is a factor: with the base-model Oculus Quest ($400 USD) plus the official USB-C Oculus Link cable ($80 USD, highly recommended for its flexibility and length), you're paying $130 USD more than the Rift S ($350 USD). If you only plan on playing PCVR, I strongly recommend against the Quest; but if you ever want to play standalone (i.e. somewhere where you don't have a PC), the Quest is the only viable option.

    2 votes
  12. Comment on Formula 1 Australian Grand Prix has been cancelled in ~sports

    zlsa
    Link
    It's been a crazy 24 hours in the runup to the Australian GP weekend, with McLaren pulling out after a team member tested positive for COVID-19, rumors going back and forth about the race being...

    It's been a crazy 24 hours in the runup to the Australian GP weekend, with McLaren pulling out after a team member tested positive for COVID-19, rumors going back and forth about the race being cancelled (including not letting spectators enter the stands for today's practice session,) reports of multiple drivers flying home, and finally an official cancellation. Check out the recent posts in r/Formula1 to see the scope of the situation (and this meme.)

    (Today was due to be a practice session, with qualifying on Saturday and the race itself on Sunday.)

    5 votes
  13. Comment on SpaceX launches final Dragon 1 mission to the ISS in ~space

    zlsa
    Link
    The recent launch of the CRS-20 ISS resupply mission for NASA is the last flight of the SpaceX Dragon 1 capsule. The specific Dragon capsule flying on this flight has already been to the ISS twice...

    The recent launch of the CRS-20 ISS resupply mission for NASA is the last flight of the SpaceX Dragon 1 capsule. The specific Dragon capsule flying on this flight has already been to the ISS twice before; on the CRS-10 and CRS-16 missions.

    SpaceX's next cargo flight to the ISS is CRS-21 in October, and will be flown with Dragon 2 (which has flown in the crew variant as DM-1.)

    The first-stage booster landing is the 50th successful landing by SpaceX (and would have been the 51st had the previous landing been successful; alas, due to faulty wind data, the booster intentionally diverted into the ocean to protect the droneship.) The trajectory of the launch (and booster return to launch site, or RTLS) can be clearly seen in this awesome photo. (You can even see the 1-3-1 engine transition in the entry burn.)

    3 votes
  14. Comment on What creative projects have you been working on? in ~creative

    zlsa
    Link
    I've been designing a 3D-printable model of a rocket (not a model rocket; this is just a mostly-accurate detailed replica, not a flyable model rocket.) One of my goals is to make the entire model...

    I've been designing a 3D-printable model of a rocket (not a model rocket; this is just a mostly-accurate detailed replica, not a flyable model rocket.) One of my goals is to make the entire model 3D-printable with a consumer-grade 3D printer, so anybody can build one at home. This leads to some inevitable parts where realism just can't be maintained (as the resolution of consumer FDM printers isn't high enough to allow for a perfect replica.) So I'm ending up spending a lot of time trying to keep the model as realistic as possible, while making sure it's still printable on normal 3D printers.

    It's a fun challenge, and I love the fast iteration time 3D printers can deliver: ~two hours from a CAD model to holding it in your hands.

    4 votes
  15. Comment on Half-Life: Alyx - 9 Minutes of Gameplay in ~games

    zlsa
    Link Parent
    That video made me nauseous, and I've had no problems even with smooth locomotion from day one. VR recordings always look like that; the video looks super shaky because the tracking captures every...

    That video made me nauseous, and I've had no problems even with smooth locomotion from day one. VR recordings always look like that; the video looks super shaky because the tracking captures every movement of your head. Being in a VR game looks nothing like the screen recordings.

    1 vote
  16. Comment on Half-Life: Alyx - 9 Minutes of Gameplay in ~games

    zlsa
    Link Parent
    The Valve Index is probably the best VR headset you can get today, and is priced accordingly. WMR headsets regularly sell for under $200 USD, and the Oculus Rift S is $350 USD. I wouldn't...

    The Valve Index is probably the best VR headset you can get today, and is priced accordingly. WMR headsets regularly sell for under $200 USD, and the Oculus Rift S is $350 USD. I wouldn't recommend the Valve Index over the Rift S for most people; sure, it's inarguably better, but not 2x better.

    1 vote
  17. Comment on What games have you been playing, and what's your opinion on them? in ~games

    zlsa
    Link Parent
    While it doesn't have the best racing dynamics, Project Cars 2 has undoubtedly the best realism and VR implementation out of all the simracing games IMO. If you enjoy zero-g movement, you might...

    While it doesn't have the best racing dynamics, Project Cars 2 has undoubtedly the best realism and VR implementation out of all the simracing games IMO.

    If you enjoy zero-g movement, you might enjoy Lone Echo and/or Echo Arena. Both of them are Oculus exclusives, but the movement implementation is second to none.

    1 vote