Hackaday Links: February 26, 2023

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It’s probably safe to say that most of us have had enough of the Great Balloon Follies to last the rest of 2023 and well beyond. It’s been a week or two since anything untoward was spotted over the US and subsequently blasted into shrapnel, at least that we know of, so we can probably put this whole thing behind us.

But as a parting gift, we present what has to be the best selfie of the year — a photo by the pilot of a U-2 spy plane of the balloon that started it all. Assuming no manipulation or trickery, the photo is remarkable; not only does it capture the U-2 pilot doing a high-altitude flyby of the balloon, but it shows the shadow cast by the spy plane on the surface of the balloon.

The photo also illustrates the enormity of this thing; someone with better math skills than us could probably figure out the exact size of the balloon from the apparent size of the U-2 shadow, in fact.

On the other hand, maybe you’re not sick of the whole balloon thing and you pine for the days when the sky was filled with them. Spoiler alert: it always was, and still is. Between the hundreds of radiosondes sent up twice a day every day to the hundreds of “pico balloons” that amateurs launch just for fun, there’s a lot of stuff floating around up there. And if you’d like a simulation of where one of these balloons might end up, check out the Spy Balloon Simulator. You can spawn a balloon onto the globe at any point and see where it would end up based on historic weather data. The simulation seems to make some assumptions about altitude, and the launch date seems fixed at November 11, 2022, so there are significant limitations. But it says right up front that it’s just for fun, and it is indeed cool to see that almost every path gets into a gyre of some kind, where the balloon just gets stuck before continuing.

In astronomy news, while the James Webb gets most of the attention these days, there are a lot of other telescopes doing fascinating work too. And one of them has captured one of the most amazing images we’ve seen — direct images of a bright exoplanet orbiting its star. Normally, exoplanets are observed indirectly, by watching for the subtle dip in a star’s brightness as the planet passes between it and us, for example. But this time, the aptly named Very Large Telescope in Chile used its adaptive optics to blot out the light from star AF Leporis in the constellation Lepus (we’d never heard of it either) and directly see one of the system’s planets.

The planet is a whopper, about five or six times the size of Jupiter, which is really big considering the star is only about the size of the Sun. What’s more, the whole system is almost brand new — only about 24 million years old and only about 87 light-years away. So looking at this system is an almost real-time look at both stellar and planetary formation.

And finally, with so few brick and mortar electronic surplus stores left, it’s sad to hear of yet another one falling on hard times. It seems like that’s the way of things, though, so we weren’t surprised to hear of yet another long-time surplus dealer feeling the pinch of reality.

P&T Surplus, located in Kingston, NY, has been a fixture of the local scene for decades. Located close to where IBM had a cluster of factories, P&T was well-positioned to buy scrap machines, excess materials, and large lots of overstock parts and resell them to a broad customer base. Over the years, though, factories closed and shut down source after source of surplus, and the customer base changed too. Squeezed from both sides and suffering from illnesses, the owners are now behind on their rent and have turned to crowdsourcing to hopefully get them over the hump. If you’re in the area, now might be a good time to stop by and see if there’s anything you need.

32 thoughts on “Hackaday Links: February 26, 2023

    1. Gradually would be very very slow potentially (since the ballon is not under pressure and large), and they wanted it to fall quickly (so it came down somewhat predictable in shallow-ish US waters)

          1. Those bullets were last used, by RFC pilots during the First World War. And indeed for balloon bursting. In fact one did and oddly enough he became an Ace for taking down fighters on the other side who also had up these balloons.

      1. Possibly stupid question, but can’t you just… No, drones with C4 won’t work, it’s too high up. Uhh, how about… Nope. Definitely. I do not want a knife missile missing the target… Shooting it won’t work…. How about just flying a dart into it… Wait… Isn’t that just a missile? The US could have also possibly used a dummy missile, and just made a huge puncture.

      2. Remember this is a low pressure balloon with a huge area, as big as 300 in diameter, so it’s not going to “pop” like a party balloon.
        How big of a hole does a 20mm projectile make? Remember, a F-35 only carries 700 rounds max. How big is the area of the balloon? How many holes are needed to take a large balloon down?
        The answer are a hell of a lot more holes are needed to take a balloon down that you could ever make. 200 F-35s couldn’t make enough holes.

    2. Actually that had been seriously worried-at by the News media companies. And by all of the crowd in here. I don’t know either, before you ask.

      However the pico balloons are another story.

    3. The USAF loves to try their pilots and hardware out on targets they aren’t trained/designed to hit, just to see how well they perform. There’s been more than one case where a high-tech military was unable to adapt well to guerilla warfare, for example. So in that respect, I’d say the knowledge gained was worth the cost of a missile.

  1. If you knew the size of a U2 Spy Plane, and you assumed the Sun was a point source you might be able to estimate the size of the Balloon. But to estimate its height you might also need to know the altitude of the U2 Spy Plane.

    If the Sun were a spot source, then the shadow of the spy plane would expand slowly. And the image of the plane on the Balloon would grow as it moves away from the plane. But you don’t know the size of the Balloon. So you assume that the shadow of the plane is the same size as the plane to estimate the size of the Balloon. No information is left to estimate anything else including the height.

    We need more information than that supplied in the image. In statistics if dF is 1 you are done. You can not extract any more information. You need at least two points to define a line.

    In systems if the matrix A = matrix B * matrix C then if matrix B has a magnitude of zero then the inverse of matrix B does not exist. There is more than one solution. You can not calculate inv(B) to use inv(B) * A = C and find a unique solution to C.

    So to calculate the height of the balloon only based on the image you would need to at least be smarter than me. I’m not a Mathematician or a Physicist. Just a curious EE.

    1. You might be able to extract all of this information, by just looking at the shadow. Essentially, a spot light projects the same shadow as a point source, except the shadow has a circular blur filter attached to it. This just means making an outline of the faintest hint of a shadow, and the innermost part of the shadow.
      I’ve done this kind of stuff before, and basically none of it requires a physics or math degree, just practice. (Experience: Reconstructing a trail bulletin from a few photos, basic calculus, and lots of geometry.)

      By measuring the length of the shadow, and assuming the balloon is a flat plane normal to the axis (which is valid here, because the curvature has little effect at this distance),
      I get a distance of 401 px (Not the true measurement, because I’m doing it zoomed in)
      A Lockheed U-2 is 63 feet long, so we get a feet-per-pixel of 0.157 ft/px

      Measuring the girth of the balloon, we get about 331 px.
      Multiplying by the ratio earlier, we get *drumroll* 52 feet in diameter. This is likely intended to be 15.5 meters, or 50 feet.
      The rest of the dimensions, including carrying capacity, left as an exercise to the reader.

      1. How did you get a 63 foot shadow to be about 25 feet long? Did you drop a decimal point. Here, I’ll use a slide rule …..140 feet in diameter. (The wing looks close enough to being on the line between the U2 and the balloon and the balloon and U2 are on a radius from the Sun so foreshortening of the shadow is minimal and the projection of the U2 on the balloon is the same as a flat disk from the camera’s perspective.)

      2. Your balloon girth measurement is smaller than the plane measurement, which does not compute. Just eye-balling it one can see that the balloon is about twice as large in diameter as the plane is long. A quick measurement shows me it’s about 2.22 times larger, yielding a balloon diameter of about 140 feet. Again, this assumes that the plane’s shadow projection matches its length.

    2. Light arriving from the sun, at 1 Au, for all practical purposes here might as well be considered parallel rays, so the length of the shadow is pretty close to the actual plane, given some penumbra due to the distance between the plane and the balloon. The U2s longitudinal axis is not perpendicular to the line of sight, so some foreshortening should be taken into account, removing a few feet from the planes length. Dropping the shadow to the centerline across the balloons circle looks pretty close to being 1 radii, so, ballpark I’m seeing this things got to be in the neighborhood of 120 feet across.

    3. All of this still assumes the photo isn’t faked. Note that the U-2 is above the balloon, which, if faked, would mean that the Air Force wants to assure whoever sees this picture that a U-2 can fly higher than some Chinese-ass balloon. But keep this in mind: the higher a plane flies, the faster it has to go to maintain enough lift to hold altitude. Knowing that, is it realistic to believe that the pilot managed to take a picture just as his shadow was on the top of the balloon, considering how short a time that shadow would take to cross the balloon? And that the shadow has no trace of motion blur? I’ve had the shadow of an airliner flash over me, and there is virtually zero chance of getting a sharp picture of that! Which, if the photo wasn’t faked, is pretty impressive in itself.

      As for the distance to the plane, I don’t want to do the math, but due to the convergence of the edges of a penumbra as you get further away from the object casting the shadow, the fact that there is a dark core to the image says that the plane is pretty close to the balloon, since its fuselage and vertical fin are completely blocking the Sun at those points on the balloon in solid shadow. I’ve watched the shadow of an airliner on the ground on final approach, and saw about this distinct a shadow at maybe 200-300 ft altitude. This would have to be scaled down to the size of a U-2 compared with a 737, which gives me a number of approximately “real close”.

      1. It could be a frame from a video, so timing would just be a matter of choosing the right frame. Given that the scene has lots of light, it would have a high shutter speed, so no motion blur seems reasonable.

        1. Yeah, a U2 pilot isn’t twisting sideways with his cellphone taking selfies. Those things have the best camera systems in existence in them, with sideways and downwards imaging. In the 1960’s they were capable of reading license plates from 10 miles away (and by away I mean above.) I bet their main issue in releasing this was trying to figure out how to downgrade the picture sufficiently to not give away information on just how good their imaging capability is.
          We know the U2 can fly at FL70. It may be able to fly higher than that. There are a surprising number of aircraft capable of overflying a balloon at FL60, which is where it was reported as flying. Most of the aircraft that can do that aren’t operational anymore, but they did exist. The A12 routinely cruised at FL90.

          1. The U2s imaging equipment does not take pictures from inside the cockpit. This was taken by the pilot. Likely the best single image from a series of rapid shots.

          2. Of course! He must have had very specific instructions:
            1) Show that you are above the balloon.
            2) Show that you are in an airplane.
            3) Show the wing so it can be identified as a U-2.
            4) If possible, get the shadow of the plane on the balloon, or at least a picture from a position where it would be plausible for this shadow to exist.

            All of this for the purpose of showing that we took it down with a 70-year-old manned aircraft, without giving up any information about the U-2’s imaging capabilities. If we could do a moon landing in 1969, or even better, fake one, we can do this!

          3. @BrightBlueJim yes the plane is indeed that old. But it travels unarmed. It’s a photo recon bird. However I’m still trying to grok the ideas that the balloon was sent and what was it gathering.

        1. Cruise speed of U2 is like 475 mph. But at 70,000 ft that’s well over 1000 mph ground speed. Zero chance a single selfie from cockpit could capture shadow on the balloon unless the balloon is also going super fast in jet stream. In that case the closing speed could be more near the stall speed of the aircraft which, using SWAG method without knowing and being to lazy to look up *minimum airspeed could still be around 100kt IAS which still seems approximately impossible.
          Also suspicious- any military pilot flying aircraft that probably still has classified flight and surveillance characteristics would be severely disciplined for releasing such a photo. Unless, as proposed above it is part of a sort of counter-PR stunt by military itself.
          For comparison in WWII Germany had weird vertical guns mounted in fighters that were functionally useless without a optics-mechanical light sensor thing. So taking this selfie seems pretty unlikely.

          1. I looked into it anyway. Lots of hand-waving and assumptions, but bear with me. Stall speed for the U2 aircraft is about 75 kt, probably Indicated Air Speed (AIS) which at 60-70k ft is still about twice that in terms of ground speed. Even accounting for that, just above stall speed and at a bank angle of an estimated 30 degrees from the photo, the radius of the turn is like 300 ft, give or take. Note that stall speed is assumed straight and level flight, so there is some fudging of numbers to make all of this work. If we are saying the balloon itself is 120ft across, then the pilot could circle the balloon from pretty darn close. From flying gliders, it actually seems pretty reasonable that a skilled pilot could “slowly” circle around the balloon and line up that photo. I’d also guess that the pilot did exactly that on the mission- circle the thing endlessly at as close a range as possible to gather intel. The U2, basically a powered glider with really long high aspect ratio wings, would be perfectly suited for this, actually. I’ll go back on what I said before and label this “plausible.”

  2. I found this week’s edition of Hackaday Links to be particularly interesting! The article about the open-source ventilator caught my attention as it showcases how the maker community can come together to solve real-world problems. It’s inspiring to see how people with different backgrounds and skill sets can collaborate and make a difference.

    I also enjoyed reading about the RetroArch emulator and how it can be used to play classic games on modern hardware. It’s great to see that old games can still be enjoyed on new devices, and it’s a testament to the longevity of the games themselves.

  3. Small gage piano wire! If small enough gage it shouldn’t fry the grid below but slice or mangle and load down that wispy bogie at those speeds. Maybe multiple strands.

    Whose balloons caused the greatest damage on earth? The Brit’s balloon blitz at the beginning of WW2. Didn’t do well with the Axis or neutrals, even came back home and bit a few butts. Heavy gage piano wire, yeah that’s what they used. Imagine if NWS balloons carried long trails of piano wire, instead of a radiosonde.

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