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Finding the B-21's hangar location from the stars in its press image

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Re: Finding the B-21's hangar location from the stars in its press image

#181

Post by gmiller123456 »

gmiller123456 wrote: post #151
gmiller123456 wrote: post #140

There's a few highly suspect details in the way the author got the 34-35 degree estimate. Maybe he was just really lucky and the errors cancelled out, but don't count on using his method to produce similar results. Polaris is about .8 degrees away from the celestial North pole, so using it alone can give a reading off by .8 degrees, and the orientation in the photo is actually nearing the worst case. The horizon does…

I extended many of the assumed parallel lines in the photo, and they all tend to converge just below and to the right of the nose of the plane. And using the known distance between two of the stars to estimate the degrees per pixel, I get a margin of error of about 4 degrees vertically estimating where the horizon is.

For what it's worth, I measured the pixels between Kochab and Pherkad and got .0161 degress per pixel. Then measured from Polaris to my visual guestimate of where the horizon should be and got 34.14 deg, about half a degree off of the real location.

I'd be interested to see what others get. For those not familiar with the stars, Polaris is just a few pixels from the top edge, nearly dead center (it's close enough to the top that you can just use the top edge of the photo as a reference). If you start with a photo the same size I did (4096x2731), you can just crop the photo from top down to where you think the horizon is, then look at the size of the resulting image, multiply the vertical pixels by .0161, and post the answer below.

Re: Finding the B-21's hangar location from the stars in its press image

#182

Post by baxtr »

jaxomlotus wrote: post #154
gmiller123456 wrote: post #140

There's a few highly suspect details in the way the author got the 34-35 degree estimate. Maybe he was just really lucky and the errors cancelled out, but don't count on using his method to produce similar results. Polaris is about .8 degrees away from the celestial North pole, so using it alone can give a reading off by .8 degrees, and the orientation in the photo is actually nearing the worst case. The horizon does…

If I were a betting man I would assume he started this exercise with the final assumed location in mind, and worked backwards from there to show how it could have been done.

That's actually what he was implying in his last tweet:

> The press conference to reveal the aircraft was held here last week so we can confirm the location. A guess likely would have landed someone in the same location but fun anyway to star match. I'm sure this entire process could be done with just stars and no google maps as well

Re: Finding the B-21's hangar location from the stars in its press image

#183

Post by thunderbird120 »

justsomehnguy wrote: post #179
thunderbird120 wrote: post #116

Earlier quoted context omitted.

I doubt it. The B-2 was cut because the cold war ended and because it was absurdly expensive to maintain thanks to its 1980s stealth tech. The radar-absorbent material used for the B-2 degraded very quickly and it's a large aircraft, so that means absolutely constant work to keep it functioning as intended. The B-2s are based out of Missouri and when they go on a mission they fly all the way to the other side of the…

> and no one to use them against Oh, you can use them just as they were used - to do the things B-52, or hell, even B-29 could do. /snark > being hunted by a bunch of nearly undetectable aircraft which can be anywhere at anytime and can each carry more than a dozen large anti-ship missiles Now this is a question. My memory was rusty so I consulted Wikipedia and looks like there is not that many options. SM6 is too we…

The near term anti-ship armament would be LRASMs, which are not actually very large. A B-1 can carry 24 of them internally at one time and the B-2 can carry 16. The B-21 is smaller but still large enough for a good load. 12 or more would not be surprising. No one is air-launching tomahawks or SM-6s (probably). The future is OASuW Increment II (HALO) which is a hypersonic anti-ship missile. The LRASM is basically a stop-gap until that happens. That missile will likely be a similar size to the LRASM given the size limitations of the platforms the navy wants to launch it from.

The security situation in the Pacific is also very unlikely to improve over the next 10 years.

Re: Finding the B-21's hangar location from the stars in its press image

#184

Post by dakr »

mierle wrote: post #26

Wow, it's cool to see astrometry.net get put to use! I worked on astrometry.net back in undergrad and grad school. If you have questions about how it works, I can answer them. How does it work? astrometry.net uses 4-star combinations to define codes, then indexes the codes on the celestial sphere. The particulars of each of these phases matter, but that's the basic idea.

I remember my jaw dropping while sitting in a colloquium hearing about astrometry.net from David Hogg back in ...2007?

Fast forwarding a few years, we started using it at SOFIA Observatory to help speed up telescope acquisitions.

Re: Finding the B-21's hangar location from the stars in its press image

#185

Post by pifm_guy »

gateorade wrote: post #158
protastus wrote: post #125

Earlier quoted context omitted.

The claims from pifm_guy are reasonable. This is a scenario with extremely high coding gain[1]. The DC value of the sky can be removed by high pass filtering. Finding the rigid transform (rotation+translation) between two images captured by the same camera, assuming no distortion[2], assuming the image pair has substantial intersection, doesn't require calibration. Dropping the "same camera" and "substantial intersec…

I’m not trying to call you guys out. Just curious for more information. I would say I have enough knowledge about signal processing to be dangerous, as it’s quite adjacent to my job. But this isn’t clicking with me. Assuming we’re not including cameras outside the visible light spectrum, are there cameras that actually have enough dynamic range to capture a recoverable amount of information about stars against a brig…

> oversampling, but oversampling of what exactly?

If you have 3 million pixels of sky, and 3 variables to find, then you have oversampled by 1 million times.

In the ideal noise-free world with no other unknowns, any 3 of those pixels would be enough to solve the problem perfectly.

Re: Finding the B-21's hangar location from the stars in its press image

#186

Post by sumofproducts »

whywhywouldyou wrote: post #171
gmiller123456 wrote: post #140

There's a few highly suspect details in the way the author got the 34-35 degree estimate. Maybe he was just really lucky and the errors cancelled out, but don't count on using his method to produce similar results. Polaris is about .8 degrees away from the celestial North pole, so using it alone can give a reading off by .8 degrees, and the orientation in the photo is actually nearing the worst case. The horizon does…

I'm sure you're correct, as the whole thing reads like "look how smart I am". 1. Extraneous details about satellites not being overhead at night -- as if government spy satellites operate on the same schedule with the same priorities as publicly known satellites. 2. Mentions things like them not scrubbing the EXIF data was a "mistake". How could it be a mistake if this was public information? 3. Says at the end "(thi…

> as if government spy satellites operate on the same schedule with the same priorities as publicly known satellites.

This bit, at least, is more or less the case. Even if you spend some fuel to alter your orbit and throw people off for a bit, you can't do anything major over the course of a few hours without sci-fi engines.

Re: Finding the B-21's hangar location from the stars in its press image

#187

Post by protastus »

gateorade wrote: post #158
protastus wrote: post #125

Earlier quoted context omitted.

The claims from pifm_guy are reasonable. This is a scenario with extremely high coding gain[1]. The DC value of the sky can be removed by high pass filtering. Finding the rigid transform (rotation+translation) between two images captured by the same camera, assuming no distortion[2], assuming the image pair has substantial intersection, doesn't require calibration. Dropping the "same camera" and "substantial intersec…

I’m not trying to call you guys out. Just curious for more information. I would say I have enough knowledge about signal processing to be dangerous, as it’s quite adjacent to my job. But this isn’t clicking with me. Assuming we’re not including cameras outside the visible light spectrum, are there cameras that actually have enough dynamic range to capture a recoverable amount of information about stars against a brig…

About planets and stars in daytime: https://www.skysurfer.eu/daystars.php

The concept here is processing gain, which is algorithmic. It's what enables the miracle of GPS, even though satellites are 20000km far away, there may be clouds, rain, etc and your phone doesn't come with a satellite dish. Also used in CDMA radio for civilian and military communications, it allows reliable transmission at negative SNR by spreading the message over a huge space. In the case of GPS/radio, the space is frequency. Here, the message is coordinates of a rectangular crop of the sky, encoded in the (huge) space of few million pixels. On a per-pixel basis, the SNR can be negative -- looking at a single pixel I can't tell you with confidence if it contains a star, because the shade of blue is just too close to average. But correlating the entire image against the correct "code" (a clean star field), tells me whether I got the location of the sky correctly. Intuitively: accumulated over the entire image, the noise statistics are such that the noise stays bounded, and the tiny amount of signal adds up.

Appropriate optics will increase the SNR so that bright stars can actually become visible. Per the link above, mag 2-3 stars are visible with a 10cm telescope (looking through the eyepiece; no filters or digital sensors needed). So if the conditions are right and the optics are good, you may actually see a few stars reliably, and the scenario reduces to the B-21 hangar scenario.

Finally, it's worth noting that even a consumer grade CMOS sensor will sample at 12 bits per pixel (4096 linear levels) with low noise. The human eye cannot discriminate a luminance difference of 1/4096 relative to full scale, not even close. Using the naked eye for intuition here is misleading, because this is a scenario where a sensor is far better at registering the small additive contribution of a star under daylight, and this is the key to enabling the processing gain through math.

Re: Finding the B-21's hangar location from the stars in its press image

#188

Post by texasbigdata »

gateorade wrote: post #153
microsoftdoes wrote: post #149

Earlier quoted context omitted.

Interesting. So do you think the author had inside information on the location?

The fact that the b21 is being built at plant 42 in Palmdale has been public info for literal years.

And they had the press release there lmao

Re: Finding the B-21's hangar location from the stars in its press image

#189

Post by jabl »

Rebelgecko wrote: post #41
NikolaNovak wrote: post #33

Related unrelated question : how come this is public? F117 was a dark skunk project shown years after being operational. That made sense to me for a super secret project with wildly new technologies and capabilities. I don't understand the announcements of such projects from the vision stage, with the details of capability, purpose, strategy, photos,etc. Is it commoditized sufficiently? Is it deterrence? Is there eno…

The secretary of defense mentioned "deterrence" as part of the reasoning. Maybe not-so-coincidentally, the aircraft (at least as they showed it) skips the old school black paint job for one that looks more like anti-flash white[0]. Part of it is probably also that this is a refinement of an existing aircraft and not anything with drastically different capabilities-- if you're planning on war with the US, you're proba…

Looks more like a typical gray color that practically all Western air forces use today, than anti-flash white. I'd speculate the implications of this are:

- They plan on operating it during the day as well as night, so they need better protection against visual observation?

- The B2 was much darker due to the coating technology it used wasn't compatible with lighter grays? And operating only at night it didn't really matter?

Re: Finding the B-21's hangar location from the stars in its press image

#190

Post by jabl »

ForHackernews wrote: post #39
NikolaNovak wrote: post #33

Related unrelated question : how come this is public? F117 was a dark skunk project shown years after being operational. That made sense to me for a super secret project with wildly new technologies and capabilities. I don't understand the announcements of such projects from the vision stage, with the details of capability, purpose, strategy, photos,etc. Is it commoditized sufficiently? Is it deterrence? Is there eno…

I've read some things that suggest the B-21 may not offer radical new capabilities (over say, the B-2) but it will be way way cheaper to build and operate. There were only 21 B-2s ever built. The Air Force has already ordered 100 B-21s.

From what I've read (which I guess is largely speculation, although by people more familiar with the topic than me), the B-21 doesn't really push the envelope. The only really new thing is the airframe itself, but that largely piggybacks on stealth technology development over the past several decades (RAM coatings, shaping etc.) compared to the B-2, and not some entirely new R&D done only for the purpose of the B-21 program. The engines apparently come from the F-35, but obviously without the afterburners (an entirely sensible choice considering the F-35 is supposed to be manufactured in very large numbers and supported for a long time into the future). Electronics is supposedly stuff already developed. Etc. etc.

If true, then yes, the B-21 has potential to be relatively cheap to build and operate.

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