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Decades-Old Mystery Put to Rest: Why Are There X's in the Desert?

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Re: Decades-Old Mystery Put to Rest: Why Are There X's in the Desert?

#41

Post by dredmorbius »

tjohns wrote: post #30
dredmorbius wrote: post #18

The Corona project. A/K/A the KeyHole satellites. If my count is right, 135 satellite launches, though not all were successful. Fun fact: this was the early 1960s. CCD technology and IP transmission bitrates were a bit primitive[1], so the film cameras would eject capsules after they'd been shot, which would re-enter the atmosphere and be recovered, most through mid-air retrieval. The project was active from 1959 to…

Nitpicking here, but I think even most modern satellites don't use IP for their downlinks. I suspect something like X.25 is used instead for digital data, if not something even more bespoke... and many satellites still send analog data. For example, this is the protocol used for NOAA weather satellites (and actually was developed in the 60s): https://en.wikipedia.org/wiki/Automatic_picture_transmission

That was a flip bit of stage-setting.

I know little about space data transmission (though I vaguely recall some good discussion around the time of the New Horizons Pluto contact), but yes, it's been a mix of analog transmissions (initially) and digital, of various descriptions. I believe there is an IP-based transmission support for the ISS, though I wouldn't swear to that.

One of the zaniest image transmission protocols was for the early Soviet lunar missions, Luna 3. Again, film cameras, an in-spacecraft photo processing lab, and a TV camera to read off the film image and transmit it back to Earth. The image quality wasn't much, but it was the first imagery of the Lunar farside ever received.

https://en.m.wikipedia.org/wiki/Luna_3

A few years back there was a story of the National Geographic lunar map timed to coincide (well, a month late) with the December, 1968, Apollo 8 mission, the first manned flight around the Moon (though without a landing). This gave us the famous Earthrise photograph, and the Christmas Day broadcast from Apollo. The story of the map, and how rapidly the Lunar far side went from terra incognito (well, luna incognito) to mapped in detail was pretty staggering. I had that map as a kid, and just figured "we knew all that". Sometimes it takes growing up to see things with childlike wonder....

The story:

http://kelsocartography.com/blog/?p=1481

http://kelsocartography.com/blog/?p=1588

(Pretty sure that's made HN at some point.)

Re: Decades-Old Mystery Put to Rest: Why Are There X's in the Desert?

#42

Post by HeyLaughingBoy »

mabbo wrote: post #31
zerooneinfinity wrote: post #23

Can someone explain to my dumbass how they helped calibrate the photos or satellites?

Okay, I just spent 20 minutes trying to figure that out and I'm still not very far. These were film cameras, so the computer on board can't look through the camera and see if the objects are in focus, can they?

Well, I'm going to assume there was no actual "computer" on board...

However, a sharply focused image has more high-frequency components than a poorly focused one, so some sort of frequency discriminator (a technology from the 1920's IIRC) could possibly suffice to check and adjust focus. Remember that we've had sophisticated servomechanisms since WW2 so the feedback theory to do this was already well known.

But that's just a guess...

Re: Decades-Old Mystery Put to Rest: Why Are There X's in the Desert?

#43

Post by sago »

snovv_crash wrote: post #40
sago wrote: post #20

Earlier quoted context omitted.

https://www.google.com/maps/d/u/0/viewer?mid=1IudNrZA1xnpWjK...

The description there implies that the other crosses no longer remain, but I was able to find the first 3 I looked for just by looking for midpoints between other markers on the grid.

Yes, it definitely doesn't have them all. I've found more too. Perhaps the map maker got bored.

Re: Decades-Old Mystery Put to Rest: Why Are There X's in the Desert?

#45

Post by grkvlt »

Also interesting are the resolution targets, using sets of black and white bars at varying widths in both X any X orientation, to determine the spatial resolution i.e. how high frequency a component could still be imaged separately as lines, similar to TV test cards. These are discussed in various blogs [1][2] with some amazing picures. I think these were for both satellite imaging and spy-plane (U2 and SR-71 plus less exotic surveillance systems) and not just the USA. This article [3] shows some satellite test targets in the Gobi desert, presumable for Chinese (PRC) spy satellites, and also has a cool picture of the world's largest compass rose, at Edwards dry lake bed, as well as explaining the crosses from the original article, and talking about radar altimeter targets (another dry-lake bed) that are mapped to centimetre accuracy in altitude for calibrating GPS and other systems.

I find it a really interesting area of industrial/scientific archaeology, with some fascinating stories.

[1] http://www.clui.org/newsletter/winter-2013/photo-calibration... [2] http://www.bldgblog.com/2013/02/optical-calibration-targets/ [3] http://www.atlasobscura.com/articles/landscapes-made-for-sat...

Re: Decades-Old Mystery Put to Rest: Why Are There X's in the Desert?

#46

Post by cyberferret »

nitrogen wrote: post #26
Bronze_Colossus wrote: post #12

Earlier quoted context omitted.

Here is a few more picture more: http://www.messynessychic.com/2013/11/15/the-forgotten-giant... I also find these kind of things cool. Forgotten structures that once served an important roll but now are mostly forgotten.

Interesting story and cool photos. Couldn't get to the end due to website design issues. Were these for horseback delivery or for airplanes? Terrible, terrible UX in the form of a jittery delayed popover that fills the entire phone screen. If you are going to do this (and I can't stand the fact that it actually works on many people), make it so easy to dismiss and fast to load that I close it instead of instictively…

For the air mail planes that used to fly through the night. Most of those arrows were painted in luminescent paint, and had a light tower nearby shining down on it so that the arrow glowed and was highly visible to the poor cold, tired mail plane pilot above.

Re: Decades-Old Mystery Put to Rest: Why Are There X's in the Desert?

#47

Post by kweks »

grkvlt wrote: post #45

Also interesting are the resolution targets, using sets of black and white bars at varying widths in both X any X orientation, to determine the spatial resolution i.e. how high frequency a component could still be imaged separately as lines, similar to TV test cards. These are discussed in various blogs [1][2] with some amazing picures. I think these were for both satellite imaging and spy-plane (U2 and SR-71 plus le…

I recently visited the Chinese ones. It tools a good day or so of driving off road (after two weeks of driving to get into the area) to reach them.

Totally in the middle of nowhere, and quite amazing to see.

Re: Decades-Old Mystery Put to Rest: Why Are There X's in the Desert?

#48

Post by Swizec »

grkvlt wrote: post #45

Also interesting are the resolution targets, using sets of black and white bars at varying widths in both X any X orientation, to determine the spatial resolution i.e. how high frequency a component could still be imaged separately as lines, similar to TV test cards. These are discussed in various blogs [1][2] with some amazing picures. I think these were for both satellite imaging and spy-plane (U2 and SR-71 plus le…

Future archeologists are going to have so much fun with these. They're not gonna say it's aliens, but it'll def have been aliens.
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