Having worked on a lot of the successors to Corona, I was surprised to see a full exhibit (including hardware) on display at the Smithsonian Udvar-Hazy Center near D.C.

Corona itself is completely unclassified now.

https://airandspace.si.edu/udvar-hazy-center

https://airandspace.si.edu/multimedia-gallery/si-97-15881-10...

https://airandspace.si.edu/multimedia-gallery/web10844-2008h...

Google Maps link with sites marked: https://www.google.com/maps/d/u/0/viewer?mid=1IudNrZA1xnpWjK...

I always thought they just used the enormous letters that spell out the name of the state, after they were placed there for the photo that goes in atlases and on globes.

The article says the exact opposite of that. Those marks weren't used for satellites.

> The idea that the Casa Grande range was developed for the CORONA program is asinine when looking at the timelines of range construction...

People really need to pay more attention to timelines. It's a pretty frequent occurrence that someone posts some pet theory of theirs, with links to support it, but the support evaporates (or is greatly weakened) when you actually look at the dates of their sources (e.g. trying to claim a news source is not credible because they reported then-reasonable speculative estimates in a time of great uncertainty (and were clear about what they were) that were contradicted years later by a more careful scientific study).

There is substantial public documentation of the extensive system of calibration targets that were built for CORONA and subsequent satellite programs, such that it's hard to imagine why so much confusion seems to exist in this area. In fact Arizona was used for both, but satellite imaging calibration targets of various types are found in California and throughout the country. The most extensive system of photogrammetric calibration targets in the US is at Edwards AFB, where features include 10 mile reference rulers. Smaller references were sometimes just painted on the tarmac at air force bases for simplicity.

That said, these kinds of things are, necessarily, obvious and accessible to anyone. Calibration targets built for various programs are sometimes used for other programs, sometimes even by rival nations, simply because they're known to be there and it's easier to use something in place than to build something new. The fact that nearly all of these programs operated under great secrecy and before retention of classified records was typical (there were not yet as extensive of records retention mandates applicable to classified programs) means that the details can now be somewhat obscure, just because all of the original documentation was destroyed or lost after the program closed.

An interesting variety of calibration targets are those intended for radar (SAR) use, since they take the form of 3D shapes rather than 2D images. Since SAR is a much more recent technical development in remote sensing there are far fewer public details, but various military and contractor installations have included, at times, oddly carefully sculpted gravel piles that are assumed to serve this purpose. An example is at the former Lockheed site in Potrero Canyon near Beaumont, CA.

Many of the images covering the US taken by CORONA and several subsequent programs, mostly for calibration or testing but sometimes by error, were declassified under Clinton-era rules and given to the USGS. You can now browse them as part of USGS's general aerial imagery collection. The resolution is insufficient for most modern uses (the USGS's collection of agricultural aerial survey photos is far more useful), but they're unrivaled in the sheer land area they cover in one large frame.

There are still some calibration pads at Stennis Space Center leftover from their heyday in remote sensing support:

https://www.google.com/maps/@30.3689672,-89.5662234,128m/dat...

https://www.google.com/maps/@30.3855351,-89.6284331,349m/dat...

Reminds me of these weird (to me) ones in China

https://www.ryanmercer.com/ryansthoughts/2011/11/17/40452107...

As an Arizonan, it was only until 2 years ago in my Appraisal practice that I came across these crosses in Arizona City (south of Casa Grande). Really cool to see in person!

While the article does not really state anything, just positing more questions about its actual use, it seems like it is anyone’s guess due to the nature of the primary sources that knew the program being retirees or that the government gave this article writer all they felt comfortable with.

This makes me wonder: How many of these types of programs existed through the Cold War?

I know that the extreme whiteness of Antarctica is used for calibration of optical satellites.