Originally published at: https://boingboing.net/2018/06/16/ampex-fr-900-drives.html
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What kind of person would think to? Not dreamers.
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The best of the images can show the lunar surface at a resolution less than 1m, much better than any other orbiter that has been there.
Or so we’re told…
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Wow look at all the censored comments!
Decades later, they did the same thing with GPS (do they still?) Personally I think this is the kind of secret our government should be keeping, unlike, say, the death toll from Hurricane Maria.
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I had to do a similar rescue operation in graduate school, pulling some of my advisor’s astronomical data from 9-track tapes. I used the sole Kennedy drive in the department, and had to constantly clean the read head as each tape slowly self-destructed after years of dormancy.
These tapes were only a decade old, so I can imagine the difficulty involved here, even if they had been better treated, storage-wise.
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GPS has had a variety of signals and a few different methods of controlling their use.
(this is from memory, so sorry if I get a few details wrong)
The primary signal is called L1 and it has two important signals on it. The first is the C/A (course aquisition) code. This is the public code that has always been available to citizens. The other signal is the P-code which is more precise but has always been reserved for the military (and other governmental uses, one supposes). Access to the P-code is controlled by not telling unauthorized parites the long code sequence used to encode the ranging signal. Without that, you can use the P-code in a very general way, but you won’t get the full benefits–so it’s not really done outside of very specialized equipment like used in surveying and some agricultural application.
Access to the C/A signal used to be moderated by what was called SA or Selective Availability. This was acheived by applying a known error to the timing signals broadcast by the GPS satallites. The corrections for this were sent on the P-code and were avilable to military users, but not to civilian users. SA was called selective because each satallite could be manipulated separately and varying with time. So, the error could be cranked up when the satallite was over unfriendly terratory and turned back down then over freindly terratory.
SA was turned off by presidential decree in, IIRC, 1992. I had just gotten back from an international business trip to a part of the world that was almost at war. When I was driving into work the day after I got back, I saw the estimated error value on my GPS was 12m (instead of the normal 45m or so) which told me that SA was off. I almost lost bowel control. It’s important to note that the only times before this that SA was turned off was in the first gulf war when there was a lack of military P-code GPS receivers available, so the DOD asked for SA to be turned off so that civilian units could be used until proper P-code units could be fileded. I though we were at war with the region I had just returned from. Yikes.
Turns out President Clinton just thought SA had outlived its usefulness as a military asset and that the increased civilian use of GPS with higher accuracy would help the country more. I think that’s been proven true. So much so that other means of making civilian accessable location systems more accurate has accelerated. We first got WAAS (Wide Area Augumentation System), then CA codes on other GPS frequencies/signals, and now an almost complete redesign of the GPS signals which will open up very precise civilian positioning.
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All I can say about this is, “cool.”
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So, what was the compression algorithm? I’ve run out of space on my Terabyte SSD because of te 650 Gigabytes of JPEG photos stored on it, which is ok, but if there’s something better… I want it… NOW! 
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Considering that it was an all-analog system in a spacecraft that almost certainly had essentially zero computing power on board, I doubt the compression algorithm would do anybody today much good - unless you were looking for a method of compressing analog data using only 1960’s transistors.
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The shocking thing to me was that they’re talking about 2GB images in 1967. That’s so far beyond the working memory of any machine of the era that about all you can do with the data is stream it to a printer. And they shot thousands of them! You know in old movies where there is a wall full of reel-to-reel tape drives? This is one of the few places where that would have been reality.
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Back in the Eighties the agency I worked for used a work tape - a copy of a master tape - to run a specific large program. One day I ordered the job run, and got the message “Tape wrapped around tape drive.” I waited until the next day and tried again. “No such tape.”
I called over and learned they’d had to destroy the work tape to get it off the drive. No problem; I told them to make another copy. The next day “Oxide came off tape.”
So both work tape and original were gone.
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I think I ate at that McDonald’s once or twice as a kid in the 1980s - my maternal grandpa was a WWII vet and naval reservist, so my grandparents could go into Moffett Field to shop at the commissary (right across from the big blimp hangar). Sometimes during the summer they’d take me along for extra schlepping power. There was also a Baskin-Robbins on base.
A decade or so later, I’d drive them to the TriCare/CHAMPUS office for medical appointments. Circle of life and all that.
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Congrats: you win the “Most Whooshed of the Month” award.
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So - what happened to the orbiter(s) and the original developed film stock onboard?
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It’s probably nothing special by today’s standards. Since it’s lossless, it’s probably some variation of an RLE scheme, which are still used today.
They were crashed into the moon at the end of their mission.
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The CIA/USAF used to drop film from orbit with the Corona spy satellites.
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Yes - very cool and very definitely qualifies as a wonderful thing!
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Were the pictures deliberately fuzzed? I don’t think we have seen any evidence for this.
I started working on image processing in the early eighties. You mounted an image on a perspex drum on something like a lathe, and you scanned it past a photomultiplier. It was difficult to get more than about 5 lines of colour image into a PDP-11 and leave any room for the program. So you scanned the image, did the image processing on the fly, and wrote the image back out to film. They were beginning to store the images onto the 300 MBy CDC drives when I started. NASA had computers that could store whole images and take out the streaks for the Viking landers ten years earlier, but this was before that. What I am see here is a first-generation image next to a second or third generation analogue copy. Even then, the main differences are in the tone curve - the old picture has much deeper shadows.
Yu. Ovschinnikov was doing histogram normalisation about this time (1967 if I remember right). This is sampling an images, and sorting the brightness levels into 6-bit ‘bins’, and then tweaking the tone curve so you got the same count in each bin - but the computer and the 64 bins was mechanical, with mechanical digit counters.
Would hiding the resolution fool the Russians? If you could do wet chemistry and radio back the results, then they can work out the resolution you ought to get at that range, and assume you can send back all that you can get off the film (including the grain) if you have the patience to do it. They could guess the bandwidth and work back from that. This does not tell them what wavelengths you would use to see a target on earth through a cloudy atmosphere while flying high enough to be in ‘space’ rather than ‘national airspace’.
NB: The clickbait title is a quote from the original article. This also claimed the used ‘lossless analogue compression’. Caveat emptor.
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Here’s what would could get on probably the same 70mm film if you pointed a camera at Earth…
This was taken in 1967. The Corona satellites returned film to earth, so you don’t get the striping from the encoding. You can see cars as rectangles, so the resolution is not far off 1m.
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