Image Intelligence concerning alien structures on the moon

Question

Meta-Background

Follow-up question to: How do you hide an investigation of alien ruins on the moon during Apollo 11

I got notice on WB:Meta that there is another approach on the question, which I would like to try here.

Scenario

1. Assume there is an alien base on the frontside of the moon (not the dark side)
2. Assume the time being 1969 (during Apollo 11 or prior)
3. Assume I want these alien base ruins to be
   • openly visible (that is not underground, obviously)
   • in ruins (there are only walls left, no ceilings)
   • aliens supposed to be about the size of an average human

Problem

I learned that signal intelligence is a thing to consider when it comes to alien bases on the moon. I am worried about the integrity of my world, if

• the base can be detected by anyone from earth

• the base cannot be detected at all from earth

I also was informed, the correct term is image intelligence (because lack of actively emitted signals like radio waves from the ruins), so I will use that term from here on.

Question

What threat or capabilities is image intelligence posing upon detection of the alien base?

Answer 1

Image intelligence, not signal intelligence

If the remains of the alien base is not emitting unusual amounts of heat, light, or radio signals, there is no "signals intelligence." Your problem reduces to that of image intelligence, and making it plausible that NASA can detect the alien base, but nobody else can.

Lunar Orbiter

For picking lunar landing sites, NASA in the real world needed better photography of the lunar surface than could be readily done from Earth. The Lunar Orbiter programme launched five photographic satellites into orbits around the Moon in 1966 and 1967, which photographed 99% of the surface of the moon at 60 meter resolution, and plausible landing sites at 5 metre resolution.

As a bonus, careful tracking of the satellites via the Doppler shifts of their transmissions allowed mapping of the Moon's gravitational field including its mass concentrations ("mascons").

Picture availability

The pictures weren't made generally available at the time, because doing that would have been expensive in an age of analogue photography. So it would have been easy for NASA to discover something obviously artificial that nobody else knew about, and to keep it secret if they wanted to, or were told to by the US government.

The USSR did not carry out a comprehensive photographic survey from orbit, so they could readily have missed a particular target. Of course, if they become suspicious that NASA seems to be especially interested in a particular area, they'll take a look with their biggest telescope of the time, which seems to have been a 2.64 metre reflector in the Crimea. If they remain suspicious, they might launch a photographic satellite especially to investigate.

Answer 2

Note: Signals intelligence is perhaps not quite the right term, it usually implies the detection of deliberate transmissions. (For instance, direction finding to triangulate the position of a mobile transmitter, traffic analysis to look at patterns even if one cannot decrypt the transmissions.) What we are talking here is simple image intellingence.

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The chances for your setting are area size and statistics. Consider the Utah monolith on Earth. Presumably an artist did erect a structure on Earth, and it is unclear just how long it stood before discovery. That's in an era with Google maps, on an inhabitated planet.

Assume that the alien ruins are visible from Earth if one uses a large telescope, if one looks at the right place, and that the ruins can be guessed to be artifical ("nature abhors a straight line") if one squints at them the right way. They are much too small to show up in any of the moon maps of the era. To complicate things, make them partially shadowed, only pictures taken at the right time will be suggestive of ruins.

• You can assume an accidental discovery by one scientist, possibly in a government-sponsored research organization. A backyard astronomer would have little chance to find it.
• If your story allows it, you can assume that somebody had coordinates and merely used the telescope to confirm them.
• Or you assume that they are large enough to show up on a smallish telescope, and some hobbyist found them by chance. That means in-story, there is time pressure before someone else finds them.

Suggestive of ruins is another important thing. Remember Martian canals and the Cydonia face? The scientific community now accepts them as errors/misinterpretation based on low-resolution sensor data. What reputable scientist would go forward and talk about "Lunar Ruins" without ironclad proof? But one might, just for a lark, aim the new, better telescope at the site which had previously mentioned by some crackpot to see just how good the new telescope is. Imagine their surprise when better magnification does not debunk the claims!

Answer 3

Requirements for SIGINT (not currently met in scenario)

The basic problem you have is that the physics of signal intelligence gathering (SIGINT) in all it's various forms relies on the target actually emitting signals. A radio transmitter needs to broadcast a signal, ditto lasers (and masers). The same for other forms of information transmission. Even a search light transmitting a simple Morse Code message needs to emit flashes of light.

Your problem is that as described the alien 'ruin' is well, actually just a ruin! I.E. it has no active power sources! And the thing is all of the above types of information transmission require an active power source which, according to the description provided doesn't exist. If it did? And the transmission device was gone/destroyed? Then at least the heat generated by that power source might still be detectable via the thermal (heat) radiation signature given off by the source. But as it stands there's no power source either. No power? No SIGINT.

All of the above being a given (unless you modify your scenario) that means the only means of remote detection left in the 1960s is sunlight and heat that reflects off the walls of the ruin in a manner that is distinct from the lunar rock around it. If the ruin is large enough? Parts of it might be observable with 1960's technology from Earth or Lunar orbit even if most of the base is hidden inside a lava tube. It all depends on the angle of the observer to the ruin and the ruin to the Sun matching up. So metal walls glittering in the Sun for a short time every (lunar) day?