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@DarkDust's comment says:

If the USSR had had just a tiny amount of doubt whether the landings were faked, they would have used that for propaganda. Loudly! They observed the landings closely and even had a spacecraft in orbit during Apollo 11's landing.

Besides (potentially) the Luna 15 spacecraft in lunar orbit (mentioned in the comment), in what ways did they observe the landings closely or carefully?

Telescopes? Earthbound dish antennas and receivers? "Embedded observers"? On TV? Enquiring minds want to know!

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  • $\begingroup$ Earthbound optical telescopes were useless to observe the lunar landings. $\endgroup$ – Uwe Jul 1 '18 at 20:46
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    $\begingroup$ Luna 15 did not observe the Apollo spacecraft. $\endgroup$ – Hobbes Jul 2 '18 at 7:33
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    $\begingroup$ For an example of how radio tracking could be used, see jb.man.ac.uk/multimedia/images/apollo11-eagle.html (Jodrell could measure the LM maneuvering on approach to the surface). $\endgroup$ – Hobbes Jul 2 '18 at 7:35
  • $\begingroup$ @Hobbes I've added some parentheticals, thanks for pointing that out. Slightly related Luna 15 vs Apollo questions; 1, 2, 3, 4 as well as your answer mentioning planned non-interference. $\endgroup$ – uhoh Jul 2 '18 at 7:42
  • $\begingroup$ You seem to know the means by which they observed, but seem to try to ascertain a degree ('closely'). Please elaborate what degree of detail 'closely' would entail, and at which point you would dub the observation 'not closely'. $\endgroup$ – bukwyrm Jul 2 '18 at 17:28
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To extend PearsonArtPhotos answer, various amateur and academic groups successfully received Apollo voice traffic so it seems safe to assume the USSR would have been doing the same. Of more interest would have been the scientific and spacecraft health information coming back in telemetry, both for the science data and for feeding into the Soviet moon program engineering. The telemetry appears to have been unencrypted but certainly complex. Data extracted from it would have been of similar value to an unmanned lunar probe that you did not have to pay for, so spending serious effort to unpack it would be worth while, and would become easier as the post flight papers were published and Apollo/Soyuz flew.

In terms of radio based measurement the crafts all had transponders, including the boost stage which reduces needed power, but reading the wiki page it looks like only one station at a time could be interrogating so a third party popping in to get their own read would have jammed the NASA one so would have been both obvious and aggressive. Doppler measurements would have been possible to extract the craft velocity with respect to the ground station even if range was not, and post flight analysis would allow things like lunar orbit height and presence on lunar surface to be verified.

Using an active radar at the moon range is certainly possible now but the link suggests the signal processing techniques used are new. Doing radar ranging of the large departing first stage+lander+CSM near Earth would have been both possible and have provided hard numbers on the engine performance.

The Wikipedia page for unified S-band provides a broken link to a Russian site that may give more information if relocated.

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  • $\begingroup$ Thanks for your thoughtful answer, and welcome to Stack Exchange! I have a small question about terminology. Is the use of signals returned by transponders, or one-way doppler determination generally considered radar per se? I've always thought of radar as something based on strictly passive reflection/scattering of the transmitted signal without local amplification and/or frequency shifting. $\endgroup$ – uhoh Jul 2 '18 at 7:08
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    $\begingroup$ The terminology I have met before is primary and secondary radar en.wikipedia.org/wiki/Primary_radar en.wikipedia.org/wiki/Secondary_surveillance_radar. So yes normal use of radar does not include active transponders but is technically under the umbrella of radio direction and ranging $\endgroup$ – GremlinWranger Jul 2 '18 at 11:01
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    $\begingroup$ Have changed the wording slightly, since there are many things that can be done with radio beyond classic radar ranging, like atmosphere detection by monitoring power as things get occluded by a body. $\endgroup$ – GremlinWranger Jul 2 '18 at 11:08
  • $\begingroup$ An example of "amateur" doppler data discussed here. $\endgroup$ – uhoh Jul 2 '18 at 12:01
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According to Wikipedia, with two books cited:

The Soviet Union monitored the missions at their Space Transmissions Corps, which was "fully equipped with the latest intelligence-gathering and surveillance equipment

Also of some note is:

The missions were tracked by radar from several countries on the way to the Moon and back.

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    $\begingroup$ While it’s not inconceivable that ground based active radar could have pinged Apollo, it seems more likely that the spacecraft’s own emissions — unified S-band system and a C-band transponder — were tracked. en.wikipedia.org/wiki/Unified_S-band $\endgroup$ – Russell Borogove Jul 1 '18 at 17:15
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    $\begingroup$ I suspect that Radar was used as far as it could go, and the radio signals were tracked by monitoring their emissions beyond that point. The passive monitoring might have been done by the same radar dishes. $\endgroup$ – PearsonArtPhoto Jul 1 '18 at 17:32
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    $\begingroup$ @PearsonArtPhoto your analogy to aircraft is probably not so useful. Aircraft use UHF for communications, and communicate only over short distances (due to line-of sight geometry in the atmosphere of the curved Earth. Apollo used microwaves, potentially closer in frequency to the radar, and they may have had more sensitive receiver front-ends as they needed to work over hundreds of thousands of kilometers, rather than just hundreds. $\endgroup$ – uhoh Jul 2 '18 at 0:40
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    $\begingroup$ Also, considering the returned signal of radar scales as 1/r^4, saying that GEO "...is a significant part of the way to the moon." might be a stretch as well; the ratio is about 10,000 or 20,000 to 1. Right now this answer says that Wikipedia says that two unspecified books say that... It would be better if we had an actual original source quoted to support this, or at least the sourced named and linked. $\endgroup$ – uhoh Jul 2 '18 at 0:59
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    $\begingroup$ @uhoh re: Tracked by radar; these days we regularly image asteroids that are far more distant than the Moon jpl.nasa.gov/news/news.php?release=2014-060 $\endgroup$ – Dave Gremlin Jul 3 '18 at 22:06
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NASA could measure the speed and distance of Apollo using the uplink and downlink signals for a very precise estimation of doppler shift (speed) and transmission delay (up and down for distance). They did not have to use radar and could avoid the 1/r^4 problem. The 1/r^2 problem must be solved for uplink and downlink anyway and could be used for speed and distance too.

But other nations and also radio amateurs could measure doppler shift with somewhat less precision using a local reference oszillator. Larger dish antennas could be used to measure the direction. It was possible to determine the elliptical transfer orbit from Earth to Moon using several measurements of direction only using mathematical methods developed for observation of planets like Ceres and Neptune. If the orbit was determined, distances could be calculated.

Passive measurements only could be used to check if Apollo was on the way to the Moon and back. No need to use radar.

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