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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!

uhoh
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  • Earthbound optical telescopes were useless to observe the lunar landings. – Uwe Jul 01 '18 at 20:46
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    Luna 15 did not observe the Apollo spacecraft. – Hobbes Jul 02 '18 at 07:33
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    For an example of how radio tracking could be used, see http://www.jb.man.ac.uk/multimedia/images/apollo11-eagle.html (Jodrell could measure the LM maneuvering on approach to the surface). – Hobbes Jul 02 '18 at 07:35
  • @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. – uhoh Jul 02 '18 at 07:42
  • 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'. – bukwyrm Jul 02 '18 at 17:28
  • @bukwyrm no, I don't seem to know that. The question is worded in this way to provide a degree of flexibility towards the directions answers may go. My "cold war humor" is just that. The word "closely" just comes directly from the quoted comment. In this case I'm not looking for some kind of "closeness coefficient" and I think the answers posted so far demonstrate that that's clear. The answers give a better understanding of the larger picture. Perhaps asking this question helps to demonstrate in fact that "closely" just means it was notable and people watched in a variety of ways. – uhoh Jul 02 '18 at 18:00
  • Seeming is in the eye of the observer. So you simply want more detail on any aspect of Soviet observation of the Apollo landings, or any observation? – bukwyrm Jul 02 '18 at 18:05
  • @bukwyrm sure, either way, or even an answer that says that the quoted comment might give the wrong impression. If you read some of the comments here, ideas that people were tracking the whole thing with radar, or trying to ping the telemetry have been fairly well shot down. Many if not most readers here may not remember the 1960's so well, so anything that sheds some light on the era and what it was like would be interesting. – uhoh Jul 02 '18 at 18:13

3 Answers3

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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.

Jens
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GremlinWranger
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  • 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. – uhoh Jul 02 '18 at 07:08
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    The terminology I have met before is primary and secondary radar https://en.wikipedia.org/wiki/Primary_radar https://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 – GremlinWranger Jul 02 '18 at 11:01
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    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. – GremlinWranger Jul 02 '18 at 11:08
  • An example of "amateur" doppler data discussed here. – uhoh Jul 02 '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.

PearsonArtPhoto
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  • Tracked by radar? Wow! Considering 1/r^4 returned signal strength dependence, those must have been some powerful stations! This is really interesting! – uhoh Jul 01 '18 at 16:55
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    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. https://en.wikipedia.org/wiki/Unified_S-band – Russell Borogove Jul 01 '18 at 17:15
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    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. – PearsonArtPhoto Jul 01 '18 at 17:32
  • Radar tracking by other nations may have disturbed the uplink receiption of Apollo, especially if the frequencies used are similar and very high radar power was used for the larger distances. – Uwe Jul 01 '18 at 20:56
  • No more then aircraft, which are regularly subject to radar. – PearsonArtPhoto Jul 01 '18 at 20:59
  • Tracking aircrafts by radar is a very small distance compared to a lunar mission. The radar equation requires 10000 times more power for 10 times the distance. The power density of the pulse at the tracked object will 100 times more. But the distance is not only 10 times more, up to 100 and 1000 times. – Uwe Jul 01 '18 at 21:22
  • Still, satellites are routinely tracked in Geostationary orbit. That is a significant part of the way to the moon. – PearsonArtPhoto Jul 01 '18 at 21:45
  • Geostationary orbit is still less than 1/10 of the distance to the Moon. Less than 10 % is not very significant in my opinion, especially when the radar equation is applicable. – Uwe Jul 01 '18 at 22:24
  • Sure, but you would have a very good idea that it was going to the Moon at that distance. But I suspect that passive means were heavily used, although I suspect some active radar was used when close to Earth. – PearsonArtPhoto Jul 01 '18 at 23:16
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    @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. – uhoh Jul 02 '18 at 00:40
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    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. – uhoh Jul 02 '18 at 00:59
  • In space, you do not need radar surveillance all the way to get a pretty good picture of a trajectory. One position and the associated vector already give you the entire unaccelerated path. – bukwyrm Jul 02 '18 at 17:18
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    @uhoh re: Tracked by radar; these days we regularly image asteroids that are far more distant than the Moon https://www.jpl.nasa.gov/news/news.php?release=2014-060 – Dave Gremlin Jul 03 '18 at 22:06
  • Asteroid imaging is done by the largest dish in the world (Arecibo) and maybe a few others. You need a lot of dish area to make this work. – Hobbes Jul 21 '18 at 08:28
  • Not to mention the asteroids that are imaged are much larger then the Apollo program spacecraft. – PearsonArtPhoto Jul 21 '18 at 11:54
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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.

Uwe
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