This answer mentions:
It's well known that other countries routinely spy on each other (i.e. the NSA tapping of Angela Merkel's phone).
NASA's Deep Space Network's space-related activities (like most of NASA's activities) are mostly if not completely a matter of public record and for activities of the Deep Space Network you can check the DSN NOW page or look at the history online.
For example at least the frequencies used for the Mars 2020 communications should be retrievable from the DSN XML data should be findable as part of an answer to China, UAE and US all sending missions to Mars in 2020 (Summer of L̶o̶v̶e Mars); how far apart are their frequencies? thought nobody has done this yet.
Also, see answers to:
- Understanding the information contained in the Deep Space Network XML data?
- Power and frequency units used in Deep Space Network XML data?
- Is there any publicly available logging, or "Wayback Machine" for DSN Now activity?
However from time to time you can see very little or no activity on the DSN now page (all dishes displayed are dark) and of course not all dishes can appear on that page at the same time. Also I thought there was a question here about DSN being completely dark but I can't find it at the moment.
Question: But what about use of the DSN to listen to other space agency's deep space spacecraft? Have there been publicly documented instances of scheduled (and paid-for) DSN listening-in to signals sent by non-NASA missions "just for the heck of it" or perhaps to see if those spacecraft are actually doing what the other space agencies say it is doing?
Note: I am not really asking if you think this happens and nor seeking answers that explain why you are personally sure this doesn't, couldn't or shouldn't happen. Just fact-based answers on hopefully publicly available sources. Thanks!