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While the Tianwen-1 orbiter will dispense commands to the Zhurong rover, the Mars Express orbiter of the European Space Agency will serve as a backup.

Wikipedia

Since Mars Express normally communicates using NASA's Deep Space Network, would the latter also be used in the contingency described above?

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    $\begingroup$ What a fascinating scenario! This is a +n! question. $\endgroup$
    – uhoh
    Jun 23 at 2:29
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I am almost certain the answer is not just no but is on the level of the underworld freezing over level of no. Congress has forbidden NASA from providing any support for China's space program.

Shortly after NASA landed men on the Moon in 1969, the Soviet Union congratulated NASA for its Moon landing. There was a hidden message in this congratulation: "We monitored your communications. We know that you did land men on the Moon." NASA congratulated China shortly after China successfully landed the Zhurong rover on Mars, with the same implied message.

It takes an hour to prepare for communications between a remote vehicle and a Deep Space Network site. The analog equipment must be tuned to the exact frequency used by the remote vehicle, a bit synchronizer must be set up to recognize the bit encoding protocol used by the remote vehicle, and the frame synchronizer must be set up to use the frame encoding protocol used by the remote vehicle.

NASA knows the Tianwen-1 orbiter downlink frequency, and probably knows the bit encoding and frame synchronization mechanisms as well. NASA would not have congratulated China as quickly as it did if NASA was not monitoring communications from Tianwen-1. Imagine now that ESA comes to NASA with a DSN request for a comm link with a vehicle orbiting Mars that does not match any of the frequency / bit encoding / frame synchronization characteristics of any ESA vehicle orbiting Mars but perfectly matches the characteristics of the Tianwen-1 orbiter. NASA will have no choice: They will have to reject this request.

NASA is not stupid, nor is ESA, nor is China. The scenario invoked in the question will never happen, at least not until the US Congress loosens the restrictions on NASA.

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    $\begingroup$ First sentence made me laugh. Your "listening to China's communications" scenario might actually explain some of the undocumented "testing" codes used by the DSN. $\endgroup$
    – DrSheldon
    Jun 23 at 5:46
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    $\begingroup$ If the Mars Express orbiter would be used as a backup, would the DSN need to use another configuration than they would normally use for ME? I think the question becomes "does NASA know (and care) what data is being sent down by Mars Express, or does it just forward it to ESA?" $\endgroup$
    – Jan Fabry
    Jun 23 at 9:23
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    $\begingroup$ Since Tianwen-1 would be in contact with the ESA orbiter, couldn't the ESA orbiter simply repackage all the received data into "ESA looking" packages before being sent through the DSN? Basically the Mars Express Orbiter would kind of act as a VPN for Tianwen-1, preventing NASA from seeing the exact contents while then the ESA groundstation would forward the data/commands from the Chinese groundstation? $\endgroup$
    – wawa
    Jun 23 at 21:11
  • $\begingroup$ I don't understand your point about the moon landing. Wasn't the Apollo 11 landing widespread knowledge? Everyone in the US was following it live. $\endgroup$
    – Barmar
    Jun 23 at 21:39
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    $\begingroup$ @Barmar these days, the situation would be a little different because you have loads of amateurs with dishes of all sizes doing radio-astronomy, many of which could probably pick up a transmission from the moon. From Mars however, you need more capability, so fewer (or perhaps none) amateurs would have the ability. $\endgroup$
    – Moo
    Jun 23 at 22:40

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