Solar atmosphere causes difficulties in communication during opposition (when Mars is almost behind the sun w.r.t. Earth).

The question is: is it possible to define an extended radius for the sun, which the Earth-Mars line of sight should never pass through it? if there is, how much is it, in terms of angular separation?

I've read in some mainstream and NASA news that there is a two week blackout period during each synodic period of Earth-Mars. But I want to know the exact numbers. I'd appreciate any answer with technical references.


2 Answers 2


The conjunction blackout is defined to be when the Sun-Earth-probe angle is less than 2°. That's about as tight as it gets, with operations usually suspended for several days before and after 2°.

  • $\begingroup$ Thank you... and does this 2 degree limit depend on the technology and communication band used? and do you know any reference on how to calculate the losses due to solar atmosphere interference? $\endgroup$
    – AliRD
    Commented Nov 19, 2016 at 14:39
  • 1
    $\begingroup$ That is for X-band. For Ka-band it's more like 1°. I don't know of any references, but you can likely find something in the DESCANSO series of papers. Try googling "descanso conjunction x-band". $\endgroup$
    – Mark Adler
    Commented Nov 20, 2016 at 3:33
  • $\begingroup$ If there are manned missions to mars in the far future, there should be a communication satellite to avoid this radio blackout. A satellite placed in the same orbit as earth but with an offset of 90 degrees should do it. This position should be useful for every opposition of earth and mars. But the orbit of mars with a small offset just to avoid the sun should be possible too. $\endgroup$
    – Uwe
    Commented Mar 18, 2017 at 9:22
  • $\begingroup$ For crewed missions, laser communications would significantly reduce that angle, potentially avoiding the blackout completely. $\endgroup$
    – Mark Adler
    Commented Mar 18, 2017 at 15:01
  • $\begingroup$ See also What exactly is the interaction that blocked Juno's data downlink near solar conjunction? $\endgroup$
    – uhoh
    Commented Nov 16, 2017 at 3:23

This is not going to be a fixed number for all applications. The noise from the solar atmosphere will reduce the received signal to noise ratio on each end (Earth/Mars) with the right equipment you could probably squeeze a few extra minutes/hours out of the comm link if you simply up the transmitter power accordingly.


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