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In space, there is a lot of electromagnetic radiation from sun and other space objects. Amidst these, how are signals from Mars rovers and other space probes received?

I see images of Mars by rovers, how is it noise-free and sharp? Wouldn't the image signal be distorted in space when transmitted to Earth?

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    $\begingroup$ EM rays travel through a vacuum in straight lines, and do not interfere with each other. So all you really need is to point the transmitter at Earth, and the receiver at Mars, and the sun's rays become irrelevant. Cosmic rays can come from any direction, but are a fairly low level (especially at the surface of the Earth) and spread across a broad range of frequencies, so then comes 'tuning to the frequency of the transmitter'. Not child's play, but hardly rocket science either. $\endgroup$
    – Andrew Thompson
    Jan 27 '17 at 19:41
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    $\begingroup$ @AndrewThompson -- Depends on what you mean by "rocket science". Knowing where the Earth is is rocket science. It's on aspect of the middle letter of GNC, short for guidance, navigation, and control. Making the vehicle's antennae point toward the Earth: That's the job of guidance (attitude guidance) and control. Knowing how to communicate is difficult topic, covered by the Consultative Committee for Space Data Systems. Knowing when to (and when not to) communicate is a carefully laid out plan. If nothing else, planning is one of the most critical aspects of "rocket science". $\endgroup$
    – David Hammen
    Jan 28 '17 at 0:35
  • $\begingroup$ @DavidHammen OK ..my poor assessment of difficulty (of aiming the transmitter). $\endgroup$
    – Andrew Thompson
    Jan 28 '17 at 0:52
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In space, there is a lot of electromagnetic radiation from sun and other space objects.

No, there isn't. In classical physics, electromagnetic radiation is a wave phenomenon. Normally, waves of light pass through each other unperturbed. In quantum physics, there is such a thing as two-photon physics, but this takes very energetic photons. Neither the visible light from the Sun nor the radio waves from a spacecraft qualify as "very energetic". In short, there is no interference.

There is a problem if (for example) Mars is close to being directly behind the Sun as seen from the perspective of the Earth. In this case, an Earth-bound antenna pointing toward Mars will also be pointing toward the Sun. This would be a very bad day for that Earth-bound antenna. This means that communications with Earth are suspended for about a week or two every other year for vehicles on or near Mars. Communications with Mars is not a problem outside of these solar connections.

I see images of Mars by rovers, how is it noise-free and sharp?

By

  • Designing communication protocols that are (to some extent) loss tolerant. This is, in part, the job of the Consultative Committee for Space Data Systems.
  • Designing the communications capabilities of the spacecraft to be in line with the data to be gathered by the spacecraft. This is a collaborative effort between the designers of the spacecraft's science team, the designers of the spacecraft's communications system, the operators of the Deep Space Network.
  • Making sure the spacecraft's antennae are properly aimed toward the Earth. This is one of the jobs of the spacecraft's guidance, navigation, and control system.
  • Filtering downloaded data to remove effects such as salt and pepper noise. This is one of the jobs of the spacecraft data processing team.
  • Plus doing a whole lot of other stuff that I didn't mention above.
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  • $\begingroup$ As the sunlight influx at Earth is in the order of 1 kw/m², I would not claim there is not a lot of EM radiation from the Sun. $\endgroup$
    – Aaganrmu
    Jan 30 '17 at 10:27
  • $\begingroup$ I did see your comment though Fred unfortunately their question. If I can't coax them to reopen it I'll post a new question specifically about salt and petter noise, at what point in the data flow it's introduced and at what point (if any) it is then handled and those pixels reinterpreted (or interpolated) to produce images for the public, the "space artists" that Emily Lakdawalla describes. $\endgroup$
    – uhoh
    Jul 4 '21 at 23:55
  • $\begingroup$ update: it's been undeleted now. $\endgroup$
    – uhoh
    Jul 5 '21 at 11:03

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