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I am currently working on a project involving designing a Mars base, and a major factor is establishing constant communication between Earth and the Mars ground base.

I am thinking of utilizing laser communication (for faster data transmission), but I'm stuck on how to actually implement it. Would it make sense to have an areostationary satellite above the base, to utilize an orbiting array of satellites, to have a satellite around the sun, or something else? There's a lot of options I've seen, but I'd like to know if anyone has derived a "best" or most viable option.

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    $\begingroup$ From context, it seems you mean between a Mars base and Earth, but communications between the base and other sites on Mars are another thing to keep in mind. Other things to consider: redundancy, bandwidth requirements, antenna/power requirements if it's meant to reach vehicles or portable equipment, availability of the DSN or alternatives on the Earth end, tradeoffs of a specialized Mars-specific solution vs. general purpose infrastructure that can support missions to asteroids and such...defining "best" is non-trivial. $\endgroup$ Jul 27 '20 at 18:55
  • $\begingroup$ A "star-link" style constellation of small satellites in LMO might be a good choice for other reasons -- it will give you point-to-point comminication on Mars, GPS-style location-finding and lots of redundancy. With a small telecope on eacg satellite (or just a proportion) you could get a global surveillance system good enough to track vehicles, or anything with a radio beacon. Basically if you are going to put humans into Mars-space you may as well install basic network infrastructure first :-) $\endgroup$ Jul 29 '20 at 11:42
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Partial answer; rather than an areostationary orbit with zero inclination, an inclined areosynchronous orbit (i.e. same period but tilted) would never lose direct line-of-sight to Earth except when it goes behind the Sun.

From the surface of Mars it would make a figure-eight in the sky once a day (see this answer for what those look like), but these days steerable phased array antennas are straightforward to implement in case you don't want to have a dish that has to track it.

It's worth pointing out that your choice of an optical instead of a radio link has the benefit that it can pass much closer to the Sun without running into noise and dispersion issues due to the plasma in the solar wind. With proper very narrow-band optical filters tuned to the laser wavelength and good coronagraphization the receiver telescopes should be able to point quite close to the Sun. For more on that see


and using Skyfield and this script: https://pastebin.com/q7RkKRHQ

Sun-Mars-Earth angle and Sun half-angle

and


Below are the kinds of moving images I've normally seen from SOHO's fixed cameras pointed towards the Sun:

enter image description here

Above: from What exactly is the interaction that blocked Juno's data downlink near solar conjunction? Below: From This answer to What is this white dot and strange line in SOHO image? Yes those are the Pleiades wizing past the Sun!

enter image description here

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  • $\begingroup$ Can you really make do with a single areosynchronous orbit? I would expect that a part of it will still get hidden behind Mars every time Earth gets close to the orbital plane. Or can you set up some clever precession to make sure that never happens (like a sun-synchronous orbit, but for Earth)? $\endgroup$
    – TooTea
    Jul 28 '20 at 10:23
  • $\begingroup$ @TooTea thanks for reminding me, I wrote an answer about a sun-synchronous orbit for ISRO's MOM spacecraft once but now I don't remember how the story ends. I think though that you are right, this may not work. I'll dig in once I get back to my laptop. $\endgroup$
    – uhoh
    Jul 28 '20 at 10:30
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    $\begingroup$ @TooTea update: this answer suggests that a sun-synchronous orbit will be possible around Mars, but that's certainly not going to be anywhere near high enough to be simultaneously areosynchronous. Since the Earth is always moving I don't think this is going to be a big problem since there are so many degrees of freedom. I'll write a simulator to prove it though. $\endgroup$
    – uhoh
    Jul 28 '20 at 11:44
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    $\begingroup$ Technically, isn't it the sun whizzing past the Pleiades? Or the Earth whizzing around . . . never mind. I'll show myself out. $\endgroup$
    – userLTK
    Jul 29 '20 at 5:53

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