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If we assume that humans will eventually visit (if not colonize) Mars, and we consider the benefits to terrestrial navigation and communication of the GPS and Iridium systems...

Would a precursor to human travel to Mars logically be the establishment of a GPS-style constellation of navigation satellites and/or an Iridium-style constellation of communication satellites in Martian orbit?

Is that something Mars mission planners have written into their plans, have considered, or have dismissed as unnecessary?

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  • $\begingroup$ Iridium style is outdated even on earth. The current generation(e.g. Thuraya and Tiantong) of satellite phones system uses one GEO/GSO satellite to aim dozens of beams onto earth, each covering one small region like Iridium's one satellite does. $\endgroup$ Aug 25, 2022 at 12:40

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A Mars GPS system cannot be a high priority considering the challenges of life support. GPS is a hit on Earth because it has billions of users. If you divide the multi billion dollar cost on say 12 astronauts on Mars, you need extremely productive use to motivate the investment.

Without global magnetic field, a compass is useless on Mars, so there is a need for navigational aid. But radio beacons on the ground at landing sites would be much more cost effective.

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    $\begingroup$ The last sentence is what makes this the right answer, at least for the foreseeable future. Beacons would be orders of magnitude cheaper than a Mars GPS system. Beacons help solve the dead reckoning problem for precision landing at a predetermined site. They are not a global solution (now you need lots of beacons), but that isn't the concern for the foreseeable future. $\endgroup$ Jun 11, 2014 at 12:29
  • $\begingroup$ Would beg to disagree: pinpoint landing at an unexplored location requires satellite-based navaids. A GPS system is too expensive, but getting range and range-rate updates from satellites with known orbits will be of much help during early trajectory correction maneuvers. $\endgroup$ Jun 11, 2014 at 13:21
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    $\begingroup$ @Deer Hunter A (visual) Terrain Relative Navigation system is considered for NASAs 2020 Mars rover. It certainly sounds like a feasible concept. Unless there is a sand storm, like when the Soviet Mars 3 landed in 1971... planetary.org/blogs/guest-blogs/van-kane/… $\endgroup$
    – LocalFluff
    Jun 11, 2014 at 13:57
  • $\begingroup$ Optical navigation is necessary for the descent phase, to compensate for the winds and atmosphere discrepancies. Satnav complements it by allowing corrections long before entry. $\endgroup$ Jun 11, 2014 at 14:34
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    $\begingroup$ Resupply aims for an existing structure. Just include a beacon in that structure. Maybe several beacons in the general vicinity for triangulation, and you're done. $\endgroup$
    – Hobbes
    Apr 28, 2015 at 6:48
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Each orbiter at Mars has a secondary mission as a data relay satellite for other Mars missions. Mars Reconnaissance Orbiter (NASA), Mars Express (ESA), Mars Odyssey (I think) are all used to relay data from the smaller landers back to Earth.

So a small network of communication satellites is already in orbit with a few more coming.

None of them have clocks of the accuracy needed for GPS style navigation, but some similar system seems likely, even if just for search and rescue, once serious manned exploration/habitation of Mars occurs.

But that is probably several decades away still, Elon Musk notwithstanding.

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  • $\begingroup$ centauri-dreams.org/?p=33059 Hoping to see some very accurate clocks in various places even if we're slow getting canned monkeys past LEO. $\endgroup$
    – HopDavid
    Apr 28, 2015 at 18:26
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A Single "Geo" Satellite Might Work

The first human use GPS / Comms "constellation" on Mars could be a a single satellite at Mar-stationary orbit.

Initial missions / colonies will probably not travel far away from the landing site: it's going to be difficult to provide life support over long distances. Even assuming a colony of several hundred people, it's unlikely that the furthest flung individuals would ever be more than a few miles away from each other.

So a single Mar-stationary satellite could provide back-to-Earth comms, "long range" comms within the colony, and - if combined with some surface transmitters - precision navigation and timing.

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  • $\begingroup$ Wouldn't a Mars-synchronous satellite spend roughly half its time with Mars between it and Earth? You'd need some additional relays at least. $\endgroup$
    – Cadence
    Aug 23, 2022 at 22:21
  • $\begingroup$ @Cadence - assuming your need 24/7 comms, you would probably need two more Mar-stationary sats as relays. But 24/7 comms might not be necessary. $\endgroup$
    – codeMonkey
    Aug 24, 2022 at 14:06
  • $\begingroup$ This is how Thuraya and Tiantong do it on earth. Iridium's "satellite based cellular tower " approach is outdated. $\endgroup$ Aug 25, 2022 at 12:43
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Apollo Lunar landings were in a similar pickle: no GPS. They used sextant angles between stars and mapped Lunar ground features to update their Lunar orbit state vector. A similar technique could be used on Mars landing approaches. This would allow approach accuracy similar to Apollo Moon landings.

If the Mars landing site had previously been equipped with radio beacons, the ground radio beacons could then come into play.

Even DECCA radio navigation systems could provide accuracy of several meters. A trio of beacons surrounding the landing site would give excellent x/y position, but elevation would likely need to be augmented with radar altimeter.

Could Apollo's Sextant navigation use similar geometry as Marine Navigation?

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  • $\begingroup$ The precision of Loran-C was not meter accuracy, under very good conditions about 10 m. $\endgroup$
    – Uwe
    Aug 26, 2022 at 21:15
  • $\begingroup$ @Uwe .. you are correct. However, DECCA (an even older system) was more accurate than LORAN. According to en.wikipedia.org/wiki/Decca_Navigator_System , DECCA accuracy could reach as high as " a few meters on the baseline". In the application being considered (Mars base landing), it would presumably be built with the LZ on the baseline. $\endgroup$
    – Woody
    Aug 26, 2022 at 21:37
  • $\begingroup$ @Uwe ... While working with the Canadian Hydrographic Service in the 1980's, we integrated GPS, LORAN and DECCA. There were too few GPS satellites at the time for 24/7 GPS fixes, so positions would be interpolated using DECCA in between. In our experience, the DECCA position was repeatable to a few meters up to several hundred miles offshore. DECCA itself would not be suitable for a Mars lander approach, but from my experience, using radio positioning for Mars lander approach seems a trivial challenge. $\endgroup$
    – Woody
    Aug 26, 2022 at 21:46

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