So when do we put up GPS satellites around Mars? It makes sense.
Or just put them on the moons I guess. They're pretty far from the surface - 9K and 14K compared to GPS of 12K so maybe not bad. And less atmosphere in the way. Also less radio noise?
The issues would be A) that Mars upper atmosphere and internal mass distribution are not as well mapped as on Earth, so knowing your orbital accuracy is much more difficult (1)- and at 8km/s small orbital error bars become giant error bars on the surface and B) Putting a full constellation of 24-30 satellites around Mars is going to be really expensive. That's more than the sum total of all satellites to successfully orbit Mars to this day (18).
1: On Earth we account for that by using ground stations to track the satellite locations, with the ground station locations determined very very precisely using non-GPS techniques (old school surveying techniques). On Mars, that's not going to be possible until we get a lot more done, probably a later human mission would be the first time that could be done.
We don't need all of mars though. One GPS receiver on your lander will give you enough information for the area you can feasibly reach - and if not just old school survey some location to park another receiver to map things out.
All good points.
The solutions for Mars will necessarily be unique to that environment. Still, a combination of ground stations and satellites will be inevitably used for location-finding.
And, the atmosphere? What atmosphere? It's negligible compared to Earth. Got to be down the list of important variables.
We can send a mission to Mars and arrive within a few meters of desired orbit, but it's going to be hard to figure out where a satellite is? My doubt-meter is hitting the pin.
Atmospheric drag on satellites- especially how it changes with solar output levels- is a hard thing to model accurately, and a major contributor to orbital uncertainty here on Earth. The Martian atmosphere is two orders of magnitude thinner, but it is far less than two orders of magnitude understood. And the level of our understanding matters for our ability to correct for it's perturbations.
NASA is very good at sending spacecraft through regular space and hitting precise windows (MCO units issues aside), it's in orbit that things get more complicated, because now there are just a lot more potential interactions to deal with. We can use LOS on planetary occultations to give you some data, but it's still a lot of work to get from there to mascon maps, upper atmospheric data, etc.
> So when do we put up GPS satellites around Mars?
A system like GPS? Probably never. It would be fantastically expensive and solve a problem that no one has. In any case, the moons would be a poor choice for signal transmitters: 1. landers are harder than satellites 2. two moons is not enough for a system like GPS 3. three-body problems mean that we can't really know the future configurations of the system with high precision on anything but the very short scale.
In any case, it costs something like $700 million per year to operate the GPS system here on Earth.
Navigation just seems comparatively easier than earth. You are much more likely to have a clear view of the terrain or sky. And the terrain is much less likely to change than the earth so computer vision should be easier.
> when do we put up GPS satellites around Mars? It makes sense
Once we have tens of Starships of annual transport between Earth and Mars such that putting about a dozen satellites in Mars orbits every decade or so [1] is cost effective.
Using Elon math that’s the 2030s. Ignoring his mortality-driven forecasts, probably the 2050s.
They competition would be balloons, which can be made from indigenous polyethylene [2], floated above a settlement with a loud radio. You’d have range and direction home, which should be good enough for decades, potentially into the 2100s when, on a very optimistic schedule, inter-settlement transfer begins to become common.
