Starlink: when can we expect Martian deployment?

[whvholst]

Apologies if this should be in the Starship section, but since Starlink threads are in this section, I thought it belongs here.

Anyway:

For Martian exploration a Starlink-like constellation would be a reasonable stepping stone. If I am not mistaken, this would already be doable with Falcon Heavy launches instead of Starship. What would be a reasonable timeline for such a thing starting to materialise?

[Robotbeat]

They prob Do have enough delta-v or could easily have it with the most minor of modifications. They have Hall effect thrusters. It doesn’t take that must to enter a high elliptical Mars orbit. Low thrust takes ~twice the delta v of hi thrust but even still. High thrust delta-v is just 0.9km/s to enter orbit. Isp of Starlink is 25km/s, and the low thrust delta-v would be less than 2km/s, so we’re looking at less than 10% of Starlink’s mass in Argon, a bit over 100 days with one thruster. (You need to do a weird trajectory to enter orbit with low thrust but it’s definitely doable.)

People always like to make the claims about how hard stuff is without actually checking the numbers. Check the numbers!!!

[intelati]

My dream intermediate Martian network is like a 20 starlink system (5 in four planes) all with a *single earth to system satellite* in a L2 point (Along that line)

I've *never* seen anyone suggest anything like that, so I don't even know if it's possible..

[jimvela]

For Martian exploration a Starlink-like constellation would be a reasonable stepping stone.

Nope.

Starlink SC are the wrong solution for Mars.  What Mars exploration needs right now are more and newer com relay spacecraft.

It may be centuries before there is enough presence on the ground for a high density of telecom spacecraft like starlink.

Even if you think I'm wrong, the starlink spacecraft are not able to close a link with Earth as-is, so you'd still need a telecommunications relay spacecraft to enable a starlink bus to function at mars.

Then there's the whole inability of a starlink to insert itself into Mars orbit. 
It's the wrong spacecraft, with the wrong telecom implementation, for Mars in the here and now.

If I am not mistaken, this would already be doable with Falcon Heavy launches instead of Starship.

You are mistaken.

What would be a reasonable timeline for such a thing starting to materialise?

Never.

Whatever goes to Mars to support exploration, it won't be anything like the current Starlink bus.  Perhaps some components and methodologies could be reused, but it would then be an all-new system.

[Robotbeat]

For Martian exploration a Starlink-like constellation would be a reasonable stepping stone.

Nope.

Starlink SC are the wrong solution for Mars.  What Mars exploration needs right now are more and newer com relay spacecraft.

It may be centuries before there is enough presence on the ground for a high density of telecom spacecraft like starlink.

Even if you think I'm wrong, the starlink spacecraft are not able to close a link with Earth as-is, so you'd still need a telecommunications relay spacecraft to enable a starlink bus to function at mars.

Then there's the whole inability of a starlink to insert itself into Mars orbit. 
It's the wrong spacecraft, with the wrong telecom implementation, for Mars in the here and now.

If I am not mistaken, this would already be doable with Falcon Heavy launches instead of Starship.

You are mistaken.

What would be a reasonable timeline for such a thing starting to materialise?

Never.

Whatever goes to Mars to support exploration, it won't be anything like the current Starlink bus.  Perhaps some components and methodologies could be reused, but it would then be an all-new system.

Way too dismissive and incorrect. Starlink can be used as relay satellites. Musk suggested it. Keep in mind Starlink includes multiple types of radios as well as laser links.

To zeroth order, Starlink satellites are free. So you can do things like multiple hop laser comms to Earth with some Starlink satellites at 1.1AU, some at 1.2AU, and so on. You can also compensate for lower gain with lower bitrate.

You’re also incorrect about inability to do insertion. High Isp on-board propulsion is sufficient; you can do low thrust insertions with the right trajectory.

Is it optimal? Maybe not, but it helps not to make technically incorrect statements to slap down an idea that is technically doable. If you want to correct something, you’d better actually be accurate in your statements.

[jimvela]

People always like to make the claims about how hard stuff is without actually checking the numbers. Check the numbers!!!

Check the conops.
It's not just about the Delta V, it's also about the impulse and trajectory design.

To insert at Mars with SEP, you need a trajectory that has a really low rate of closure with the planet because the thrust provided by the SEP thruster is so low. 

A conventional high-thrust insertion does all of its burn in minutes or tens of minutes, where the same delta-V from SEP takes days or weeks.

Then there's the whole power and thermal issue from being at 1.4 to 1.6 AU, and not being able to close a telecom link with Earth using the existing bus.

Starlink is not a Mars-capable bus without enough changes to make it an entirely new spacecraft.

[DanClemmensen]

Apologies if this should be in the Starship section, but since Starlink threads are in this section, I thought it belongs here.

Anyway:

For Martian exploration a Starlink-like constellation would be a reasonable stepping stone. If I am not mistaken, this would already be doable with Falcon Heavy launches instead of Starship. What would be a reasonable timeline for such a thing starting to materialise?

Use Aerosynchronous Mars (AMO) or medium height (MMO) instead. We used GEO for decades before launching LEO constellation. We need LEO constellations because we have millions of geographically-dispersed customers needing high bandwidth.  Until Mars has more than a few million people, most in cities, the higher satellites will be more than adequate. For AMO, three satellites and add four Molinyas if you insist on Polar coverage. For MMO, maybe 12 satellites.

[Robotbeat]

Apologies if this should be in the Starship section, but since Starlink threads are in this section, I thought it belongs here.

Anyway:

For Martian exploration a Starlink-like constellation would be a reasonable stepping stone. If I am not mistaken, this would already be doable with Falcon Heavy launches instead of Starship. What would be a reasonable timeline for such a thing starting to materialise?

In spite of the technically incorrect responses to your post, it is feasible. Not sure they’ll do it, though. FH launches cost real money and they’re focused on scaling out Starlink to meet regulatory deadlines plus readying Starship for Artemis.

[Robotbeat]

Apologies if this should be in the Starship section, but since Starlink threads are in this section, I thought it belongs here.

Anyway:

For Martian exploration a Starlink-like constellation would be a reasonable stepping stone. If I am not mistaken, this would already be doable with Falcon Heavy launches instead of Starship. What would be a reasonable timeline for such a thing starting to materialise?

Use Aerosynchronous Mars (AMO) or medium height (MMO) instead. We used GEO for decades before launching LEO constellation. We need LEO constellations because we have millions of geographically-dispersed customers needing high bandwidth.  Until Mars has more than a few million people, most in cities, the higher satellites will be more than adequate. For AMO, three satellites and add four Molinyas if you insist on Polar coverage. For MMO, maybe 12 satellites.

It only takes like 66 satellites to make a doable LMO constellation. One refueled Starship could launch that many Minis in a single go.

[Robotbeat]

People always like to make the claims about how hard stuff is without actually checking the numbers. Check the numbers!!!

Check the conops.
It's not just about the Delta V, it's also about the impulse and trajectory design.

To insert at Mars with SEP, you need a trajectory that has a really low rate of closure with the planet because the thrust provided by the SEP thruster is so low. 

…

Well yeah, that’s what I already said. “Oh well you have to use a differEnt trajectory.”

Is that even hard? No. Is it a showstopper, enough to claim it can’t be done and slap down someone’s post? Hell no!

[jimvela]

Well yeah, that’s what I already said. “Oh well you have to use a differEnt trajectory.”

Is that even hard? No. Is it a showstopper, enough to claim it can’t be done and slap down someone’s post? Hell no!

Again, the mission systems engineering can't be dismissed with a hand wave so easily.

Could you fling a batch of current generation Starlink busses to Mars as a dumbass publicity stunt? Yep.
Would they be useful? Nope.

Some further questions for you:
How do you close the link with earth?
After insertion to Mars orbit, what prop budget remains, and what mission life do you get out of the arrived vehicles?

What vehicles at Mars currently or in the near term future would be able to communicate with Starlink? (None.)
What planned spacecraft would be able to use the starlink? (None.)
What actual value is provided by this? (None.)


Now, if you want to talk about what would actually benefit Mars exploration in a way that actually helps science, exploration, and colonization- that's a whole different bird, and that's a good topic of discussion/debate. 

It still isn't a current generation starlink bird. I stand by my assessment.

[laszlo]

So we've moved on from LEGO rockets to LEGO comsats?

[waveney]

Well - I've considered this for a while (I am a retired telecoms consultant). 

Starlink for Mars will need beefed up optical links.   The protocols would need changing, to handle the delays, but not drastically.  Both are quite practical once they have it working well around the Earth.  It would offer significant bandwidth for about 10 months of the year (apart from when Mars is in Conjunction or Opposition - losing about a month each time).  The Sun's glare has a significant effect on optic links.

Its direct to cell use would be very applicable for smaller Mars equipment, not needing the complexity of the current transport via the current relay sats.

I predict that they will be deployed the first time a starship gets to Mars.

I have called it MarsLink in my Mars Book to be.

[Robotbeat]

Well yeah, that’s what I already said. “Oh well you have to use a differEnt trajectory.”

Is that even hard? No. Is it a showstopper, enough to claim it can’t be done and slap down someone’s post? Hell no!

Again, the mission systems engineering can't be dismissed with a hand wave so easily.

Could you fling a batch of current generation Starlink busses to Mars as a dumbass publicity stunt? Yep.
Would they be useful? Nope.

Some further questions for you:
How do you close the link with earth?
After insertion to Mars orbit, what prop budget remains, and what mission life do you get out of the arrived vehicles?

What vehicles at Mars currently or in the near term future would be able to communicate with Starlink? (None.)
What planned spacecraft would be able to use the starlink? (None.)
What actual value is provided by this? (None.)


Now, if you want to talk about what would actually benefit Mars exploration in a way that actually helps science, exploration, and colonization- that's a whole different bird, and that's a good topic of discussion/debate. 

It still isn't a current generation starlink bird. I stand by my assessment.

You ask a lot of questions as if to prove it's possible I need to give you a design document. The term for asking a lot of questions so when one objection is answered there are a dozen others behind it is called "Gish Galloping."

And you say "not a current generation starlink bird" as a very nice mobile goalpost that can be moved wherever you like once SpaceX demonstrates using Starlink for Mars in the future.

[DanClemmensen]

Well - I've considered this for a while (I am a retired telecoms consultant). 

Starlink for Mars will need beefed up optical links.   The protocols would need changing, to handle the delays, but not drastically.  Both are quite practical once they have it working well around the Earth.  It would offer significant bandwidth for about 10 months of the year (apart from when Mars is in Conjunction or Opposition - losing about a month each time).  The Sun's glare has a significant effect on optic links.

Its direct to cell use would be very applicable for smaller Mars equipment, not needing the complexity of the current transport via the current relay sats.

I predict that they will be deployed the first time a starship gets to Mars.

I have called it MarsLink in my Mars Book to be.

I think any AMO, MMO, or LMO constellation will be used to create the Mars-to-Mars internet. You need a separate link to Earth. Mars-to-Earth uses completely different protocols even if it uses some of the same hardware. The existing V.2 mini Starlinks already have 100Gbps laser ISL, and this will be more than adequate for the Mars Internet until the Mars population exceeds several million dispersed. I'm assuming that cities will use local fiber. The links back to Earth may either be on the ground or on separate satellites. A link back to Earth has very different physical and usage characteristics than an ISL.

[waveney]

Well - I've considered this for a while (I am a retired telecoms consultant). 

Starlink for Mars will need beefed up optical links.   The protocols would need changing, to handle the delays, but not drastically.  Both are quite practical once they have it working well around the Earth.  It would offer significant bandwidth for about 10 months of the year (apart from when Mars is in Conjunction or Opposition - losing about a month each time).  The Sun's glare has a significant effect on optic links.

Its direct to cell use would be very applicable for smaller Mars equipment, not needing the complexity of the current transport via the current relay sats.

I predict that they will be deployed the first time a starship gets to Mars.

I have called it MarsLink in my Mars Book to be.

I think any AMO, MMO, or LMO constellation will be used to create the Mars-to-Mars internet. You need a separate link to Earth. Mars-to-Earth uses completely different protocols even if it uses some of the same hardware. The existing V.2 mini Starlinks already have 100Gbps laser ISL, and this will be more than adequate for the Mars Internet until the Mars population exceeds several million dispersed. I'm assuming that cities will use local fiber. The links back to Earth may either be on the ground or on separate satellites. A link back to Earth has very different physical and usage characteristics than an ISL.

Agree on the total bandwidth.

Mars to Marslink - as Starlink today. 

Marslink to Earth orbit - New beefy optics (probably needs WDM), new highly delay tollerant protocols with handling for different routing, different ordering of packets, inverse muxing, differing procedures, switching between the satellites will have to change - lots of things, nothing a showstopper.

Earth obit to Earth - as Starlink today

[waveney]

The one month block out at conjunction and opposition can be worked around by placing a relay at Earth or Mars L4 or L5.   This would basically be a pair of Marslink sats back to back.   I don't expect those to be provided for quite while though.   

These links would be useful out side conjunction/opposition for slower than normal data transfers most of the time.

[DanClemmensen]

The one month block out at conjunction and opposition can be worked around by placing a relay at Earth or Mars L4 or L5.   This would basically be a pair of Marslink sats back to back.   I don't expect those to be provided for quite while though.   

These links would be useful out side conjunction/opposition for slower than normal data transfers most of the time.

A link at Mars L4 or L5 will more than double the transit delay. A link a Earth L4 or L will add at least 8 minutes. Three satellites in the same solar orbit, as near to the sun as the engineering easily allows, would be ideal. I have no idea how close that would be: maybe Mercury orbit?

[waveney]

The one month block out at conjunction and opposition can be worked around by placing a relay at Earth or Mars L4 or L5.   This would basically be a pair of Marslink sats back to back.   I don't expect those to be provided for quite while though.   

These links would be useful out side conjunction/opposition for slower than normal data transfers most of the time.

A link at Mars L4 or L5 will more than double the transit delay. A link a Earth L4 or L will add at least 8 minutes. Three satellites in the same solar orbit, as near to the sun as the engineering easily allows, would be ideal. I have no idea how close that would be: maybe Mercury orbit?

They would have long delays, but would be good for quantity of data and the ability to always have some link capacity.

Relays in a near sun orbit would not help.   Too close to the Sun and the glare ruins optic links.  Also there are large DeltaV requirements to get into inner orbits.  The Earth's L4/L5 are the easiest to reach.

Add a relay at one of the 4 points (Earth or Mars, L4 or L5) and you have comms most of the time. 

Add a relay at both L4 and L5  of either Earth or Mars and you have a comms link always, and two (or more) links 90+% of the time.

[steveleach]

The one month block out at conjunction and opposition can be worked around by placing a relay at Earth or Mars L4 or L5.   This would basically be a pair of Marslink sats back to back.   I don't expect those to be provided for quite while though.   

These links would be useful out side conjunction/opposition for slower than normal data transfers most of the time.

A link at Mars L4 or L5 will more than double the transit delay. A link a Earth L4 or L will add at least 8 minutes. Three satellites in the same solar orbit, as near to the sun as the engineering easily allows, would be ideal. I have no idea how close that would be: maybe Mercury orbit?

Does additional transit delay even really matter all that much, in practical terms?

When the best case delay is 15 minutes or so, your comms are already going to be more like email exchanges than phone calls or instant messaging. Without instant feedback, you are also going to want to spend more time crafting your message as well, and I can imagine that adding more delay than an L4/L5 relay does.

[sdsds]

Could someone please provide a sample trajectory for a low-thrust, constant acceleration Mars orbit insertion?

[Brigantine]

L4/L5 are nice stable orbits, but is that a requirement?

Just put one in a nearby earth-trailing heliocentric orbit... it will be many years before orbital interactions cause issues, and even then you have on-board propellant. The orbit doesn't need to last forever, just until the satellite is obsolete and replaced.

Not even any real loss if you launch a new one for each conjunction

As for when... it will probably depend a lot on semantics, which particular Mars-bound hardware can be called "Starlink". They won't exactly be 2nd hand satellites from the LEO constellation, they'll be traditional mission-specific relay sats with incrementally more Starlink-like features and mission extensions.

Take the "Starlink" semantics out of it, set a specific criteria for surface coverage or interplanetary bandwidth for the whole Mars-relay fleet. Or if you want, only the "SpaceX" Mars-relay fleet.

[sdsds]

What's the estimated mass of a Mars Starlink or two? Am I reading the attached table correctly and a low marginal cost F9 RTLS launch delivers ~1.4 t through TMI?

(Screengrab from https://spaceflight101.com/members/falcon-9-falcon-heavy-performance-data/)

[whvholst]

As for when... it will probably depend a lot on semantics, which particular Mars-bound hardware can be called "Starlink". They won't exactly be 2nd hand satellites from the LEO constellation, they'll be traditional mission-specific relay sats with incrementally more Starlink-like features and mission extensions.

Take the "Starlink" semantics out of it, set a specific criteria for surface coverage or interplanetary bandwidth for the whole Mars-relay fleet. Or if you want, only the "SpaceX" Mars-relay fleet.

That is a very fair point. I would not expect those to be identical to the current generation of StarLink satellites because I would expect a Martian StarLink-like constellation to fulfill also a GPS and Mars (atmosphere) remote sensing role. The latter because aerobraking becomes much less risky with up-to-date information about the atmosphere of the celestial body you try to aerobrake in. And the relays, whether they will be in Earth, Mars or even Venus Lagrange points, or in the alternative orbits you described, will be different anyway.

[steveleach]

I think it is likely that there will eventually be a constellation of cheap satellites in low/medium Mars orbit, launched and operated by SpaceX, using technologies developed under the "Starlink" brand, providing (amongst other things) point-to-point ground communication services. It will probably be in place before or at roughly the same time as the first human presence on Mars.

[ZachF]

I think it is likely that there will eventually be a constellation of cheap satellites in low/medium Mars orbit, launched and operated by SpaceX, using technologies developed under the "Starlink" brand, providing (amongst other things) point-to-point ground communication services. It will probably be in place before or at roughly the same time as the first human presence on Mars.

Probably before, I mean SpaceX could sell “Martian Starlink” services to probes from national space programs for the price of several million per year. The data rate will be far superior and much cheaper than setting up your own data relay system. When starship is flying and SpaceX is already building thousands of SL satellites per year it’s not like the cost would be huge… a few customers could probably pay the whole venture off.

[ZachF]

People always like to make the claims about how hard stuff is without actually checking the numbers. Check the numbers!!!

Check the conops.
It's not just about the Delta V, it's also about the impulse and trajectory design.

To insert at Mars with SEP, you need a trajectory that has a really low rate of closure with the planet because the thrust provided by the SEP thruster is so low. 

A conventional high-thrust insertion does all of its burn in minutes or tens of minutes, where the same delta-V from SEP takes days or weeks.

Then there's the whole power and thermal issue from being at 1.4 to 1.6 AU, and not being able to close a telecom link with Earth using the existing bus.

Starlink is not a Mars-capable bus without enough changes to make it an entirely new spacecraft.

Entirely new? Cmon man. They’ll need modification sure, but you’re making mountains of molehills. I wouldn’t be surprised if V3 (or V4) are already being designed to allow the required modifications in mind.

Deploying them is easy if starship is flying (and if SS isn’t flying yet, there’s not point in bothering with this yet), you aero brake into mars orbit, circularize, release, then land on mars or dispose.

[DanClemmensen]

I think it is likely that there will eventually be a constellation of cheap satellites in low/medium Mars orbit, launched and operated by SpaceX, using technologies developed under the "Starlink" brand, providing (amongst other things) point-to-point ground communication services. It will probably be in place before or at roughly the same time as the first human presence on Mars.

Probably before, I mean SpaceX could sell “Martian Starlink” services to probes from national space programs for the price of several million per year. The data rate will be far superior and much cheaper than setting up your own data relay system. When starship is flying and SpaceX is already building thousands of SL satellites per year it’s not like the cost would be huge… a few customers could probably pay the whole venture off.

I think the initial constellation will be multi-purpose, serving as both GPS and comms. The Earth GPS system uses 24 satellites (plus spares) in MEO orbits and provides global coverage. For Mars, each satellite would only provide at most the same throughput as one Starlink satellite, but because of the sparseness of customers, the bandwidth per customer would be higher than here on Earth. The satellites might also have some imaging capabilities.

[waveney]

I think it is likely that there will eventually be a constellation of cheap satellites in low/medium Mars orbit, launched and operated by SpaceX, using technologies developed under the "Starlink" brand, providing (amongst other things) point-to-point ground communication services. It will probably be in place before or at roughly the same time as the first human presence on Mars.

Probably before, I mean SpaceX could sell “Martian Starlink” services to probes from national space programs for the price of several million per year. The data rate will be far superior and much cheaper than setting up your own data relay system. When starship is flying and SpaceX is already building thousands of SL satellites per year it’s not like the cost would be huge… a few customers could probably pay the whole venture off.

I think the initial constellation will be multi-purpose, serving as both GPS and comms. The Earth GPS system uses 24 satellites (plus spares) in MEO orbits and provides global coverage. For Mars, each satellite would only provide at most the same throughput as one Starlink satellite, but because of the sparseness of customers, the bandwidth per customer would be higher than here on Earth. The satellites might also have some imaging capabilities.

I think there will be a Mars GPS (Martian Positioning System - MPS?), but I think it will be a little later. and use different satellites.

GPS needs both satellites and ground stations (with extremely known location and elevation)  This wont be practical until you have at least 3 landers (or people on the ground) to do that.   6 MPS Satellites in high orbits would probably be sufficient for Mars.   

Starlink (on Mars) would need ~50 satellites for a global coverage.

If however they main starlink sats are the same as for Earth, then the high powered relays could also act as the MPS sats.

[DanClemmensen]

I think it is likely that there will eventually be a constellation of cheap satellites in low/medium Mars orbit, launched and operated by SpaceX, using technologies developed under the "Starlink" brand, providing (amongst other things) point-to-point ground communication services. It will probably be in place before or at roughly the same time as the first human presence on Mars.

Probably before, I mean SpaceX could sell “Martian Starlink” services to probes from national space programs for the price of several million per year. The data rate will be far superior and much cheaper than setting up your own data relay system. When starship is flying and SpaceX is already building thousands of SL satellites per year it’s not like the cost would be huge… a few customers could probably pay the whole venture off.

I think the initial constellation will be multi-purpose, serving as both GPS and comms. The Earth GPS system uses 24 satellites (plus spares) in MEO orbits and provides global coverage. For Mars, each satellite would only provide at most the same throughput as one Starlink satellite, but because of the sparseness of customers, the bandwidth per customer would be higher than here on Earth. The satellites might also have some imaging capabilities.

I think there will be a Mars GPS (Martian Positioning System - MPS?), but I think it will be a little later. and use different satellites.

GPS needs both satellites and ground stations (with extremely known location and elevation)  This wont be practical until you have at least 3 landers (or people on the ground) to do that.   6 MPS Satellites in high orbits would probably be sufficient for Mars.   

Starlink (on Mars) would need ~50 satellites for a global coverage.

If however they main starlink sats are the same as for Earth, then the high powered relays could also act as the MPS sats.

Starlink is not needed until there are multiple ground locations, and they can serve as ground station locations. Starlink requires precise location information, basically the same as GPS, to operate.  Today, that information comes from GPS receivers embedded in the user equipment. After a user station is already in the net, it could use the net instead of GPS, but why?

I actually have a patent on deployable ground stations, not user stations, for a constellation. I'm not happy with that patent since IMO the alleged co-inventor and the patent attorney messed it up. However, the reading I did as part of this "invention" means I learned a bit about the requirements. And yes, the crew that deploys a ground station uses GPS.

[waveney]

I think it is likely that there will eventually be a constellation of cheap satellites in low/medium Mars orbit, launched and operated by SpaceX, using technologies developed under the "Starlink" brand, providing (amongst other things) point-to-point ground communication services. It will probably be in place before or at roughly the same time as the first human presence on Mars.

Probably before, I mean SpaceX could sell “Martian Starlink” services to probes from national space programs for the price of several million per year. The data rate will be far superior and much cheaper than setting up your own data relay system. When starship is flying and SpaceX is already building thousands of SL satellites per year it’s not like the cost would be huge… a few customers could probably pay the whole venture off.

I think the initial constellation will be multi-purpose, serving as both GPS and comms. The Earth GPS system uses 24 satellites (plus spares) in MEO orbits and provides global coverage. For Mars, each satellite would only provide at most the same throughput as one Starlink satellite, but because of the sparseness of customers, the bandwidth per customer would be higher than here on Earth. The satellites might also have some imaging capabilities.

I think there will be a Mars GPS (Martian Positioning System - MPS?), but I think it will be a little later. and use different satellites.

GPS needs both satellites and ground stations (with extremely known location and elevation)  This wont be practical until you have at least 3 landers (or people on the ground) to do that.   6 MPS Satellites in high orbits would probably be sufficient for Mars.   

Starlink (on Mars) would need ~50 satellites for a global coverage.

If however they main starlink sats are the same as for Earth, then the high powered relays could also act as the MPS sats.

Starlink is not needed until there are multiple ground locations, and they can serve as ground station locations. Starlink requires precise location information, basically the same as GPS, to operate.  Today, that information comes from GPS receivers embedded in the user equipment. After a user station is already in the net, it could use the net instead of GPS, but why?

I actually have a patent on deployable ground stations, not user stations, for a constellation. I'm not happy with that patent since IMO the alleged co-inventor and the patent attorney messed it up. However, the reading I did as part of this "invention" means I learned a bit about the requirements. And yes, the crew that deploys a ground station uses GPS.

As someone with ~35 patents to my name (all telecoms)...

Starlink wouldn't need GPS on Mars.  On Mars you don't start with territories and the need to treat different users differently.

I can see merit in having both integrated in some way.   Martian GPS would I think only be of use once explorers and rovers start covering serious distances on Mars,  it would be a complete overkill for the first people there.

Starlink would be of use as soon as it is deployed to handle traffic from the existing infrastructure there. 

For example: MRO (HiRise) is heavily constrained as to how much it can observe each day, to keep it within its ability to send the results back.

[DanClemmensen]

As someone with ~35 patents to my name (all telecoms)...

Starlink wouldn't need GPS on Mars.  On Mars you don't start with territories and the need to treat different users differently.

I can see merit in having both integrated in some way.   Martian GPS would I think only be of use once explorers and rovers start covering serious distances on Mars,  it would be a complete overkill for the first people there.

Starlink would be of use as soon as it is deployed to handle traffic from the existing infrastructure there. 

For example: MRO (HiRise) is heavily constrained as to how much it can observe each day, to keep it within its ability to send the results back.

GPS is not about geopolitical boundaries, although it is also used for that.

I spent about 40 years as a systems programmer and system architect in fixed communications. I then shifted to GEO satcomms for 9 years before shifting to LEO satcomms.

The biggest change from fixed comms is that satcomms uses TDMA. TDMA requires extremely tight control in the time domain to keep two transmissions from stepping on each other at the satellite. The speed of light is 300 meters per microsecond. As the distance from sender to satellite varies, the sender must vary the time offset so the signal reaches the satellite at it's allocated time. For GEO this is (almost) a fixed offset for each terminal location. For LEO, this offset is adjusted by feedback continuously after the terminal is in the net. However, to enter the net  or switch to the next satellite the terminal must know where it is to a close approximation, which is why the terminals have GPS.

[waveney]

As someone with ~35 patents to my name (all telecoms)...

Starlink wouldn't need GPS on Mars.  On Mars you don't start with territories and the need to treat different users differently.

I can see merit in having both integrated in some way.   Martian GPS would I think only be of use once explorers and rovers start covering serious distances on Mars,  it would be a complete overkill for the first people there.

Starlink would be of use as soon as it is deployed to handle traffic from the existing infrastructure there. 

For example: MRO (HiRise) is heavily constrained as to how much it can observe each day, to keep it within its ability to send the results back.

GPS is not about geopolitical boundaries, although it is also used for that.

I spent about 40 years as a systems programmer and system architect in fixed communications. I then shifted to GEO satcomms for 9 years before shifting to LEO satcomms.

The biggest change from fixed comms is that satcomms uses TDMA. TDMA requires extremely tight control in the time domain to keep two transmissions from stepping on each other at the satellite. The speed of light is 300 meters per microsecond. As the distance from sender to satellite varies, the sender must vary the time offset so the signal reaches the satellite at it's allocated time. For GEO this is (almost) a fixed offset for each terminal location. For LEO, this offset is adjusted by feedback continuously after the terminal is in the net. However, to enter the net  or switch to the next satellite the terminal must know where it is to a close approximation, which is why the terminals have GPS.

We have similar backgrounds, though I haven't done much with sats.   (Fixed Telecoms (both sides of the pond) - System programmer, system architect, strategic long term vision, consultant, independent consultant, now retired).   

Handling TDMA over fibres adds another dimension where temperature changes can change the apparent distance.   For a while I was working in picoseconds per kilometer per second - to measure the rate of drift.   The system I was involved with tracked the changes and sent nudges down to the terminals to move up/down by a bit.  These could be sent ~250 times a second (if I remember correctly).  The fun job was getting a new terminal in synch...   It could not send data to be timed and hence nudged until it was in synch.   (One of my Patents).   GPS was not an option for that system.

[waveney]

I now agree mixing GPS and Starlink in the same sats for Mars makes sense.

They would operate in higher orbits than normal for Starlink, but a service with delays is wanted with a few dozen sats.  You don't need 2000 sats to support a population of a hundred people on Mars.

Operating at lower altitudes the GPS shouldn't be a problem.   It is very much Space X's style to have one design that does everything.

[whvholst]

Starlink wouldn't need GPS on Mars.  On Mars you don't start with territories and the need to treat different users differently.

The point of having both Starlink-like and GPS-like constellations early on would be to allow for semi-autonomously operating robotic tools. Think stuff like this

Mind you, a GPS satellite at its core is a atom clock (those can be made remarkably small nowadays) that is broadcasting its local time and position. That would not necessarily constitute a trivial modification to Starlink satellites (on top of the bigger solar PV panels), of course.

An additional application would be Mars remote sensing (including atmosphere, for dust storms, actual atmospheric conditions in the upper layers, the latter being vital for safely aerobraking of large vehicles coming in from Terra. That would require additional telescopes on top of the laser interlinks, with photo sensors and maybe even more sensor equipment. This would even be a further departure from the original Starlink design. Although I fully expect this capability to be added to the normal Starlink constellation anyway, or at least to Starshield. Too tempting not to.

[DanClemmensen]

Mind you, a GPS satellite at its core is a atom clock (those can be made remarkably small nowadays) that is broadcasting its local time and position. That would not necessarily constitute a trivial modification to Starlink satellites (on top of the bigger solar PV panels), of course.

I would be very surprised if the Starlink satellites do not have highly accurate ("atomic") clocks, probably rubidium clocks. These should be good enough if they add the sophisticated corrections based on a master clock at the central base. The true magic of GPS is the waveform that encodes the data such that inexpensive receivers can use it.  All of the satellites transmit continuously on the same frequency, using extreme spread codes so a receiver listening on the frequency can decode all of the satellites simultaneously from the same channel.

[launchwatcher]

Mind you, a GPS satellite at its core is a atom clock (those can be made remarkably small nowadays) that is broadcasting its local time and position. That would not necessarily constitute a trivial modification to Starlink satellites (on top of the bigger solar PV panels), of course.

I would be very surprised if the Starlink satellites do not have highly accurate ("atomic") clocks, probably rubidium clocks. These should be good enough if they add the sophisticated corrections based on a master clock at the central base. The true magic of GPS is the waveform that encodes the data such that inexpensive receivers can use it.  All of the satellites transmit continuously on the same frequency, using extreme spread codes so a receiver listening on the frequency can decode all of the satellites simultaneously from the same channel.

Moreover, there have been a number of research papers published recently which demonstrate how to use existing Starlink signals for positioning even without the cooperation of SpaceX.   A direct-sequence spread spectrum beacon with a long enough spreading code is a clock signal; combine a few of them with information about the position and trajectory of the transmitters and you can start making position estimates.

One such paper I found recently:

Nabil Jardak, Ronan Adam: "Practical Use of Starlink Downlink Tones for Positioning"
https://www.mdpi.com/1424-8220/23/6/3234

With help from SpaceX -- particularly around improving estimates of the satellite orbits -- they could do better.

(that said, returning to the main topic of this post, I think it's going to be a while before we see some form of Starlink in orbit around Mars; there are many other more important things to set up first).

[DanClemmensen]

Mind you, a GPS satellite at its core is a atom clock (those can be made remarkably small nowadays) that is broadcasting its local time and position. That would not necessarily constitute a trivial modification to Starlink satellites (on top of the bigger solar PV panels), of course.

I would be very surprised if the Starlink satellites do not have highly accurate ("atomic") clocks, probably rubidium clocks. These should be good enough if they add the sophisticated corrections based on a master clock at the central base. The true magic of GPS is the waveform that encodes the data such that inexpensive receivers can use it.  All of the satellites transmit continuously on the same frequency, using extreme spread codes so a receiver listening on the frequency can decode all of the satellites simultaneously from the same channel.

Moreover, there have been a number of research papers published recently which demonstrate how to use existing Starlink signals for positioning even without the cooperation of SpaceX.   A direct-sequence spread spectrum beacon with a long enough spreading code is a clock signal; combine a few of them with information about the position and trajectory of the transmitters and you can start making position estimates.

One such paper I found recently:

Nabil Jardak, Ronan Adam: "Practical Use of Starlink Downlink Tones for Positioning"
https://www.mdpi.com/1424-8220/23/6/3234

With help from SpaceX -- particularly around improving estimates of the satellite orbits -- they could do better.

(that said, returning to the main topic of this post, I think it's going to be a while before we see some form of Starlink in orbit around Mars; there are many other more important things to set up first).

You can in fact use the Starlink signals for positioning and timing, but that's because the Starlink satellties themselves know their own positions and time with extreme accuracy, very like GPS satellites. However, it's hard to begin listening to a Starlink satellite in the first place unless you know where it is and where you are, because your Starlink antenna is directional in order to get the gain it needs and because the satellite's transmission is directional to get the gain it needs. You can only receive signal from a satellite that is transmitting in your general direction and that your antenna is looking at.  By contrast, a GPS satellite transmission is omnidirectional, and your little GPS receiver's antenna is also omnidirectional. This means you receive from every GPS satellite in line of sight in any direction, but with an extremely weak signal. That's where the magic extreme spread codes come in. They allow GPS to send a relatively small amount of data over this extremely weak link.

[launchwatcher]

Mind you, a GPS satellite at its core is a atom clock (those can be made remarkably small nowadays) that is broadcasting its local time and position. That would not necessarily constitute a trivial modification to Starlink satellites (on top of the bigger solar PV panels), of course.

I would be very surprised if the Starlink satellites do not have highly accurate ("atomic") clocks, probably rubidium clocks. These should be good enough if they add the sophisticated corrections based on a master clock at the central base. The true magic of GPS is the waveform that encodes the data such that inexpensive receivers can use it.  All of the satellites transmit continuously on the same frequency, using extreme spread codes so a receiver listening on the frequency can decode all of the satellites simultaneously from the same channel.

Moreover, there have been a number of research papers published recently which demonstrate how to use existing Starlink signals for positioning even without the cooperation of SpaceX.   A direct-sequence spread spectrum beacon with a long enough spreading code is a clock signal; combine a few of them with information about the position and trajectory of the transmitters and you can start making position estimates.

One such paper I found recently:

Nabil Jardak, Ronan Adam: "Practical Use of Starlink Downlink Tones for Positioning"
https://www.mdpi.com/1424-8220/23/6/3234

With help from SpaceX -- particularly around improving estimates of the satellite orbits -- they could do better.

(that said, returning to the main topic of this post, I think it's going to be a while before we see some form of Starlink in orbit around Mars; there are many other more important things to set up first).

You can in fact use the Starlink signals for positioning and timing, but that's because the Starlink satellties themselves know their own positions and time with extreme accuracy, very like GPS satellites. However, it's hard to begin listening to a Starlink satellite in the first place unless you know where it is and where you are, because your Starlink antenna is directional in order to get the gain it needs and because the satellite's transmission is directional to get the gain it needs. You can only receive signal from a satellite that is transmitting in your general direction and that your antenna is looking at.  By contrast, a GPS satellite transmission is omnidirectional, and your little GPS receiver's antenna is also omnidirectional. This means you receive from every GPS satellite in line of sight in any direction, but with an extremely weak signal. That's where the magic extreme spread codes come in. They allow GPS to send a relatively small amount of data over this extremely weak link.

Did you look at the paper I linked?   If I'm reading it correctly, the researchers were able to use an LNB without a dish as an omnidirectional antenna to receive the Starlink signals.

https://www.mdpi.com/1424-8220/23/6/3234

[ccdengr]

Nabil Jardak, Ronan Adam: "Practical Use of Starlink Downlink Tones for Positioning"
https://www.mdpi.com/1424-8220/23/6/3234

With help from SpaceX -- particularly around improving estimates of the satellite orbits -- they could do better.

Having skimmed the paper, it's not clear to me that precise info about the satellite positions is needed, but some information is.  The authors used the NORAD TLEs for the satellites and say

Therefore, the frequency error state has captured most of the satellites’ orbit and clock errors, preventing
their total propagation into the user position state. The remaining position error is mainly
due to measurement noise combined with weak satellite geometry.

That suggests to me (though maybe I'm wrong) that satellite position knowledge is not the dominating error source.

I don't know how much better Starlink knows the satellite positions, or how.

[edzieba]

Mind you, a GPS satellite at its core is a atom clock (those can be made remarkably small nowadays) that is broadcasting its local time and position. That would not necessarily constitute a trivial modification to Starlink satellites (on top of the bigger solar PV panels), of course.

The clock is only half the solution. The other half is the accurate and up to date measurement of the true orbital parameters of each satellite from a fixed reference (for earth-bound GNSS, that's a reference to fixed ground stations). Orbits will drift and timings will drift - even for atomic clocks - over time, so the system requires constant measurement of those parameters and updating of the satellites that broadcast that up to date orbit reference data along with the timecodes - for Navstar GPS, that would be the Operational Control Segment.

[DanClemmensen]

Mind you, a GPS satellite at its core is a atom clock (those can be made remarkably small nowadays) that is broadcasting its local time and position. That would not necessarily constitute a trivial modification to Starlink satellites (on top of the bigger solar PV panels), of course.

The clock is only half the solution. The other half is the accurate and up to date measurement of the true orbital parameters of each satellite from a fixed reference (for earth-bound GNSS, that's a reference to fixed ground stations). Orbits will drift and timings will drift - even for atomic clocks - over time, so the system requires constant measurement of those parameters and updating of the satellites that broadcast that up to date orbit reference data along with the timecodes - for Navstar GPS, that would be the Operational Control Segment.

GPS is an incredible achievement, but its basic architecture is 45 years old. Adding explicit positioning capability to Starlink could take advantage of existing Starlink features like the ISL links and much more capable onboard computers. Adding hardware-assisted timestamps (conceptually similar to IEEE 1588 but with sub-nanosecond precision) to the ISL links would increase the satellite position accuracy and clock accuracy for all the satellites, averaging out the uncertainties in the positions as determined by the ground control links.

I am not a GPS professional. Basics for those of us who are not GPS professionals: GPS works by allowing the receiver to solve an equation in four unknowns (X,Y, Z, time) given four inputs: the signals from four satellites. Each signal includes the (X,Y,Z,T) of the satellite at the time the signal was transmitted. The receiver does not explicitly know the actual distance to each satellite. Instead, it computes the difference in distances to each satellite by comparing the differences in received time. (With more satellites, you get to solve a system with 4 unknowns and five or more equations. This lets you reduce the uncertainties.) This means that satellite position accuracy is as important as satellite clock accuracy: one microsecond of clock accuracy is equivalent to 300 meters of position accuracy.

[waveney]

Additionally by measuring the detailed errors and corrections needed, the gravity maps of Mars could be very significantly enhanced.  These are very good for detecting hidden features such as buried craters and buried volcanoes.

They do this already on the orbits of MRO (and others) but this would yield much higher detail.

[jak Kennedy]

Whether or not Starlink in it's current configuration will be used in Mars orbit, my question is could they be deployed by Starship after a deorbit burn (if it uses one) even if then placed into a highly elliptical orbit?

[waveney]

Whether or not Starlink in it's current configuration will be used in Mars orbit, my question is could they be deployed by Starship after a deorbit burn (if it uses one) even if then placed into a highly elliptical orbit?

Yes

[Brigantine]

could they be deployed by Starship after a deorbit burn (if it uses one) even if then placed into a highly elliptical orbit?

AIUI the plan was direct EDL from a hyperbolic transfer orbit. So it sounds like your suggestion is to propulsively capture (0.67 km/s) before closest approach, then deploy, then adjust closest approach to enter Mars' atmosphere for EDL.

That might be possible, but at a cost of 20+ tons of payload. (roughly)
You'd need to think about extra propellant storage/conditioning for the propulsive capture, if typical Mars ships don't use the main tanks for the Mars landing burn.

An alternative is to direct "E" from a hyperbolic transfer orbit, Starlinks still on board, but save the "DL" for later.
- Come in from heliocentric orbit at the appropriate Starlink inclination,
- in 1 pass aerocapture/aerobrake to some Mid-Mars-Transfer orbit,
- then at Mid-Mars height, small burn/deploy/small burn and
- then EDL (perhaps in 2 further passes if your destination isn't at a convenient latitude).

This will cost you hours to sols of time, but shouldn't cost much in terms of payload - you may even get a small (<25%) discount on your Starlink payload.

Does that seem right?

[edzieba]

Mind you, a GPS satellite at its core is a atom clock (those can be made remarkably small nowadays) that is broadcasting its local time and position. That would not necessarily constitute a trivial modification to Starlink satellites (on top of the bigger solar PV panels), of course.

The clock is only half the solution. The other half is the accurate and up to date measurement of the true orbital parameters of each satellite from a fixed reference (for earth-bound GNSS, that's a reference to fixed ground stations). Orbits will drift and timings will drift - even for atomic clocks - over time, so the system requires constant measurement of those parameters and updating of the satellites that broadcast that up to date orbit reference data along with the timecodes - for Navstar GPS, that would be the Operational Control Segment.

GPS is an incredible achievement, but its basic architecture is 45 years old. Adding explicit positioning capability to Starlink could take advantage of existing Starlink features like the ISL links and much more capable onboard computers. Adding hardware-assisted timestamps (conceptually similar to IEEE 1588 but with sub-nanosecond precision) to the ISL links would increase the satellite position accuracy and clock accuracy for all the satellites, averaging out the uncertainties in the positions as determined by the ground control links.

That doesn't actually solve the problem: Mars has no groundside measurement reference and control system, and Mars has no independent baseline geodetic survey to align to or from.

Lets assume for a moment that our satellites have magical super-atomic clocks that never ever drift and can ignore relativistic effects, such that we do not need to concern ourselves with satellite-to-satellite relative drift, we can synchronise all the clocks at launch and then ignore sync forever. Lets also assume that the satellites themselves have such exquisitely precise ISL steering gimbals (well above the requirements for laser communicaitons) and truly outstanding laser pulse timing (for accurate ranging) that each satellite can create an exact model of satellite relative positions independently of any ground stations. (Both of these are extremely generous assumptions that either vastly inflate satellite cost or are plain not physically possible).
Even in that situation, all your GNSS system will tell you is your position relative to that satellite constellation. Not your position relative to Mars, which is what you actually care about - as a gross example, a difference in "what time is it" of 1 minute (a difference of what time the satellite constellation thought Mars had when it was set up vs. the actual local time, not a timing error in the constellation itself) would leave you over 14km away if you were standing at Mars' equator. To solve that, you need to accurately align your constellation to the moving surface of Mars. That needs a minimum of 3 independent ground stations, sufficiently spaced to allow trilateration of sufficient accuracy, and those ground stations need a precisely known relationship to each other (e.g. ground-based surveying or some independent triangulation method). Coordinate system alignment is no simple task at planetary scales where assumptions like "gravity always points straight down" or "the ground does not change length" are not strictly true.
If you then incorporate more realistic assumptions, where clocks drift, satellite positions need to tracked at multiple ground sites to allow accurate triangulation, and satellite orbits continuously shift from surface gravity influence and influence from Phobos and Deimos, the demands on the ground segment only increase.

On Earth, its easy to overlook these baseline requirement because we were producing accurate geographic and geodetic surveys centuries before the first satellite was ever launched. On Mars, we do not have that baseline available. We have satellite imagery of the surface, but that is very much not the same as geodetic survey.


A GNSS system for Mars is obviously not impossible, but it is much more complex than just throwing some clocks on some satellites.

[steveleach]

That doesn't actually solve the problem: Mars has no groundside measurement reference and control system, and Mars has no independent baseline geodetic survey to align to or from.

Lets assume for a moment that our satellites have magical super-atomic clocks that never ever drift and can ignore relativistic effects, such that we do not need to concern ourselves with satellite-to-satellite relative drift, we can synchronise all the clocks at launch and then ignore sync forever. Lets also assume that the satellites themselves have such exquisitely precise ISL steering gimbals (well above the requirements for laser communicaitons) and truly outstanding laser pulse timing (for accurate ranging) that each satellite can create an exact model of satellite relative positions independently of any ground stations. (Both of these are extremely generous assumptions that either vastly inflate satellite cost or are plain not physically possible).
Even in that situation, all your GNSS system will tell you is your position relative to that satellite constellation. Not your position relative to Mars, which is what you actually care about - as a gross example, a difference in "what time is it" of 1 minute (a difference of what time the satellite constellation thought Mars had when it was set up vs. the actual local time, not a timing error in the constellation itself) would leave you over 14km away if you were standing at Mars' equator. To solve that, you need to accurately align your constellation to the moving surface of Mars. That needs a minimum of 3 independent ground stations, sufficiently spaced to allow trilateration of sufficient accuracy, and those ground stations need a precisely known relationship to each other (e.g. ground-based surveying or some independent triangulation method). Coordinate system alignment is no simple task at planetary scales where assumptions like "gravity always points straight down" or "the ground does not change length" are not strictly true.
If you then incorporate more realistic assumptions, where clocks drift, satellite positions need to tracked at multiple ground sites to allow accurate triangulation, and satellite orbits continuously shift from surface gravity influence and influence from Phobos and Deimos, the demands on the ground segment only increase.

On Earth, its easy to overlook these baseline requirement because we were producing accurate geographic and geodetic surveys centuries before the first satellite was ever launched. On Mars, we do not have that baseline available. We have satellite imagery of the surface, but that is very much not the same as geodetic survey.


A GNSS system for Mars is obviously not impossible, but it is much more complex than just throwing some clocks on some satellites.

Surely if all the satellites know where they are in relation to each other in X,Y,Z,T (which, as you say, is not trivial) then all you need is a single reference point on the surface that 4 or more sats can reach.

From there, any other point that can be reached by 4 or more sats can be located relative to the reference point, right?

Or am I missing something?

[waveney]

That doesn't actually solve the problem: Mars has no groundside measurement reference and control system, and Mars has no independent baseline geodetic survey to align to or from.

Lets assume for a moment that our satellites have magical super-atomic clocks that never ever drift and can ignore relativistic effects, such that we do not need to concern ourselves with satellite-to-satellite relative drift, we can synchronise all the clocks at launch and then ignore sync forever. Lets also assume that the satellites themselves have such exquisitely precise ISL steering gimbals (well above the requirements for laser communicaitons) and truly outstanding laser pulse timing (for accurate ranging) that each satellite can create an exact model of satellite relative positions independently of any ground stations. (Both of these are extremely generous assumptions that either vastly inflate satellite cost or are plain not physically possible).
Even in that situation, all your GNSS system will tell you is your position relative to that satellite constellation. Not your position relative to Mars, which is what you actually care about - as a gross example, a difference in "what time is it" of 1 minute (a difference of what time the satellite constellation thought Mars had when it was set up vs. the actual local time, not a timing error in the constellation itself) would leave you over 14km away if you were standing at Mars' equator. To solve that, you need to accurately align your constellation to the moving surface of Mars. That needs a minimum of 3 independent ground stations, sufficiently spaced to allow trilateration of sufficient accuracy, and those ground stations need a precisely known relationship to each other (e.g. ground-based surveying or some independent triangulation method). Coordinate system alignment is no simple task at planetary scales where assumptions like "gravity always points straight down" or "the ground does not change length" are not strictly true.
If you then incorporate more realistic assumptions, where clocks drift, satellite positions need to tracked at multiple ground sites to allow accurate triangulation, and satellite orbits continuously shift from surface gravity influence and influence from Phobos and Deimos, the demands on the ground segment only increase.

On Earth, its easy to overlook these baseline requirement because we were producing accurate geographic and geodetic surveys centuries before the first satellite was ever launched. On Mars, we do not have that baseline available. We have satellite imagery of the surface, but that is very much not the same as geodetic survey.


A GNSS system for Mars is obviously not impossible, but it is much more complex than just throwing some clocks on some satellites.

Surely if all the satellites know where they are in relation to each other in X,Y,Z,T (which, as you say, is not trivial) then all you need is a single reference point on the surface that 4 or more sats can reach.

From there, any other point that can be reached by 4 or more sats can be located relative to the reference point, right?

Or am I missing something?

Some poor service would be possible with a single reference point.

A better service needs at least 3 (probably more) reference points.

It depends on what the point of the service is?  If it is a few kilometre accuracy you need, then one reference point is probably fine.  If you want to know the precise location of a rock or for a Seismometers you need high accuracy.   What is the Martian GPS for?

[Brigantine]

Surely if all the satellites know where they are in relation to each other in X,Y,Z,T (which, as you say, is not trivial) then all you need is a single reference point on the surface that 4 or more sats can reach.

From there, any other point that can be reached by 4 or more sats can be located relative to the reference point, right?

Or am I missing something?

Apparently the Chandler wobble is only 10cm - 2 orders of magnitude less than on Earth

[steveleach]

Surely if all the satellites know where they are in relation to each other in X,Y,Z,T (which, as you say, is not trivial) then all you need is a single reference point on the surface that 4 or more sats can reach.

From there, any other point that can be reached by 4 or more sats can be located relative to the reference point, right?

Or am I missing something?

Some poor service would be possible with a single reference point.

A better service needs at least 3 (probably more) reference points.

It depends on what the point of the service is?  If it is a few kilometre accuracy you need, then one reference point is probably fine.  If you want to know the precise location of a rock or for a Seismometers you need high accuracy.   What is the Martian GPS for?

Why do you need more than one ground-based reference point, out of interest?  As far as I can figure, all you need is one point in the ground to fix the planet in relation to the shell of satellites.

[waveney]

Surely if all the satellites know where they are in relation to each other in X,Y,Z,T (which, as you say, is not trivial) then all you need is a single reference point on the surface that 4 or more sats can reach.

From there, any other point that can be reached by 4 or more sats can be located relative to the reference point, right?

Or am I missing something?

Some poor service would be possible with a single reference point.

A better service needs at least 3 (probably more) reference points.

It depends on what the point of the service is?  If it is a few kilometre accuracy you need, then one reference point is probably fine.  If you want to know the precise location of a rock or for a Seismometers you need high accuracy.   What is the Martian GPS for?

Why do you need more than one ground-based reference point, out of interest?  As far as I can figure, all you need is one point in the ground to fix the planet in relation to the shell of satellites.

1) Mars is NOT a perfect sphere. (This will perturb the sats)
2) Mars has moons (these will perturb the sats)
3) The solar system has other bodies (these will perturb the sats)

etc etc.

Finding out the perturbation of the sats is quite useful for mapping gravity anomalies

[steveleach]

Why do you need more than one ground-based reference point, out of interest?  As far as I can figure, all you need is one point in the ground to fix the planet in relation to the shell of satellites.

1) Mars is NOT a perfect sphere. (This will perturb the sats)
2) Mars has moons (these will perturb the sats)
3) The solar system has other bodies (these will perturb the sats)

etc etc.

Finding out the perturbation of the sats is quite useful for mapping gravity anomalies

Yep, but why do you need more than one ground station to handle that perterbation?

Not that it matters, because I've since realised that you need multiple groundstations anyway: you have a sphere within a sphere (sorta) and with just one point on the inner sphere there is still a fair amount of freedom to rotate it slightly.

[DanClemmensen]

Mind you, a GPS satellite at its core is a atom clock (those can be made remarkably small nowadays) that is broadcasting its local time and position. That would not necessarily constitute a trivial modification to Starlink satellites (on top of the bigger solar PV panels), of course.

The clock is only half the solution. The other half is the accurate and up to date measurement of the true orbital parameters of each satellite from a fixed reference (for earth-bound GNSS, that's a reference to fixed ground stations). Orbits will drift and timings will drift - even for atomic clocks - over time, so the system requires constant measurement of those parameters and updating of the satellites that broadcast that up to date orbit reference data along with the timecodes - for Navstar GPS, that would be the Operational Control Segment.

GPS is an incredible achievement, but its basic architecture is 45 years old. Adding explicit positioning capability to Starlink could take advantage of existing Starlink features like the ISL links and much more capable onboard computers. Adding hardware-assisted timestamps (conceptually similar to IEEE 1588 but with sub-nanosecond precision) to the ISL links would increase the satellite position accuracy and clock accuracy for all the satellites, averaging out the uncertainties in the positions as determined by the ground control links.

That doesn't actually solve the problem: Mars has no groundside measurement reference and control system, and Mars has no independent baseline geodetic survey to align to or from.

Lets assume for a moment that our satellites have magical super-atomic clocks that never ever drift and can ignore relativistic effects, such that we do not need to concern ourselves with satellite-to-satellite relative drift, we can synchronise all the clocks at launch and then ignore sync forever. Lets also assume that the satellites themselves have such exquisitely precise ISL steering gimbals (well above the requirements for laser communicaitons) and truly outstanding laser pulse timing (for accurate ranging) that each satellite can create an exact model of satellite relative positions independently of any ground stations. (Both of these are extremely generous assumptions that either vastly inflate satellite cost or are plain not physically possible).
Even in that situation, all your GNSS system will tell you is your position relative to that satellite constellation. Not your position relative to Mars, which is what you actually care about - as a gross example, a difference in "what time is it" of 1 minute (a difference of what time the satellite constellation thought Mars had when it was set up vs. the actual local time, not a timing error in the constellation itself) would leave you over 14km away if you were standing at Mars' equator. To solve that, you need to accurately align your constellation to the moving surface of Mars. That needs a minimum of 3 independent ground stations, sufficiently spaced to allow trilateration of sufficient accuracy, and those ground stations need a precisely known relationship to each other (e.g. ground-based surveying or some independent triangulation method). Coordinate system alignment is no simple task at planetary scales where assumptions like "gravity always points straight down" or "the ground does not change length" are not strictly true.
If you then incorporate more realistic assumptions, where clocks drift, satellite positions need to tracked at multiple ground sites to allow accurate triangulation, and satellite orbits continuously shift from surface gravity influence and influence from Phobos and Deimos, the demands on the ground segment only increase.

On Earth, its easy to overlook these baseline requirement because we were producing accurate geographic and geodetic surveys centuries before the first satellite was ever launched. On Mars, we do not have that baseline available. We have satellite imagery of the surface, but that is very much not the same as geodetic survey.


A GNSS system for Mars is obviously not impossible, but it is much more complex than just throwing some clocks on some satellites.

Of course. You need at least two ground stations, and more are better, but each ground station is not much more than a grounded satellite. You designate one as the Martian base location, like Greenwich on Earth. During initial operation of the system, these stations learn and then refine their locations over a period of weeks as the system calibrates itself. Reference time is a consensus based on all of the clocks, like UTC here on Earth, and would be a lot more stable and accurate than any one of the clocks. It might be helpful to install more accurate clocks at the ground stations, and coordinate them and then slave the satellite's clocks to them, but this is a refinement.

[DanClemmensen]

Lets assume for a moment that our satellites have magical super-atomic clocks that never ever drift and can ignore relativistic effects, such that we do not need to concern ourselves with satellite-to-satellite relative drift, we can synchronise all the clocks at launch and then ignore sync forever. Lets also assume that the satellites themselves have such exquisitely precise ISL steering gimbals (well above the requirements for laser communicaitons) and truly outstanding laser pulse timing (for accurate ranging) that each satellite can create an exact model of satellite relative positions independently of any ground stations. (Both of these are extremely generous assumptions that either vastly inflate satellite cost or are plain not physically possible).

The clocks do not need to be perfect. They will be adjusted to reach a consensus among all the clocks in the network. This requires software, not expensive hardware.

The ISL only needs to be accurate enough to allow intersatellite communication. The  only thing a pair of communicating satellites need on this link is an extremely precise tic embedded in the signal, similar to the IEEE 1588 hardware-supplied tic. One of these every second will be more than adequate. A single tic can be as precise as the baud rate (i.e., the symbol rate, not the bit rate.) I do no know the baud rate for a Starlink ISL but with an aggregate transmission rate of 100Gbps the baud rate is unlikely to be less than 1GHz and the tic is precise to within one nanosecond (30 cm). The two satellites determine their separation by communicating the time of receipt of the tic as measured by their own clock. This requires a very small amount of extra functionality in the transmitter's encoder electronics and the receiver's decoder electronics, plus software.

Note that this can all be done using the "GPS" omnidirectional radio signals instead of the lasers, albeit much more slowly. They already have the equivalent of an extreme precision tic. This may be needed during deployment so the satellites can find each other in the first place.

[CuddlyRocket]

What is the Martian GPS for?

This is the fundamental question, which no-one is answering. People seem lost in the engineering romance of having a Martian GPS. And a Mars-wide communications network. But what's the actual need; who needs it, and when will they need it?

Who's going to design and install these capabilities? And who goes to pay for design, installation and maintenance? Are these the same people who have the need? If not, how to deal with the financial mismatch?

[intelati]

What is the Martian GPS for?

This is the fundamental question, which no-one is answering.... And a Mars-wide communications network. But what's the actual need; who needs it, and when will they need it?

Who's going to design and install these capabilities? And who goes to pay for design, installation and maintenance? Are these the same people who have the need? If not, how to deal with the financial mismatch?

NASA. And honestly they *should be* buying/investigating commercial options.

Their "communication network" consists of "Mars Reconnaissance Orbiter" (a Martian 'Spy Sat') and (a couple? [Currently listening to back episodes of WeMartians, so I forget the State of Mars currently]) other SATs with other uses (and Rover communication takes away from their scientific value)

Hence my recommendation to take that use off of said satellites with Starlinks??!!?

[DanClemmensen]

What is the Martian GPS for?

This is the fundamental question, which no-one is answering. People seem lost in the engineering romance of having a Martian GPS. And a Mars-wide communications network. But what's the actual need; who needs it, and when will they need it?

Who's going to design and install these capabilities? And who goes to pay for design, installation and maintenance? Are these the same people who have the need? If not, how to deal with the financial mismatch?

If humans or robots are going to Mars at all, they need to know where they are and they need to communicate.

GPS is the most cost-effective way to do precision surveying. It is used for this purpose now here on Earth to dramatically increase the efficiency of survey crews.

The comms part of the system ("starlink") can be quite modest: maybe 24 satellites in medium-altitude orbits. This is also exactly the constellation size and orbit that can implement GPS.

There is no need for a bigger constellation until the small one saturates. If it saturates, it will be because the demand is high and there are enough customers to pay for a larger constellation.

[ccdengr]

GPS is the most cost-effective way to do precision surveying.

Certainly, but that doesn't count the $12B the DoD spent on initial deployment and the roughly $2B annual operations cost.

I think people are not appreciating the difficulty of building out a GPS system, though I'm sure it could be done for less than DoD.

[DanClemmensen]

GPS is the most cost-effective way to do precision surveying.

Certainly, but that doesn't count the $12B the DoD spent on initial deployment and the roughly $2B annual operations cost.

I think people are not appreciating the difficulty of building out a GPS system, though I'm sure it could be done for less than DoD.

The first GPS satellite launched 45 years ago. It was bleeding edge and hyper-expensive. Basically everything except the satellite busses and the launches are now cheaper by a factor of 1000 or more. You could almost certainly launch a new-design GPS constellation in a single launch.

[ccdengr]

You could almost certainly launch a new-design GPS constellation in a single launch.

It cost 10 billion euros to deploy Galileo, was that just incompetence and waste?

[Solarsail]

What if we go half way between Starlink/GPS block III and MRO?

I'll propose some relaxed requirements:  Atomic clocks may be required of ground terminals, ground terminals may use 2-way communication with the satellites in position determination.  Each ground terminal may add compute load to satellites and visa-versa. Location precision is 20km, and you only need contact with it on a daily basis.  To do terrain surveys, drop portable terminals in a breadcrumb trail on the ground and wait for them to get contact with the orbiting system.  Pick them up a day later.  Comms also only needs to be available at least daily.

How few satellites can you get away with now?  I'd read somewhere that you could do a GPS system on mars using 1 satellite, if you can smear your position determination across the orbital arc, and require compute work on the satellite.  Could the same satellite take on communications work in a store-forward architecture?  Do you need 1 ground station worth of calibration to reach 20km precision?  More?  Can you do it with a synthetic-aperture-radar instead?  3 ground stations and 1 satellite?  1 ground station and 3 satellites?  If you can get to useful position date with 1 satellite and a single beacon, can the system gradually improve with expansions of the satellite constellation?

[edzieba]

Lets assume for a moment that our satellites have magical super-atomic clocks that never ever drift and can ignore relativistic effects, such that we do not need to concern ourselves with satellite-to-satellite relative drift, we can synchronise all the clocks at launch and then ignore sync forever. Lets also assume that the satellites themselves have such exquisitely precise ISL steering gimbals (well above the requirements for laser communicaitons) and truly outstanding laser pulse timing (for accurate ranging) that each satellite can create an exact model of satellite relative positions independently of any ground stations. (Both of these are extremely generous assumptions that either vastly inflate satellite cost or are plain not physically possible).

The clocks do not need to be perfect. They will be adjusted to reach a consensus among all the clocks in the network. This requires software, not expensive hardware.

The ISL only needs to be accurate enough to allow intersatellite communication. The  only thing a pair of communicating satellites need on this link is an extremely precise tic embedded in the signal, similar to the IEEE 1588 hardware-supplied tic. One of these every second will be more than adequate. A single tic can be as precise as the baud rate (i.e., the symbol rate, not the bit rate.) I do no know the baud rate for a Starlink ISL but with an aggregate transmission rate of 100Gbps the baud rate is unlikely to be less than 1GHz and the tic is precise to within one nanosecond (30 cm). The two satellites determine their separation by communicating the time of receipt of the tic as measured by their own clock. This requires a very small amount of extra functionality in the transmitter's encoder electronics and the receiver's decoder electronics, plus software.

Note that this can all be done using the "GPS" omnidirectional radio signals instead of the lasers, albeit much more slowly. They already have the equivalent of an extreme precision tic. This may be needed during deployment so the satellites can find each other in the first place.

You missed (or ignored) the entire previous post. Just having an accurate clock is not sufficient for a trilateration-based GNSS. You need precise knowledge of the exact satellite positions (both relative to each other and relative to the planet's surface) and precise knowledge of timing difference - not just averages, as its the timing differences you rely on for the critical time-of-flight ranging so accurate absolute timebases are required.

It is not as easy as you want to pretend.

[sdsds]

It is not as easy as you want to pretend.

Yes, establishing a Mars GNSS system will not be easy, and there's no current use case.

In stark contrast, a UHF-to-X-band store-and-forward communications system already exists and is in active use: MaROS. It utilizes payload packages on MRO, Maven and Mars Odyssey to forward data received via UHF from Mars surface stations to Earth surface DSN X-band stations.

For the first Starship landed mission does SpaceX want to rent time on that service? I somehow doubt it.

How does that well-defined MaROS payload package compare in size and mass to the standard Starlink payload? Maybe SpaceX could provide the launch service and satellite bus in exchange for a MaROS payload and time on the DSN. Alternately maybe Starlink could leap-frog MaROS and establish a UHF-to-Laser store-and-forward communications system between (specialized) Starlinks in Mars orbit and their equivalent in Earth orbit....

[waveney]

It is not as easy as you want to pretend.

In stark contrast, a UHF-to-X-band store-and-forward communications system already exists and is in active use: MaROS. It utilizes payload packages on MRO, Maven and Mars Odyssey to forward data received via UHF from Mars surface stations to Earth surface DSN X-band stations.

It is horrendously overloaded.  The available data rate seriously limits the science done by orbiters and landers.

[DanClemmensen]

Lets assume for a moment that our satellites have magical super-atomic clocks that never ever drift and can ignore relativistic effects, such that we do not need to concern ourselves with satellite-to-satellite relative drift, we can synchronise all the clocks at launch and then ignore sync forever. Lets also assume that the satellites themselves have such exquisitely precise ISL steering gimbals (well above the requirements for laser communicaitons) and truly outstanding laser pulse timing (for accurate ranging) that each satellite can create an exact model of satellite relative positions independently of any ground stations. (Both of these are extremely generous assumptions that either vastly inflate satellite cost or are plain not physically possible).

The clocks do not need to be perfect. They will be adjusted to reach a consensus among all the clocks in the network. This requires software, not expensive hardware.

The ISL only needs to be accurate enough to allow intersatellite communication. The  only thing a pair of communicating satellites need on this link is an extremely precise tic embedded in the signal, similar to the IEEE 1588 hardware-supplied tic. One of these every second will be more than adequate. A single tic can be as precise as the baud rate (i.e., the symbol rate, not the bit rate.) I do no know the baud rate for a Starlink ISL but with an aggregate transmission rate of 100Gbps the baud rate is unlikely to be less than 1GHz and the tic is precise to within one nanosecond (30 cm). The two satellites determine their separation by communicating the time of receipt of the tic as measured by their own clock. This requires a very small amount of extra functionality in the transmitter's encoder electronics and the receiver's decoder electronics, plus software.

Note that this can all be done using the "GPS" omnidirectional radio signals instead of the lasers, albeit much more slowly. They already have the equivalent of an extreme precision tic. This may be needed during deployment so the satellites can find each other in the first place.

You missed (or ignored) the entire previous post. Just having an accurate clock is not sufficient for a trilateration-based GNSS. You need precise knowledge of the exact satellite positions (both relative to each other and relative to the planet's surface) and precise knowledge of timing difference - not just averages, as its the timing differences you rely on for the critical time-of-flight ranging so accurate absolute timebases are required.

It is not as easy as you want to pretend.

It may in fact be a lot more complicated than I would want it to be, but I neither missed nor ignored any post on this thread. I have not responded to the "Galileo" post because I do not know enough about its funding decisions.

From a theoretical perspective, a system of multiple reasonably precise clocks that can communicate their local (X,Y,Z,T) with each other will be able to collectively refine their (X,Y,Z,T)s. When two or more of them are in "fixed" locations (e.g., on the Martian surface) This will eventually converge into a system with GPS-like functionality. Yes, I know satellites move.

To your points:

There is no such thing as "absolute" time. Here on earth, we use UTC and its kin. UTC is a consensus time based on coordination among multiple extreme-precision atomic clocks. Rubidium clocks are atomic clocks of lower quality but they still derive their accuracy from atomic transitions, and averaging enough of them will provide an adequate "absolute" time.

We used "fixed" ground reference locations that were originally surveyed by non-GPS means, because that's all we had to start with. The relative positions of those stations have since been refined using GPS, including any changes due to plate tectonics.

Relevance to Martian Starlink: Starlink depends on GPS-like positioning and will not work without it.

[ccdengr]

[MarOS] is horrendously overloaded.  The available data rate seriously limits the science done by orbiters and landers.

I'm not sure if "horrendously" is fair.  There are only two rovers operating now.  But certainly more capacity could be used.

Of course "Martian Starlink" for communication back to Earth would not only need sats to talk to the surface, but sats to talk to Earth.

As for positioning, it depends on how much accuracy you want.  https://en.wikipedia.org/wiki/Transit_%28satellite%29 got 200-meter accuracy with just a few sats.  Getting meter-scale accuracy or better is a lot harder, and I would argue is not needed any time soon.  Even if landers needed positioning information, it would be much simpler to set up a fixed network at the landing sites.  SpaceX only uses GPS now because it's an available resource they get for free.

[waveney]

[MarOS] is horrendously overloaded.  The available data rate seriously limits the science done by orbiters and landers.

I'm not sure if "horrendously" is fair.  There are only two rovers operating now.  But certainly more capacity could be used.

Of course "Martian Starlink" for communication back to Earth would not only need sats to talk to the surface, but sats to talk to Earth.

As for positioning, it depends on how much accuracy you want.  https://en.wikipedia.org/wiki/Transit_%28satellite%29 got 200-meter accuracy with just a few sats.  Getting meter-scale accuracy or better is a lot harder, and I would argue is not needed any time soon.  Even if landers needed positioning information, it would be much simpler to set up a fixed network at the landing sites.  SpaceX only uses GPS now because it's an available resource they get for free.

The main instruments on MRO can only be used for a limited amount each day.   HiRise in particular.  They could use 10 times the current bandwidth easily.

[DanClemmensen]

[MarOS] is horrendously overloaded.  The available data rate seriously limits the science done by orbiters and landers.

Of course "Martian Starlink" for communication back to Earth would not only need sats to talk to the surface, but sats to talk to Earth.

Agreed. "Martian Starlink" is for on-Mars and near-Mars communication. Starlink satellites are not optimized for Mars-to-Earth comms, which need different hardware and different protocols. The planet-to-planet links can and should be on different satellites. These satellites could connect to their Mars users via ISL links to the Starlink satellites.

[waveney]

[MarOS] is horrendously overloaded.  The available data rate seriously limits the science done by orbiters and landers.

Of course "Martian Starlink" for communication back to Earth would not only need sats to talk to the surface, but sats to talk to Earth.

Agreed. "Martian Starlink" is for on-Mars and near-Mars communication. Starlink satellites are not optimized for Mars-to-Earth comms, which need different hardware and different protocols. The planet-to-planet links can and should be on different satellites. These satellites could connect to their Mars users via ISL links to the Starlink satellites.

I thought that originally, but now think it would be simpler to equip them all with the planet to planet capability.  They can then be used in parallel to provide a much larger inter planet capability.  Different Sats would use different wavelengths to communicate to Earth at the same time. 

I originally thought a Martian GPS (MPS) would use separate sats to Starlink, but I now accept your arguments and think one design that can do everything is better.

One design that does all three functions is I think the best.  it provides redundancy, needs less sats in total.  One starship could deliver enough to provide all the comms and GPS needed for a long time,  It would have spare space for delivering other payloads to Martian orbit as well.

[edzieba]

From a theoretical perspective, a system of multiple reasonably precise clocks that can communicate their local (X,Y,Z,T) with each other will be able to collectively refine their (X,Y,Z,T)s. When two or more of them are in "fixed" locations (e.g., on the Martian surface) This will eventually converge into a system with GPS-like functionality. Yes, I know satellites move.

The entire mechanism of action of current GNSS trilateration systems is to use the timing differences between satellite clocks and the actual time of arrival. You cannot bootstrap clock offsets using the clock offsets, it's like trying to determine the absolute length of a standard metre by averaging three pieces of string of unknown length: averaging does not work that way.

There is no such thing as "absolute" time. Here on earth, we use UTC and its kin. UTC is a consensus time based on coordination among multiple extreme-precision atomic clocks. Rubidium clocks are atomic clocks of lower quality but they still derive their accuracy from atomic transitions, and averaging enough of them will provide an adequate "absolute" time.

The 'absolute' time used for GNSS is by ground reference clock, and the key is that every satellite is referenced to the same clock, giving each satellite an absolute time reference rather than just references to neighbouring satellites. Combined with accurate positioning for each satellite, that is what allows trilateration GNSS to work at all - it is a fundamental assumption that if you receive a timestamp of 1200 + 1us from one satellite and 1200 + 2us from a second satellite, that 1200 will be the same for both satellites. If it is not, then you have no way to tell if the 1us differential time of arrival is actual a differential time of arrival, or if the first satellites clock is running 3ms slow and the second running 1ms fast and the actual DToA is -3us.

If you goal is to measure the distance between two satellites by using the relative difference in time of arrival of their reference clocks, then you cannot also use the relative difference in time of arrival of their clocks to both derive a pseudo-reference-clock and to also measure the distance. That's just throwing unknown error terms together and then ignoring them and hoping they go away.

We used "fixed" ground reference locations that were originally surveyed by non-GPS means, because that's all we had to start with.

We use ground reference locations derived from alternative geodetic measurements because that is what is required to produce a baseline measurement against which to calibrate GNSS.
In order to calibrate a system you either need an external refence standard to calibrate to, or to start from absolute fundamental physical parameters in order to create the standard standard to calibrate to. Traceability of measurement standards is not a case of just taking some clocks and averaging them together, that is fundamentally not how metrology works.

Relevance to Martian Starlink: Starlink depends on GPS-like positioning and will not work without it.

Starlink requires positioning for self-avoidance and for avoidance of other satellites in nearby orbits. That is not going to be an issue encountered around Mars for quite some time, much more gross and irregularly updated orbital parameters will suffice in the near to mid term.

[DanClemmensen]

In order to calibrate a system you either need an external refence standard to calibrate to, or to start from absolute fundamental physical parameters in order to create the standard standard to calibrate to. Traceability of measurement standards is not a case of just taking some clocks and averaging them together, that is fundamentally not how metrology works.

Like other atomic clocks, Rubidium clocks "start from some absolute fundamental physical parameters." These parameters are expressed in the transition frequencies of Rubidium atoms. All Rubidium clocks tic at the same rate, with tiny implementation errors. Both general and special relativity have non-trivial effects when comparing two clocks and must be taken into account.

Clock synchronization depends on another fundamental physical parameter: The speed of light. Distances are measured based on speed-of-light delay, which is measured using using a technique that does not depend on prior knowledge of positions or absolute time. I send you a message at my time M1. You receive it at your time Y2. You respond at your time Y3. I receive it at my time M4. Your message contains your values of Y2 and Y3. I compute the round-trip time as M4-M1 - (Y3-Y2).   This is all pretty much exactly like IEEE 1588. If we have agreed to use "my" clock as the base clock, you will now offset your absolute clock by this computed difference.  All of these measurements and computations have uncertainties. The combined and repeated measurements reduce the total uncertainty.

Yes this is how metrology works, at least for creating the practical UTC time standard.

[sdsds]

Yes, deriving and updating ephemerides for each station is both difficult and necessary. Note in the inertial frame, fixed surface stations are moving too, at one rotation every ~24.6 hours (sol). And orbital stations are moving on non-Keplerian trajectories due to any number of factors (moons, non-uniform Mars mass distribution, solar wind, etc.) Some truth can be derived from accelerometers, star-trackers and other navigation aids to assure the consensus ephemerides remain "grounded."

Lots of equations; lots of unknowns; lots of uncertainties. Protocols like NTP manage decent clock synchronization despite uncertain transmission latency.

(FWIW I'm liberally interpreting the topic of this thread to include both "when" Marslink service is first established and also "what" that service will include and "how" it will be established. Apologies to @whvholst if that wasn't the intent of creating the topic.)

[Solarsail]

Apparently the current mars satellites are able to do radio location determination to 100m accuracy already. (Even with just 1 satellite)  Far better than my guess of 20km...  100 meters needs the satellite and ground terminal to do 2-way communication during line-of-sight events, and then use doppler shift measurements on the signals.  Doing such measurements on discreet satellite passes allows for gradual triangulation of ground position of an object.  I wonder how valuable it is to improve upon that when Mars has 1 town / city on it, 1 satellite in orbit for positioning and data relay...  Can an algorithm like that support gradual improvement as new satellites are added?

When comparing that to 20-60m tall radio masts on nearby hills, we get a trade space of solutions for different kinds of navigational problems.  If you want to locate which rock an astronaut tripped and fell behind, you're better off with live location data to <5m accuracy.  This is only necessary near base.  If you have a mars rover traveling 50m per day, visual navigation is probably far better than radio solutions.  Surveys of terrain probably don't kneed fast resolution of location, but probably aren't helped by location precision as large as 20km...  (Are you on top of Olympus Mons?  Or somewhere dramatically lower?)  If you're flying an airplane thousands of miles between airports, you probably want live location knowledge through your trip...  But you don't need the accuracy to find the runway.  The airport's own beacons can handle local navigation.  What if you're driving a land train (or rail train) thousands of miles through terrain between two cities?  What trade space do you find between speed of update, precision requirements, continuity of location knowledge, and how much of those things can be accomplished with local visual navigation?

Then we've got in-space navigation for vehicles attempting Mars EDL.  They will want a triangulated location in a direction that GPS satellites don't support.

[DanClemmensen]

Yes, deriving and updating ephemerides for each station is both difficult and necessary. Note in the inertial frame, fixed surface stations are moving too, at one rotation every ~24.6 hours (sol). And orbital stations are moving on non-Keplerian trajectories due to any number of factors (moons, non-uniform Mars mass distribution, solar wind, etc.) Some truth can be derived from accelerometers, star-trackers and other navigation aids to assure the consensus ephemerides remain "grounded."

Lots of equations; lots of unknowns; lots of uncertainties. Protocols like NTP manage decent clock synchronization despite uncertain transmission latency.

(FWIW I'm liberally interpreting the topic of this thread to include both "when" Marslink service is first established and also "what" that service will include and "how" it will be established. Apologies to @whvholst if that wasn't the intent of creating the topic.)

NTP is insufficiently precise. That's  why I keep referring to the hardware-assisted version of IEEE 1588, which is also called PTP -- Precision Time Protocol.

[StraumliBlight]

When asked "what markets are particularly exciting for your company?" at today's keynote session. Gwynne Shotwell replied "I'm really looking forward to having communications to bases on the Moon and Starlink around Mars".

[StraumliBlight]

SpaceX has been awarded a ~$300,000 contract by NASA to investigate adapting Starlink for Mars. The study will conclude in August and results released later this year.

[Emmettvonbrown]

And now NASA has public-private partnerships for a) ISS cargo (ex- COTS)  b) ISS crews (CCDEV)  c) ISS replacement (CLD) d) lunar cargo and science (CLPS)  and e) lunar crews (HLS). With f) Mars orbit cargo and science : incoming.

They are building a bridge all the way to Mars.