SpX Mars Communication Constellation?

[AncientU]

From a 2015 speech by Elon

That same system we could leverage to put into a constellation on Mars, because Mars is going to need a global communications system too and there's no fiber optics or wires or anything on Mars. We're definitely going to need that. We're going to need high bandwidth communications between Earth and Mars. So I think a lot of what we do in developing an Earth-based communication system could be leveraged for Mars as well. Crazy as that may sound.

SpaceX seattle opening in 2015.

The first pair of BFSs to land on Mars are going to need broadband communications.  Internet of things will be established from Sol 1.

Imagine each BFS bringing along a dozen Tesla-based dune buggies, some equipped for prospecting (ground penetrating radar, mineral mapping hardware, sample collecting, lots of cameras, AI brain -- ranges of a hundred km in all directions), some equipped for distributing a solar farm (battery banks remain on board the spacecraft), some for mining, drilling, digging (mining droids).  Each sets out from the landing site and begins to relay mapping and other data back to the ship where its central data banks begin to assemble a local and regional map, detailed down to the boulder/ridge/cliff/crater.  Solar farm building is similarly enacted with precise positions of each panel and cable being recorded -- charging facilities maintained near the ship at first.  Mining droids get to work on collecting water/ice or water directly -- may need remote solar field, battery bank, and charging stations near work site(s).  Samples with precise collection data are returned to the bio/minerological lab for analysis.   Water is also sampled and then purified and input to the on-board Hydrolysis/Sabatier train.  Real-time, high bandwidth comms are the basis for the entire effort.

Earth-based analysts monitor progress and do some macro-directing of the efforts. 
Real-time direction on Mars is AI only.

Of course, this all requires the satellite network be established in advance of landing, including a high bandwidth relay to Earth.  Maybe a dozen sats to start with in a single or a couple low-inclination planes.  Constellation planned to be expanded each synod.

[speedevil]

On the related topic of 'what else can a communications satellite do'.
explains measurements of the atmosphere using GPS occultation by the GRACEs satellites.

It skims the measurement of the atmosphere as the signal between two satellites is increasingly absorbed as the geometry changes.

Also, more directly, measurement of the path delays between all satellites may give GRACE-like results, mapping the gravity field of Mars to really quite high precision. (not nearly as good as GRACE due to the higher altitude).

Grazing incidence measurement of varying paths between satellites could be enormously useful for giving live accurate densities for aerobraking.

[biosehnsucht]

Been cogitating on this topic a bit tonight, and if my math (and use of math aids) is correct, a single FH can put a useful if limited "constellation" at Mars and just a few extra flights could pad it out more.

Assumptions:
A) FH-R can put 7900kg on trans-Mars injection [1]
B) Need 2.1km/s to brake into LMO [2]
C) Using 300s isp [3] Dracos instead of SuperDracos (300s vs 235s ISP), need ~4100kg of prop

7900 - 4100 leaves us with 3800kg for Marslink satellites, the dispenser they ride on to Mars, any additional course correction / orbit fixing dV prior to dispensing, etc

It looks like for basic data coverage you can get by with 3 satellites.

Let's assume they're heavier than their Earth counterparts (bigger solar panels, bigger mirrors for the Earth links), but still assume they have 5 mirrors (forward/back in same plane and left/right in adjacent planes plus 5th for Earth link) - we could cut this to 3 but then if you want to expand the network to more than equatorial (or any single plane) coverage you would have to replace them - plus it means fewer changes from Starlink satellites at Earth. Let's call them 500kg, seems reasonable to me.

So now we're down to 3800kg - (3x 500kg) = 2300kg for everything else. I'm going to call the dispenser / mars transfer / braking burn stage the "space bus". Space bus includes the dispensers for 3 Marslink satellites, Draco thrusters, the prop tanks for the Dracos, it's own set of solar panels to power it during the journey, communication gear for the journey, etc.  This may not seem like much but remember we've already subtracted the mass of the prop itself. Should be doable in 2300kg, seeing as fully fueled Boeing 702SP with customer payload is around that mass (it's using ion thrusters but ...)

Depending on how much mass is needed on the space bus, you might cram some nice big Mars observation optics (and/or radar and/or... ) on it and drop it into a lower altitude and let it be a microwave client of the Marslink satellites.

I figure first launch should be equatorial, but then a 2nd and 3rd launch into different inclinations so that you can use these for some level of positioning.

You could send more Marslink satellites with FH-E instead of FH-R of course... the question is whether sending 2-3x the number of Marslink satellites per launch is worth the expended stages (and at least at early colony development stages, 3 per inclination is probably enough, so maybe not worth "wasting" extras in a single plane since plane change would be too costly).

TL;DR : Potentially a single FH-R mission can both pre position basic communication infrastructure and also deliver a satellite usable for investigating potential landing zones in greater detail.

[1] https://space.stackexchange.com/questions/25452/how-much-payload-can-falcon-heavy-reusable-lift
[2] https://space.stackexchange.com/questions/12660/delta-v-to-low-mars-orbit
[3] https://en.wikipedia.org/wiki/Draco_(rocket_engine_family)
[4] http://www.strout.net/info/science/delta-v/intro.html

[MikeAtkinson]

I'm not convinced a Mars satellite communication network is needed or even particularly desirable for the initial Mars landings (first few synods).

Firstly, round trip delays are such that the benefits of 24/7 high bandwidth comms are mostly not needed initially. A few MBit/sec is all that is required for autonomous rovers and on-board BFS systems.

Secondly, the constellation will cost a significant amount to design, deploy, operate and replace (every 5 years or so). IMHO this money is better spent elsewhere.

Third, it is better in my opinion, to wait as long as possible, so that more advanced technology can be used, bugs and poor design decisions can be avoided and Mars surface infrastructure does not have to support legacy systems.

Lastly, and system needs to be able to cope with comms failure, so not having global comms is not a problem.

An alternative system where there is high bandwidth radio comms using large antennae on Mars and on Earth seems easier and cheaper initially, although it will not have 24/7 high bandwidth.

[meekGee]

I'm not convinced a Mars satellite communication network is needed or even particularly desirable for the initial Mars landings (first few synods).

Firstly, round trip delays are such that the benefits of 24/7 high bandwidth comms are mostly not needed initially. A few MBit/sec is all that is required for autonomous rovers and on-board BFS systems.

Secondly, the constellation will cost a significant amount to design, deploy, operate and replace (every 5 years or so). IMHO this money is better spent elsewhere.

Third, it is better in my opinion, to wait as long as possible, so that more advanced technology can be used, bugs and poor design decisions can be avoided and Mars surface infrastructure does not have to support legacy systems.

Lastly, and system needs to be able to cope with comms failure, so not having global comms is not a problem.

An alternative system where there is high bandwidth radio comms using large antennae on Mars and on Earth seems easier and cheaper initially, although it will not have 24/7 high bandwidth.

For a single colony site, all you really need is to have a satellite in view at all times.  That satellite can do any necessary local-area relaying, and be the comm link to earth.

You can do that with a small number of medium-altitude satellites, which you can choose to call a "constellation", but are really a much loose arrangement than the kind of constellation we're talking about around Earth.

[DistantTemple]

Needs for high quality independent SpaceX coms on Mars. (much of this has been said before)

1. Once humans are on the surface highly reliable, highly reliable coms between them and home are "very highly" desirable. From the human perspective alone, psychological issues could well be mitigated by relatively high quality, free and easy (social) contact with family friends and colleagues (and (cached)internet) on this overall (approx) 5+26+5 month mission.

2. The same for mission, professional, research and educational purposes; for productive use of mission personnel, for professional involvement with (SX, or the aeronaut's particular agency/university/company) projects and teams on Earth.

3. For media purposes. At times, media of multiple countries will "need" "near (as light allows!)" real-time voice and video reports and communications, particularly if their country/organisation has aeronauts and/or projects aboard. This may also be related to funding and sponsorship. For access to data, research, etc on the internet, or university/company servers.

4. For mission data, including high quality stills, video, sound, telemetry, and remote control/management/fault-finding/software updates. Aeoronaut time has to be considered as expensive, and avoiding ANY preventable delay due to limited coms must have high priority and be worth investing in.

5. For point-to-point on the surface. Possibly there will be remote equipment (rovers, seismometers, etc, on the other side of Mars, or at the poles, or even human rovers or science missions, 10's of days away from base. Points 1, 2, 3, and 4 all apply both for inter-mars coms, and back to earth.

6. Minimum safety and emergency communications to ensure function, safety, and notification, etc Text, small files, minimum telemetry etc.

Independent: Provision from NASA, etc, should be considered an emergency fall-back provision (6 above). Their systems are not designed to support the needs of these SX missions. They have limited bandwidth, daily coverage, and are already tasked with their own missions. If they were relied upon and failed, a surface backup system would be diurnal, and limited, and not fulfill the above points.

Prior "robotic" synod. (some) coms support should be in place to make this a successful as possible. This inputs into the success of the human mission. Minimum would be one satellite.

(Much of this applies to the journey there and back, and between the ship and Mars, as well as Earth.)

The time delay can't be altered, but quality, reliability, bandwidth, and the freedom to use it frequently and casually can be. We are not in the 19th century where a ship's crew was out of contact for months, and its not just a few weeks where privations may be considered lightly. The aeronauts are living and working away from earth for three years, lets support them by making their time as productive, convenient, and pleasant as we can, without breaking the bank.

[DistantTemple]

For a single colony site, all you really need is to have a satellite in view at all times.  That satellite can do any necessary local-area relaying, and be the comm link to earth.

You can do that with a small number of medium-altitude satellites, which you can choose to call a "constellation", but are really a much loose arrangement than the kind of constellation we're talking about around Earth.

Agreed, except the plan is that the colony will develop, and not be boots and flags. Any investment will have continued value. And EM has said Starlink will link to Mars. However I suppose initial essential coms sat(s) could be independent of that, but that would be a waste.

[Nomadd]

 A lot of geo links start having problems when the sat is within 2 or 2 1/2 degrees of the sun with 1.2m dishes. Does anybody know offhand about how long Mars/Earth outages range every 26 months?

[speedevil]

A lot of geo links start having problems when the sat is within 2 or 2 1/2 degrees of the sun with 1.2m dishes. Does anybody know offhand about how long Mars/Earth outages range every 26 months?

Mars orbit is also inclined by 1.8 degrees, so often will not quite be obscured by the sun.
LASER can go moderately closer to the sun - with care.
Also, if you do in fact have cheap launch, tossing some sats out halfway to TMI would largely work, even if they are not in an absolutely ideal orbit.

[spacenut]

I think there should be at least 3-4 GSO around Mars with at least two one on each side of the sun to communicate with Mars when it is on the opposite side of the sun as earth.  24 hour/365 communications.  Maybe laser communications so it can get to earth quicker. 

[IntoTheVoid]

Maybe laser communications so it can get to earth quicker.

You want to try that again? Or maybe explain this new FTL laser physics?

[Nomadd]

I think there should be at least 3-4 GSO around Mars with at least two one on each side of the sun to communicate with Mars when it is on the opposite side of the sun as earth.  24 hour/365 communications.  Maybe laser communications so it can get to earth quicker. 

That looked a little like one of my four Guinness posts on a phone in a dark pub that made sense when it was in my brain.

[biosehnsucht]

It seems reasonable to me to plan for "global" coverage of Mars before even robotic BFS cargo missions arrive since even if you position an areosynchronous satellite directly over the landing zone, it spends a good portion of every day out of view of Earth (being on the far side of the planet). So you have the other satellites so you can relay around the planet to Earth.

Since you now have multiple satellites, why not place them lower? The latency improvement won't really matter for comms to Earth, and likely not within the operational lifetime of the initial satellites will it matter for anyone on Mars, but getting them closer to Mars should mean less station keeping work from orbital perturbations caused by Phobos and Deimos, right? Also makes it easier to make useful observations if you have any kind of sensing package installed on them.

[ThereIWas3]

An antenna on top of the BFS (40m) should have line-of-sight to any remote vehicles involved in the initial synod landing.  It will be on pretty flat terrain or maybe in a broad valley.   10km should be doable easy.  So I don't think satellite relay is a prerequisite for the first landing.

[DistantTemple]

Maybe laser communications so it can get to earth quicker.

You want to try that again? Or maybe explain this new FTL laser physics?

y'r'all takin' the pi**. Its obvious, laser, straight, line o'sight clippin' the sun is faster than a cocked hat, wi' some ol' sat followin' 90 degrees behind Mars. Root 2 times as fast, Mars to Earth.

An I thort y'r'all rokit scintists an all!

Edit: Humor aside. One satellite leading or trailing Mars or Earth some degrees, in a solar orbit ... or some other arrangement will be needed to avoid Sun-in-the-middle problems, altogether.

[biosehnsucht]

An antenna on top of the BFS (40m) should have line-of-sight to any remote vehicles involved in the initial synod landing.  It will be on pretty flat terrain or maybe in a broad valley.   10km should be doable easy.  So I don't think satellite relay is a prerequisite for the first landing.

Sure, if you're fine with buying time on the DSN which is neither cheap nor available in a dedicated 24/7 fashion (there are other users of the service, as I understand it you have to take turns). It would severely limit time efficiency in getting things done. Also, are there enough orbiters spaced appropriately to provide round the clock relaying of DSN when on the wrong side of Mars from Earth? (I don't actually know)

A single FH launch could provide round the clock connectivity without any dependency on DSN (just Starlink which should already be sufficiently operational by 2022). You might even be able to sell bandwidth to other orbiters/landers in place of DSN, if your SDR / phased array / etc hardware is sufficiently able to emulate the DSN connection.

[guckyfan]

If the constellation has the ability to connect to MRO a deal could be made with NASA that SpaceX provides data transmission capacity and get part of the increased observation time to check potential landing sites. To be useful such a capacity would need to be available in 2020 or 2 years ahead of first unmanned landing.

[speedevil]

If the constellation has the ability to connect to MRO a deal could be made with NASA that SpaceX provides data transmission capacity and get part of the increased observation time to check potential landing sites. To be useful such a capacity would need to be available in 2020 or 2 years ahead of first unmanned landing.

Conversely, a deal could be made to allow all spacecraft in orbit around Mars to talk to the constellation, and offload the DSN, as well as providing basically continuous opportunities to send data for every vehicle not constrained at all by DSN capacity.

The constellation would of course need to have extra hardware to talk on the right frequencies.

This could in principle have value for other spacecraft - imagine TESS, for example, being able to send data without needing to turn to earth.

[biosehnsucht]

Depending on how versatile the phased array hardware is, you might be able to manage it without extra hardware, just special software (since it's probably using some flavor of software-defined radio anyways to begin with). If not, well, surely it's not that hard to add a couple of extra antenna / radio packages.

[lamontagne]

Can we roll GPS into the communication/constellation package?

Does the BFS need to be used for transportation all the way to Mars?    Would it be possible to put a number of satellites on a relatively high orbit, then move to Mars using a SEP drive?  about 5,6 km/s of deltaV, vs 3,9 for geostationnary.  I understand SpaceX hhas some ion drives that would be about right for the need?

And these could leave well ahead of the actual first transit to MArs and be in place when needed....