Communication between Mars and Earth

[Slarty1080]

This topic was briefly discussed here: https://forum.nasaspaceflight.com/index.php?topic=53108.100
But is deserving of a thread of its own.

What are the options for Mars – Earth communications over the next 5 years? And what technologies might we see deployed? What sort of data transfer rates might be expected and when might they be set up and by who?
Answers to these questions will be important for the amount and quality of data that can be returned from Mars for some of the early Starship attempts.

[RotoSequence]

This topic was briefly discussed here: https://forum.nasaspaceflight.com/index.php?topic=53108.100
But is deserving of a thread of its own.

What are the options for Mars – Earth communications over the next 5 years? And what technologies might we see deployed? What sort of data transfer rates might be expected and when might they be set up and by who?
Answers to these questions will be important for the amount and quality of data that can be returned from Mars for some of the early Starship attempts.

If someone wants to broadcast HD video from Mars back to Earth, megawatt class transmission power is needed over the DSN's frequencies. That level of output power involves low transmission efficiencies in the order of single digits, which further defines the requirements for such a broadcast. Overall, several dozen acres of solar array would be needed to drive a sufficiently powerful transmitter to relay the ideal PR material back to Earth.

[Redclaws]

RotoSequence,

I am not disagreeing, but do you have references or more detail on this?  What are the current power levels and bit rates achieved by the various craft and rovers?  Are there other fréquence options?  What else might be possible?  Etc.

[RotoSequence]

RotoSequence,

I am not disagreeing, but do you have references or more detail on this?  What are the current power levels and bit rates achieved by the various craft and rovers?  Are there other fréquence options?  What else might be possible?  Etc.

I'm wholly unqualified to speak in any kind of detail on this. I only did enough poking around to figure out that on the Ka-band frequencies the Deep Space Network uses, you need high transmission power to broadcast a high bandwidth signal between Earth and Mars. The much smaller, much less powerful transmitters on the rovers and orbiting satellites are limited to a few dozen kilobits per second.

[Levy]

This topic was briefly discussed here: https://forum.nasaspaceflight.com/index.php?topic=53108.100
But is deserving of a thread of its own.

What are the options for Mars – Earth communications over the next 5 years? And what technologies might we see deployed? What sort of data transfer rates might be expected and when might they be set up and by who?
Answers to these questions will be important for the amount and quality of data that can be returned from Mars for some of the early Starship attempts.

Section 10 of the Starlink Terms of Service speaks about future Starlink services on Mars

[oldAtlas_Eguy]

Two of the limiting factors for near term and even far term high bandwidth planetary comm systems is mass and power usage. A planetary ISL is a mass efficient and power efficient for the bandwidth system. For both RF and Laser comm the basic principles are the transmit/laser power, antena/telescope gain, and the signal to noise level required for the data rate desired. From those three a set of design requirements can be derived. Also for a system that would be based on a satellites orbiting in LEO and LMO three additional engineering concerns are the mass of the system, the power that such a system consumes and thereby the heat generated that must be dissipated to space (the last two both have mass tradeoffs which is its own mass problem). All of these six basic parameters are tradeoff components in the design of the comm system.

A laser system seems to be the best when it comes to mass and power efficiency but there are some probable upper economic limits that can make a very high bandwidth single system too expensive per bit. So it may be best for a laser system to first start with a reasonable (high gain and not expensive design) telescope. Also next to then go as high in laser beam power output without also getting into the more expensive laser beam producing hardware.  These two item would then define the remaining 4 parameters of data bandwidth, power required, thermal dissipation, and total mass. Mass being a result of the other 5 based on the technology, parts, and designs used.

Next you take an economical design sat based system that would have near identical sats around Mars and Earth and make multiples of them and distribute them far enough apart that a separate ISL on each sat can connect to just one of the other sats at the other planet.  The notion here is that there would likely be three targets the planet's close orbit and then the LS4 and LS5 of the planet and sun. This gives a multiple of 9X for the total bandwidth between planets than that capable from a single economical system. It also allows for communication during solar passage when the sun is blocking/between several of the connections but not all of them. Note that instead of 3 planetary comm devices on a single sat it may be better from a reliability/redundancy standpoint to have three separate but close (in orbital mechanics terms) sats. Each of these sats would also have a much lower power/smaller ISL but with just as high of bandwidth as the primary planetary link that then communicates with the sats in LEO or LMO.

The basic thing about this architecture is its ability to easily scale up and over time go from a few 100Mbps to a few Tbps as technology improves.

The next concern is the store and forward protocols. Anything that is sent across the "void" has to be stored until confirmation of the data received at the other planet without errors (not an absolute requirement in a few cases but would be very rare in the beginning of the comm systems). Not only the data is stored went sent it also has to be store when received. But for the received end the duration of storage time is very short until the data has been confirmed it made it to its planetary destination. The storage time is not long because the normal Internet TCP/IP would be just a function of distance at the most for a sat at LS4/5 in a couple of seconds. But for send the round trip for Earth/Mars is in minutes to as in like up to 45 minutes round trip. So the ratio of send storage vs recieve storage (<.1% of send) is so large that the amount of received storage can effectively be ignored (a ratio of a TB for send and a GB for receive). A single 10 Gbps Earth/Mars comm link would need ~30TB of storage. So for true high bandwidth comm links >100Gbps. The storage requirement can become a significant factor in the sat design.

Basically everything outlined here is not that difficult to achieve. The primary problem is the shipment of the sats and then deployment about Mars thus their mass and volume may have more of an economic impact on the $/bit costs than other concerns. Also the outline is also applicable to a great extent to use of RF vs laser for Earth/Mars at least for initial setup of a few 10Mbps links to ensure high bandwidth of enough that supports effective continuous streams of even 4K video along with high amounts of telemetry and other scientific, etc data.

[paulthew]

I can see how putting relay satellites in Earth's L4 and L5 would be a good thing.  Also putting relay sats in Venus L3, L4, and L5 might work well for when Mars is more distant and when Earth and Mars are on opposite sides of the sun.

[Redclaws]

I'm wholly unqualified to speak in any kind of detail on this. I only did enough poking around to figure out that on the Ka-band frequencies the Deep Space Network uses, you need high transmission power to broadcast a high bandwidth signal between Earth and Mars. The much smaller, much less powerful transmitters on the rovers and orbiting satellites are limited to a few dozen kilobits per second.

NASA says the MRO can do up 4 megabits per second:

Mars Reconnaissance Orbiter sends data to Earth for 10 to 11 hours, and does that for about 700 days. The data rate is about 0.5 to 4 megabits per second.

https://mars.nasa.gov/mro/mission/communications/#:~:text=So%2C%20out%20of%2016%20hours,to%204%20megabits%20per%20second.

So, rather more than a few dozen kilobits per second.

[oldAtlas_Eguy]

I'm wholly unqualified to speak in any kind of detail on this. I only did enough poking around to figure out that on the Ka-band frequencies the Deep Space Network uses, you need high transmission power to broadcast a high bandwidth signal between Earth and Mars. The much smaller, much less powerful transmitters on the rovers and orbiting satellites are limited to a few dozen kilobits per second.

NASA says the MRO can do up 4 megabits per second:

Mars Reconnaissance Orbiter sends data to Earth for 10 to 11 hours, and does that for about 700 days. The data rate is about 0.5 to 4 megabits per second.

https://mars.nasa.gov/mro/mission/communications/#:~:text=So%2C%20out%20of%2016%20hours,to%204%20megabits%20per%20second.

So, rather more than a few dozen kilobits per second.

It is not a question of whether the capability for 10's of Mbps is achievable but the ability to get something larger than MRO in orbit at Mars. Which would need the Starship. But then again without Starship the need is also not there.

[Asteroza]

NASA was making noises like divesting some of the TDRS infrastructure in expectation of a commercially operated lasercomm system (possibly with some RF responsibility as well) for LEO to interplanetary purposes, as opposed to new NASA owned TDRS replacement sats with both RF and lasercomm, so Musk setting that up himself saves NASA the trouble of a full TDRS replacement...

[Nascent Ascent]

Is such a robust comm system a prerequisite for humans on Mars?

[RotoSequence]

I'm wholly unqualified to speak in any kind of detail on this. I only did enough poking around to figure out that on the Ka-band frequencies the Deep Space Network uses, you need high transmission power to broadcast a high bandwidth signal between Earth and Mars. The much smaller, much less powerful transmitters on the rovers and orbiting satellites are limited to a few dozen kilobits per second.

NASA says the MRO can do up 4 megabits per second:

Mars Reconnaissance Orbiter sends data to Earth for 10 to 11 hours, and does that for about 700 days. The data rate is about 0.5 to 4 megabits per second.

https://mars.nasa.gov/mro/mission/communications/#:~:text=So%2C%20out%20of%2016%20hours,to%204%20megabits%20per%20second.

So, rather more than a few dozen kilobits per second.

The higher speeds are only for Mars Surface to Mars Orbit. Mars to Earth transmissions are much slower.

This is wrong.

[ugordan]

I'm wholly unqualified to speak in any kind of detail on this. I only did enough poking around to figure out that on the Ka-band frequencies the Deep Space Network uses, you need high transmission power to broadcast a high bandwidth signal between Earth and Mars. The much smaller, much less powerful transmitters on the rovers and orbiting satellites are limited to a few dozen kilobits per second.

NASA says the MRO can do up 4 megabits per second:

Mars Reconnaissance Orbiter sends data to Earth for 10 to 11 hours, and does that for about 700 days. The data rate is about 0.5 to 4 megabits per second.

https://mars.nasa.gov/mro/mission/communications/#:~:text=So%2C%20out%20of%2016%20hours,to%204%20megabits%20per%20second.

So, rather more than a few dozen kilobits per second.

The higher speeds are only for Mars Surface to Mars Orbit. Mars to Earth transmissions are much slower.

No, that is in fact the supported Mars->Earth data rate for MRO. That was pretty much a mission requirement as the HiRISE camera generates a tremendous data volume.

https://mars.nasa.gov/mro/mission/communications/commxband/

[RotoSequence]

No, that is in fact the supported Mars->Earth data rate for MRO. That was pretty much a mission requirement as the HiRISE camera generates a tremendous data volume.

https://mars.nasa.gov/mro/mission/communications/commxband/

Well I'll be. I guess I know even less than I thought. 

[Slarty1080]

I'm wholly unqualified to speak in any kind of detail on this. I only did enough poking around to figure out that on the Ka-band frequencies the Deep Space Network uses, you need high transmission power to broadcast a high bandwidth signal between Earth and Mars. The much smaller, much less powerful transmitters on the rovers and orbiting satellites are limited to a few dozen kilobits per second.

NASA says the MRO can do up 4 megabits per second:

Mars Reconnaissance Orbiter sends data to Earth for 10 to 11 hours, and does that for about 700 days. The data rate is about 0.5 to 4 megabits per second.

https://mars.nasa.gov/mro/mission/communications/#:~:text=So%2C%20out%20of%2016%20hours,to%204%20megabits%20per%20second.

So, rather more than a few dozen kilobits per second.

It is not a question of whether the capability for 10's of Mbps is achievable but the ability to get something larger than MRO in orbit at Mars. Which would need the Starship. But then again without Starship the need is also not there.

So going forward a couple of years is it reasonable to suppose that a fairly high capacity link of say 10Mbps between Mars and Earth might be established? Perhaps the first Starship to be sent to Mars might deploy a sat for this purpose? It would certainly be good for early publicity and it would be a sin for the first crewed landing to be broadcast in low res.

[maquinsa]

I'm wholly unqualified to speak in any kind of detail on this. I only did enough poking around to figure out that on the Ka-band frequencies the Deep Space Network uses, you need high transmission power to broadcast a high bandwidth signal between Earth and Mars. The much smaller, much less powerful transmitters on the rovers and orbiting satellites are limited to a few dozen kilobits per second.

NASA says the MRO can do up 4 megabits per second:

Mars Reconnaissance Orbiter sends data to Earth for 10 to 11 hours, and does that for about 700 days. The data rate is about 0.5 to 4 megabits per second.

https://mars.nasa.gov/mro/mission/communications/#:~:text=So%2C%20out%20of%2016%20hours,to%204%20megabits%20per%20second.

So, rather more than a few dozen kilobits per second.

It is not a question of whether the capability for 10's of Mbps is achievable but the ability to get something larger than MRO in orbit at Mars. Which would need the Starship. But then again without Starship the need is also not there.

So going forward a couple of years is it reasonable to suppose that a fairly high capacity link of say 10Mbps between Mars and Earth might be established? Perhaps the first Starship to be sent to Mars might deploy a sat for this purpose? It would certainly be good for early publicity and it would be a sin for the first crewed landing to be broadcast in low res.

Having a live video feed would be amazingI don't care if it's 140p

[RotoSequence]

Having a live video feed would be amazingI don't care if it's 140p

I'd be kind of upset if it was so low quality, if I'm honest.

[ugordan]

So going forward a couple of years is it reasonable to suppose that a fairly high capacity link of say 10Mbps between Mars and Earth might be established? Perhaps the first Starship to be sent to Mars might deploy a sat for this purpose?

I don't see why it wouldn't be possible even with current technologies. An optical link would allow even higher bitrates, but it comes with certain drawbacks like very tight pointing constraints and obviously would be at an even greater mercy of Earth weather than radio and microwaves are.

Keep in mind that any single satellite will experience periods of eclipses if you put it in an areostationary orbit where its line of sight to Earth is masked by Mars itself, at certain points in the Martian year.

If it's not in areostationary orbit, then you won't have continuous coverage of the ground of interest.

[JaimeZX]

Having a live video feed would be amazingI don't care if it's 140p

I'd be kind of upset if it was so low quality, if I'm honest.

I mean, understanding the available bandwidth, I wouldn't be TOO upset if it were 140p live but then available in 640x480 after a few tens of minutes* and 4k within a day or so. The improved resolution there would have to take a back-seat to the ongoing livestream of activity, fitting in bits where able. Then presumably during the crew's sleep cycle the "live" data rate would drop quite a bit and there's your time for filling in higher-resolution versions of the landing, first steps, and other things deemed noteworthy. 

* I mean, how long have we "tolerated" the droneships losing link during F9 landings?  That's gotta be a piece of cake compared to Mars comms...

[su27k]

Some previous threads on this:

SpX Mars Communication Constellation?

Mars Starlink 2021 or 2023

SpaceX and DSN

SpaceX's DSN plans

Note NASA is also looking for industry to contribute a constellation of Mars communication relay satellites: NASA considering commercial Mars data relay satellites