Author Topic: Martian Communication Networking  (Read 2314 times)

Offline redliox

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Martian Communication Networking
« on: 07/18/2017 08:31 PM »
Putting up a fresh thread to discuss how and what form functional communications at Mars should take.

Previous threads worth reviewing:
Mars Telecom Orbiter redux
NASA Selects Five Mars Orbiter Concept Studies
Ramifications of a positioning and communications constellation in LMO or MMO
There are likely many more threads bringing up Martian communication in one form or another, but they are getting difficult to track and like all threads inevitably get buried.

Next to Mars Sample Return, there seems to be a perception that we'll face a crisis in handling regular Martian communication.  Mostly this takes the form of needing a fresh orbiter with stronger capabilities in case we lose Odyssey and MRO.  We will likely still have MAVEN and the ESA orbiters to draw upon for a few years yet, but preparing for the future, especially if you seriously aim to take human expeditions into account, would be wise.

Basically post any information and links related to communication on Mars, both in orbit and also on the surface, here.  Try to stay close to topic.  This will continue to be a serious matter for Mars for years to come.

« Last Edit: 07/18/2017 09:06 PM by Lar »
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Offline redliox

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Re: Martian Communication Networking
« Reply #1 on: 07/19/2017 10:16 PM »
To seed some discussion, I'll mention my take and concern on Mars sats: the obsession with low Mars orbit.

Here at Earth, we benefit from using satellites in a broad mixture of orbits: LEO, MEO (think where most GPS sat constellations are), and GEO.  LEO is somewhat newer but it is easy to get satellites with many high-tech advancements into constellations that service the selfies and cells.  Using LEO is efficient, so long as you have more than 1 satellite to rely on.

With Mars, we can't guarantee the presence of multiple satellites.  Currently we have Odyssey, MRO, and Maven for USA-specific orbiters with Mars Express and ExoMars for ESA.  Only 2 of those 5, Maven and ExoMars, could be safely expected to last a while yet simply because they're the youngest; the other 3 are a gamble since they're aging veterans.  This of course is old news...

My thought is that if we're stuck with sporadic orbiters we should consider wider coverage and footprints as opposed to low orbits with high rates; i.e. higher orbits with strictly communication satellites whereas something like MRO or the (conceptual) 2022 orbiter continue to operate in LMO.  While synchronous comes to mind like GEO, for Mars this might not be the case as I've read that, especially due to the likes of lumps like Tharsis, parts of that orbit are unstable not unlike how a low lunar orbit is.  Something in a mid-Mars-orbit (like a half-sol or perhaps Phobos orbit as examples) should be fine though, and ensuring the satellite makes at least 2 passes daily (especially if it's solo) seems like a good baseline.
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Offline guckyfan

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Re: Martian Communication Networking
« Reply #2 on: 07/19/2017 10:45 PM »
I know little about it. But I think part of the equation is that there are no dedicated com sats at Mars. They have science payloads that dictate their orbit and do comms at the side.

Offline Robotbeat

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Re: Martian Communication Networking
« Reply #3 on: 07/19/2017 11:58 PM »
At the ISS R and D conference talk that Musk was hosted at, some reference was made to SpaceX and NASA collaboration on Mars communications.
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Offline MickQ

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Re: Martian Communication Networking
« Reply #4 on: 07/20/2017 10:09 AM »
One Comms station on Phobos and two or three other dedicated sats in the same orbit means that there will always be at least one sat above the horizon for all the equatorial and mid latitude areas where the earliest landings and activities are likely to be.

Offline redliox

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Re: Martian Communication Networking
« Reply #5 on: 07/20/2017 09:45 PM »
One Comms station on Phobos and two or three other dedicated sats in the same orbit means that there will always be at least one sat above the horizon for all the equatorial and mid latitude areas where the earliest landings and activities are likely to be.

If there's any equipment sent to either of the moons, even if only used once, it would make sense to repurpose it for com duty.  Phobos makes multiple passes whereas Deimos remains in-sight for almost 3 days straight (downside being you also have to wait 3 days for it to rise again); both have their strengths and weaknesses.  Moonbases (in this case the Martian moons as opposed to a Lunar "Moonbase") in themselves aren't required for Mars but certainly could be a communication asset.

Putting 2 or 3 satellites in the same orbit I wholly agree with as is covering the mid and lower latitudes for early landings.  For high/polar latitudes, that'd be an example where low polar orbits have their strength; there's always numerous passes of the poles.

Specifically three orbits come to mind, excluding low Mars orbits:
A) Phobos Orbit (or otherwise roughly 8 hour period)
B) Half-Sol Orbit (close to a 12.5 hour period)
C) Deimos Orbit (or otherwise roughly 30 hour period)
I'm aware Phobos is visible up to 70⁰ and Deimos 83⁰ of latitude, but I am curious how you'd figure out how much of Mars a single com sat can cover from these 3 respective orbits.  For example: would a Phobos orbit need an additional satellite to minimize coverage loss as opposed to the higher Half-Sol and Deimos positions?
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Offline gosnold

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Re: Martian Communication Networking
« Reply #6 on: 08/04/2017 11:26 AM »
There was a FISO telecon recently on geostationary Mars telecom orbiters:

http://spirit.as.utexas.edu/%7Efiso/telecon/Edwards-Lock_8-2-17/

Offline redliox

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Re: Martian Communication Networking
« Reply #7 on: 08/07/2017 04:42 AM »
There was a FISO telecon recently on geostationary Mars telecom orbiters:

http://spirit.as.utexas.edu/%7Efiso/telecon/Edwards-Lock_8-2-17/

Awesome for mentioning!  :D

I am quite surprised they're considering areostationary orbit after all.  A single satellite would cover a third of the planet with the most benefits towards sites within 30 degrees of the equator; considering both MERs, Curiosity, InSight, and possibly ExoMars will all fall in this range this kind of satellite would easily meet their needs.

They appear to have 2 options: a small orbiter that's dropped off and a large orbiter that flies directly there.  Both apparently could be launched with other spacecraft.
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Offline Dao Angkan

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Re: Martian Communication Networking
« Reply #8 on: 08/12/2017 10:13 PM »
You'd probably want to put them into one of these four areostationary orbits to minimise stationkeeping. Three might cover most of the planet longitudinally, but there might be a gap.

Stationkeeping in Mars orbit



Quote
And that would be the end of the story if the planets were spherical and homogeneous and there were no other perturbing effects. But of course the real world isn't as simple as that. At Earth, the major effects on satellites trying to stay in one position are the presence of the Moon and Earth's polar flattening. These combine to tilt the plane of the satellite's orbit. Also, Earth's nonspherical shape -- the lumps and bumps that make its equator noncircular -- causes the satellite to migrate in longitude over time. There are two stable points (at 75.3E and 104.7W, corresponding roughly to the longitudes of India and Mexico) and two unstable points (at 165.3E and 14.7W, corresponding to longitudes of the Solomon Islands and the western edge of Africa), where the drift rate is negligible; but satellites not located at these points tend to shift in longitude away from the unstable toward the stable point over time. The stable points are where Earth's gravity has a local low, the unstable ones where it has a local high.

To stay in the intended position, geostationary satellites currently have to use thrusters to counteract these forces. Using thrusters means using up a limited resource -- fuel -- so stationkeeping is one thing that sharply limits a geostationary spacecraft's lifetime. To discuss fuel budgets, space navigators talk of "delta v," which is kind of a measure of how much change in velocity a spacecraft can accomplish, measured in units of speed. It takes about 50 meters per second of delta v per year to keep a geostationary satellite in Earth orbit, and almost all of that has to do with counteracting the tendency to tilt north and south in latitude rather than the tendency to drift east or west in longitude. The maximum delta v needed to counteract longitude drift for a satellite located right in between the stable and unstable points is about 2 meters per second. Since it's so small, the choice of longitude doesn't have a major effect on the lifetime of your geostationary satellite.

Silva and Romero show in their paper that the story is quite different at Mars, because Mars is much less spherical than Earth. It has a monstrous large pile of dense volcanic material deposited on one side (the Tharsis volcanoes and Olympus Mons), balanced on the opposite side by a broad gravity rise, that give its gravitational field much larger deviations from ideal smoothness than Earth has. Like at Earth, there are stable points over the two gravity lows and unstable points over the two gravity highs. Unlike at Earth, there is a huge cost if you want to put your satellite at a longitude between the stable and unstable points: Silva and Romero calculated that it can cost up to 22 meters per second of delta v per year in order to put a geostationary spacecraft at one of these spots. You would also have to perform stationkeeping maneuvers much more frequently at Mars than you do at Earth: approximately once every few days, rather than once every few weeks.


Offline redliox

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Re: Martian Communication Networking
« Reply #9 on: 08/14/2017 08:16 AM »
You'd probably want to put them into one of these four areostationary orbits to minimise stationkeeping. Three might cover most of the planet longitudinally, but there might be a gap.

Stationkeeping in Mars orbit

The blog that informed me about the station keeping issues of areosynchronous orbit, I remember it well.  The two stable points correspond roughly to the easternmost end of Valles Marineris and southeastern Elysium Mons.

Emily Lakdawalla, in her blog, points out the practicality issue that exists in Martian communication satellites:
Quote
But one thing that works against us is that since Curiosity and Opportunity are located nearly on opposite sides of the planet, no one geostationary satellite could serve both spacecraft. And another problem, that I haven't even gotten into, is that it's costly in terms of delta v to get a spacecraft into such an orbit.

So don't expect to see a geostationary orbiter at Mars anytime soon. What has been proposed (but canceled) for Mars is a telecommunications orbiter that might circle at an intermediate altitude of around 5000 kilometers, giving it nice long communications passes over landers and a view of Earth that's only rarely obstructed by Mars.
That orbit would be a bit over half of Phobos' height, so probably a period around 3 hours.  I would think a 12.5 hour, half-sol orbit would be the best compromise myself.
« Last Edit: 08/14/2017 08:17 AM by redliox »
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Offline Ludus

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Re: Martian Communication Networking
« Reply #10 on: 08/30/2017 01:41 AM »
It might be worth waiting to see what SpaceX comes up with as standardized systems mass produced for its Constellation. How might they be adapted for Mars. It ought to be possible to have high bandwidth low latency internet everywhere on Mars before the first human footprint. It's what would make serious robotic exploration and work possible. The same satellites ought to be able to provide constant detailed surveillance of the whole planet. The Constellation would need a high powered laser relay to earth.

If a SpaceX Mars internet isn't funded at all by government or NGOs it might make sense as a spec project. Just build it and charge service fees.
« Last Edit: 08/30/2017 01:42 AM by Ludus »

Offline oldAtlas_Eguy

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Re: Martian Communication Networking
« Reply #11 on: 08/31/2017 04:24 PM »
It might be worth waiting to see what SpaceX comes up with as standardized systems mass produced for its Constellation. How might they be adapted for Mars. It ought to be possible to have high bandwidth low latency internet everywhere on Mars before the first human footprint. It's what would make serious robotic exploration and work possible. The same satellites ought to be able to provide constant detailed surveillance of the whole planet. The Constellation would need a high powered laser relay to earth.

If a SpaceX Mars internet isn't funded at all by government or NGOs it might make sense as a spec project. Just build it and charge service fees.
The sats around Mars is only half the problem. The other half is the bottle neck with the DSTN on Earth. An alternate communications system besides the DSTN is needed if higher data rates on a near constant basis is desired. For this a Laser communication package on the Mars orbiters with the corollary of a hosted Laser comm package on Earth GEO sats preferably HTS ones would provide high data rates at near constant communication without needing the DSTN. This freeing up the very expensive DSTN assets for other deep space missions is a big plus.

Offline meberbs

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Re: Martian Communication Networking
« Reply #12 on: 08/31/2017 05:05 PM »
It might be worth waiting to see what SpaceX comes up with as standardized systems mass produced for its Constellation. How might they be adapted for Mars. It ought to be possible to have high bandwidth low latency internet everywhere on Mars before the first human footprint. It's what would make serious robotic exploration and work possible. The same satellites ought to be able to provide constant detailed surveillance of the whole planet. The Constellation would need a high powered laser relay to earth.

If a SpaceX Mars internet isn't funded at all by government or NGOs it might make sense as a spec project. Just build it and charge service fees.
The sats around Mars is only half the problem. The other half is the bottle neck with the DSTN on Earth. An alternate communications system besides the DSTN is needed if higher data rates on a near constant basis is desired. For this a Laser communication package on the Mars orbiters with the corollary of a hosted Laser comm package on Earth GEO sats preferably HTS ones would provide high data rates at near constant communication without needing the DSTN. This freeing up the very expensive DSTN assets for other deep space missions is a big plus.
I believe that the "high powered laser relay to Earth" part of Ludus' post was intended to address that part without going into detail.

Any such constellation on Mars would probably be significantly higher orbit with many fewer sats to provide wider coverage. High capacity and very low latency would not be relevant for a long time.

Also, SpaceX's comm sats at Earth are designed to be replaced frequently. Many probably would not survive the trip or have a long lifetime. Some parts could probably be reused, but a lot would be a whole new design. When you can only send things every 2 years and the environment is harsher, your design requirements change.