Author Topic: Mars Internet Constellation and making money from Mars  (Read 27944 times)

Offline savuporo

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Re: Mars Internet Constellation and making money from Mars
« Reply #20 on: 10/16/2015 08:13 am »
Just out of curiosity, why does the distance influence the data rate?
You mean why does inverse square law affect link budget ?

I dont know what you mean by link budget, but yeah. Double distance, 1/4th of the energy arrives. But the data is a modulated signal, either in wavelength (radio) or brightness (laser). Why does the distance i.e. power of the signal influence the rate at which one can make bright and dark segments in the stream? Is the signal so weak that you need to integrate the light on the detector longer just to get above the noise floor? I think I just answered my own question...

You are pretty much almost there. Here is the elementary explanation
http://www.piscespacific.org/livesite/files/Link_Budget_Calculation.pdf

EDIT: actually probably not the best overview. Just read on link budgets and free space loss on wikipedia, or wireless comms textbook better.

More on topic:
Free space loss 101
Who budgets links and why
« Last Edit: 10/16/2015 08:26 am by savuporo »
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Offline Robotbeat

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Re: Mars Internet Constellation and making money from Mars
« Reply #21 on: 10/16/2015 11:35 pm »
In case anyone is confused, yes, your link budget and acheivable data rate (including the effect of errors/error-correction) follows the inverse square law, too.
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Offline Ludus

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Re: Mars Internet Constellation and making money from Mars
« Reply #22 on: 10/24/2015 02:44 am »
I was kinda assuming that any high bandwidth link would have to be laser based. NASA had some success with experiments from the distance of the moon but as far as I know nothing at the couple orders of magnitude greater distances for Mars.

Even though SpaceX is dedicated to Mars settlement there aren't many projects they might pursue now with any direct relevance to Mars that also have some sort of business case. Red Dragon is a conventional example where they might get paid if a space agency project could get it budgeted.

If SpaceX could provide high bandwidth data streams from Mars, they might sell that as a service to various space agencies who might benefit.

Compared to many other Mars projects this seems comparatively practical though it involves pushing technological limits.

I appreciate the links to resources about how this has been handled in the past but as objections they seem like the objections to SpaceX building an Internet constellation based on the failure of Teledesic or the fact that Satellite internet now has high latency and low bandwidth. Since the only way to do this effectively would use different technology than prior projects, issues with past approaches don't necessarily apply.

Offline ThereIWas3

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Re: Mars Internet Constellation and making money from Mars
« Reply #23 on: 10/24/2015 04:19 am »
I am pretty sure that laser communication links use phase modulation, not on-off modulation.

Offline Robotbeat

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Re: Mars Internet Constellation and making money from Mars
« Reply #24 on: 10/26/2015 12:33 am »
I am pretty sure that laser communication links use phase modulation, not on-off modulation.
Laser modulation can be many different things, like phase, frequency, amplitude (1-bit is "on-off"), and even polarization. Or a combination. But the gain for all of them follows the inverse square law.
« Last Edit: 10/26/2015 12:33 am by Robotbeat »
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Offline Burninate

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Re: Mars Internet Constellation and making money from Mars
« Reply #25 on: 10/26/2015 10:36 am »
Just out of curiosity, why does the distance influence the data rate?
You mean why does inverse square law affect link budget ?
I am pretty sure that laser communication links use phase modulation, not on-off modulation.
Real communications signals can go down quite close to the noise floor, given enough time to integrate the signal.  We still talk with Voyager, out at the edge of the solar system, down at 17 bits per second;  The equipment can and has done far higher data rates, but there just aren't enough photons coming out of the transmitter and hitting the receiver, in excess of the noise signal from the sky background and pickup electronics, to do better;  If you try to raise the data rate above these constraints, the error rate goes up asymptotically.
« Last Edit: 10/26/2015 10:42 am by Burninate »

Offline Ludus

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Re: Mars Internet Constellation and making money from Mars
« Reply #26 on: 10/26/2015 11:22 pm »
I'm just not getting it. Is there an argument being made that much high data rates aren't possible from Mars? I know a Mars orbiter was planned a decade ago with laser based much higher data rates but canceled.

I think I'm following the comments but I don't get the relevance.
« Last Edit: 10/26/2015 11:24 pm by Ludus »

Offline Craig_VG

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Re: Mars Internet Constellation and making money from Mars
« Reply #27 on: 10/27/2015 01:41 am »
What solution would SpaceX use to get past the Sun blocking the straight-line path between Earth and Mars?

Also, what is the minimum and maximum data latency that would be experienced on Mars? (I understand that a local backup of most the internet would be needed for instant access to many of the things we take for granted).

Offline Robotbeat

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Re: Mars Internet Constellation and making money from Mars
« Reply #28 on: 10/27/2015 02:07 am »
What solution would SpaceX use to get past the Sun blocking the straight-line path between Earth and Mars?
A relay at Earth- or Mars-Sun Lagrange point 3 or 4.

Quote
Also, what is the minimum and maximum data latency that would be experienced on Mars? (I understand that a local backup of most the internet would be needed for instant access to many of the things we take for granted).
Round-trip, roughly between 45 minutes and 8 minutes. And keep in mind that most Internet traffic is already cached. Google, Facebook, Amazon, etc have local data centers all over the world where their content is mirrored. Smaller firms can do so as well by utilizing Content Delivery Networks. For example, you can mirror almost all of Netflix's online content with a few hundred terabytes and keep it up to date with roughly a gigabit connection (as of last year).
« Last Edit: 11/04/2015 02:52 am by Robotbeat »
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Offline AncientU

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Re: Mars Internet Constellation and making money from Mars
« Reply #29 on: 10/27/2015 11:27 am »
A relay at Earth- or Mars-Sun Lagrange point 3 or 4.

That's L4 or L5; L3 is in line with sun on opposite side from planet, so doesn't help with problem.
A pair of relay satellites at Earth/Sum L4 and L5 (at about 1AU from Earth each) would provide continuous coverage to Mars.
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Offline ScepticMatt

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Re: Mars Internet Constellation and making money from Mars
« Reply #30 on: 10/28/2015 06:41 am »
Looks like it isn't happening - for now.

Quote from: Shotwell
I would say that this is actually very speculative at this point. We don’t have a lot of effort going into that right now.
Certainly I think that from a technical perspective this could get done. But can we develop the technology and roll it out with a lower-cost methodology so that we can beat the prices of existing providers like Comcast and Time Warner and other people? It’s not clear that the business case will work.

http://spacenews.com/spacex-president-downplays-commitment-to-building-broadband-constellation/

Offline symbios

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Re: Mars Internet Constellation and making money from Mars
« Reply #31 on: 10/28/2015 06:57 am »
I have to put emphasis on the "for now" part of that statement.

SpaceX have about 4.000 employees. How many have they had time to hire in Seattle? 20-40? So her statement is true, it is still a small effort in SpaceX terms. But it is growing.

There might be a lot of reasons for this statement. The want to focus on the return to flight. Maybe she just did not want to talk about it at that summit. The timeframe is still too far away to put any focus on the effort. They might have had design or other problems  etc. etc.

The statement is so vague that it could mean anything and nothing.

Only time will tell.


Looks like it isn't happening - for now.

Quote from: Shotwell
I would say that this is actually very speculative at this point. We don’t have a lot of effort going into that right now.
Certainly I think that from a technical perspective this could get done. But can we develop the technology and roll it out with a lower-cost methodology so that we can beat the prices of existing providers like Comcast and Time Warner and other people? It’s not clear that the business case will work.

http://spacenews.com/spacex-president-downplays-commitment-to-building-broadband-constellation/
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Offline savuporo

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Re: Mars Internet Constellation and making money from Mars
« Reply #32 on: 10/28/2015 08:06 am »
Emphasis in this article is in all the forms of the term 'speculation' or 'speculative' and 'denied'. Internet rumor mill fueled by seeing Google and billion dollars in the same article.
Plus again, as discussed upthread, LEO constellation has very little to do with any interplanetary communications so not sure how is that relevant for 'Mars internet constellation' - which currently kind of exists, but works very differently from what we call 'internet' here.
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Online guckyfan

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Re: Mars Internet Constellation and making money from Mars
« Reply #33 on: 10/28/2015 08:13 am »
The connection would be satellite type. They would use the same kind of satellite over Mars as the internet constellation over earth.

Also dedicated satellites at Mars and Earth could do interplanetary connection and feed locally into the internet constellation for downlinking without need of a network of ground stations around earth. At least I think they could do it that way.

Offline Robotbeat

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Re: Mars Internet Constellation and making money from Mars
« Reply #34 on: 10/28/2015 11:31 pm »
A relay at Earth- or Mars-Sun Lagrange point 3 or 4.

That's L4 or L5; L3 is in line with sun on opposite side from planet, so doesn't help with problem.
A pair of relay satellites at Earth/Sum L4 and L5 (at about 1AU from Earth each) would provide continuous coverage to Mars.
Ah, yes. You are perfectly correct!
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Offline Robotbeat

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Re: Mars Internet Constellation and making money from Mars
« Reply #35 on: 10/28/2015 11:33 pm »
Keep in mind, swarms of non-synchronous satellites around Mars preclude a space elevator from ever being built there.  Eventually their paths do meet.

Ya can't have both!
Sure you can. Satellites will have high-isp propulsion and can be actively controlled. Trajectories can be shaped to avoid obstacles, especially when it is known well ahead of time.

Besides, a Mars elevator is a long ways away. Easier than an Earth elevator, but still very hard.
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To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Robotbeat

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Re: Mars Internet Constellation and making money from Mars
« Reply #36 on: 10/28/2015 11:34 pm »
The connection would be satellite type. They would use the same kind of satellite over Mars as the internet constellation over earth.

Also dedicated satellites at Mars and Earth could do interplanetary connection and feed locally into the internet constellation for downlinking without need of a network of ground stations around earth. At least I think they could do it that way.
Indeed. Regular satellite internet connections could be your "ground stations" if you wanted to.
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To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Robotbeat

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Re: Mars Internet Constellation and making money from Mars
« Reply #37 on: 10/28/2015 11:38 pm »
Looks like it isn't happening - for now.

Quote from: Shotwell
I would say that this is actually very speculative at this point. We don’t have a lot of effort going into that right now.
Certainly I think that from a technical perspective this could get done. But can we develop the technology and roll it out with a lower-cost methodology so that we can beat the prices of existing providers like Comcast and Time Warner and other people? It’s not clear that the business case will work.

http://spacenews.com/spacex-president-downplays-commitment-to-building-broadband-constellation/
Who says it isn't happening? SpaceX is still actively hiring for it (look at their "open positions"), although to build this network will require massive expansion in several areas, something which you wouldn't want to pull the trigger on until you had the basic work finished, which is probably what Shotwell is talking about. And do we forget that SpaceX core business of space launch was speculative, by Musk's own admission, early on? Just because it's speculative does not at all mean they aren't working on it. I mean heck, even if the odds of them succeeding at it are merely 50:50, the potential up-side is so huge, they'd be dumb not to try.
« Last Edit: 10/28/2015 11:40 pm by Robotbeat »
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Offline ScepticMatt

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Re: Mars Internet Constellation and making money from Mars
« Reply #38 on: 10/29/2015 08:07 am »
Quote
Who says it isn't happening?
They don't count on it as a funding basis for their mars plans anymore, as the opening post suggests.
They don't see a valid business case right now. What I don't doubt is that research is ongoing.

Offline savuporo

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Re: Mars Internet Constellation and making money from Mars
« Reply #39 on: 10/29/2015 06:21 pm »
The connection would be satellite type. They would use the same kind of satellite over Mars as the internet constellation over earth.
No. Any random LEO comsat would not work in Martian orbit, especially something built with COTS electronics. Space environments are different, and require different engineering solutions.
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