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The First Detailed Look at How Elon Musk's Space Internet Could Work (newscientist.com)
SpaceX has been granted permission by the Federal Communications Commission (FCC) to set up a vast network of thousands of low Earth orbit communication satellites. But the company has been tight-lipped about the project, known as Starlink. Mark Handley, University College London built a simulator based on public details from the FCC filings to understand the latency properties of the network. New Scientist reports: Although Musk has said he wants more than half of all internet traffic to go through Starlink -- Handley's simulation suggests that the project will be most appealing to high-frequency traders at big banks, who might be willing to fork out large sums for dedicated, faster connections. To create the simulation, Handley took what information he could from SpaceX's public FCC filings and combined this with his knowledge of computer networks. Initially, Starlink will consist of 4425 satellites orbiting between 1100 and 1300 kilometres up, a greater number of active satellites than are currently in orbit. There is only one way to arrange this many in a configuration that minimises collisions, says Handley. So he is confident that his simulation reflects what SpaceX is going for.
When sending an internet message via Starlink, a ground station will begin by using radio waves to talk to a satellite above it. Once in space, the message will be fired from satellite to satellite using lasers until it is above its destination. From there, it will be beamed down to the right ground station using radio waves again. Between distant places, this will allow messages to be sent about twice as fast as through the optical fibres on Earth that currently connect the internet, despite having to travel to space and back. This is because the speed of the signal in glass is slower than it is through space.
When sending an internet message via Starlink, a ground station will begin by using radio waves to talk to a satellite above it. Once in space, the message will be fired from satellite to satellite using lasers until it is above its destination. From there, it will be beamed down to the right ground station using radio waves again. Between distant places, this will allow messages to be sent about twice as fast as through the optical fibres on Earth that currently connect the internet, despite having to travel to space and back. This is because the speed of the signal in glass is slower than it is through space.
Solving the worlds problems, step by step.
No sig today...
Just dropping by to mention that, while existing fiberoptic networks have index of refraction around 1.7 (so signal speed is c/1.7) , there is a relatively new thing referred to as "holey fiber." It's essentially analogous to microwave hollow guides, with the hole pattern sized to match the TE/TM modes of the injected light. The speed thru these waveguides is close to the vacuum limit.
https://app.box.com/WitthoftResume Code: https://github.com/cellocgw
High speed trading looking for a timing edge has already upgraded to shortwave which traverses an even shorter distance (bouncing through the lower atmosphere) right at the speed of light.
https://sniperinmahwah.wordpress.com/2018/05/07/shortwave-trading-part-i-the-west-chicago-tower-mystery/
Iridium et al. Just a bunch of space junk now.
Is it? Iridium's problem was lack of customers who needed the service and had money to pay for it. Prices where so high that few people in areas that didn't have cellular service already could afford to pay the subscription fees. Their business model wasn't viable.
In this case, there is actually a different business model and possible paying customers who actually have money and a need for internet service. Are there enough of them who have enough money to make this viable? Maybe... Given Musk's access to exceptionally low cost launch rates, this might just work out this time. I'd not bet on it either way myself.
"File to fit, pound to insert, paint to match" - Aircraft Maintenance 101
The distances among all the end-to-end points, be they game or gross margin, is a constant, and does not vary as does the speed of light in a medium, be it glass, copper, or over the air.
Of those, over the air is much faster.
It little behooves the best of us to comment on the rest of us.
SpaceX's revised FCC filing calls for about 1.6k of the initial 4.4k constellation to be at 550km orbit. Brings the minimum latency down to 15ms, instead of 25-35ms.
https://www.theverge.com/2018/...
https://forum.nasaspaceflight....
"'Tis great confidence in a friend to tell him your faults, greater to tell him his." --Poor Richard's Almanac
Iridium's problem was...
Actually, AMONGST Iridium's problems was that it was not designed as a data transport system, and the horrible data capabilities that they offered were based on running a modem over their voice lines.
Iridium Next will expand those offerings to 128 kb/s to mobile, 1.5 Mb/s to marine and 8 Mb/s to fixed land stations.
This leaves a lot of room for improvement and Musk might force iridium's hand to provide faster upgrades than their 20 year turn around on iridium to Iridium Next
Problem is, fiber on the ground is faster as the distance is shorter.
Only true in general for relatively short trips with fixed destinations.
Unless you live in some remote place that depends on geo-stationary satellites for internet, you are better off going along the ground, at least where latency is concerned.
A) These are not geo-stationary satellites SpaceX is proposing. Geostationary orbit is about 35,700km away versus the 1200km being proposed here. That difference is very significant. B) Ground is only faster in some use cases but not all and the longer the transmission the less advantage it has.
The lower latency could be useful for games, too.
Probably not, because the potential savings scale with distance. Halfway across the world and back is 40000 km/300000 km/s = 133 ms at light speed, at c/1.7 it's 226 ms so at most 93 ms to save. But I wouldn't try to play a twitch game at those ping rates while at reasonable gaming ping times the gains are mostly eaten up by the base latency. Unless you really desperately want to play with your guild from another continent, it's not going to matter much. It mainly matters for HFT where your buy/sell orders arrive a few milliseconds before the competition.
Live today, because you never know what tomorrow brings
Or more like building the technological infrastructure needed for a Mars colony, step by step.
Maybe but a lot of those problems are the same problems we have here on earth. We need electric powered vehicles to reduce oil dependence. We need low cost to orbit rockets. We need solar powered homes. We need cheaper/better tunnel making. We need more ubiquitous internet access globally. Whether you like Musk or not, you have to admit he's working on solving serious and important problems. (and if you don't think those are serious problems then you don't understand the problems) The fact that there is a lot of overlap with problems we'd face colonizing Mars is just a cherry on top of the sundae.
Who gave them the authority to do that? They should probably only be allowed to have a say about the airspace above the US.
Yes, I'm left. You have a problem with that?
I still prefer the notion of a network of ocean line-dancing sharks supporting a mesh net of laser beams just skimming the surface.
The training and fish bill is high, and this network facilitates phishing too, but you can't have everything.
Rgds
Damon
http://m.earth.org.uk/
A better question would be: What's the cumulative latency of the bucket brigade?
It little behooves the best of us to comment on the rest of us.
If you care enough about latency to have access to a massive grid of satellites as part of your route, then you're better off using a terrestrial radio link. You'll get faster speed and save tons of cash.
If you are on Verizon, and I am on Comcast, there is a good chance of jumping 20+ times. In contrast, starlink will cut that way done
I prefer the "u" in honour as it seems to be missing these days.
Glass is 31% slower, not a rounding error. Speed of light through air is much closer to matching your description. While this article from 2013 talks about using air-based conduits, I don't think it's reached full deployment yet.
Fortunately, I have them.
Space Communications Protocol Specifications
Consultative Committee for Space Data Systems
CCSDS Technical Specifications
Space Assigned Numbers Authority
Spacecraft ID list and manual
Disruption Tolerant Networking
Exploration and Space Communications at NASA
Free Space Optical Communication
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
Rule of thumb: light does:
* 1 m / 3 ns - signal in vacuum
* 1 m / 4 ns - signal in copper wire
* 1 m / 5 ns - signal in fiber optic cable
It's a lot slower in in a bent fiber optic cable, of course, but long runs are effectively straight.
Socialism: a lie told by totalitarians and believed by fools.
"There is only one way to arrange this many [satellites] in a configuration that minimises collisions, says Handley."
Hadley's statement above is actually false. It suffices to present two viable configurations to prove his statement false.
There are at least two basic configurations for plotting the vertices in a geodesic dome: class one and class two. Thus there is more than one way to arrange this many [satellites] in a configuration that minimises collisions.
If the satellites are not plotted like the vertices in a geodesic dome, then there are at least three ways to plot the satellites.
I think this has great promise. And in theory will be awesome, quick and high capacity. Right up until China reroutes all the traffic through Beijing.
- Tjp
I am in wallow with my inner money grubbing capitalistic pig. ... Oink!
Which is basically what this is. No matter how you slice this, the ground based path will be physically shorter and thus has a latency advantage, even with LEO satellites in the mix.
A) Unless you are talking about some specific use case, ground based paths are NOT always physically shorter because they are not all point to point connections. B) Ground based routing of any significant distance routinely has to go through more devices and at slower speeds through fiber/copper. C) Latency is not just a function of distance
But my point here is that if you are looking at latency, the shortest route unusually wins and LEO orbits add quite a bit of distance.
Not when you are talking about distances the size of a continent. It's 4500km from NYC to LA across the earth's surface assuming a relatively straight line connection (which probably won't happen but let's say it does for sake of argument). The difference in distance going to LEO across 1 satellite is only marginally longer if you calculate the sides of the triangle. Let's do some over simplified math. Simplify to an isoceles triangle with hypotenuse of 4500km and height of 1200km and you are at ~5100km for the trip. You've added 600km but can send the signal at 2X the speed. So the signal going into space will arrive faster than the one going on the ground.
The distance between end-points doesn't change, but the path between them does.
And going via satellite is potentially much lower than any other alternative, at least to get halfway around the world - after all, the speed of light in a straight line through vacuum is pretty much the limit, nothing else can be faster. And you can't send signals in a straight line on Earth - the Earth gets in the way. Realistically you've only got line-of-site of 80km or so - even at 10,000 feet altitude that only increases to ~200 km
At 1000km up, a satellite would have direct line-of-site with other satellites up to...
2 * asec( (6371km+1000km)/6371km) = ~60 degrees away
So best case of 3 hops to get a signal half-way around the world, assuming communication lasers can be tightly enough focused to be useful at a distance of 7371km (because 60* separation = equilateral triangle with the Earth's center.)
Add in the worst-case scenario of relaying to a satellite directly overhead at both ends, and you've got a total transmission distance of 3*7371km+2*1000km = ~24,000 km with 5 total hops to get a signal halfway around the planet. 80ms of travel time
Compared to the ideal great-circle fiber-optic line on Earth, which would be 20,000km, or 67ms. Except for one tiny detail - light travels about 1.467x faster in a vacuum than through a fiber-optic cable, so really that'd take 98ms
So, light-speed delays alone could give a satellite link a ~20% transmission latency advantage over point-to-point surface fiber. And of course real fiber isn't laid point-to-point, so add even more advantage for every turn the signal has to take.
But transmission delay is only half the problem, you also add delays at every hop as the signal is processed by the router and waits in queues to be resent - getting a 200ms ping to somewhere halfway around the world would actually be quite impressive - New York to Tokyo averages about 215ms, and that's only a bit over 1/4 of the way around the world.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
>Problem is, fiber on the ground is faster as the distance is shorter.
The distance is shorter, but the speed is much slower - typical fiber optic cable has a refractive index of 1.467, which means that light travels 46.7% faster through vacuum than cable.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
What do we know? About SpaceX SAT architecture, network topology and service niche opportunity?
Even the simulator doesn't layout the business case much less a technological opportunity for SAT use.
Handley's simulation suggests that the project will be most appealing to high-frequency traders at big banks, who might be willing to fork out large sums for dedicated, faster connections.
Well that's just dumb. High frequency traders at big banks merely locate their data center / computing presence in close physical proximity to the point where the trades occur. Relying on a massive, expensive space network to come into existence just for high frequency trading is absurd.
This will most appeal to the millions of people that do not have broadband. The money to be made is in the masses, not in "high-frequency traders at big banks".
Better known as 318230.
Patent: The internet ... but in space.
You aren't thinking big enough. Patent "space" - with an Internet. Then shut down anyone doing anything in space with data communications that go through more than one hop...
The speed of light though glass (fiber) vrs a vacuum is almost a rounding error, you don't see it until you get to 3 significant digits.
How does refraction work then?
Given the choice of delivery of information OTA or struggling through a non-superconductive conduit, I'd like mine airborne, please.
It little behooves the best of us to comment on the rest of us.
What about GPS? That's cheap and anybody can use it.
Problem is, fiber on the ground is faster as the distance is shorter.
The ground distance must be shorter by at least 32% because the speed of light in fiber is 32% lower than the speed of light in free air.
Ezekiel 23:20
Sorry, that's copper that's 30% slower. Some fiber connections are about 99,7% the speed, plus microwave though air is a rounding error from a vacuum.
So a series of microwave links or fiber still is shorter time wise.
"File to fit, pound to insert, paint to match" - Aircraft Maintenance 101
What optical material has a refraction index of 1.003? According to this table, the closest one is liquid helium. Surely that is not the case.
Ezekiel 23:20
You RECEIVE a GPS signal. You don't upload to it. And it's not suited to doing much beyond broadcasting the current time. And they're about 12000 miles up. So no.
Very true, but just because they lack the ability to upload on the GPS network, does not mean a purpose built network wouldnt work. My point is GPS is available for all, and it is a "massive grid of satellites". Sure you will have to have a dish/antenna on the ground to be able to communicate and have full internet connection. But it can be done. And apparently they have some sort of idea on how to do it cheap enough to make it worth while. People also didn't think he would be able to reuse rockets, then people said he would never be able to gracefully land said rockets. Well, so far his off the wall ideas seem to be working. Im all for faster, cheaper internet. Imagine when its a large sat network, and its like dial-up where you can get service from any multitude of companies. Hell with it being satellite you will be able to get internet service through companies that solely exist on another continent. That is the internet I hope to come from this.
Now, these satellite services are great for under-served areas of the world. The problem is, the customers available, those willing and able to pay, and needing service in those under-served geographies, there aren't that many of them really. Most people in the under-served geographies are poor, or they don't need this service. But put all that aside for a moment and consider this. The majority of people worldwide live in (or near) cities and already have internet and cell and WiFi service.
The people paying the telephone and cable monopolies are under served also.