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Comment by legolas2412 | Hacker News Reader

But isn't it still cheaper to lay fiber cables?

For example, 23*4400 = 101Tbps, but I guess many of the satellites will end up above water, so maybe around 60Tbps. One cable by google did that for 300mil$ [1]

Maybe it is good for last mile connectivity, which is probably a good target, but only for less populated areas where LTE isn't available.

[1] https://www.extremetech.com/internet/231074-googles-faster-u...

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Laying fiber isn't going to get your Tesla connected.

Interesting idea but wouldn't a satellite to car connection be pretty unreliable?

Since the line of sight would often have things in the way. I'm assuming trees, bridges, and being in a garage would interfere with it.

Yet GPS works.

AIUI, GPS isn't a connection. It's broadcast, one-way communication. Also, I assume the information transferred is much lower, not much more than time and position, plus redundancy to handle things like interruptions due to landscape.

Well, there's going to be 800 of the suckers. There are only about 33 GPS satellites. Although 700 miles is lowish orbit, it's still above the horizon over 2000 miles away.

Wow. I read this comment and thought, "This has to be bullshit." But lo and behold, the core satellite 'constellation' is only 24 satellites[1]. That's mega impressive.

https://www.faa.gov/about/office_org/headquarters_offices/at...

And they transmit with about 50 watts.

Look up the connection between Einstein's general relativity and GPS accuracy for more fun. Especially early on in its deployment.

That's actually a myth, since the GPS satellites all experience a similar relativistic time skew.

http://www.alternativephysics.org/book/GPSmythology.htm

"The presence of Special and General Relativity effects has no bearing on the accuracy of GPS operation. In summary, it wouldn’t matter whether clocks aboard GPS satellites ran faster or slower than Earth’s clocks or even changed their speed each day. Just so long as the satellites’ clocks remained synchronised with each other and the time-difference relative Earth’s clocks didn’t become too large, GPS receivers would continue to calculate their correct position."

That page constructs its own argument and then deconstructs it. It doesn't actually disprove the OP's statement.

The reason that GR and SR have "no bearing" is because they've already been designed into the system...

From "Understanding the NAVSTAR" 2nd Edition, by Tom Logsdon ( one of the designers of the system ) the time-dilation is compensated through:

1. Off-setting the clock ticking-rate during manufacture of each satellite.

2. Applying a unique onboard corrective factor according to the eccentricity ( egg-shapedness ) of each satellite's current orbit. The latter is correction is constantly recalculated for each satellite.

Without these corrections against relativistic effects the accuracy would suffer by 14 nm after 24 hours ( without tick-offsetting ) and 100 feet or so per day due to orbital eccentricity.

That's the one. There's pages one can get from Google with some of the data and illustrations if they can't get the book. It tripped me out when I found out they had to design relativity into it.

I knew I shouldn't have questioned you so flippantly... Lesson learned.

Feel free to question as Im a human acting on incomplete information like the rest. ;) Just don't assume or read in too much as that can get you. Happened to me plenty here, too, haha.

Well, GPS is more like radio, you only listen to the broadcast, you don't talk back.

But this is more like cellular access points. You have a private channel.

You don't establish a communication channel with GPS. You merely listen to the broadcast.

Like a radio tower can service an entire town, but you need many many cellular access points.

I used to have a sat phone (Thuraya) and it was pretty reliable if you were outside. They don't work well inside buildings.

You'll get around that in your home by having the satellite module thing up on your roof and a cable to your wifi router.

What I don't understand about this though is the number of frequencies available to connect to all these satellites and how it might extend to ~300 million people (let alone a billion potentially).

I think they focus a beam on each user in turn and so don't need different frequencies.

Can't lay fiber to the entire planet for $300mil

Yeah the cost advantage is entirely in last mile connectivity. It doesn't really make sense to compare the cost of a single cable to the cost of the end customer getting a connection. LTE is a much better comparison, but I think the cost will actually be pretty similar or cheaper than LTE (see my other post for napkin math) and cover a lot of areas/applications that LTE can't.

They're presumably aiming for some amount of economy of scale by using their own rocketry service. Dollar for dollar comparison doesn't account for the fact that they're investing some of that cost into further rocketry development.

Maybe it's a lot quicker - Google Fiber has been taking forever. Not that rocket science is easy, but it's probably a lot quicker than striking the earth.

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