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Comment by Veratyr | Hacker News Reader

To take home users as an example, the residents generally sleep 8-10 hours a day, work 9 hours a day, commute ~1 hour a day, leaving only about 6 hours of free time at home a day. Assuming they spend that entire time watching 4K Netflix (25Mbit), they'll have used ~2TB in a month, or ~6Mbit/s total. Averaging bandwidth out over the whole month, each satellite would be able to support 3800 people. With the 4400 satellites they intend to deploy, they could support 16 million people.

Of course you generally need to provision for peak bandwidth rather than average so these numbers aren't even close to accurate but I think it's a rough explanation for why you don't need to fully provision every link.

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But also bear in mind that the all the satellites over New Zealand (for example) will be wasted while we are asleep and at any given time a lot of satellites will be over empty ocean (sending 4K Netflix to cruise ships maybe).

I';; also counteract may own argument as to numbers with the idea that 16 million people could really mean 16 million households if they watch the movie together :-)

2TB/month is a lot. Home data caps tend to be more 10 - 40GB and I've got 4GB data on my phone which is fine for most stuff except video. I doubt the service will be very cheap - sat services are usually more than cellphone data.

Yeah, most people sleep at the same time.

Working for a CDN, we see our POPs gets about 4x traffic at peak compared to low times.

Most people sleep at the same time in one given geography, but if you're looking at the world, those times are pretty well distributed. Assuming I'm sleeping 8 hours a day, even the continental US only has 5 hours per day when everyone is asleep when you account for time zones. But APAC, ME/Africa, and Europe are all pretty reliably awake at that time.

Yeah, but that doesn't mean you can just put all the satellites right above the part of the world that is awake - so you are still going to not have a perfectly efficient system.

Why not? I wonder if you could construct a polar orbit that followed the daylight around the earth. Add higher concentrations of satellites to the orbits that correspond to the higher traffic hours of the day.

Yes, it's called a sun-synchronous orbit https://en.wikipedia.org/wiki/Sun-synchronous_orbit

The exact orbit has to be arranged so that it precesses once a year, keeping it aligned with a particular local time of day. "Typical sun-synchronous orbits are about 600–800 km in altitude, with periods in the 96–100 minute range, and inclinations of around 98°"

There are 5 planes of 75 satellites planned by SpaceX later on for 81 degrees inclination which might be sun syncronous during the day but the initial 32 planes of 50 satellites are all headed for 53 degrees inclination which I'm sure isn't. You can't have sun synchronous orbits anyways for those satellites providing coverage during the night.

> You can't have sun synchronous orbits anyways for those satellites providing coverage during the night.

Um, what? Of course you can.

Well, I mean you can put a satellite in orbit so that it always goes over the equator at midnight local time. But then it's solar panels will never get any juice and it won't function.

If it's in a sun-synchronous orbit when it is crossing the equator at midnight local time, then it will also cross the equator at midday local time on the other side of the world.

We have weather satellites in this exact orbit right now.

You're right, my mistake.

Yet another reason to do away with DST

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