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Comment by londons_explore | Hacker News Reader

Every time you see a claim like this, remember the Shannon–Hartley theorem[1].

If you want to get a decent bandwidth in aggregate for your mobile network, you're going to need to consider:

* Maximize transmit Power: which is hard because phones are battery powered, and power is limited by law. Satellites are also battery powered.

* Maximize bandwidth: Also limited by rules and regulations.

* Maximize Directionality: If you have physically large antennas, you can direct your transmit power towards the receiver to make best use of it.

* Minimize Distance: Received signal power goes down the the square of he distance. Double the distance, and you get one quarter of the bandwidth, all other things being the same.

This proposal uses tiny existing antennas in phones, which means it must be making other tradeoffs. My guess is it seriously sacrifices the total throughput.

[1]: https://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theore...

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> Satellites are also battery powered.

I thought they have solar panels.

Also, don't phones and satellites use small antenna arrays to direct power in a certain direction?

I think the panels recharge a battery. Is the satellite always within line of sight of the sun?

Solar panels when illuminated by the sun, battery power while in the Earth's shadow.

To be low latency they need to be in a low orbit, so probably on battery power for a significant fraction of the time.

The batteries are powered by solar panels. In either case the same arguments apply - space is notoriously low power.

Phones can't use directional antennas, otherwise you'd have to point them at radio towers. Using phased array antennas in which directionality is software controlled, there's a trade off between size of antenna and how much you can focus the beam - it wouldn't work in a phone (and would be too expensive anyway).

Ok, but there is a lot of power to be saved. If you can prevent the beam from going in the "opposite" general direction, you can already save 50%. I'm not convinced there is nothing to be gained by using a small array.

Its just physically not feasible. For an antenna array with 2 dimensional beamforming you need an array of NxN antennas, which all have the dimension of a fraction of a wavelength, so we are talking about a not insignificant size. Additionally, to limit mutual coupling via substrate and stray radiation, you need certain distances. Third, you need to be careful to prevent grating lobes (side emissions of unwanted radiation).

And even then, you will need individually controlled phase shifters for each array element, adding cost, complexity and mostly negating energy savings.

Edit: All of that in addition to the problem that you need to know the location of the base station and have you array antenna roughly oriented towards it.

In addition to all the above, phones move a lot during a call. You'd need very good sensors to keep track of the phone's orientation in space. If you're only shooting for 50%, the sensors in phones are probably good enough, but what happens when the user puts their head between the phone and the base station? The phone could say "please rotate your body to reconnect call" but that would be a lousy user experience.

There are neat tricks to keep phased array antennas in alignment. One for example is to just send the signal back in the same direction you're receiving from. (ie. Same phase delays in every antenna element)

Then however much the phone is tumbling, you'll always be exactly sending the data in the right direction.

Turns out the problem is moot anyway - unless you have a huge antenna to get a really narrow beam, sub-degree positional errors won't make any impact.

Saving 50% gets you 3dB. You'll need something on the order of 20dB. The inverse-square law bites hard.

Space is notoriously expensive... until it isn’t. Launch costs have reduced by an order of magnitude and may reduce by another as full reuse becomes feasible. All of a sudden, you’re using near-commodity solar cells with a higher capacity factor (and more consistency) than on the ground. Power is thus not so expensive any more.

Industry rules of thumb are only good if the industry is stagnant.

And yet SpaceX still struggles to find launch volume.

I'm not sure what you're trying to say here. That SpaceX's launch business struggles to find enough customers, or that SpaceX's satellite business struggles to get enough launches to orbit?

Ironically both are sort of true... and I'm not sure how either of them respond to the post you replied to.

SpaceX has been struggling to get enough external customers recently, the launch market has been in a bit of a slump and external customers haven't yet substantially responded to the lowering launch costs.

SpaceX's Starlink constellation needs a huge number of launches, to the point where it seems at best barely feasible in both cost and launch volume to launch it on current rockets. They hope to fix this with their in-development starship rocket which should be able to launch an order of magnitude more satellites at a time (400 vs 60), at an order of magnitude less cost as a result of full re-usability and easier construction of the rocket.

Space isn't javascript. It takes years and many millions of dollars to build a sophisticated satellite, and SpaceX's market dominance didn't happen until last year. Most those who may want the take advantage of the lowered launch costs aren't yet in a position to do so

...which is why they're creating their own megaconstellation: to produce their own demand.

This has always been a conundrum for space launch: demand is, in the short term, very inelastic and the market is small, so if you reduce prices through reuse, you might actually reduce your own revenue if you're not careful. The way around it is to create your own demand.

Anyway, this new firm is an example of a new source of demand. This will provide additional launch volume.

While the cost of putting more solar panels and batteries in space is one limiting factor, the ability to reject heat in a near vacuum is another issue to consider. This is another thing which usually limits the practical power budget of things in space.

What you mean is either achieved with conventional high-gain antennas (Dishes, mostly) or with beamforming by either a passive, or in this case more likely, active phased array. TBH, I dont know of any commercial handsets doing so (albeit I am not that deep into the consumer market). On Base Stations, on the other hand, yes they are using this technology to improve reception and to limit inter-cell interference.

They also have batteries. When their orbit takes them into Earth's shadow, the solar panels stop working.

Reading your comment I immediately thought probably enough throughput to covertly track a phone. I thought maybe this company isn’t really trying to sell to the public but rather get some attention to their new tech before they ultimately sell it off to the government.

I'm pretty sure you can already track all phones from satellites already.

Phone initial handshakes with the tower are done at high power and are always identical, meaning you can get a ridiculous coding gain to detect them.

But starlink. Seriously how are they going to make it work?

I've wondered about that too, but their satellites are close to the ground - 620 miles vs 22,236 miles.

I don't know how far away the average cellular tower is, but I imagine line of sight could be a better signal than a closer occluded signal.

Wikipedia says cell tower range on hilly terrain can be 5 miles, while on flat ground it can be 30-45 miles (which is still over the horizon).

What I wonder about is how many phones per satellite is supportable.

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