Starlink Innovation Part 2

The second key SpaceX innovation that makes Starlink possible is an affordable, reasonably sized phased array antenna. Let’s take a look at what that is and why it matters.

In order to make satellite internet competitive with terrestrial internet, SpaceX needs to fly their satellites at a very low orbit. Traditional internet satellites fly very high, at an altitude that allows the satellite to sit in the same spot in the sky relative to the ground. This is good for making the user’s antenna dish as simple a device as possible. Once you properly point the dish at the satellite, the dish just sits there and does its job. It’s bad, however, for a responsive internet because a satellite that sits in one place in the sky needs to be so far away that it takes ages (about half a second or more) to establish a connection between the satellite and the user’s antenna on the ground.

SpaceX flies its Starlink satellites in a very low orbit so the distance from the user’s antenna to the satellite isn’t so great and the connection latency is much improved (about 65 times better than traditional satellite internet.) But this comes with a challenge. At low altitudes, the satellites don’t sit in one place in the sky, they move across the sky, and rather quickly. That means your antenna needs to track the satellites as they move.

One way to do that would be to put some motors on the antenna so it could rotate to follow a satellite’s movement across the sky. But then you run into the problem of swinging the antenna back in the opposite direction to point at the next incoming satellite. You’d need to do that really fast to not have a gap in connectivity and that’s just not practical with motors. Perhaps you could have two antennas then, one tracking the satellite that’s leaving view and another tracking the satellite that’s coming into view. Now you’ve increased the cost and complexity of the system and doubled the number of failure points though — and made the user’s terminal large and cumbersome.

So, how does SpaceX solve this problem? With something called a phased array antenna. Phased array antennas are not new technology but they’ve traditionally been very large and very expensive. How they work is a bit complicated but a simplified description is something like this: you have many small antennas that act as one larger antenna. By powering those antennas individually and selectively you cause them to interfere with each other in such a way that the antenna’s collective beam is bent. This steerable beam can track movement and change direction and location almost instantaneously.

Big and expensive doesn’t sound like such a great solution though. And this is where SpaceX’s innovation comes in. Their hardware team miniaturized the technology, putting hundreds of small integrated circuit antennas onto a single computer board about the size of a typical internet satellite dish. And, they’ve managed to get the cost of building this phased array antenna down to something like $2500. Now, that’s still pretty expensive and so SpaceX is actually subsidizing most of that, charging users only $500 for the $2,500 antenna terminal. They hope future innovation plus mass production will get the cost down further but I suspect that it’ll be some time before they get costs down low enough to no longer need to subsidize. Instead, they’ll lose some money on the terminal and make it back up with the monthly internet service fee. If everyone that signs up for Starlink keeps the service for a couple of years, that will pay for the terminal and then start to be profitable for SpaceX.

If you’d like to read more about phased array antennas, and you should because they’re very cool and if you’ve read this far you’re probably into that kind of thing, start with the Wikipedia article at https://en.wikipedia.org/wiki/Phased_array It’s a good primer and has some nice animations that help a lot to describe phased arrays.