ASTS - Simplified

When I first heard of AST SpaceMobile, my initial instinct was: bullshit.

Having a cursory understanding of what kind of technologies existed today as well as their limitations - namely cellphones need a cell tower around a few dozen kilometers away, and that satellite devices need specialized antennas - ASTS's claims sounded more in the realm of science fiction than science fact. This post is my last few months of research consolidated for those who haven't put in as much time understanding the technology, and want to read just one thing that'll likely answer all your questions.

[META] Also, while this sub does an ok-ish job on keeping up with current events (from people like CatSE), you guys are honestly terrible evangelists. When someone genuinely curious about the company asked a very relevant question a while ago, most of the responses were basically along the lines of "wow dumbass, go figure it out yourself." Some people even linked dense complicated equations that would have clearly convinced them of whether this is theoretically possible (I don't even think those equations answered the original question).

If you want this company to have a fanbase with a strong belief like, say, Tesla - that is not how you should present or be explaining the technology to the skeptical masses. So this post is also for you guys: to be able to link to something of substance without sounding like pretentious assholes.

Let's start.

The Science

The first question that will be in many doubters' minds, is: How? My cellphone today can't get a signal if it's more than a few dozen kilometers away from a cell tower.

And great question! That was my first question too. But consider this: we can still communicate with the Voyager spacecrafts that have left the solar system! Surely, the signal from even a large antenna 23.3 billion kilometers away is fainter than a mobile phone from low-earth orbit. Ok. So faint signals can be detected with enough effort - but how? Let me introduce you to the Link Budget Calculation.

In short, the signal strength you'd get is determined by this equation:

Received Signal Strength = (Transmitting Power) + (Transmitting Antenna Gain) − (Loss of Signal as it Travels) + (Receiving Antenna Gain)

I've done all the calculations for you in this StackExchange post, so head over there for further reading.

But as you can see, if you have a large enough gain (antenna) on the satellite side, you can detect a mobile phone signal from LEO. And what does ASTS satellites have? Big antennas. Bigger is better in this case.

Past Endeavours

It may surprise some of you, but this isn't actually the first time that a smartphone was able to connect to a satellite. Some of you might go "ah, yes - Lynk!" But no, I'm talking about a much older company - TerreStar.

The TerreStar Genus was a Windows Mobile 6.5 smartphone that was able to connect to TerreStar-1, a satellite that was in geosynchronous orbit - or 40-50x further away than where ASTS satellites will be. While not a modern smartphone, it was not too much thicker than phones of today, and most importantly - had no visible external antenna.

I bought the thing and tore it apart myself in this StackExchange post to identify the antennas. And I'm pretty dang confident that the satellite antenna was that tiny, thin strip of metal with the label E000118 REV F.

So even back in 2010, this kind of technology was already possible!

Scalability

But what about scale! You say. Sure, a satellite might be able to connect to one device, but what about hundreds? Thousands? Millions? And again, great question! This is one of the bigger unknowns of such a system. Let's start our discussions from the theoretical side first.

ASTS satellites will use beamforming to transmit down thousands of beams. I'm sure you heard this many times already if you've done any bit of research in the company, so let's answer of the questions I personally had about these beams:

Q: Are each beam independent from each other? That is to say, are you able to transmit simultaneously from beams A, B and C at the same time?

A: Yes.

Q: Is the satellite able to receive signals of the same frequency from different spot beams?

A: Yes. What works in the transmit direction works exactly the same in receive.

For a much more detailed answer, head over to this StackExchange post.

There is also a great Windover Productions video that describes how Cell Service works and is a great primer on thinking about scalability. In short - as long as you have enough power and processing power to add/separate all the signals, each beam is effectively separate from the other in a phased array.

From the first StackExchange post, jpa calculated that the size of the beams on the ground would probably be in the neighborhood of 300km^(2) (radius = 10km). If we combined that with the information in the Windover Productions video, that should mean in that 300km^(2) area, we would have at least 448 call/data channels (this is also a lower limit, as I'm not including CDMA which allows for even more transmissions mentioned in the last part of the video). Of course, not all cellphones are going to use the phones at the same time in an area, so depending on the over-subscription ratio, we can probably get at least a few thousand in that 300km^(2) area - as long as we have enough (electrical) power to power the phased array and enough processing power.

Is that scalable enough though? Will we have enough electrical power or processing power? There are still things we can do here if things don't go perfectly according to plan, such as turning off spot beams, putting in a larger battery... or even building an even bigger satellite, but ┐(￣ー￣)┌

The Economics

Alright, hopefully I've shown enough evidence to at least convince you that this can work theoretically. And if it works theoretically, it means we can probably build such a system - the question is, at what cost?

Obviously, ASTS wouldn't be an attractive investment if we can only manage to build such a system for 20 trillion dollars.

So let's analyze the costs. Cell towers are obviously not free. It costs carriers money to set one up and maintain one (something in the tune of $200k to a million dollars). If carriers can serve enough underserved rural areas to save all of the money building and maintaining random cell towers for small pockets of users, then cell towers in space just makes a lot of economic sense.

A system like ASTS will therefore become inevitable in the future if only one factor holds true:

cost of cell towers in space < cost of not having worldwide coverage

And what determines the cost of building cell towers in space? Rockets and regulations. Thanks to SpaceX, the cost of launching things into space has come to a historic low, and projected to be even lower in the future. Regulation is a bit harder to quantify as a dollar amount, but I suspect as the cost to build cell towers in space drops, there will be a lot more pressure to actually build cell towers in space.

Even if ASTS itself fails, if future economic conditions becomes even more favorable for cell towers in space - I'm sure I'd risk a bit into that company as well.

The Risks

So far, I've only talked about the upsides. Let's not fool ourselves though. ASTS is a very, very high risk, high reward stock.

Everything I've written about is only from a theoretical standpoint, and just like how nuclear fusion is theoretically possible, actually achieving fusion is always 30 years away. What we do have going for us is that thankfully, it's not nuclear science. RF is a very well understood field and we even have past projects like TerreStar, or even Iridium to lean upon for learnings and experience.

I personally think the timelines given by management are, quite frankly, ambitious. If you are going into this stock, I suggest going in for the long term, or make plays around significant de-risking events (i.e., BlueWalker 3). If we were to compare to a similar effort, Starlink was announced in 2015, and didn't make it to public beta until 2020. The first satellites also weren't launched until 2019.

^(And of course, the disclaimer: This isn't financial advice, just sharing my research - make do with it as you will. I do have a decently-sized, though not crazy ASTS position that has been underwater for the past few months. Barring significant events - like actually not being possible due to some scientific or economic reasons -) ^(I plan on holding this either to rock bottom or to the moon.)