SpaceMobile Constellation (AST & Science)

[RedLineTrain]

As far as I can tell, it's the difference between 45 big antennas by the end of 2026 versus 800 smaller antennas by the end of 2024.  I think it's a race for the highest number of cells/cell density.  Don't know which system will have the most cells, but I believe that Starlink aims eventually to have all of its Gen2 7500+ constellation equipped with suitable antennas.

Would be interested in learning more details and nuances.

[RedLineTrain]

Here's an on-point tweet with some bullet points.  It seems indeed to boil down to a race for cell density, at least as laid out here.  The comparisons on the frequencies used wouldn't seem relevant because Starlink can always add more frequency coverage when it wishes to do so.

https://twitter.com/thekookreport/status/1796421991223984145

[gongora]

The normal Starlink services are on different frequencies than the direct-to-cell stuff, with completely different licensing.  Direct-to-cell requires partnering with the other companies who have already licensed those frequencies, and the regulations are still being worked out.

On the technical side, I think it's still to be seen how many simultaneous connections AST can really serve at high data rates.

[RedLineTrain]

I may have misunderstood MET's post.  Starlink is going for an "all of the above" approach regarding frequencies, ASTS only the lowest frequencies.  From highest to lowest frequencies.

Terminal Use/Ground Station Use (the current Starlink system)
E band = shareable frequencies so no frequency purchase/lease required, directional (ground station only)
V band = shareable frequencies so no frequency purchase/lease required, directional (ground station currently + terminal in future)
Ka band = shareable frequencies so no frequency purchase/lease required, directional (ground station currently + terminal in future)
Ku band = shareable frequencies so no frequency purchase/lease required, directional (terminal only)

Handset Use
PCS/BigLeo/S/L = some shareable, some non-shareable frequencies so frequency purchase/lease sometimes required, omnidirectional (Starlink's new D2C payload)
UHF/lowband = non-shareable frequencies so frequency purchase/lease required, omnidirectional (ASTS sats, future Starlink)

[RedLineTrain]

More comparisons.  It appears that some on X are misunderstanding that ASTS somehow has a fundamentally better approach, but to me it's still just a race for cell density.

Ben Longmier @longmier

Perhaps your initial difference of opinion is based on some different data? This is what I’m tracking for data rates (single beam, beam center, demo from space).

SpaceX: 17 Mbps
https://x.com/elonmusk/status/1764032892663906313?s=46&t=72FzIx9YO04nsdGjnGpCag

AS&T: 15 Mbps
https://x.com/ast_spacemobile/status/1763550098796016122?s=46&t=72FzIx9YO04nsdGjnGpCag

Terrestrial 5G in the US: 150-200 Mbps
https://lightreading.com/5g/t-mobile-is-still-the-fastest-5g-provider-in-the-us

https://twitter.com/longmier/status/1796700279582425455

[Danderman]

AST is going with a small number of sats in higher orbits with really large antennas.

As a competitor to AST, I don't want to get into the disadvantages of that approach here.

SpaceX has in place a system to provide internet for millions of users, using 1000s of satellites in lower orbits. To add cellphone coverage, SpaceX must modify future satellites by adding bigger antennas (although not as big as AST). This reduces capacity on Falcon from 66 to 22 sats per launch, a major disadvantage for SpaceX, since the build out of their internet network will proceed more slowly (until Starship is available).

However, if their new sats had really large antennas like AST, perhaps they could launch 1 or 2 sats per mission. This would throttle the internet system build out significantly.

I would go into the issue of Starlink user channels vs cellphone user channels, but that would add more confusion.

[Danderman]

Concern speed, downlink is trivial. The issue is dealing with the narrowband cellphone uplink signal.

AST's huge antenna is really about that.

[RedLineTrain]

SpaceX has in place a system to provide internet for millions of users, using 1000s of satellites in lower orbits. To add cellphone coverage, SpaceX must modify future satellites by adding bigger antennas (although not as big as AST). This reduces capacity on Falcon from 66 to 22 sats per launch, a major disadvantage for SpaceX, since the build out of their internet network will proceed more slowly (until Starship is available).

Rather, adding the cellphone coverage decreases capacity on Falcon from ~22 sat per launch to ~18 sats per launch.

To your broader point, SpaceX is filing with the FCC to open up the lowest orbit shells (~340-360km) for the sats with cellphone coverage.  AST's constellation will be at ~730-740km.

[catdlr]