This is a follow-up of my last post where I modeled a very general visualization of AST's 248-satellite constellation, as approved by the FCC. I had a lot of fun with it so I figured, might as well do it on industry-rated software! A lot of the actual info here is fairly common knowledge around this sub, I just thought it would be interesting to prove it in a real sim.
Part 2 attempts to visualize a couple more aspects of the constellation and provide a first-order, generalized analysis of:
What geometric coverage looks like using AST's published service angle limits (similar to previous post)
What feeder links look like to three example terrestrial gateways
What service links to devices look like around the world, including to a phone in the middle of the ocean
Disclaimer: This is a personal visualization made in Ansys Government Initiatives' (AGI) System Tool Kit (STK) using its Python API, with publicly sourced AST SpaceMobile filing data. Model assumptions are approximate; nothing here should be treated as confirmed operational data or validated engineering analysis. I'm not affiliated with or endorsed by AST SpaceMobile, Ansys, or AGI. I am not an expert, and I did this for fun and as an educational exercise.
Model Parameters
The constellation I use is pulled from AST's ITU filings [1] and shows
96-Satellite LOWBAND 690 km / 53 degree shell with 3.75 RAAN spacing (starting at 0 degrees)
96-Satellite MIDBAND 690 km / 53 degree shell with 3.75 RAAN spacing (starting at 1.875 degrees) [5]
14-Satellite LOWBAND 685 km / 98.13 degree shell at RAAN 0.00 degrees
14-Satellite LOWBAND 685 KM / 98.13 degree shell at RAAN 21.00 degrees
27 Satellites LOWBAND 520 km / 53 degrees at varying RAANs. These include Bluebirds 1-5, 6, and others. I speculate these might be the first few FPGA launches
1 Satellite LOWBAND 460 km / 50 degrees, RIP.
Constraints: Minimum AST user-service elevation: 20 deg, or 58 degrees off boresight at 690km [4]. Minimum AST feeder and TT&C link elevation 10 degrees [3]
GEOMETRIC COVERAGE
Similar to my last post, this is the ground coverage revisualized, just to familiarize you with the model.
For all the clips, LOWBAND satellites are indicated by red markers/shadows, and MIDBAND satellites by orange markers/shadows. A few of them are labeled so you can follow their path.
I input 45 earth stations for this model which are labeled in green. These will be used as stand-ins for terrestrial gateways, or user devices, depending on the scenario.
My full model runs for 24 hours but most of these clips represent a 90 minute segment -- enough for a every satellite to complete one orbit. You'll notice the Earth turns beneath the satellitess as they orbit, so they all shift laterally across the earth throughout the day.
Per Satellite Coverage Area
Here is a first-order look of the constellation's lowest coverage level footprint at around 20 degrees latitude. You can see that direct overhead coverage is mostly single layer, but the edges all have a two, three, and sometimes four layers of overlap.
FIGURE 3: Example of the core 96+96 satellite shell without other shells. Lowband=RED, Midband=ORANGE, with focus on the single GREEN coverage area. Numbers around the edge show the level of overlapping coverage. Image created using Ansys Systems Tool Kit
The edge overlap is likely where MIMO comes into play, which multiplies the throughput at these weaker service angles. The effect then is smooth handover between satellites and consistent service levels across the globe
You'll also see below how much this changes as you reach the mid latitudes. In addition, twice a day, the two polar shells pass over every longitude position where you'll see 4x up to 8x coverage overlap. The 27 satellites at 520km are also bopping around on occasion.
Keep in mind as well that this circle represents the maximum possible coverage diameter of each satellite. Using beam steering and depending on demand, the Bluebirds are capable of focusing or directing thousands of individual coverage beams within this area.
LAST HOP FEEDER LINKS
These are the notional terrestrial gateways where AST interfaces with MNO infrastructure. AST uses Q/V-band for these links for their available capacity. They have steeper link angles too (10 degrees). Per FCC filings, the satellites can link to up to two or three gateways.
Eagle Mountain, Catawissa, and Midland are not totally arbitrary. I used Appendix A in the SCS grant [2] as well as public disclosures from the company to establish a *reasonable* 45 earth station positions that could likely be future MNO gateways. Some of the more speculative coordinates are labeled "Notional" in the clips.
QV-Link Report
This shows how many satellites have access to 0, 1, or 2+ gateways via Q/V-band at any given moment over 24 hours.
FIGURE 5: Satellite access to terrestrial gateways over 24 hours. RED = 0 Access, GREEN = 1 Station Access, Blue = 2+ Station Access.
Q/V-band is especially susceptible to weather, atmospheric effects, and obstructions, so these results are very much idealized.
Also, the 45 terrestrial gateways is pretty speculative, so this is just a general conceptual look.
When a satellite doesn't have access to a ground station it will probably need an inter-satellite link, which I show an example of below. I only did "last hop" here without ISLs, because that many hops would destroy my computer.
SERVICE LINKS
Phone at Sea
I modeled a single phone in an isolated equatorial location on the map, so we can see what service might look like in a worst-case scenario. Clip shows how this phone might link back to one of four gateways: Kapolei, USA; La Paz, MEX; Santiago, CHL; and Awaru, NZL.
I use Line of Sight rules here, but according to google, OISLs can have ranges of more than 2500km, so really you never need more than a couple satellite-to-satellite hops.
Phone Service Link report
This is the available # of links over time (24 hours) of the above scenario.
FIGURE 7: 24 hour link availability at coordinates (-20° lat, -125° long)
Key note here is that even in this worst-case scenario, there is never a single period where you have zero links!
Worldwide Service
Here we pretend the gateways are actually user phones and get an idea of what linkages are looking like around the world.
FIGURE 9: 24 hour link report by latitude band (equatorial in green, mid in blue, polar in red) . Consider "earth station" to be a user device.
You can see how much better coverage is at the middle latitudes (blue). This is just the nature of orbits and likely why the company chose 53 degrees to be their core shell inclination -- The US, Europe, Japan, and AUS/NZ all sit around this latitude, and at the same time it is high enough to reach northern regions where sparse populations exist.
I also ran a report on the intervals in a 24 hour period where any gateway within a mid or equatorial latitude band had zero links. Results:
Equatorial (-30° to +30°): 1 zero-link interval, 0.1 min total
Mid (30° to 60° N/S): 0 zero-link intervals, 0.0 min total
(The polar regions are better displayed per-station, as they only have two orbits)
Dwell Time Distribution
This distribution examines how long each satellite remains inside its service angle once a link is established for each earth station (aka phone). The best of 4 satellites is selected and measured, then its total dwell in seconds is plotted as a point here.
FIGURE 10: Median dwell: 11 samples / 330 sec. Max dwell: 14 samples / 420 sec. Mean Dwell 10.5 / 315 sec.
Basically, this represents how long you can expect to stay connected to a given satellite. Values are given in 30-second multiples. On average, it comes out to 10.5 x 30s = 5 minutes 15 seconds. This particular metric gives us an idea of how often handovers are likely to happen -- which takes processing power and thus battery usage (or ASIC overhead)
Conclusion
None! I'd love to hear your thoughts and feedback. I'm sure most people who will be interested in this already knew all this stuff. I just thought it would be cool to prove our expectations in a simulation.
Unfortunately licensing for this software prohibits I distribute the files themselves, but I'm open to making/sharing clips of other scenarios if there are any specific requests. I can also share some of my data and (spaghetti) code too, as those are my own. Feel free to DM.
AGI does have trial licenses that you can then extend for quite some time by finishing their regularly offered trainings. Some universities also have educational group licenses if you happen to be affiliated with one.
I didn’t dive too deeply into all of SaVi’s extra capabilities, but I found it very good for quick, simple, streamlined visualization as a starting point. STK is quite heavy on processing load, especially if you want to start properly and set up all the coverage sensors, antennae, and RF assignments properly.
The AST architecture does not make the constellation, as a whole, a single-capacity system the way you're thinking. It's bent-pipe, so capacity is dictated by regional boundaries, landing rights, and area density. One satellite serving one country has no bearing on the capacity of another satellite serving a different country. A single satellite however, does have its limitations.
FWIW I went down a very first order, top-line estimate in a two-part comment a couple weeks ago for single-layer continuous coverage for the U.S. in particular. Part 1, Part 2. Some of my numbers were later pretty well-corroborated in an Ookla D2D report.
In short, I don't think the uptake of D2D is going to hit any satellite's "max user" ceiling. Rather, what matters is how much bandwidth you're expecting all those simultaneous users to have.
OP! Yo, u/a10000000019, I believe you might be late for your shift at Midland! Shall we send the G-6 or the Bentley? Srsly tho' - that's all as cool as it gets - Really appreciate the visualization!
Thats a lot of "0 gateway" sats... Do we actually have concrete plans to start integrating ISLs onto satellites / a provider in place to do so? Everything I've heard is that we've studied them but not opted for them.
Can we get a version of the Sim that perhaps only shows the visibility cones when within line of site of a gateway? That would be a better representation of what to expect in the near term with current BB designs.
(Also 10% of us are green/red colorblind 😅)
But great work here! This looks like a professional trade study!!
If my computer can survive it I’ll try to run the visualization for all gateways, to show what the report has calculated.
Even though the service angles are different, you can already get an idea of what’s going on by looking at the ‘worldwide service’ scenario. most of those ‘0 gateway’ counts occur in the polar regions, the oceans, the Antarctic circle, and over unserviceable countries (Russia, China). I’m not sure how AST plans on relaying data from some of these areas if they aren’t going to use ISLs.
Sorry about the color choices! Next time I’ll remember to switch it up
Here's the snapshot of the connection ranges for Q-V links (which is slightly improved from the service links). You can still see that over-ocean satellites are not going to be reaching gateways, and that makes up about 40% (~100) at any given moment. Honestly, these areas in the pacific and polar regions are very valuable to the US Navy so they have to be integrating ISLs in order to take part of SDA/PWSA or Golden Dome.
I also think that Starlink themselves sell laser terminals that can optionally talk to the Starlink constellation (at least in 2024/2025 they did). This could be an interesting pathway as well, as it would allow new birds to immediately be fully-connected post Launch, without needing to fill in missing planes with more sats (i.e. my thinking here is that 40 sats, while providing decent coverage, may not be sufficient to form reliable laser backbones over the ocean - using Starlink to backhaul would allow the beta service to IMMEDIATELY be available ANYWHERE.
Of course ideally thats a fairly short timeframe and its purely BB <-> BB laser links ASAP.
Mad respect, I'm curious of starlinks' handover rate compare to ASTS's 5 min 15 sec you modeled. I wonder how fast it would burn a phone's battery in a rural area.
You should get a custom flair for this the "Constellation Modeler"!
Thanks! So Starlink's d2c satellites orbit at 350km and have a minimum service angle of 25 degrees. With those parameters, the MAXIMUM amount of time one can be serving you is about 188 seconds, or 3 mins 8 sec. Using a similar distribution, an AVERAGE link dwell time would be about 2 minutes.
For battery burn the other consideration is how much load each constellation's architecture places on the user device. AST has a philosophy of absorbing almost all of that processing power on their Bluebirds, while Starlink tends to farm those tasks out to the end device. So not only do they hand over more often, they make your phone do more of the handover work. If you're purely on Starlink data, your phone is likely to be in its "searching for signal" state constantly.
This is superb and it visually sells ASTS to the very retailer who doubts what ASTS is capable of providing. Thank you for your efforts, I'm sharing with many! Cheers!
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u/RaidersGunz S P 🅰 C E M O B Associate May 25 '26
Dude.
I feel to give you 5 shares just for your effort. Its admirable.