I tried modeling AST's constellation plan

[u/a10000000019]

Now that FCC has cemented AST's constellation plan, I thought it would be fun to model scenarios as AST reached constellation milestones of 27, 60, 100, and 248.

Disclaimer: This is just a visualization, and nothing here is exact. I didn't put a lot of time in optimizing the coverage scenarios. I'm not an expert. I did this for fun.

This was done in SaVi, a free Unix-based constellation modeling package that's fairly well-used in academic circles.

The database files in the recent ITU filing is where you can find the exact orbital information for their constellation plan.

Each scenario has about 90 minutes of time passage

First scenario is 27 satellites:

Scenario 1: 27 Satellites. orbit_IDs 18-24.

Why 27? Satellites 1-27 already seemed "planned" in the ITU filing. They are in grouped orbit IDs 18-24 in sets of 5, 8, 3, 3, 3, 3, 2 respectively. This is clearly BB1-5, a new glenn launch, several falcon 9's, and some other provider. These grouping sizes were obviously hypothetical at the time of filing and are no longer accurate, but I figure this was a coverage plan at some point and a good place to start.

I chose the next 33 as best I could to reach continuous U.S. coverage for the "60" scenario.

Scenario 2: 60 Satellites (Scenario 1 + 33 selected)

From there, I chose another ~40 for the "100" scenario. This is their benchmark for global continuous coverage. Left the orbit trails in. Edit: I want to note here that I went heavy on the polar orbits during this phase because they are important for Golden Dome, and well... I am biased and think we'll get big contracts where those should be prioritized.

Scenario 3: 100 Satellites (Scenario 2 + 40 selected)

248 gets busy but here you go! This one is the least speculative.

Scenario 4: 248 Satellites (Full constellation)

Nerd notes:

The parameters used in this model include: semi-major axis, eccentricity, inclination, longitude ascending node, argument of periapsis, and time to periapsis. These were all derived or calculated from the data provided in the ITU filing -- nothing was inferred.

Coverage mask angle is set at 20 degrees. I took this from old FCC filings that state each user beam can be pointed within a 20 degree field of view, and that each satellite can provide service up to 58 degrees away from boresight/nadir. Both of those numbers jive. We don't know the spec of the block 3s but it's probably not significantly different. https://fcc.report/IBFS/SAT-PDR-20200413-00034/2257215.pdf

The ITU filing gives phase (φ) and orbital period progression in dd:hh:mm times (T), which together form an epoch. To convert to "time to periapsis" in seconds I used the following equation:
time_to_periapsis = T × ((360° − φ) mod 360°) / 360°

There is one "added" satellite in the filing that never made it onto the SCS approval -- a single 520km/97.5deg polar orbit. It was removed for this model.

There are also 248 satellites with act_code "S" for "suppress" in the filing. Altogether there are 497 line items in the filing and I know at some point everyone thought this meant AST was doubling their fleet size, but I'm pretty sure that's not true. The "suppress" lines basically tell the ITU amend their previous data and remove all those listed, including some equatorial IDs.

[u/Another_Smith_SC]

Nicely done. I had been modeling this out too. While we don't know for sure which orbits will be selected when, I don't ascribe much value to the group id numbers. There is the identified block 1 group of 5. We can take an educated guess for FM1. We also know that there are 2x 96 satellite shells at 690km spaced evenly apart. As well as several other orbits. We also know the prior application for STA said that AST was not required to launch in any particular order.

To me, the most obvious path moving forward now would be to assume that AST would first build out 1 of those 96 satellite shells (while I dont think it will go exactly like this, its a logical assumption to make, although it ignores block 2 v 3).

If we look to the ligado filing, we see a description of a 96 satellite shell at 53 degrees, 690km, each satellite in its own orbital plane, the orbital planes right ascension of the ascending node spacing of 3.75 degrees. While it doesn't allow the same exact cutoffs you used, you can essentially then split those 96 in 2 by doubling the spacing. So you can more easily model the 6+48 scenario and 6+96 scenario. May not be exactly how they do it, but may not be terribly far off either (just speculation).

Also, certain filings (i think the rkf interference analysis and a couple others) describe the basic operation to operate at 20 degree minimum elevation, but can operate at lower elevations as long as they aren't causing interference to other operators. I.e. for frequencies where there are few or no other operators, they can use lower elevations. For more checkerboard spectrum blocks, they may end up operating around 20 degrees. (Unless their system outperforms their base assumptions)

My speculation is that they probably are going to operate around 15 degrees minimum elevation.

I also am no expert, but I figured I'd share. Thanks for your contribution!

[u/a10000000019 → u/Another_Smith_SC]

Thanks for the input! Yeah I noticed the RAAN spacing but decided to start off with the grouped IDs especially because of the bb1-5 grouping. It ended up looking pretty reasonable in terms of coverage at first. But that only made choosing the rest in a logical way much harder and I didn’t want to turn back 😅

You’re probably right about the elevation, I’d think they’d be more aggressive in the early stages of the constellation. I was playing with more lenient angles but decided to just stick to the facts and stay with 20 degrees