[Starlink] Re: Starlink and Iran

Ulrich Speidel
2026-01-28T03:09:22Z

On 20/01/2026 9:39 am, David Lang wrote:
> Ulrich Speidel wrote:
>
>> David Lang wrote:
>>> have you looked at what the latest changes allow?
>
>> No - if anyone has a pointer to what the official source for the
>> latest SpaceX-FCC licensing interactions is ... I'd been hoping to
>> figure that out but haven't yet.
>
> not much info here, but hopefully a start
> https://www.fcc.gov/document/fcc-approves-next-gen-satellite-constellation
>
> A few days before this, spacex announced it was lowering the orbit for
> ~4000 of it's satellites by ~70km
> https://www.space.com/space-exploration/satellites/spacex-lowering-orbits-of-4-400-starlink-satellites-for-safetys-sake
>

OK, this took a moment. There are a few references to waivers of EPFD
limits in the document but these needed a little research. The crux is
in point 4 of the grant document, which makes reference to sections
25.146(a)(2) and (c) of the FCC rules. Now 25.146(a)(2) references
Article 22 and Resolution 76 of the ITU radio regulations. These impose
EPFD limits on interference to geostationary systems from the aggregate
operation of non-geostationary systems.

While these may or may not require SpaceX to stick to lower transmit
power at times than the limits in Article 21 (which haven't been waived
for all I can tell), it's the limits imposed by Article 21 that continue
to put a lid on things.

So this doesn't look like good news in terms of being able to throttle up.

Either way, it's worth noting here that while the relationship between
transmit power and and received power is linear, the relationship
between received power and achievable bit rate is logarithmic in nature.
For those not so mathematically inclined: Starlink is starting off with
64QAM (6 bits per symbol) at current EPFD limits, and each extra bit
beyond that requires a doubling of the received power. Turning up the
volume is not a game you can stay ahead in for long, regardless of
regulatory constraints.

Some interesting tidbits from the grant document though:

* 4. a. No more than 8 satellite beams "in the same frequency" (I
presume there's the word "band" missing here) into the same or
overlapping areas at a time. That means at most 8 beams per cell.
* 4. b. "SpaceX must maintain a minimum GSO arc exclusion zone of at
least four (4) degrees with respect to operational GSO satellites".
Finally a clear word?

--
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Dr. Ulrich Speidel

School of Computer Science

Room 303S.594 (City Campus)

The University of Auckland
u.speidel@auckland.ac.nz
http://www.cs.auckland.ac.nz/~ulrich/
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