[Starlink] Re: Starlink and Iran

Ulrich Speidel
2026-01-16T04:18:37Z

I suspect (and may be wrong there) it's not that the uplink beam is
narrow: That would be hard to do with an antenna that's size limited by
the need to keep it a consumer device that the customer can be expected
to handle and install. Rather, I suspect that it's the compute overhead
involved at the ground end when it comes to recalculating the correct
phases for tracking the fast-moving satellite. Basically, if you had
unlimited compute power at the Dishy, you could recompute the beam
frequently enough to always keep the satellite at the centre of the
beam. Instead, if you position the beam such that the satellite moves
across it, you can wait with recomputation until the satellite is about
to leave the beam. This means less computation, cheaper chips, and less
power use.

That all said, a 2 km deviation isn't what I had in mind with "precision
location" - I was thinking more of the type of deviation seen when the
US military still applied "selective availability" to the civilian
signal, and positions tended to be a few dozen to maybe a couple of
hundred metres out. The 2 km more than cover this - and your
observations actually confirm that position accuracy down to a couple of
metres isn't needed here.

On 16/01/2026 10:47 am, Oleg Kutkov via Starlink wrote:
> Actually, a precise location is required to calculate the uplink beam.
> For the downlink, it's not so critical (at least for the initial
> sky_search procedure), since the satellite beam covers the whole cell.
> But the uplink beam is quite narrow, and the terminal needs to
> pinpoint the moving satellite.
> From my experiments, shifting the GPS data for more than 2km breaks
> the math and disrupts the connection. With an incorrect position,
> Starlink is stuck in NO_SCHEDULE mode.
>
> On 1/15/26 22:07, Ulrich Speidel via Starlink wrote:
>> Military-grade GPS kind of lost its exclusivity a long time ago when
>> people came up with DGPS (differential GPS), where a local reference
>> station with known position transmits a "delta" signal to the GPS
>> signal received at that location. And then of course came GLONASS &
>> Co., so there's currently about four GPS-like systems out there, and
>> most modern receivers support all. That said - these signals can all
>> be interfered with and spoofed.
>>
>> For Starlink, precision location isn't actually required (it's enough
>> for Dishy to know which cell it's in because that determines the
>> beams).  But GPS receiver chips are cheap and extra position accuracy
>> doesn't do any harm.
>>
>> On 16/01/2026 6:10 am, J Pan wrote:
>>> easier to attack gps?
>>> https://github.com/narimangharib/starlink-iran-gps-spoofing/blob/main/starlink-iran.md
>>>
>>> although not all technically correct. "inhibitGps" is a user choice
>>> through the mobile app ("Use Starlink positioning exclusively") not
>>> system determination, but gps spoofing is indeed there. starlink could
>>> be authorized to decode military-grade gps signals as well?
>>> --
>>> J Pan, UVic CSc, ECS566, 250-472-5796 (NO VM), Pan@UVic.CA,
>>> Web.UVic.CA/~pan
>>>
--
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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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