[Starlink] Re: Starlink and Iran

[Ulrich Speidel <u.speidel@auckland.ac.nz>]

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
>>>
-- 
****************************************************************
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/
****************************************************************