Comment by perihelions
13 hours ago
Seems like a big flaw that low-orbit constellations have a dependency on GPS, which are high-altitude satellites. They're 40x further away and so have 1,600x greater path loss. Why can't they use their own satellites for this?
> "But Starlink receivers use GPS to locate and connect to satellites. “Since its 12-day war with Israel last June," The Times says, “Iran has been disrupting GPS signals.”"
This isn’t even true; Starlink can use the local starlink constellation for positioning and the option is available in the customer facing configuration specifically for GPS denied areas (since about two years ago), where it’s been used for ages.
Something else is going on here - perhaps there’s an edge case where Starlink can be made to perform poorly without falling back away from GPS, but I wouldn’t expect this since it’s been “tested” in the most GPS hostile places for quite some time now.
It sounds like Starlink uses GPS to localize the receiver, rather than for any active step in the communication link. Since most receivers are static, I wonder if an effective workaround to this is for the receiver to just remember its last GPS fix for longer, or worst-case allow a manual location specification in lieu of a GPS fix.
A user provided location cannot be trusted for geofencing purposes. A GNSS (GPS or other) is needed sooner or later. This is a legal requirement for sanction and regulation enforcement (US, if not others).
The user-provided location would only be used for the initial bootstrapping. After it connects, the Starlink network itself will localize the receiver to within 1 km.
If the user inputs a bogus lat/lon, it would simply fail to connect. There's no way to 'spoof' your location on this type of global satellite comm network.
EDIT It will be interesting to see what anti-censorship and anti-DOS hardening features are coming in future software updates. Full GPS denial bootstrapping is the most obvious, and actually this should be possible without needing to input a location. Adding offline update packages, so signed anti-denial firmware updates can "sneakernet" across oppressive regimes to recover DOSed terminals, would be even better.
Starlink system inevitably knows the terminal location down to a service cell, which is what, a 20km grain? Good enough for "regulation enforcement".
The satellites know where they are TX beamforming to a fine-enough degree of specificity for geofencing.
Gps is free to use. Running your own gnss service requires an atomic clock and possibly separate transmission hardware, which is possible, but adds cost, volume, and weight.
According to [1], “[o]ne of the current generation of GPS satellites (Block III) weighs over 2,200 kg (4,850 lb), the weight of an average pickup truck. The body of these satellites are 1.8 m x 2.5 m x 3.4 m (5.9’ x 8.2’ x 11.2’) in size”. In comparison, “the current V2 Starlink satellite version weighs approximately 1,760 lbs (800 kilograms) at launch, almost three times heavier than the older generation satellites (weighing in at 573 lbs or 260 kg)” [2]
[1] https://novatel.com/an-introduction-to-gnss/basic-concepts/s... [2] https://www.space.com/spacex-starlink-satellites.html
> Gps is free to use. Running your own gnss service requires an atomic clock and possibly separate transmission hardware, which is possible, but adds cost, volume, and weight.
Thanks you provide some great insights on why starlink didnt use gps but still if starlink wants to focus itself as the uncensorable internet in places like protests etc. I feel like they can probably do this after this recent incident
I just can't feel but sad right now because starlink was still providing activists ways to report outside and that helped protestors a lot and information. Now even starlink got removed because starlink tried to save money and I think might not have thought about what if gps itself gets blocked.
This is giving very bad signals for Iran. Is there any way now that Protestors are able to communicate to the outside world/ activists be able to report data outside?
> if starlink wants to focus itself as the uncensorable internet in places like protests etc
I’m not sure Musk would actually want that though, especially these days.
9 replies →
Yes, ask their Mossad direct and local handlers (as per Mike Pompeo [1]) about how things are going, I’m sure that this being Mossad they have a ground-based way to get the information out.
[1] https://xcancel.com/mikepompeo/status/2007180411638620659
3 replies →
[flagged]
1 reply →
Chip scale atomic clocks are quite small[1], have been used in space, and could be part of the existing Starlink satellites. Finding reliable details about the orbital vehicles the internet eludes me.
[1] https://ww1.microchip.com/downloads/aemDocuments/documents/F...
GPS comparison is moot in this case, as there's no need for Starlink constellations to provide full GNSS capability, just locating the satellites precisely enough to facilitate beamforming.
Musk tweeted a while back that the constellation could be used as its own GPS service, but it wasn’t a priority right now. Maybe later.
A CRPA should still work.
If the GPS satellites are above the starlink ones how is Iran able to disrupt the GPS signals?
GPS signals are extremely weak, and they're necessarily received from omnidirectional antennas that can't provide much antenna gain. In some sense it's a miracle of signal processing that GPS can ever be received.
There have been developments in receiving antennas that are harder to jam.
Most jamming is horizontal and limited to a few bands. So by having a directional antenna and listening to all services for now it seems to work. But this is a cat and mouse game.
https://furuno.eu/gr-en/marine-solutions/gnss-positioning-ti...
By jamming the receivers on the ground
Ok that makes a lot of sense, thank you.
For legal reasons I base this off of nothing but just turn your jammer to the sky. Could get fancy and point out directly at the satellites since my understanding is it's pretty easy to know where they are.
Edit to add: I do not mean the GPS satellites or the starlink ground terminals. That was not the question so that is not my answer. I mean the starlink satellites
That doesn't work. GPS is broadcast, not bidirectional communication, so preventing the satellites from seeing the GPS receiver does nothing: they're not looking to begin with.
9 replies →
This whole stalink for military use (Starshield) was a scam Elon sold the military from the beginning. Just like his dumb ass tunnels and his self driving cars. He is putting the military at risk.
Is there any actual evidence that Starshield doesn't work substantially as promised?
[flagged]
2 replies →