GPS jamming occurs local to the receiver, not the transmitter. So, you'd have to worry about the dish on your roof / vehicle, not the ones on the satellite.

I'm that sense, a phased array can help by filtering out signals that are not in line of sight with your satellite, but only one satellite fix does not provide a great estimate of the receivers position. Esp when signal strength is used to estimate bearing.

If you have a phased array, you can point it at a series of sats in rapid succession, or even all at once with more electronics.

That is a good point about pinging many sats. However all at once doesn't make sense to me in the context of a jamming scenario

well, anyone having to deal with you (and I) do. I wouldn't put it past a APT to be able to do better and take action in space if their hand were forced.

Interesting! Is it theoretically possible to launch a "GPS jamming" satellite constellation? And if so, could you do it with far less satellites than the quantity you are attempting to jam?

It's much cheaper to just shoot them down.

The gps antennas on the starlink satellites will be pointed “up” i.e. away from the earth’s surface. Jamming from the ground to a receiver in space pointed away from earth would be… difficult. Especially when the satellites orbit about every 90 minutes, so you’d really have to do a global very very loud gps attack… it’d be simpler trying to hit several gps satellites with missiles than to accomplish that.

no, but they're a different frequency so if someone was only jamming GPS, this would get through.

They are massively more resistant to jamming. The antennas are very good at rejecting signals that are coming from the wrong direction, that is, not from above.

This is the correct answer, phased array antennas have much more directivity so they are much harder to jam with a ground-based jammer. Although I suppose in some cases you might want to put the jammer on a drone anyway, to cover a larger area. In that scenario you would probably not see a significant difference for phased array antennas vs "normal" antennas.

Caveat btw: for both starlink and GPS, the satellite you are talking to will not always be "up". For GPS in particular, it is possible that some of the satellites are only barely above the horizon. So an antenna that only looks "up" is generally not what you want anyway, which makes ground-based jammer more effective again.

Phased arrays are good at rejecting incidental interference, which is why they were used to address radar jamming. Of course that also meant that billions were poured into developing technology to counter that resilient property. Anyone capable of blocking GPS on a non-trivial scale would be easily capable of blocking Starlink as well.

It depends strongly on how the phased array is being steered. If the components prior to phasing and summation are saturated by the interference then phased array beamforming will not reject the interference.

Phased array antennas are mostly for getting programmable beam forming, and don’t have much to do with jamming, which works by destructively interfering with incoming waves. Starlink operating on a different frequency means that GPS jammers won’t be able to jam them out of the box, but presumably if they’re jammers built in the last 20-30 years they’d have onboard SDRs which can dynamically hop frequencies. It’s a neat trick to get GPS from Starlink, but won’t stop nation state attackers from jamming access to GPS.

There are different kinds of jamming. It's my understanding that interference jamming is fairly uncommon nowadays. If it's not perfect, it mainly gets you a reduction in SNR and GPS is already way down below the noise floor, so receivers are inherently designed to mitigate the effects even if they aren't explicitly designed for anti-jamming. Even when they work, spectral filters exist. Broadband and spoofing are what Russia typically use. The defenses against those benefit from lots of processing power and large, beamforming arrays.

It's an arms race though.

Jamming isn't destructive interference, which would require knowledge of the exact signal being sent as well as the exact location of the transmitter and receiver. Jamming is overwhelming the receiver with a stronger signal in the same frequency band so the weaker one cannot be received. Think someone screaming over someone else whispering.

Phased array beamforming absolutely helps make jamming more difficult. Jamming is all about reducing the signal to noise ratio in the channel until it is unusable. Directional antennas (of which phased arrays are electronically steerable versions) have more gain in the direction of the desired signal and less towards unwanted signals located in another direction.