[robxorb]

Good points but neither of them rule out being reconfigured and used in an emergency, potential hijack situation to locate what could be a significant security threat. Airliners were used for the biggest attack on US ground since WW2. Priority number one.

[_djo_]

Only if there’s enough forewarning, the radar is operational, the aircraft is within its range given prevailing space weather conditions, and that it’s pointing in the right direction. The latter is important because OTH radars are almost all fixed and can’t be steered.

Yes, governments would love to have global 24/7 coverage even over the open ocean. In practice that’s neither possible nor practical.

[robxorb]

> OTH radars are almost all fixed

Given their strategic advantage, you can bet the military will have prioritised steerable.

I disagree with the general premise regarding global coverage. With the US military, capabilities, especially in surveillance, have historically been shown to be decades ahead of what the public thinks is possible.

Personally, if a post appeared tomorrow showing some HN had figured out how to trace the movements of any airliner, without using its adsb and relying instead on anything and everything else that's publicly available, from satellite imagery, to radio frequency data, to radar, even weather data (contrails are often detectable), it would seem cool, sure - but, not unbelievable.

That hypothetically believable scenario would be one person, with no budget, in likely a few weeks or months of their spare time.

The US military has trillions of dollars, the best talent in the world, and decades of dedicated effort in exactly this area, and a propensity to keep such advances secret for decades (as shown recently enough by the Trump photo).

[_djo_]

> Given their strategic advantage, you can bet the military will have prioritised steerable.

This is not something you can really prioritise. OTH radar designs are a trade-off between range, angular resolution, frequency, and mobility. For the longest-ranged systems with good angular resolution you can't steer them outside their set beam pattern, because their sheer size makes that kind of steering impossible. So if you want steerable radars you necessarily have to compromise on range, angular resolution, etc.

> I disagree with the general premise regarding global coverage. With the US military, capabilities, especially in surveillance, have historically been shown to be decades ahead of what the public thinks is possible.

Again, there are fundamental limits here. As much money as the US military has, it can't break the laws of physics. We also have a good sense of what types of assets it has and where they are, including satellites.

> Personally, if a post appeared tomorrow showing some HN had figured out how to trace the movements of any airliner, without using its adsb and relying instead on anything and everything else that's publicly available, from satellite imagery, to radio frequency data, to radar, even weather data (contrails are often detectable), it would seem cool, sure - but, not unbelievable.

Doing so over the vast open ocean would indeed be unbelievable. Even doing so for an individual over an ideal location would not be believable, as available resources don't make this possible at any real scale with the necessary granularity.

> The US military has trillions of dollars, the best talent in the world, and decades of dedicated effort in exactly this area, and a propensity to keep such advances secret for decades (as shown recently enough by the Trump photo).

See my point above. As for the Trump photo, by which I presume you're referring to the satellite image of the failed Iranian launch, the displayed resolution was within what experts had already presumed was within the capabilities of deployed US satellites given all available information. The photo didn't display surprising capabilities, it merely provided an official confirmation about what was already widely assumed.