US spy satellites built by SpaceX send signals in the “wrong direction”

It seems US didn't coordinate Starshield's unusual spectrum use with other countries.

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[Komarov]

Strictly speaking, they're allowed to operate in a non-interfering manner (which they're apparently doing) in any band without consultation. It's only after a country complains that there's interference that we can just the US's diplomatic method.

Strictly speaking, they also don't give a fuck. Which is not surprising for a country where a certain person being caught cheating at golf becomes a national security issue.

 

[Komarov]

Doppler radar gives you the velocity along the transceiver direction. So a down-looking radar would see a velocity of zero for an aircraft at level flight. Sure, you can use image processing to give you velocities, but that takes processing.

Doppler radar gives you the velocity on the return signal directly. There's no more work than the heterodyning you have to do on a radar signal. If you're looking at the horizon, you're getting the component of velocity to/from the satellite. You can then filter for velocity ranges such that hypersonic vehicles would stick out like a sore thumb.

[my emphasis] To be pedantic, in special relativity, you do get a Doppler effect on EM bounced off objects moving perpendicular to the direction of view. I have no idea whether modern SAR can take advantage of that. At LEO speeds, the effect would be quite small.

 

[Komarov]

The second paragraph states: "The signals are sent from space to Earth in a frequency band that’s allocated internationally for Earth-to-space and space-to-space transmissions." (emphasis mine)

Then goes on to exhaustively explain how using these frequencies Space-to-earth is not according to the norms.

So how did Scott Tilley and the author conclude that the emissions are NOT being used space-to-space and are not being received as an unintended sideband of the satellites using them as space-to-space communications? I mean other than seeing that it's SpaceX so Musk adjacent and jumping to the conclusion that it HAS to be judged the worst way possible.

Is there a technical reason for excluding these frequencies being used in space-to-space communications?

The high signal-to-noise ratio is a dead giveaway. You wouldn't get that from an accidentally scattered transmission, it requires a high-gain antenna pointed in the right direction, i.e., towards the ground.