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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[butcherg]

Thoughts as to whether these satellites would have enough receive gain to be using these bands for Doppler radar?

Why not? Satellite-sourced SAR is a pretty well-understood mechanism , and the band they're using would seem to be good for medium-resolution imaging.

https://www.earthdata.nasa.gov/learn/earth-observation-data-basics/sar

 

[butcherg]

Doppler radar would be specifically for moving targets if it's more focused toward the horizon than down-looking. Full global awareness of all moving craft seems like a military advantage.

Doing a bit of surmising here, but I don't think Doppler would be performant in all axes of movement, no matter the power/gain? I'd envision OpenCV-style motion detection analysis as a better situation solution.

 

[butcherg]

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.

If the target is flying at a vector perpendicular to the beam, with doppler you're going to get a very different velocity than if it were flying head-on to the beam. Might be okay for detection, but to develop an intercept I'd think you 'd need a much better velocity vector. Now, if you have multiple radars painting the same bogey, fusion might make doppler sources work, but that's processing.

 

[butcherg]

What you're describing is the mentality of "it's not wrong if we get away with it". If radio frequency spectrum was reserved for specific purposes, it should only be used for those purposes.

Do you have a frequency management background? Not picking at you, if you do I'd like to know how what you assert fits with the command media.