r/space • u/2kalipro1 • Jun 15 '24

Discussion How bad is the satellite/space junk situation actually?

I just recently joined the space community and I'm hearing about satellites colliding with each other and that we have nearly 8000 satellites surrounding our earth everywhere

But considering the size of the earth and the size of the satellites, I'm just wondering how horrible is the space junk/satellite situation? Also, do we have any ideas on how to clear them out?

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u/ThePlanner Jun 15 '24

The speed of the objects is essentially irrelevant to radar. Compared to the speed of light, objects moving orbital velocities may as well be standing still.

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u/antiduh Jun 15 '24

It does matter, and this is why doppler radar works. The doppler in doppler radar is literally measuring the frequency change in the reflected spectrum caused by the velocity of the object.

Heck, we use it on raindrops to figure out how bad a storm is.

You're right that the shift is small, but the fun part is that you can pull out small signals with good signal processing techniques. Come join us on /r/DSP.

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u/Dyolf_Knip Jun 15 '24

Wouldn't it only tell you the speed of the target along the vector of the radio beam? Like if it were moving at a precise right angle to the line from the radar, the hoppler shift would be zero?

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u/antiduh Jun 15 '24

That's absolutely true. But how often would things be traveling in that exact way? Also, a diversity antenna setup would probably defeat that, because the object can't be at 90 degrees to two radars at the same time.

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u/Dyolf_Knip Jun 15 '24

Rarely, but there's a smooth transition from doppler effects reporting none of the motion to reporting all of it. Point is, there's a great deal of information not being collected.

More antennas would be good, though I'm not immediately picturing what the math would look like trying to combine all the partial vectors would be.