What makes a defunct upper stage of a rocket a heightened risk compared to a spent satellite out of fuel?

Answer

It might still contain residual propellant that could cause an explosion

While both are debris, a defunct upper stage retains residual propellant, creating an elevated risk of explosion compared to a spent satellite that has already exhausted its fuel.

What makes a defunct upper stage of a rocket a heightened risk compared to a spent satellite out of fuel?

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Why is space debris such a big issue? - What in the World podcast ...

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