I have a simple question: Why isn't space junk orbiting Earth used for gravity boosts to launch small cubesats into higher orbits or to other planets?
I know the current gravity boost and gravity braking math is built from numerical solutions to the 3 and 4 body problem in astrodynamics, but couldn't something similar be done in Low Earth Orbit between space junk and a small satellite (maybe a cubesat or kicksat)?
From my understanding, if the cubesat is launched into orbit opposing the space junk, if it makes a close enough pass to the space junk, the cubesat can get a massive velocity boost (almost 8 km/s) as its orbit is changed by the space junk. Am I missing something here? (maybe overestimating the gravitational influence of the space junk?)