Plume Molecules
The deployment of 100MT of SBSP (25 TW) using LOX/LH rockets could result in as much as 40 MT of plume molecules in retrograde orbits.
Other "rockets" might use electrically superheated hydrogen, or ion engines (though there is not nearly enough xenon and krypton for that). Laser ablation thrusters are possible, but those make a dog's breakfast of hot, poorly collimated molecules and ions compared to "clean" hydrogen-based thrust.
Let's focus on LOX/LH chemical engines with an oxidizer:fuel mass ratio of 5:1, resulting in a 15:1 mass ratio of H₂O and H₂ plume molecules. For 40 MT of plume, that is 1.67e36 H₂0 molecules, and 1e36 H₂ molecules.