No Gram Left Behind
An additional space launch requirement important to me is "no gram left behind".
A rocket exhaust plume (neglecting small trim thrusts) should not end up in a semi-permanent Earth orbit. The plume should either fall to Earth, or escape into interplanetary space. Long duration retrograde plumes are especially nasty. What stops them is another spacecraft, and if that is an SSPS or space laser mirror, bye-bye reflectivity.
You can estimate plume propellant velocities by subtracting average exhaust velocity from vehicle velocity over the span of the delta V burn, then adding the Maxwellian thermal velocity distribution at the exhaust temperature.
Which sounds more complicated than it is, mostly you are looking for "soft boundaries" in the 3D velocity distribution for escape and for re-entry, then estimating the fraction of the plume within those boundaries.
Raleigh scattering teaches us (sadly) that the amount of momentum accumulated by a molecule from sunlight will be small; in day-period Earth orbits, a tiny momentum gain in the half-orbit away from the Sun will tend to balance the momentum loss orbiting towards the Sun. The small differences will add statistically, and the molecules will eventually "random walk" their way to reentry or escape. That might take millenia.
If the atoms ionize, they can add to the van Allen belts and rev up to MeV energies.
All in all, errant molecules in Earth orbit are corrosive spacecraft killers. Multi-decade accumulations shed from a gigatonne-to-orbit-per-year spacefaring civilization will imprison that civilization long before we complete the process of colonizing the solar system, much less spreading into the galaxy.