Tommy
Well-known member
I'm not really sure, because I have not fully tested this yet, but before reading your post, I thought they canceled out. Launching Prograde gives you the advantage of the Earth's spin, but you are chasing a target that is moving away from you.
Doing the opposite means that you are moving towards a target that is moving towards you.
I prefer to use Groundspeed in the equation, because it reflects the rate at which you are approaching your target.
I guess it depends on whether you are trying for a ballistic trajectory, or plan for a multiple skip re-entry. If you plan to go ballistic, you would need a much higher groundspeed to attain the ballistic trajectory - around 8.4 km/s. If you'll use aerodynamics (ie, a Sanger Re-Entry), I suspect they more or less cancel out.
In my experience, the retrograde option has always cost me significantly more fuel.