I'm trying to estimate the delta-v (and, by applying the Rocket Equation, the propellant) required to lift a payload from LEO to a higher orbit. As I understand it, the standard way to do this is with a Hohmann Transfer: first, boost from a circular orbit at r1 (which in this case is LEO) to an elliptical orbit with apogee at r2 (the altitude of my target orbit); then, boost the elliptical orbit into a circular orbit at r2.
Using the equations described here:
r1 = 6451000m (i.e., an orbital altitude of 80km + the radius of the earth)
r2 = 95896000m (orbital altitude of 89,500km + earth radius)
I come up with a delta-v of about 4,215 m/s.
However, if I am instead transferring from my 80km LEO altitude to 179,000km, I get a delta-v of about 4,150 m/s. I.e., increasing the altitude of my target orbit by 80,000km decreases the total delta-v by about 75m/s.
Mathematically, I can see why it's happening. The value of Δv2 is decreasing faster than Δv1 is increasing. But it doesn't seem right. Am I misunderstanding the purpose of the delta-v value in the Hohmann Transfer equation? Or is that actually the way it is?