I am trying to calculate the delta-v between Kerbin and Duna from a 70 km circular orbit around Kerbin just to do a flyby of Duna. However, I am running into a couple of difficulties with my calculations. Everything that I read tells me to deal with the heliocentric transfer orbit first, and that is where my problem lies.
The periapsis of the transfer orbit between Kerbin and Duna is the orbit of Kerbin which is 13,599,840,256 m.
the transfer apoapsis is Duna's semimajor axis: 20,726,155,264 m.
This gives a semimajor axis of the transfer orbit of 17,162,997,760 m.
To find the delta-v of the transfer, I need to find the velocity at periapsis of the transfer orbit and subtract Kerbin's orbital velocity from that.
Using $v^2=GM(2/r-1/a)$, I get a transfer velocity at periapsis of 10203 m/s. Kerbin's orbital velocity is 9284.5 m/s.
This gives me a delta-v of 919 m/s. However, the delta-v maps that I am reading say it is 130 m/s from Kerbin escape to Duna intercept.
What am I doing wrong? Why do my numbers not match?