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## Deboning the Porkchop Plot

3 Jan 2013, 22:40 UTC
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Deboning the Porkchop PlotChanging direction causes ΔV (change in velocity), often more than a change in speed. Compare the velocity vectors below. When going the same direction, the difference is 1 km/s. When at right angles the difference is 5 km/s. We know this from driving in traffic. Two cars going almost the same speed hit each other. If they’re in the same lane going the same direction, it’s a mild bump. If one car runs a red light and T-bones a car in cross traffic, the impact is serious: This is the strength of a Hohmann transfer orbit. Velocity vectors are pointing the same direction at departure as well as destination. No direction change is needed, only a speed change:Note the Hohmann transfer path moves 180 degrees about the sun:A Hohmann transfer assumes the departure and destination orbits are co-planar. But what if the destination orbit is inclined?Orbit Planes and Spherical TrigonometryA plane passing through a sphere’s center cuts the sphere along a great circle. A group of planes all sharing a common point can be represented as great circles on a sphere. Since every orbit about the sun is a conic section having the sun as a focus, ...