1.5 Honorable Mentions

Here I list some additional resources which may be helpful. 

Physics: Calculus 

• Author: Eugene Hecht 

I'm not sure if this book is still in print, but in the copy I have, Section 7.10: Gravity and Kepler's Laws has an excellent, concise explanation and diagrams of the relationship between Newton's law of gravity and Kepler's laws, without getting bogged down in heavy derivations. 

Introduction to Flight

• Author: John D. Anderson 

This book has a chapter on orbital mechanics. It has a derivation of the orbit equation that does not use vectors. It may be useful to contrast this approach with the vector-based approach found in the Curtis text. Personally, I find the vector-based approach easier to follow, but that's just me.

Fundamentals of Astrodynamics

• Authors: Roger R. Bate, Donald D. Mueller, and Jerry E. White

This book has a chapter dedicated to Earth-Lunar trajectories, and another chapter dedicated to interplanetary trajectories. The content will be similar to what you find in Chapter 8 (Interplanetary trajectories) of the Curtis text. 

Basics of Space Flight

• Author: Dave Doody

This is a free book published by NASA; it contains tons of well-explained general information.