Both these books are on my book shelf and are very good. Bate et. al. especially since it is a Dover book and very affordable. The book that is always on my DE

Both these books are on my book shelf and are very good. Bate et. al. especially since it is a Dover book and very affordable. The book that is always on my DESK is "Fundamentals of Astrodynamics and Applications" by Vallado. There is also a website with code from the book for Hohmann and Lambert transfers among other things. <self-promotion>This has been indispensable in creating my Unity Asset "Gravity Engine".</self-promotion>