Ulrich Walter - Astronautics

Some sections have been substantially revised and there a hundreds more or less significant extensions of established topics of space fight as already covered in the 2nd version of this textbook.

I put a lot of effort into introducing and using a proper terminology, or establishing one if not existent. An example of the former is the distinction between orbital velocity v , angular velocity , angular frequency , and orbital frequency n , which are sometimes confused. Orbital velocity v is the speed of motion of a body on an orbit. Angular velocity is the instantaneous speed of angular motion, while angular frequency is the number of revolutions in a given time. Finally, orbital frequency n (a.k.a. mean motion) is the time average of the angular velocity over one orbital period T (see Eq. ( )). Thus, ; it therefore can be considered both as a mean angular velocity (i.e., mean angular motion) and as a frequency, the orbital frequency. Because proper terminology is essential, the conventional symbols used table on the following pages also serves the purpose of enabling one to look up the proper terminology for a physical quantity.

Because physics is independent of the choice of the reference system, the third version consequently uses a reference system-free vector notation (except auxiliary corotating reference systems in Sects..

Finally, I feel the need to a very personal comment on textbooks in general. When I was a student, I bought some expensive but basic physics textbooks, which are still in my office shelf and serve as my reference books, because true physics is eternal. Compare buying a textbook with a marriage. You do not just buy it. It must have a kind of visuala tactile sensuality: You open it with joyful anticipation. Your fingers glide over the pages, and they slowly turn one page after the other. You like the layout, the way the book talks to you, and how it explains the world from a point of view you have never considered before. You just love it, and thus it will become part of your daily scientific work. You may forget little physical details, but you will always remember that the one you are looking for is on top of the left-hand page somewhere in the middle of the book. You will never forget that visual detail, and therefore you will always find the answer to your question quite swiftly. I have about a handful of such key textbooks, which I would not sell in my lifetime. I sense that these books were written for guiding me through my scientific life. For me, writing this book was for giving back to other people what many scientists before had given to me. We all are standing on the shoulders of giants. May this textbook keep and pass the body of basic knowledge to you and future generations.