By a very strange coincidence, at the time Change'3 was making its descent to the lunar surface , the book "An Introduction to the Mathematics and Methods of Astrodynamics , Revised Edition" by Richard H. Battin - which I had ordered some weeks ago from an Amazon dealer - arrived by UK Royal Mail . Literally, 4 minutes before touchdown of Change'3 :-))

How strange is that !

For those not familiar with the name Richard H. Battin he was the Technical Director, Mission Development for the Apollo Guidance and Navigation Program during the 1960s. In fact, I have several of Dr Battin's papers including one called "Explicit and Unified Methods of Spacecraft Guidance" which carries a very good "easy mathematical" treatment of the Apollo trajectory from Earth to the Moon.

The book "An Introduction to the Mathematics and Methods of Astrodynamics , Revised Edition" is a different mathematical "animal " though :-))

Phill Parker