My special thanks are due to Nora Konopka, publisher of Taylor & Francis
books, for believing in the importance of the topic and the value of a second
edition. I appreciate the support of Michele Smith, Jennifer Ahringer, Michele
Dimont and Ellin Anderson in the preparation of this volume.
I thank my coworkers, Dr. Leonard Hoﬀnung, for his meticulous veriﬁcation
of the derivations, and Mr. Chris Mehling, for his very diligent proofreading.
Their corrections and comments greatly contributed to the quality of both
editions of the book.
I appreciate the thorough review of the ﬁrst edition by Dr. John Brauer,
then at the Milwaukee School of Engineering, and I am still indebted to Pro-
fessor Bajcsay P´al of the Technical University of Budapest for initiating my
original interest in calculus of variations.
I am grateful for the courtesy of Sierra Nevada Corporation for the model
in the cover art. The model depicts the re-entry conﬁguration of the Dream