Acknowledgements
The career described in this paper is the culmination of many collaborations with mentors, colleagues and trainees from numerous laboratories in government, academia, and industry, all of whom I owe a debt of gratitude. I am especially thankful to mentoring I received from Drs. Jim Bosco, John Greenleaf, Ed Bernauer, Hal Sandler, Jack Wilmore, and Joan Vernikos, and the loving support of my wife Barbara.
Figure 2 is presented in memory of the late Dr. Alan B. Chambers, former Chief of the Man-Vehicle Systems Research Division and Director of Space Research at NASA Ames Research Center. Permission was obtained from the people whose photographs appear in Figs. 5 and 6 to publish these images as part of the manuscript.

Competing interests
The author has no competing interests.
Disclaimer The opinions or assertions contained herein are the private views of the author and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense.