The past 50 years have brought forward a unique capability to conduct research and expand scientific knowledge of the Solar System through the use of radar to conduct planetary astronomy. This technology involves the aiming of a carefully controlled radio signal at a planet (or some other Solar System target, such as a planetary satellite, asteroid, or a ring system), detecting its echo, and analyzing the information that the echo carries.

This capability has contributed to the scientific knowledge of the Solar System in two fundamental ways. Most directly, planetary radars can produce images of target surfaces otherwise hidden from sight and can furnish other kinds of information about target surface features. Radar also can provide highly accurate measurements of a target's rotational and orbital motions. Such measurements are obviously invaluable for the navigation of Solar System exploratory spacecraft, a principal activity of NASA since its inception in 1958.

Andrew J. Butrica has written a comprehensive and illuminating history of this little-understood but surprisingly significant scientific discipline. Quite rigorous and systematic in its methodology, To See the Unseen explores the development of the radar astronomy specialty in the larger community of scientists.

More than just a discussion of the development of this field, however, Butrica uses planetary radar astronomy as a vehicle for understanding larger issues relative to the planning and execution of "big science" by the Federal government. His application of the "social construction of science" and Kuhnian paradigms to planetary radar astronomy is a most welcome and sophisticated means of making sense of the field's historical development.

Andrew J. Butrica received his Ph.D. in the history of science and technology at Iowa State University. He is a research historian in Franklin Park, New Jersey, specializing in the history of science. In 1990 Praeger Publishers issued his Out of Thin Air: A History of Air Products and Chemicals, Inc., 1940-1990.

About the Cover: "Big Dish Antenna," painting by Paul Arlt. Courtesy of the NASA Art Program, no. 74-HC-467.

- Dedication -

To my dear friends and former colleagues at the Center for Research in History of Science and Technology: Bernadette Bensaude-Vincent, Christine Blondel, Paulo Brenni, Yves Cohen, Jean-Marc Drouin, Irina and Dmitry Gouzevitch, Anna Guagnini, Andreas Kahlow, Stephan Lindner, Michael Osborne, Anne Rasmussen, Mari Williams, Anna Pusztai, and above all Robert Fox.

- Contents -

Acknowledgments.

Introduction.

Chapter One: A Meteoric Start.

Chapter Two: Fickle Venus.

Chapter Three: Sturm und Drang.

Chapter Four: Little Science/Big Science.

Chapter Five: Normal Science.

Chapter Six: Pioneering on Venus and Mars.

Chapter Seven: Magellan.

Chapter Eight: The Outer Limits.

Chapter Nine: One Step Beyond.