October 1995 marked the fiftieth anniversary of Arthur C. Clarke's famous article in Wireless World proposing the use of satellites placed in geosynchronous orbit for worldwide communications relay. The article proved prophetic, for it heralded the modern era of telecommunications. Beginning in the early 1960s, several series of satellites were launched into Earth's orbit; collectively they transformed the latter twentieth century, creating a global village of instantaneous communications. Previously, the ionosphere had defined the limits of radio communication; today, by going beyond the ionosphere, broadband telecommunication has entered a new age. This book describes the first attempts to go beyond the ionosphere, including both the earliest uses of the Moon as a passive, natural relay satellite and Project Echo, the massive inflated satellite off which Earth stations bounced radio signals, as well as contemporary communications via active-repeater artificial moons in orbit about the Earth. It analyzes both American and foreign satellite communications, the histories of several satellite communications companies, the roles of government agencies, and the contribution of research laboratories. The book is a collection of papers originally presented during an international symposium held in Washington, D.C., at the time of the fiftieth anniversary of Clarke's 1945 article. Contributions from historians and other scholars from throughout the world present a stimulating analysis of one of the most important global technologies at work today-and how it originated and evolved.

This is the story behind NASA's successful exploration of the solar system. For a half century, NASA has sent one probe after another into space, achieving scientific and technological successes along the way and adding to humanity's knowledge of the solar system. NASA has reaped these great rewards thanks to a small investment in deep-space navigation. With rare exceptions, navigation's great achievements-and scientific accomplishments-have gone unobserved. The failures of the Mars Climate Orbiter and Mars Polar Lander shed navigation (wrongly) in a negative light. Yet, the indispensable role of navigators behind NASA's many successes over the past half century has not come to light-until now. The institutional home of deep-space navigation is the NASA's Jet Propulsion Laboratory. JPL navigation originated long before it became part of NASA, when the lab developed and tested missiles for the nation's military space effort. From the start, deep-space navigation was an endeavor built on science and mathematics and dependent on the Deep Space Network for tracking spacecraft and on digital computers and software for processing data. Navigation is multidisciplinary. It involves astronomy and radio astronomy, geodesy and geophysics, cartography and meteorology, ionospheric physics and radio science. Navigators interact with a panoply of institutions, whether the Bureau International de l'Heure, the International Polar Motion Service, the International Union of Geodesy and Geophysics, and the International Astronomical Union. JPL navigation started as a consumer of Naval Observatory data, practices, and ephemerides, but in the 1970s became the source of ephemerides, constants, models, and ephemerides for the world's almanac offices. Navigators have been project scientists on many NASA missions, performing experiments in celestial mechanics and gravitational fields, undertaking radio occultations, and testing Einstein's General Theory of Relativity. They also have made a number of memorable scientific discoveries: mascons on the Moon and Mars, volcanism on Io, and over a dozen satellites of the outer planets. The nature of deep-space navigation began to change with the introduction of optical navigation, which uses a probes science camera and telemetry to determine its position relative to a planet, moon, or asteroid. Deep-space navigation began-and remains-an activity carried out entirely on Earth. Radio signals from the Deep Space Network constituted the only information processed. Optical navigation began to move some of the process-and equipment-to spacecraft. At first, image processing was a labor-intensive and computer-intensive effort. Software improvements and advances in spacecraft computers paved the way for autonomous navigation, which transferred many basic navigation processes to the onboard computer: estimating trajectories, planning and executing imaging, and analyzing pictures. The most recent evolutionary stage has been the merger of this autonomous software with spacecraft guidance and control functions.

The past 50 years have brought forward a unique capability to 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, an 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 activity. 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 discussing 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.

The story of Air Products and Chemicals, Inc., is exciting--full of struggle, determination, crisis, and heroic endeavor. Air Products grew out of the vision and drive of one individual, Leonard Pool. In the course of fifty years, Pool's precarious project has become a major, multinational corporation. Words like entrepreneurship, sales, finance, engineering, and technology are central to the history of Air Products. So too are concepts like being a late entrant to an established business, struggling to find market niches, moving into fields of endeavor, developing human resources, and breaking through to the level where economies of scale and scope would allow a secure future as a major player on a global scale. The story is one of success; plain luck at some points. But it also contains its share of hard knocks, disappointments, and mistaken strategies.

The enduring style of Air Products--its customer-focus and its emphasis on sales and growth--emerged from the interactions of Leonard Pool's personality, the engineering skills of his colleagues, and the opportunities offered by the industrial gas supplier in the world. It is also a major chemical company and a pioneer in the emerging field of environmental and energy systems. Multinational, technology-based firms like Air Products are an important part of American society and of the emerging global economy. The history of Air Products will be of value to everyone interested in the industrial gas and chemical industries, business history, entrepreneurial history, and American studies.