The following HTML text is provided to enhance online
readability. Many aspects of typography translate only awkwardly to HTML.
Please use the page image
as the authoritative form to ensure accuracy.
Earth Observations from Space: The First 50 Years of Scientific Achievements
tion that can never reach the earth’s surface because of the intervening atmosphere” (PSAC 1958).
Even in 1958, scientists knew that Earth-orbiting satellites would encounter and be able to measure the charged plasma of the solar wind, the three-dimensional structure of Earth’s gravitational and magnetic fields, and other energy fluxes and fast-moving particles in near space. Satellites could detect incoming cosmic rays and be used to test Einstein’s general theory of relativity; they could measure solar energy at the top of the atmosphere to determine how much is reflected and radiated back to space by clouds, oceans, continents, and ice sheets; and they could look down at Earth to expand surveillance of weather systems from about 10 percent to practically 100 percent of Earth’s surface. The scientific accomplishments of five prominent early satellites (Explorer 1, Explorer 7, TIROS 1 [Television Infrared Observing Satellite], ATS 1 [Application Technology Satellite], and the Nimbus series), all launched in the first two decades of the space age, fulfilled many of these expectations.
EARLY SATELLITES AND PIONEERS
“At the dawn of the Space Age, the nature of space exploration was already apparent: It always leads to unexpected discoveries about our universe and the processes that shape our environment” (Friedman 2006). On May 1, 1958, University of Iowa scientist James Van Allen (Box 2.1, Figure 2.2) announced that Geiger-Müller counters aboard the Jet Propulsion Laboratory (JPL) Explorer 1 (Figure 2.3) and Explorer 3 satellites had been swamped by high radiation levels at certain points in their orbits, indicating that powerful radiation belts, later known as the Van Allen belts, surround Earth (Van Allen et al. 1958, Van Allen and Frank 1959). Vanguard 1, the fourth artificial satellite launched, provided important geodetic information about the shape of the Earth, specifically its north-south asymmetry (O’Keefe et al. 1960).
NASA launched the world’s first weather satellite, TIROS 1, on April 1, 1960 (Figure 2.4). TIROS 1 flew in a nearly circular, prograde orbit of 48 degrees inclination. It took television (Figure 2.5) and (on later flights) infrared photos of weather patterns from space, serving as a “storm patrol” for early warnings, an aid to weather analysis and forecasting, and a research tool for atmospheric scientists (Wexler and Caskey 1963). The images revealed surprising new cloud features: ocean storms, including the spiral band structure of hurricanes and an unreported typhoon near New Zealand; the unexpectedly great extent and structure of mountain wave clouds over South America; and rapid changes occurring during cyclogenesis. In a posthumous article published in 1965, Harry Wexler (Box 2.2, Figure 2.6) wrote, “The TIROS satellites disclosed the existence of storms in areas where few or no observations previously existed, revealed unsuspected structures of storms even in
James A. Van Allen (1914-2006)
James A. Van Allen (Figure 2.2) was born in Mount Pleasant, Iowa; he earned a Ph.D. in physics from the University of Iowa and spent almost his entire career there in the Department of Physics and Astronomy. During World War II he served in the Navy, working at the Carnegie Institution of Washington and the Johns Hopkins University Applied Physics Laboratory, where he helped develop and test the radio proximity fuse. After the war he developed instrument packages for upper-atmosphere and near-space scientific exploration and was head of development for the Aerobee sounding rocket.
In 1950, Van Allen hosted a dinner at his home where plans were initiated for the IGY—a coordinated, international, and comprehensive study of Earth conducted in 1957-1958. Two of the most prominent achievements of the IGY were the discovery of the Van Allen radiation belts and a new, pear-shaped model of Earth. Van Allen subsequently served as principal investigator for more than 25 space science missions. He was active in NASA, National Academy of Sciences, and American Geophysical Union affairs and was an articulate and outspoken advocate of small, inexpensive space missions.
FIGURE 2.2 James A. Van Allen, in his office on the University of Iowa campus in Iowa City, 1990. SOURCE: Photo by Tom Jorgensen, University of Iowa. Reprinted with permission from Tom Jorgensen, University of Iowa.