The space age provided astronomers an opportunity to expand research far beyond the capabilities offered by ground-based observatories of earlier eras. During the 1960s they began using space-based technology to enhance humanity’s understanding of the universe. In addition to greatly enhanced capabilities for observation in the visible light spectrum, NASA and other institutions supported the development of a wide range of X-ray, gamma ray, ultraviolet, infrared, microwave, cosmic ray, radar, and radio astronomical project. These efforts collectively informed the most systematic efforts yet to explain the origins and development of the universe.
Fundamental to this was the development of a series of Orbiting Astronomical Observatories (OAO), first conceptualized not long after the birth of NASA. Two of these aluminum, octagonally-shaped, solar-powered spacecraft were launched during the 1960s. The first failed less than two days into its mission because of a power system failure, but with the launch of OAO 2 on December 7, 1968, the potential of the program began to pay off as it provided an abundance of information on ultraviolet, gamma ray, x-ray, and infrared radiation, on the structure of stars, and on the distribution and density of matter in the interstellar environment. A series of six Orbiting Geophysical Observatories (OGO) also contributed to this study, as well as to the study of the Solar System, by taking measurements of cosmic rays, particles and fields in the interplanetary medium as well as radio emissions.
One of the exciting projects in this arena was x-ray astronomy. On June 12, 1962, the first rocket was launched using instruments to detect whether or not x-rays were present in any particular quadrants of the galaxy. It discovered a power source in the center. Calculations demonstrated that x-ray emissions from this source were ten times that of the Sun. In July 1963 another instrument package sent above the atmosphere took readings of the Crab Nebula and found intense x-ray activity emanating from it. In December 1970 the x-ray observatory Uhuru mapped about 85 percent of the sky, then located and measured the intensity of 161 x-ray sources. Many of these turned out to be black holes, a truly significant discovery of a segment of space where mass is so compressed and gravity so great that neither matter nor light can escape. Large amounts of x-rays, however, are emitted and can help explain much about the evolution of the universe.
By the early 1970s satellite astronomy had helped to generate a major change in the larger field of astronomy and had reordered thinking on the subject. This occurred in spite of the fact that much of the research was built on the foundations laid by earlier astronomers. While space science did not make news in the 1980s, as the last decade of the twentieth century dawn, NASA moved forward with its “Great Observatories” program and astounded the science world with its findings.
The $2 billion Hubble Space Telescope was the first of these “Great Observatories,” launched from the Space Shuttle in April 1990. A key component of it was a precision‑ground 94‑inch primary mirror shaped to within microinches of perfection from ultra‑low expansion titanium silicate glass with an aluminum‑magnesium fluoride coating. The first photos provided bright, crisp images against the black background of space, much clearer than pictures of the same target taken by ground‑based telescopes. Controllers then began moving the telescope’s mirrors to better focus images. Although the focus sharpened slightly, the best image still had a pinpoint of light encircled by a hazy ring or “halo.”
At first many believed that the spherical aberration would cripple the 43‑foot-long telescope, and NASA received considerable negative publicity, but soon scientists found a way with computer enhancement to work around the abnormality. Because of the difficulties with the mirror, in December 1993 NASA launched the shuttle Endeavour on a repair mission to insert a new camera and corrective lenses for the remaining instruments into the telescope and to service other instruments. During a week-long mission, astronauts conducted a record five spacewalks to repair the spacecraft.
The first reports from the Hubble spacecraft indicated that the images being returned were afterward more than an order of magnitude clearer than those obtained before. For instance, as recently as 1980, astronomers had believed that an astronomical grouping known as R‑136 was a single star, but the Hubble showed that it was made up of more than 60 of the youngest and heaviest stars ever viewed. The dense cluster, located within the Large Magellanic Cloud, was about 160,000 light years from Earth, roughly 5.9 trillion miles away.
Other “Great Observatories” followed. The Chandra X-Ray Observatory, launched on July 23, 1999, engaged in X-ray astronomy of the universe, concentrating on the remnants of exploded stars and even particles up to the last second before they fall into a black hole. More recently, the Compton Gamma-ray Observatory and the Spitzer Space Telescope (SST) observed the gamma-ray and infrared spectrum. Collectively these great observatories, led by the stunningly successful Hubble Space Telescope, have transformed our understanding of the cosmos.
As Jennifer Levasseur has written, “The tremendous success of the Hubble Space Telescope, COBE, and ESA’s Herschel Telescope supplied even more unknowns about our universe, and perhaps, our first reasons to believe in life beyond this ‘pale blue dot’.” To this one might add the Kepler space telescope seeking extrasolar planets and the SOFIA airborne observatory.
We are, however, presently at a crossroads. Ground-based observatories such as the Multiple Mirror Telescope (MMT) near Tucson, Arizona, and the Atacama Large Millimeter/submillimeter Array (ALMA) telescope in Chile have proven the success of new designs in ground-based observing. The James Webb Space Telescope (JWST), NASA on-going development in space astromony, has been close to cancellation several times because of technical, cost, and schedule difficulties.
Will there be a new generation of space-based observatories similar to those of the “Great Observatories” constellation? Is such a new generation needed at this point? Might we do all we need to do in astronomical observation from the ground and in air-borne observatories, allowing scientists to forego space-based telescopes altogether. While these modern observatories are enormously expensive, they are certainly less costly and more readily serviced and enhanced than anything in space.
What do you think?