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This Week In Space History | Eyeing the Violent Universe
by dave dooling
The future Nobel laureate crawled into the nose cone and personally removed the red plastic “remove before flight” covers from the telescopes, and then crawled back out. He would be the last person to touch what soon would become the most successful X-ray telescope yet flown.
The Einstein Observatory, properly called High-Energy Astronomy Observatory-2 (HEAO-2), launched on Nov. 13, 1978, 35 years ago this week. It almost became just another neat-but-canceled idea. Instead, it redrew our view of the universe.
“Gone is the classical conception of the Universe as a serene and majestic ensemble whose slow evolution is regulated by the consumption of the nuclear fuel,” Dr. Ricardo Giacconi said in his lecture when he received the Nobel Prize in physics for his pioneering work in X-ray astronomy in December 2002. In its place he described a violent universe seething with surprises.
“The Universe we know today is pervaded by the echoes of enormous explosions and rent by abrupt changes of luminosity on large energy scales,” Giacconi wrote. “From the initial explosion to formation of galaxies and clusters, from the birth to the death of stars, high energy phenomena are the norm and not the exception in the evolution of the Universe.”
Scientists had long suspected that the universe glowed brightly in X-rays, but were unable to observe until rockets let them boost rudimentary detectors above the atmosphere following World War II. In 1949 the Sun was discovered to emit X-rays. In 1962 Giacconi led a team that discovered X-rays coming from a celestial source now called Sco X-1, in the constellation Scorpius.
More suborbital rockets totaling an hour of observing time revealed increasing detail about the universe in X-rays and hinted at more mysteries. The Uhuru Small Astronomy Satellite, launched in 1970, showed the sky was peppered with hundreds of sources. If we could see this much with a tiny satellite, what might be seen by bigger detectors? Thus was born HEAO, a quartet of massive satellites that would be launched by a Titan III rocket.
The program soon became too expensive and was canceled—almost. Vague wording in the NASA budget left enough wiggle room for scientists and TRW to design a smaller trio of satellites that would still greatly expand our view of the universe. These would be launched by smaller Atlas-Centaur rockets. The second of the series would carry the second X-ray astronomy telescope.
Giacconi, then with American Science & Engineering, had been working on the concept since 1959. He wrote that more sensitivity meant detectors that could cover a football field, which is impractical in space. A telescope could concentrate more X-ray energy onto a small detector and produce a sharp image. But how to focus something that passes through solid matter?
The answer was grazing incidence, an idea suggested in the 1940s for X-ray microscopes. If light strikes glass at a shallow angle, the glass acts like a mirror and reflects the light. Coat the glass (or other material) with metal and make the angle very shallow, and the mirror now reflects X-rays. The angle has to be so shallow, though, that the mirror looks more like a gently curved tube. That means very little X-ray energy is captured, so you have to nest multiple mirrors inside each other to have an effective telescope. Alignment and polishing become exquisitely demanding because the wavelengths of X-rays are much shorter than their less energetic cousin, visible light.
Early versions of this design, called a Wolter Type 1, studied the Sun in the 1960s and led to the X-ray solar telescope carried by Skylab in 1973-74.
HEAO-2 would be next, with Giacconi at the helm as principal investigator. At the eyepiece, as it were, of its ground-breaking telescope were several types of detectors on a carousel that would rotate the right one into position and a grating that would act like a prism spreading light into a rainbow.
HEAO-2 was the heaviest of the trio, weighing in at 6,866 pounds. Before it departed Earth, one last task remained: Remove protective covers from the X-ray telescope and other instruments, a job normally done by the launch pad crew. But Giacconi had a lot riding on this. He crawled inside the nose cone and carefully removed the covers himself. Soon, HEAO-2 soared into orbit.
The first surprise came before HEAO-2 even started its warm-up exercises. At the post-launch press conference, Giacconi dubbed it the Einstein Observatory. No one was more surprised than NASA, which planned no names for any of the HEAO series. It’s still unofficial, but the name stuck.
What followed were 2-1/2 years of observing the most violent realms of space. Dr. Martin Weisskopf, an investigator with HEAO-2 and now NASA project scientist on the Chandra X-ray Observatory, recalled in a 1999 interview how our view of the universe changed.
“We discovered [with HEAO-2] that X-ray emission was not just an oddity but is, if I can use a fancy word, ubiquitous: it’s everywhere,” Weisskopf said. “Every known major class of astronomical objects emits X-rays. In many cases this was an outstanding discovery, and a very surprising discovery. We X-ray astronomers brought astrophysics the first unique evidence that black holes exist based on X-ray observations of Cygnus X-1.”
HEAO-2 revealed that Jupiter has X-ray auroras caused by its intense radiation belts; showed nova and supernova stars as well as conventional main-sequence stars, all glowing in X-rays; and study binary sources in our galaxy and distant, pulsars, and quasars.
Contact was lost on April 17, 1981, and HEAO-2 decayed from orbit a year later. But it had opened the way for a series of satellites with names like Beppo, Rossi, Roentgen, and—most famously today—the Chandra X-ray Observatory, the X-ray counterpart to the Hubble Space Telescope.
Giacconi, now president of Associated Universities, which operates radio telescopes, and his colleagues erased peaceful universe. It its place they gave us something far more violent, even dangerous, and exciting.
This story draws on Dr. Giacconi’s Nobel Prize Lecture, The Dawn of X-ray Astronomy, and NASA references and the author’s coverage of the HEAO-2 launch.
Links: http://www.nobelprize.org/nobel_prizes/physics/laureates/2002/giacconi-lecture.html
http://science1.nasa.gov/science-news/science-at-nasa/1999/ast14jul99_1/
Dave Dooling is education director at the New Mexico Museum of Space History. He is a former space journalist and past recipient of the National Space Club’s Press Award and Goddard History Essay Award.
Source: http://moonandback.com/2013/11/10/this-week-in-space-history-eyeing-the-violent-universe/
