The Spitzer Space Telescope:
Ten years of viewing the Universe’s dark side By Ben Evans More than ten years have now passed since NASA’s fourth “Great Observatory”—the Space Infrared Telescope Facility (SIRFT)—was boosted into orbit from Cape Canaveral Air Force Station, Fla., atop a Delta II rocket. It was intended to complement is three older siblings, the Hubble Space Telescope, the Compton Gamma Ray Observatory and the Chandra X-ray Observatory, in exploring the cosmos across almost the entire electromagnetic spectrum. Later renamed the Spitzer Space Telescope, in honour of U.S. astronomer Lyman Spitzer, the 2,100 lb (950 kg) observatory has since carved its own niche in the annals of astrophysics and cosmology and continues to make astounding scientific discoveries. As the only one of the four Great Observatories not launched by the Space Shuttle, it is more than a little ironic than SIRTF was originally conceived as a pallet-only Spacelab facility, with a 3.3 foot (1 metre) telescope and optical bench, operating from the payload bay of the reusable orbiter. In a 1979 report from the National Research Council of the National Academy of Sciences, it was described as “one of two major astrophysics facilities for Spacelab” and was deemed important for the development of long-duration, cryogenically-cooled space telescopes. The significance of SIRTF was that it would utilize a “dewar” of cryogenic helium to sufficiently cool its infrared detectors and thus meet the requirements to resolve its desired astronomical targets. Subsequent data from the 1983-launched Infrared Astronomy Satellite (IRAS) made the usefulness of SIRTF more obvious. Anticipated for a first shuttle launch in 1990, and flying at one-yearly intervals thereafter, SIRTF encountered its first major hurdle when Challenger flew the Spacelab-2 payload of telescopes and astronomical detectors aboard
Shuttle mission STS-51F in July-August 1985. Although this eight-day mission was an enormous scientific success, it demonstrated that the “dirty” environment of particulate contaminants around the Shuttle was poorly suited to the needs of high-energy astrophysics instruments. Contributing to the eventual demise of SIRTF as a Shuttle-borne payload was the Challenger disaster in January 1986, and after several phases of “re-scoping” and redesign it emerged as a spacecraft which would be lofted into orbit atop a Delta II booster. As part of the redesign, SIRTF would be inserted into an “Earth-trailing” orbit, which is “heliocentric” (Sun-circling), rather than “geocentric” (Earth-circling), and involved the spacecraft drifting away from Earth’s orbit at a rate of about 9.3 million miles (14.9 million km), or 0.1 Astronomical Units, per year. The reason was that Earth generates The Spitzer Space Telescope was a large heat load launched on a Delta II rocket on August and emplacement 25, 2003 from Cape Canaveral, Florida. at this sufficiently Photo: NASA/KSC distant point would enable SIRTF to utilise passive cooling technologies, including a large Sunshield, to greatly reduce its operating temperature and the mass of cryogenic helium it needed to carry. Its telescope and cryogenic assembly were built by Ball Aerospace and its scientific instruments—the Infrared Array Camera
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