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Spitzer Space Telescope : ウィキペディア英語版
Spitzer Space Telescope

The Spitzer Space Telescope (SST), formerly the Space Infrared Telescope Facility (SIRTF), is an infrared space observatory launched in 2003. It is the fourth and final of the NASA Great Observatories program.
The planned mission period was to be 2.5 years with a pre-launch expectation that the mission could extend to five or slightly more years until the onboard liquid helium supply was exhausted. This occurred on 15 May 2009. Without liquid helium to cool the telescope to the very low temperatures needed to operate, most of the instruments are no longer usable. However, the two shortest-wavelength modules of the IRAC camera are still operable with the same sensitivity as before the cryogen was exhausted, and will continue to be used in the Spitzer Warm Mission. All ''Spitzer'' data, from both the primary and warm phases, are archived at the Infrared Science Archive (IRSA).
In keeping with NASA tradition, the telescope was renamed after its successful demonstration of operation, on 18 December 2003. Unlike most telescopes that are named after famous deceased astronomers by a board of scientists, the new name for SIRTF was obtained from a contest open to the general public.
The contest led to the telescope being named in honor of astronomer Lyman Spitzer, who had promoted the concept of space telescopes in the 1940s. Spitzer wrote a 1946 report for RAND Corporation describing the advantages of an extraterrestrial observatory and how it could be realized with available or upcoming technology. He has been cited for his pioneering contributions to rocketry and astronomy, as well as ''"his vision and leadership in articulating the advantages and benefits to be realized from the Space Telescope Program."〔''
The ''Spitzer'' was launched from Cape Canaveral Air Force Station, on a Delta II 7920H ELV rocket, Monday, 25 August 2003 at 13:35:39 UTC-5 (EDT).
It follows a heliocentric instead of geocentric orbit, trailing and drifting away from Earth's orbit at approximately 0.1 astronomical unit per year (a so-called "earth-trailing" orbit). The primary mirror is in diameter, ''f''/12, made of beryllium and was cooled to . The satellite contains three instruments that allow it to perform astronomical imaging and photometry from 3.6 to 160 micrometers, spectroscopy from 5.2 to 38 micrometers, and spectrophotometry from 5 to 100 micrometers.〔
== History ==

By the early 1970s, astronomers began to consider the possibility of placing an infrared telescope above the obscuring effects of Earth's atmosphere.
In 1979, a report from the National Research Council of the National Academy of Sciences, ''A Strategy for Space Astronomy and Astrophysics for the 1980s'', identified a Space Infrared Telescope Facility (SIRTF) as "one of two major astrophysics facilities (be developed ) for Spacelab", a Shuttle-borne platform. Anticipating the major results from an upcoming Explorer satellite and from the Shuttle mission, the report also favored the "study and development of ... long-duration spaceflights of infrared telescopes cooled to cryogenic temperatures."
The launch in January 1983 of the Infrared Astronomical Satellite, jointly developed by the United States, the Netherlands, and the United Kingdom, to conduct the first infrared survey of the sky, whetted the appetites of scientists worldwide for follow-up space missions capitalizing on the rapid improvements in infrared detector technology.
Earlier infrared observations had been made by both space-based and ground-based observatories. Ground-based observatories have the drawback that at infrared wavelengths or frequencies, both the Earth's atmosphere and the telescope itself will radiate (glow) strongly. Additionally, the atmosphere is opaque at most infrared wavelengths. This necessitates lengthy exposure times and greatly decreases the ability to detect faint objects. It could be compared to trying to observe the stars at noon. Previous space-based satellites (such as IRAS, the Infrared Astronomical Satellite, and ISO, the Infrared Space Observatory) were operational during the 1980s and 1990s and great advances in astronomical technology have been made since then.
Most of the early concepts envisioned repeated flights aboard the NASA Space Shuttle.
This approach was developed in an era when the Shuttle program was expected to support weekly flights of up to 30 days duration.
A May 1983 NASA proposal described SIRTF as a Shuttle-attached mission, with an evolving scientific instrument payload.
Several flights were anticipated with a probable transition into a more extended mode of operation, possibly in association with a future space platform or space station.
SIRTF would be a 1-meter class, cryogenically cooled, multi-user facility consisting of a telescope and associated focal plane instruments.
It would be launched on the Space Shuttle and remain attached to the Shuttle as a Spacelab payload during astronomical observations, after which it would be returned to Earth for refurbishment prior to re-flight.
The first flight was expected to occur about 1990, with the succeeding flights anticipated beginning approximately one year later.
However, the Spacelab-2 flight aboard STS-51-F showed that the Shuttle environment was poorly suited to an onboard infrared telescope due to contamination from the relatively "dirty" vacuum associated with the orbiters.
By September 1983 NASA was considering the "possibility of a long duration () SIRTF mission".
''Spitzer'' is the only one of the Great Observatories not launched by the Space Shuttle, which had been originally intended.
However after the 1986 Challenger disaster, the Centaur LH2/LOX upper stage, which would have been required to place it in its final orbit, was banned from Shuttle use.
The mission underwent a series of redesigns during the 1990s, primarily due to budget considerations. This resulted in a much smaller but still fully capable mission which could use the smaller Delta II expendable launch vehicle.
One of the most important advances of this redesign was an Earth-trailing orbit.
Cryogenic satellites that require liquid helium (LHe, T ≈ 4 K) temperatures in near-Earth orbit are typically exposed to a large heat load from the Earth, and consequently entail large usage of LHe coolant, which then tends to dominate the total payload mass and limits mission life.
Placing the satellite in solar orbit far from Earth allowed innovative passive cooling such as the sun shield, against the single remaining major heat source to drastically reduce the total mass of helium needed, resulting in an overall smaller lighter payload, with major cost savings.
This orbit also simplifies telescope pointing, but does require the Deep Space Network for communications.
The primary instrument package (telescope and cryogenic chamber) was developed by Ball Aerospace & Technologies Corp., in Boulder, CO. The individual instruments were developed jointly by industrial, academic, and government institutions, the principals being Cornell, the University of Arizona, the Smithsonian Astrophysical Observatory, Ball Aerospace, and Goddard Spaceflight Center. The shorter-wavelength infrared detectors were developed by Raytheon in Goleta, California. Raytheon used indium antimonide and a doped silicon detector in the creation of the infrared detectors. It is stated that these detectors are 100 times more sensitive than what was once available in the beginning of the project during the 1980s.〔(Raytheon Company : Investor Relations : News Release ). Investor.raytheon.com (8 January 2004). Retrieved on 21 July 2013.〕 The Far-IR detectors (70 - 160 micrometers) were developed jointly by the University of Arizona and Lawrence Berkeley National Laboratory using Gallium-doped Germanium. The spacecraft was built by Lockheed Martin. The mission is operated and managed by the Jet Propulsion Laboratory and the ''Spitzer Science Center'',〔(Spitzer Science Center Home Page -- Public information ).〕 located on the Caltech campus in Pasadena, California.

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