Early History | Recent History
Infrared astronomy dates from the 1960s, when balloon-borne telescopes were lofted above the obscuring effects of Earth's lower atmosphere. By the early 1970s, measurements made by small telescopes aboard high-flying Lear jets and on sounding rockets identified a few thousand celestial infrared (IR) sources.
In the meantime, astronomers exploited narrow atmospheric transmission windows to observe from the ground at selected near- and mid-infrared wavelengths. New infrared instruments were added to telescopes at Mauna Kea in Hawaii, at Mount Wilson in Southern California, and at Mount Lemmon in Arizona. NASA converted a cargo plane into the Kuiper Airborne Observatory in 1974, and this flying platform would provide research flights for infrared astronomers over the next two decades.
None of these observatories, however, could take advantage of the pristine observing conditions of space. By the early 1970s, astronomers began to consider the possibility of placing an infrared telescope above the obscuring effects of Earth's atmosphere. Most of the early concepts, such as the Shuttle InfraRed Observatory, envisioned repeated flights aboard the NASA Space Shuttle. This approach was developed in an era when the Shuttle program was presumed to be capable of supporting weekly flights of up to 30 days duration. Moreover, it assumed that the contaminant environment of the Shuttle (e.g., vapors and small particles) could be minimized.
National Academy Press
In 1979, the National Research Council of the National Academy of Sciences published the recommendations of a committee of scientists (the Field Committee) selected to identify priorities for new astronomical telescopes, facilities and initiatives for the next decade. This report, A Strategy for Space Astronomy and Astrophysics for the 1980s, identified a Shuttle Infrared Telescope Facility (SIRTF) as "one of two major astrophysics facilities [to be developed] for Spacelab," a Shuttle-borne platform. Anticipating the exciting 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."
NASA solicited proposals in May 1983 to build instruments and to conduct observations with a large Shuttle-based infrared telescope. According to the NASA Announcement of Opportunity:
SIRTF is envisaged as an attached Shuttle mission with an evolving scientific payload. Several flights are anticipated with a probable transition into a more extended mode of operation, possibly in association with a future space platform or space station. The SIRTF will be a 1-meter class, cryogenically cooled, multi-user facility consisting of a telescope and associated focal plane instruments. It will be launched on the Space Shuttle and will remain attached to the Shuttle as a Spacelab payload during astronomical observations, after which it will be returned to Earth for refurbishment prior to re-flight.
Moreover, the AO stated that "the first flight of SIRTF is expected to occur about 1990, with the second flight anticipated to be approximately one year after the first flight."
First Infrared Satellite
As NASA prepared to issue this invitation for proposals, a rocket was launching the first infrared telescope into space. The Infrared Astronomical Satellite, an Explorer-class satellite designed to conduct the first infrared survey of the sky, was a collaborative effort between the United States, the Netherlands and the United Kingdom. The American team constructed the telescope, infrared detectors, and cooling system. The Dutch team provided the spacecraft, which included the on-board computers and pointing system. The British built the satellite ground station and control center. The 10-month mission proved to be a spectacular success, and whetted the appetites of scientists worldwide for a follow-up mission capitalizing on the rapid improvements in infrared detector technology.
In recognition of the early and impressive scientific returns from the Infrared Astronomical Satellite, NASA issued an addendum to the Announcement of Opportunity in September 1983 "... to provide flexibility for the possibility of a long duration [free-flyer] SIRTF mission."
In 1984, NASA selected a team of astronomers to build the instruments and help define the science program for a free-flying SIRTF observatory. This decision proved to be prophetic when the Infrared Telescope flew aboard the July 1985 flight of Spacelab 2. This modest 15.2 cm diameter telescope, developed by a team based at the Smithsonian Astrophysical Observatory, revealed that the contaminating infrared emission due to the Shuttle was considerable. Nonetheless, the experiment (developed prior to the Infrared Astronomical Satellite mission) successfully demonstrated a cryogenically cooled telescope design and superfluid helium management in a zero-gravity environment.
The decision to proceed with a free-flyer observatory led to the first, but not the last, transformation for Spitzer, changing the meaning of "SIRTF" to the Space Infrared Telescope Facility.