Spitzer Space Telescope

History

By the early 1970s, astronomers began considering placing an infrared telescope above Earth's atmosphere, since most of the infrared spectrum is strongly absorbed by the atmosphere except for the infrared window. In 1979, a National Research Council report identified a Shuttle Infrared Telescope Facility (SIRTF) as one of two major astrophysics facilities to be developed for Spacelab. The launch of the Infrared Astronomical Satellite (IRAS) in January 1983, which conducted the first far-infrared survey of the sky, increased interest in follow-up missions.

Earlier ground-based observatories suffered because the atmosphere and the telescope itself radiate brightly at infrared wavelengths, and the atmosphere is opaque at most such wavelengths, requiring lengthy exposure times and greatly decreasing the ability to detect faint objects. Previous space observatories such as IRAS and the Infrared Space Observatory (ISO) were launched during the 1980s and 1990s, and great advances in astronomical technology have been made since then.

Most early concepts envisioned repeated flights aboard the NASA Space Shuttle, but after the 1986 Challenger disaster, the Shuttle-Centaur upper stage was abandoned. The mission underwent a series of redesigns during the 1990s due to budget considerations, resulting in a much smaller but still fully capable mission using the smaller Delta II expendable launch vehicle. One of the most important advances was an Earth-trailing orbit, which allowed innovative passive cooling and drastically reduced the total mass of helium needed, resulting in major cost savings with a mirror the same diameter as originally designed.

Instruments

Spitzer carried three instruments that allowed astronomical imaging and photometry from 3.6 to 160 micrometers, spectroscopy from 5.2 to 38 micrometers, and spectrophotometry from 55 to 95 micrometers. The primary mirror is 85 cm in diameter, made of beryllium, and was cooled to 5.5 K. The shorter-wavelength infrared detectors were developed by Raytheon using indium antimonide and doped silicon, and are 100 times more sensitive than what was available during the 1980s.

The far-infrared 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 primary instrument package (telescope and cryogenic chamber) was developed by Ball Aerospace & Technologies in Boulder, Colorado. The individual instruments were developed jointly by Cornell University, the University of Arizona, the Smithsonian Astrophysical Observatory, Ball Aerospace, and Goddard Spaceflight Center.

Results

The planned mission period was 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, most instruments were no longer usable.

However, the two shortest-wavelength modules of the IRAC camera continued to operate with the same sensitivity as before the helium was exhausted, and continued to be used into early 2020 in the Spitzer Warm Mission. During the warm mission, the two short wavelength channels of IRAC operated at 28.7 K and were predicted to experience little to no degradation at this temperature. The Spitzer data, from both the primary and warm phases, are archived at the Infrared Science Archive (IRSA).

Did You Know?

• The telescope was renamed through a public contest, unlike most telescopes named by a board of scientists after famous deceased astronomers.
• After its liquid helium supply was exhausted on 15 May 2009, the two shortest-wavelength modules of the IRAC camera continued operating with the same sensitivity into early 2020.