Background and Technology

Infrared Astronomy From Earth Orbit

In the 1970s, astronomers around the world began to consider the possibility of placing an infrared telescope on a satellite in orbit around the Earth. This telescope would be above the Earth's atmosphere and could view the sky at the far-infrared wavelengths which were difficult to detect on Earth. It could view a large area of the sky and observe regions for a longer period of time.

By 1977, an international collaboration was formed by the Netherlands, United States and Great Britain to develop IRAS - The Infrared Astronomical Satellite. The American team built the telescope, detectors and cooling system. The British built the satellite ground station and control center and the Dutch team built the spacecraft which included the on-board computers and pointing system.
It takes a great deal of effort to build an infrared space telescope. After many years of hard work and after overcoming several complications, IRAS was successfully launched on January 25, 1983. The telescope was housed in a dewar, filled with 127 gallons of liquid helium and contained 62 detectors. The entire telescope was cooled to a temperature of just a few degrees above absolute zero because otherwise the telescope itself would emit infrared radiation (heat) which would interfere with the observations. A space infrared telescope must be cooler than the objects in space that it will observe.

The IRAS mission would last as long as the liquid helium did. For the next ten months, IRAS scanned more than 96 percent of the sky four times, providing the first high sensitivity all sky map at wavelengths of 12, 25, 60 and 100 microns. IRAS detected about 500,000 infrared sources, doubling the number of cataloged astronomical sources. IRAS discoveries included a disk of dust grains around the star Vega, six new comets, and very strong infrared emission from interacting galaxies as well as wisps of warm dust called infrared cirrus which could be found in almost every direction of space. IRAS also revealed for the first time the core of our galaxy, the Milky Way.

IRAS in orbit - Artist Rendition

The Space Shuttle With Spacelab 2
Several successful infrared satellite missions were launched after IRAS. During July and August of 1985, an infrared telescope was flown onboard the Space Shuttle's Spacelab 2 to complement observations made by the IRAS mission. This mission produced a high quality map of about 60% of the plane of our galaxy.

In November 1989, NASA launched the COBE satellite to study both infrared and microwave characteristics of the cosmic background radiation (the remains of the extreme heat that was created by the Big Bang). Over a ten month period, COBE mapped the brightness of the entire sky at several infrared wavelengths and discovered that the cosmic background radiation is not entirely smooth, showing extremely small variations in temperature. These variations may have led to the formation of galaxies.

The Infrared Telescope in Space (IRTS), launched in March 1995, was Japan's first infrared satellite mission. During its 28 day mission, IRTS surveyed about 7% of the sky with four instruments: A Near and Mid Infrared Spectrometer which covered wavelengths of 1.4 to 4 microns and 4.5 to 11 microns respectively, a Far Infrared Line Mapper which studied Oxygen and Carbon spectral lines at 63 and 158 microns, and a Far infrared Photometer which studied the sky at four bands centered at 150, 250, 400, and 700 microns. This data should add to our knowledge of cosmology, interstellar matter, late type stars and interplanetary dust.

The European Space Agency launched the Infrared Space Observatory (ISO) in November 1995. ISO, which observed at wavelengths between 2.5 and 240 microns, not only covered a much wider wavelength range than IRAS but was also thousands of times more sensitive than IRAS and viewed infrared sources with much better resolution. ISO took data for about 2.5 years (3 times times longer than IRAS). It ceased operations in April 1998 when its supply of liquid helium ran out. ISO contained instruments which measured details of both the shorter and longer wavelength regions of the infrared spectrum, an infrared camera which had two infrared arrays, and a photometer. Unlike IRAS, which was an infrared survey mission, ISO is operated like a ground based observatory, having astronomers submit observing proposals to study specific astronomical objects in detail. As hundreds of astronomers from several countries study the data from ISO, important new discoveries about our universe are expected to emerge. ISO has already detected dry ice in interstellar dust and hydrocarbons in some nebulae.

The Midcourse Space Experiment (MSX) was launched in April 1996 and lasted until its liquid helium coolant ran out in Feb 1997. During its 10 months of operation, MSX gathered a vast amount of data at 4.2 - 26 microns. MSX studied the infrared emission from the gas and dust which permeates the universe. MSX had 30 times the spatial resolution as IRAS and surveyed areas of the sky which were missed by IRAS.

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