The Infrared Astronomical Satellite (IRAS), launched Jan. 25, l983, last night used the last of the superfluid helium refrigerant that cooled the telescope, ending the science mission.
The orbiting telescope discovered wealth of new phenomena in the universe during its l0-month lifetime. Engineering tests will be conducted for about one week before the satellite ceases operations, according to mission officials.
IRAS is joint project of the U.S., The Netherlands and the United Kingdom.
Throughout the highly successful mission, the telescope's focal plane was cooled to temperature of about 2.5 degrees above absolute zero, or -455 degrees Fahrenheit making the instrument the coldest manmade object ever flown in Earth orbit.
At launch, IRAS was expected to operate for only seven months. After launch, based on flight data which measures the rate at which the helium was being used, mission engineers estimated that the 75 kilograms of refrigerant would last through early January, l984. But there were uncertainties in the calibration estimates of the flow rate of helium, which accounts for the difference.
Mission engineers at the Rutherford Appleton Laboratory in Chilton, England, where IRAS is tracked, said the satellite depleted its supply of helium at l:30 a.m. Greenwich Mean Time on Tuesday Nov. 22 (5:30 p.m., Monday Nov. 2l, PST).
The telescope focal plane has been warming at rate of about two-tenths of degree Kelvin (four-tenths of degree Fahrenheit) per hour since the helium was depleted. Useful science observations can continue until the focal plane has heated to about ll degrees Kelvin (-448 degrees Fahrenheit).
Engineering tests will be conducted for about one week, project officials said. Information gained during these tests will be useful in designing future spacecraft and infrared telescopes that will operated in space.
The telescope successfully surveyed more than 95 percent of the sky, pinpointing the locations and intensities of more than 200,000 infrared objects.
During its 300 days of observations, IRAS has carried out the first complete survey of the infrared sky and has made many discoveries, including detection of ring of solid material around the star Vega, five comets, and bands of dust around the Sun between the orbits of Mars and Jupiter.
In addition, the telescope provided new look at our own galaxy, the Milky Way, and detected many new mysterious objects.
More than 200 billion bits of data have been received from IRAS, and the results announced so far represent very preliminary look at very small portion of the data, according to IRAS scientists. It is clear, however, that IRAS will have major impact on many areas of astronomy and that astronomers will be making new discoveries from its data for many years to come.
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