(SpaceViews) The launch of an infrared telescope, the last of NASA's "Great Observatories," will be delayed, possibly by several months, because of an instrument problem, NASA officials confirmed Friday.
The Space Infrared Telescope Facility (SIRTF) will miss its December 2001 launch date because of a problem with an infrared camera currently under investigation, NASA spokesperson Dolores Beasley told SpaceViews. Word of the delay was reported earlier in the month on the project's website, but without any explanation for the delay.
The problem, which could be hardware- or software-related, has delayed shipment of the instrument from NASA's Goddard Space Flight Center, where it is being built, to Ball Aerospace, the contractor integrating IRAC with SIRTF's other instruments.
The delayed shipment of the instrument will in turn delay the launch of SIRTF. The length of the delay will not be known until a project meeting in late September, but Beasley said that the delay would be on the order of several months.
SIRTF is billed as the final element of NASA's "Great Observatories" program, a project conceived more than two decades ago to develop and launch a series of space-based telescopes that would perform world-class science not possible with ground-based telescopes over a wide range of wavelengths.
The cornerstone of the Great Observatories program is the Hubble Space Telescope, launched in 1990. It was followed a year later by the Compton Gamma Ray Observatory, whose mission ended in June when the spacecraft was deorbited after encountering problems with its gyros. The third Great Observatories spacecraft, the Chandra X-ray Observatory, was launched in July of last year.
SIRTF had to go through a number of major changes in order to avoid cancellation. As originally planned, SIRTF was a 12,540-pound (5,700-kilogram) spacecraft that would have been placed into Earth orbit by a Titan 4 booster, at a total mission cost of $2.2 billion. SIRTF has now slimmed down to a 2,990-pound (950-kilogram) spacecraft that will be launched on a Delta 2 booster at a total cost of only $450 million.
One key decision that shaped the SIRTF redesign was to launch the spacecraft not into Earth orbit but into a heliocentric orbit that recedes from Earth at the rate of 9.3 million miles (15 million kilometers, or 0.1 astronomical units) per year. Moving SIRTF away from Earth reduced the amount of thermal radiation it receives, making it easier to keep the spacecraft at the low temperatures needed for infrared observations.
SIRTF was originally scheduled for a five-year mission, but the reduced size of the spacecraft, including a reduction of the amount of liquid helium that keeps the spacecraft's instruments cold, cut its lifetime in half. However, project officials are now optimistic that SIRTF's design is robust enough to keep it in operation for the original five years.
IRAC is one of three major instruments that will share light collected by SIRTF's 33.5-inch (85-centimeter) primary mirror. While IRAC will provide images at near-infrared wavelengths, the Multiband Imaging Photometer (MIPS) for SIRTF will provide coverage at longer wavelengths. A third instrument, the Infrared Spectrometer (IRS), will provide spectra of astronomical objects at near- and mid-infrared wavelengths.
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