NASA’s Space Infrared Telescope
Facility (SIRTF) is in test at Lockheed Martin Space Systems in
Sunnyvale, California. SIRTF’s Cryogenic Telescope Assembly, which
includes the scientific instruments, has been received from Ball
Aerospace in Boulder, Colo., and integrated with the Lockheed
Martin-built spacecraft.

“We are very enthusiastic about having taken delivery of the SIRTF
cryogenic telescope assembly and its three high performance science
instruments,” said Tom Dougherty, Lockheed Martin SIRTF program manager.
“We have completed the careful process of integrating the payload and
spacecraft, and are beginning to perform environmental and other tests
that will verify that SIRTF is ready for launch early next year.”

SIRTF is a cryogenically-cooled space observatory that will conduct
infrared (IR) astronomy during a two and one-half-to-five year mission
beginning in 2003. SIRTF completes NASA’s family of Great Observatories
that also includes the Hubble Space Telescope, the Chandra X-Ray
Observatory and the Compton Gamma Ray Observatory. The SIRTF program, a
cornerstone of NASA’s Origins Program, is managed by the Jet Propulsion
Laboratory in Pasadena, Calif. for NASA’s Office of Space Science in
Washington DC.

The spaceborne SIRTF observatory comprises a 0.85-meter diameter
telescope and three scientific instruments capable of performing imaging
and spectroscopy in the 3-180 micron wavelength regime. Incorporating
the latest in large-format infrared detector array technology, SIRTF
will offer orders-of-magnitude improvements in sensitivity over previous
IR missions. Cornell University, University of Arizona, and the
Harvard-Smithsonian Center for Astrophysics have provided the
instruments for SIRTF.

An important feature of the SIRTF mission is the adoption of a solar
orbit. To reach this orbit, the spacecraft will be launched on a Delta
7920 launch vehicle with slightly greater than terrestrial escape
velocity. The resulting orbit will have SIRTF trailing the Earth in its
orbit around the Sun. This orbit makes better use of launch capability
than does a conventional Earth orbit, and it permits excellent,
uninterrupted viewing of a large portion of the sky without the need for
Earth-avoidance maneuvers. In addition, the absence of heat input from
the Earth provides a stable thermal environment and allows the exterior
of the telescope to reach a low temperature via radiative cooling.

A one meter-diameter transmitting antenna fixed to the bottom of the
spacecraft will be used twice each day to transmit 12 hours of stored
science data to stations of NASA’s Deep Space Network. In this manner,
an adequate average data rate of 85 kbps– corresponding to one image
from SIRTF’s largest array every 10 seconds — can be maintained over
the lifetime of the mission.

SIRTF’s scientific potential is rooted in four basic physical principles
that define the importance of infrared investigations for studying
astrophysical problems:

. Infrared observations reveal cool states of matter: Solid bodies in
space — ranging in size from sub-micron-sized interstellar dust grains
to giant planets — have temperatures spanning the range from 3K to
1500K (above which nearly all solids evaporate). Most of the energy
radiated by objects in this temperature range lies in the infrared part
of the spectrum. Infrared observations are therefore of particular
importance in studying low-temperature environments such as dusty
interstellar clouds where stars are forming and the icy surfaces of
planetary satellites and asteroids.

. Infrared observations explore the hidden Universe: Cosmic dust
particles effectively obscure parts of the visible Universe and block
our view of many critical astronomical environments. This dust becomes
transparent in the infrared, where observers can probe optically
invisible regions such as the center of our Galaxy (and other galaxies)
and dense clouds where stars and planets may be forming. For many
objects — including dust-embedded stars, active galactic nuclei, and
even entire galaxies — the visible radiation absorbed by the dust and
re-radiated in the infrared accounts for virtually the entire luminosity.

. Infrared observations access unique spectral features: Emission and
absorption bands of virtually all molecules and solids lie in the
infrared, where they can be used to probe conditions in cool celestial
environments. Many atoms and ions have spectral features in the infrared
that can be used for diagnostic studies of stellar atmospheres and
interstellar gas, exploring regions that are too cool or too
dust-enshrouded to be reached with optical observations.

Infrared observations reach back to the early life of the cosmos: The
cosmic redshift which results from the general expansion of the Universe
inexorably shifts energy to longer wavelengths in an amount proportional
to an object’s distance. Because of the finite speed of light, objects
at high redshift are observed as they were when the Universe and those
objects were much younger. As a result of the expansion of the Universe,
most of the optical and ultraviolet radiation emitted from stars,
galaxies, and quasars since the beginning of time now lies in the
infrared. How and when the first objects in the Universe formed will be
learned in large part from infrared observations.

Apart from a few windows at short wavelengths, all of the infrared
radiation emitted by the above objects is absorbed by Earth’s
atmosphere. Worse, the infrared emission of the atmosphere itself blinds
astronomers peering through those windows. Hence the need for a cooled
space-based infrared observatory with high sensitivity — SIRTF.

NASA’s Origins Program follows the chain of events that began with the
birth of the Universe at the Big Bang. It seeks to understand the entire
process of cosmic evolution from the formation of chemical elements,
galaxies, stars and planets, through the mixing of chemicals and energy
that cradles life on Earth, to the earliest self-replicating organisms
and the profusion of life. In short, Origins hopes to answer the
fundamental question: Are we alone in the Universe?

Lockheed Martin Space Systems Company is one of the major operating
units of Lockheed Martin Corporation. Space Systems designs, develops,
tests, manufactures, and operates a variety of advanced technology
systems for military, civil and commercial customers. Chief products
include a full-range of space launch systems, including heavy-lift
capability, ground systems, remote sensing and communications satellites
for commercial and government customers, advanced space observatories
and interplanetary spacecraft, fleet ballistic missiles and missile
defense systems.

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NOTE TO EDITORS: Low- and high-resolution JPEG images of the SIRTF
spacecraft in a cleanroom at Lockheed Martin Space Systems in Sunnyvale
are available at the following URL:

http://lmms.external.lmco.com/photos/civil_space/space_infared_tele_sirtif/sirtf.html

For more information about Lockheed Martin Space Systems, see our
website at http://lmms.external.lmco.com