The Spitzer Space Telescope:
Ten years of viewing
the Universe’s dark side
By Ben Evans
More than ten years have now
passed since NASA’s fourth “Great
Observatory”—the
Space
Infrared
Telescope Facility (SIRFT)—was boosted
into orbit from Cape Canaveral Air Force
Station, Fla., atop a Delta II rocket. It was
intended to complement is three older
siblings, the Hubble Space Telescope,
the Compton Gamma Ray Observatory
and the Chandra X-ray Observatory, in
exploring the cosmos across almost the
entire electromagnetic spectrum. Later
renamed the Spitzer Space Telescope, in
honour of U.S. astronomer Lyman Spitzer,
the 2,100 lb (950 kg) observatory has
since carved its own niche in the annals
of astrophysics and cosmology and
continues to make astounding scientific
discoveries.
As the only one of the four Great
Observatories not launched by the
Space Shuttle, it is more than a little ironic
than SIRTF was originally conceived as a
pallet-only Spacelab facility, with a 3.3
foot (1 metre) telescope and optical
bench, operating from the payload
bay of the reusable orbiter. In a 1979
report from the National Research
Council of the National Academy of
Sciences, it was described as “one
of two major astrophysics facilities for
Spacelab” and was deemed important
for the development of long-duration,
cryogenically-cooled space telescopes.
The significance of SIRTF was that it would
utilize a “dewar” of cryogenic helium to
sufficiently cool its infrared detectors and
thus meet the requirements to resolve its
desired astronomical targets. Subsequent
data from the 1983-launched Infrared
Astronomy Satellite (IRAS) made the
usefulness of SIRTF more obvious.
Anticipated for a first shuttle launch in
1990, and flying at one-yearly intervals
thereafter, SIRTF encountered its first
major hurdle when Challenger flew
the Spacelab-2 payload of telescopes
and astronomical detectors aboard
Shuttle mission STS-51F in July-August
1985. Although this eight-day mission
was an enormous scientific success,
it demonstrated that the “dirty”
environment of particulate contaminants
around the Shuttle was poorly suited to
the needs of high-energy astrophysics
instruments. Contributing to the eventual
demise of SIRTF as a Shuttle-borne
payload was the
Challenger disaster
in January 1986, and
after several phases
of “re-scoping” and
redesi gn it emerged
as
a
spacecraft
which
would
be
lofted into orbit atop
a Delta II booster.
As part of the
redesign, SIRTF would
be inserted into an
“Earth-trailing” orbit,
which is “heliocentric”
(Sun-circling), rather
than
“geocentric”
(Earth-circling),
and involved the
spacecraft
drifting
away from Earth’s
orbit at a rate of
about 9.3 million miles
(14.9 million km), or
0.1
Astronomical
Units, per year. The
reason
was
that
Earth
generates The Spitzer Space Telescope was
a large heat load launched on a Delta II rocket on August
and emplacement
25, 2003 from Cape Canaveral, Florida.
at this sufficiently
Photo: NASA/KSC
distant point would
enable SIRTF to utilise passive cooling
technologies, including a large Sunshield, to greatly reduce its operating
temperature and the mass of cryogenic
helium it needed to carry. Its telescope
and cryogenic assembly were built
by Ball Aerospace and its scientific
instruments—the Infrared Array Camera
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