Charli Schuler (818) 354-3965
Jet Propulsion Laboratory, Pasadena, Calif.
Equipped with advanced infrared technology, NASA will peer into
unknown territories of the universe with the long-anticipated Space
Infrared Telescope Facility. The space-based observatory, managed by
NASA’s Jet Propulsion Laboratory in Pasadena, Calif., is scheduled to
launch in mid-April.
“This observatory is like the infrared cousin of the Hubble Space
Telescope. It sees things the Hubble can’t see, which is part of the
reason why we have the Great Observatories Program,” said Dr. Michael
Bicay, assistant director of the Space Infrared Telescope Facility
Science Center.
With the Space Infrared Telescope Facility, scientists will seek out
infrared light shrouded by cosmic dust. Infrared light, which is not
visible to the human eye, is typically absorbed by Earth’s atmosphere.
Using infrared, scientists expect the observatory will help them probe
the early life of the cosmos and detect discs around other stars,
where planets may be forming.
The Space Infrared Telescope Facility is the final mission under
NASA’s Great Observatories Program, which includes Hubble, the Chandra
X-ray Observatory and the Compton Gamma-Ray Observatory. The mission
is also an important part of NASA’s Origins Program, which seeks to
answer the questions: Where did we come from? Are we alone?
The mission brings with it several technological advancements, the
most significant of which is that of infrared detector technology.
“The interesting science has always been out there, but until recently
we didn’t have the technology to discover and characterize it,” Bicay
said.
When infrared detector technology was first discovered, the U.S.
Department of Defense used it to look down on Earth, a bright object,
and view missile trails from space. Doing the reverse – viewing space,
a dark environment containing faint astronomical objects, from Earth –
wasn’t possible without further refining the detectors to measure weak
signals such as those in the infrared. This required the combined
efforts of researchers and observers from NASA, several educational
institutions and the aerospace industry.
Built to Last for Less
The observatory has an innovative architectural design. Like cellular
phones, the package just keeps getting smaller.
Previous infrared telescopes in space have used “cold-launch”
cryogenic architecture, in which all the spacecraft’s components (the
telescope, science instruments and a tank containing liquid helium
coolant) were dropped into a big container that functioned like a
thermos. In this new “warm-launch” cryogenic architecture, a much
smaller container surrounds only the instrument chamber and a much
smaller liquid helium tank, but not the telescope. The result is a
lighter, smaller spacecraft that is less costly and easier to launch.
Contributing to the observatory’s lightness is a sturdy,
heat-resistant telescope, with a total mass of less than 110 pounds
(50 kilograms). (The Hubble Space Telescope weighs 24,500 pounds or
11,475 kilograms). The innovative launch architecture, combined with
95 gallons (360 liters) of liquid helium, yields an estimated mission
lifetime of at least two and a half years. NASA plans to adopt this
approach, with variations, in the design of future space-based
observatories and infrared telescopes such as the James Webb Space
Telescope, scheduled to launch in 2010.
Letting Mother Nature Call the Shots
Also contributing to the observatory’s originality is its resourceful
choice of orbit. Scientists abandoned the idea of placing the
observatory into an Earth orbit; instead they will put it into an
Earth-trailing heliocentric orbit. In other words, the observatory
will be launched into an orbit where it will simply drift behind Earth
as it circles the Sun. The observatory will then drift away from Earth
at the rate of about 1 astronomical unit per year. (An astronomical
unit is the average distance between the Sun and Earth, about 150
million kilometers or 93 million miles.)
The Earth-trailing orbit takes full advantage of Mother Nature to
enable its “warm-launch” architecture. As the observatory drifts from
Earth into deep space, it will use the temperature of its surroundings
to cool itself. Within a few weeks after launch, it will have cooled
down to deep space temperatures of about 35 degrees Kelvin (-238
degrees Celsius or -397 degrees Fahrenheit). This natural cooling
process allows the observatory to carry much less liquid helium
cryogen than it would need in an Earth orbit, where temperatures can
reach 250 degrees Kelvin (-23 degrees Celsius or -10 degrees
Fahrenheit).
“We let Mother Nature do most of the cooling for us,” Bicay said.
“It’s as if I were having a picnic and wanted cold soda. If the soda
was already kept cold in a refrigerator, I wouldn’t need as much ice.”
Another benefit of the orbit is that the observatory will have a
large, instantaneous view of the celestial sky. The view will be
limited only by two pointing constraints, as sensitive observatories
such as this one and the Hubble Space Telescope must avoid looking at
or anywhere near extremely bright objects like the Sun, Earth and
Moon. The observatory cannot point closer than 80 degrees in the
direction of the Sun, in order to minimize the heating of the
telescope by solar radiation. Also, the observatory cannot point more
than 120 degrees away from the Sun because it needs to illuminate the
solar panels and produce electricity to power itself. Even with these
constraints, a third of the sky will be instantaneously visible to the
observatory at any given time, allowing scientists optimum viewing
efficiency and streamlining mission operations.
JPL is responsible for the observatory’s mission operations, while all
scientific data is processed at the Space Infrared Telescope Facility
Science Center at Caltech.
More information about the mission is available at:
