cycle, it turned out, coincided with that
of a heater, which kicks on periodically to
keep a battery aboard Spitzer at a certain
temperature. The heater caused a strut
between the star trackers and telescope
to flex a bit, making the position of the
telescope wobble compared to the stars
being tracked.
Ultimately, in October 2010, the
engineers figured out that the heater did
not need to be cycled through its full hour
and temperature range – 30 minutes and
about 50 percent of the heat would do.
This tweak served to cut the telescope’s
wobble in half.
Spitzer’s engineers and scientists were
still not satisfied, however. In September
2011, they succeeded in repurposing
Spitzer’s Pointing Control Reference
Sensor “Peak-Up” camera. This camera
was used during the original cryo mission
to put gathered infrared light precisely
into a spectrometer and to perform
routine calibrations of the telescope’s
star-trackers, which help point the
observatory.
The telescope naturally wobbles
back and forth a bit as it stares at a
particular target star or object. Given this
unavoidable jitter, being able to control
where light goes within the infrared
camera is critical for obtaining precise
measurements. The engineers applied
the Peak-Up to the infrared camera
observations, thus allowing astronomers
Astronomers using the Spitzer Space Telescope have detected an
alien world just two-thirds the size of Earth. The exoplanet candidate, known as UCF-1.01, orbits a star called GJ 436, which is
located 33 light-years away.
Image: NASA/JPL-Caltech/R. Hurt (SSC)
76
76
The Spitzer Space Telescope points its high-gain antenna towards
the Earth for downlinking recent observations and uplinking new
observing instructions.
Image: NASA/JPL-Caltech/R. Hurt (SSC)
to place stars precisely on the center of a
camera pixel.
Since
repurposing
the
Peak-Up
Camera, astronomers have taken
this process even further, by carefully
“mapping” the quirks of a single pixel
within the camera. They have essentially
found a “sweet spot” that returns the most
stable observations. About 90 percent
of Spitzer’s exoplanet observations are
finely targeted to a sub-pixel level, down
to a quarter of a pixel.
“We can use the Peak-Up camera to
position ourselves very precisely on the
camera and put light right on the best
part of a pixel,” said Carey. “So you put
the light on the sweet spot and just let
Spitzer stare.”
These three accomplishments – the
modified heater cycling, repurposed
Peak-Up camera and the in-depth
characterization of individual pixels in
the camera – have more than doubled
Spitzer’s stability and targeting, giving
the
telescope
exquisite
sensitivity
when it comes to taking exoplanet
measurements.
“Because
of
these
engineering
modifications,
Spitzer
has
been
transformed into an exoplanet-studying
telescope,” said Carey. “We expect
plenty of great exoplanetary science to
come from Spitzer in the future.”
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