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'Broken
Heart' Image the Last for NASA’s Long-Lived Polar Mission
Tuesday, April 29, 2008
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Polar
Mission scientists dubbed the mission’s final image,
taken April 16, 2008, “The Broken Heart” because
of its shape.
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Credit:
NASA/Polar
As far as endings go, this
one’s a real heart breaker. NASA’s Polar satellite
concludes its successful mission at the end of April with a
breathtaking visible-light image of the colorful dancing lights
of the aurora. The Polar team has dubbed this final image "The
Broken Heart."
When the Polar satellite launched
February 24, 1996, the plan was for a two-year science mission to
study the lights that form a ring around Earth’s north and
south magnetic poles, known as the Northern and Southern Lights,
or auroras. Polar has exceeded expectations by a decade.
“We’ve
gone well beyond our original plan and into our dreams,”
says John Sigwarth of NASA’s Goddard Space Flight Center in
Greenbelt, Md., of Polar’s amazing 12-year run.
Polar
orbits from Earth’s North Pole to its South Pole to study
how solar wind particles and their energy enter Earth’s
magnetosphere, the area surrounding Earth dominated by its
magnetic field. Polar also revealed how those particles and their
energy end up in Earth’s atmosphere, and how the radiation
belts form and dissipate.
The satellite completes an
orbit every 17½ hours, passing over one pole at a maximum
altitude of about 32,000 miles and diving past Earth’s
equator to the opposite pole at a minimum distance of only about
3,200 miles. As Polar flies over the north and south poles, three
of the satellite’s 12 instruments capture images of auroras
in ultraviolet, X-ray, and visible light. The other nine
instruments take measurements of charged particles and Earth’s
electric and magnetic fields throughout its journey around
Earth.
“Polar ran out of fuel during its final
maneuver in February,” says Sigwarth, project scientist for
the Polar spacecraft. “But even after the fuel was
exhausted, we continued to maneuver on the cold helium gas that
was left in the tank,” he explains.
Sigwarth likens
the satellite’s post-fuel feat to “using the force of
your breath as you breathe out to propel yourself backwards”
if you happen to be traveling through space like a satellite. But
now Polar has run out of breath.
The plan is to turn off
the satellite April 28 slightly ahead of a likely fatal encounter
with the sun. From its current orientation, Polar will drift
slowly, allowing the energy from our nearest star to quickly
overwhelm the satellite. If Polar were left on, first to go would
be its radiators, batteries, and transmitters. These would
overheat and probably fail. The satellite’s planned turn
off at the end of April will allow controllers to send the final
commands before Polar meets its fate.
During its lifetime,
Polar has had many accomplishments. Observations of energetic
neutral atoms have provided the first-ever global images of
substorm injections that are the sequence of events that lead to
energetic auroral displays. These neutral atom images clearly
show the broad extent in space of these energetic atoms and their
instantaneous nature in time.
Source:
NASA / GFSC / Laura Layton
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