For nearly two years, NASA’s TIMED (Thermosphere, Ionosphere, Mesosphere,
Energetics and Dynamics) spacecraft has made great strides in its
exploration of one of Earth’s last atmospheric frontiers during a time when
the sun’s activity has been near the peak of its 11-year cycle. As its
initial 2-year orbital mission draws to a close this winter, the team is
preparing to embark on an extended mission to study how declining solar
activity affects a portion of the upper atmosphere that serves as the
gateway between Earth’s environment and space, where the sun’s energy is
first deposited into our environment.

NASA extended the TIMED mission for another three years of operations and
data analysis beginning in January 2004. This will be followed by an
additional year of data analysis in 2007, to be conducted after orbital
operations are completed.

In a society increasingly dependent on satellite technology and
communications, it’s vital to understand the variability within a critical
region of our upper atmosphere known as the MLTI (Mesosphere, Lower
Thermosphere/Ionosphere). A better understanding will help scientists
predict this region’s effects on communications, satellite tracking,
spacecraft lifetimes, degradation of spacecraft materials and on the reentry
of piloted vehicles.

“Solar cycle variations strongly affect our upper atmosphere,” says Sam Yee,
TIMED project scientist from The Johns Hopkins University Applied Physics
Laboratory (APL) in Laurel, Md. “As solar activity levels transition from
maximum to minimum, we see dramatic changes in solar ultraviolet radiation,
in the frequency and intensity of
magnetic storms and substorms, and in the nature of high energy particles
entering the upper atmosphere. TIMED’s extended mission is critical to
exploring these variations and improving our understanding of the final link
in the energy chains connecting the sun and Earth.”

During the next phase of operations, TIMED’s science team will focus on how
changes in the solar cycle affect: solar radiation; the MLTI region’s
composition, temperature, wind and seasonal variations; atmospheric waves;
and the variance of geomagnetic disturbances within the upper atmosphere.
Scientists will also look at how different radiative, chemical,
electrodynamic and dynamic processes within the upper atmosphere vary with
solar radiation inputs during times of reduced solar activity.

Unprecedented Observations

Since January 2002, TIMED and a worldwide network of ground-based
observation sites have collected unprecedented global observations of the
MLTI region’s basic structure, temperature, pressure, wind and chemical
composition, as well as measurements of the region’s energy inputs and
outputs. “TIMED is the first mission to simultaneously measure all critical
parameters so that we can better understand the processes that control
changes in the upper atmosphere,” Yee says.

“To date we’ve collaborated with science teams from other NASA Sun-Earth
Connections missions, which has provided a powerful test bed for
investigating the sun-Earth energy chains responsible for disturbances in
the upper atmosphere,” Yee says. “We’ll continue this approach during the
next phase of TIMED’s operations – a step that will allow the science
community to begin to piece together an integrated view of the physical
processes linking the sun and Earth.”

As TIMED continues its exploration of one of Earth’s last atmospheric
frontiers, APL will continue to lead the project’s science effort and manage
the mission’s Science Data Center for NASA. The Laboratory for
Extraterrestrial Physics at NASA’s Goddard Space Flight Center, Greenbelt,
Md., oversees the TIMED mission for NASA Headquarters’ Office of Space
Science in Washington, D.C.

TIMED is the first mission in NASA’s Solar Terrestrial Probes Program.

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