For nearly two years, NASA's
TIMED 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 two-year orbital mission draws to a
close this winter, the project's 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 Thermosphere,
Ionosphere, Mesosphere, Energetics and Dynamics--for
another three years of operations and data analysis
beginning in January 2004. This will be followed by a year
of data analysis after orbital operations are completed.
In a society increasingly dependent on satellite
technology and communications, it is vital to understand
the variability within a critical region of our upper
atmosphere known as the MLTI, for 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 piloted vehicles' re-entry.
"Solar cycle variations strongly affect our upper
atmosphere," said APL's Sam Yee, TIMED project scientist.
"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 also will 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.
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 said.
"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," he said. "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 oversees the
TIMED mission for NASA Headquarters' Office of Space
Science.
TIMED is the first mission in NASA's Solar Terrestrial
Probes Program.
For more information about the mission, go to
http://www.timed.jhuapl.edu.