University of Colorado Satellite Readied for NASA Launch Jan. 25

An $85 million NASA satellite carrying five instruments designed and
built at the University of Colorado at Boulder to study how and why
variations in the sun affect Earth’s atmosphere and climate is slated
for launch on Jan 25.

The mission, known as the Solar Radiation and Climate Experiment, or
SORCE, is a free-flying satellite that will launch from Florida’s
Kennedy Space Center. CU-Boulder’s Laboratory for Atmospheric and
Space Physics designed and built the instruments and contracted
Orbital Sciences Corp. of Dulles, Va. to build the satellite bus.
The project is part of NASA’s Earth Observing System.

“We need a long-term record of the natural variation in Earth’s
climate, including changes in the sun, land and sea surfaces to hang
our hat on in order to model future climate change,” said Gary
Rottman, a LASP senior research scientist and principal investigator
on the SORCE project. “Precisely measuring changes in solar
radiation is a large key to this challenge.”

Rottman also is the principal investigator on an instrument dubbed
SOLSTICE, which launched on NASA’s Upper Atmosphere Research
Satellite in 1991. Originally scheduled to orbit Earth for three
years, SOLSTICE is still orbiting and functioning and has given
researchers a full 11-year solar cycle. An article that appeared in
the Dec. 20, 2002 issue of Science magazine — perhaps the most
respected weekly science journal in the world — cited the sun-Earth
connection as one of five key areas to watch in 2003.

“From a financial standpoint, SORCE is the largest single project
LASP ever has been involved in,” said Rottman. “Ultraviolet
radiation in Earth’s atmosphere influences many of chemical
processes, including the natural production and destruction of ozone.”

The SORCE spacecraft will be launched from a Pegasus
expendable-launch vehicle built by Orbital Sciences. The Pegasus
will be carried to an altitude of 40,000 feet by a jet aircraft and
dropped in a five-second free-fall.

It will then ignite horizontally and roar in front of the jet, and
begin ascending, placing the SORCE satellite in a circular orbit
about 400 miles above Earth within 10 minutes.

“The SORCE spacecraft specifically will study solar variability and
its influence on climate change,” said Rottman. “We are interested
in understanding the sun’s influence on Earth’s atmosphere and
climate so that we can more reliably determine how humans are
changing the environment.”

According to Tom Sparn, the SORCE project manager, understanding the
sun is crucial to evaluating its influence on Earth. “Everything
about climate, from droughts and ozone loss to human health problems
like eye cataracts and skin cancer revolve around our understanding
of the sun,” he said. “We need to integrate our long-term solar data
with supercomputers that model Earth’s climate system to see what is
occurring in the big picture.”

Two nearly identical copies of SOLSTICE will be flying on SORCE,
which will be controlled at LASP’S CU Research Park facility.

SORCE also will include the Total Irradiance Monitor, or TIM, to
monitor changes in the total amount of sunlight reaching Earth. The
spacecraft also will carry a Spectral Irradiance Monitor, or SIM, a
prism-like device to gather visible and infrared data, said Rottman.
The fifth CU-Boulder-built instrument is the X-ray Photometer System,
or XPS, a package of 12 photodiodes to measure extreme ultraviolet
sunlight.

“Because SOLSTICE has been flying on UARS for so long we have the
calibration to match up with our new data sets,” said Sparn. We have
finally an anchor point.”

Evidence indicates the release of man-made chlorofluorocarbons, or
CFCs, were largely responsible for the decline in stratospheric ozone
levels in the 1990s, said Rottman. “There really doesn’t seem to be
any doubt that significant changes are occurring in stratospheric
ozone levels,” said Rottman. “By understanding and removing the
natural variability due to variations of solar radiation, we can more
accurately establish how much of the change is the result of human
activity.”

SORCE research and education efforts are for the scientific community
and the general public, said LASP Director Daniel Baker.
“Understanding fluctuations in the sun have become crucial in the
last several years, ranging from space weather to the sun’s impact on
our everyday lives. We want to share this information with the top
solar scientists as well as K-12 students, college students, and the
general public, and we now have the NASA mission to do it.”