ince UARS launched in 1991 on shuttle mission
STS-48,
the UARS satellite and SOLSTICE instrument
have performed well. There is almost a continuous data set of solar UV irradiances
on a daily basis since October 3, 1991. There are however some gaps in the
SOLSTICE data related to satellite problems, mostly the solar array drive
subsystem. The largest data gap is a 6 week period in June 1992 when the
solar array drive problems were studied extensively. Since May 1995 when
the solar array was parked in a constant position, the UARS has been operated
in a low power mode where only about half of the UARS instruments are operated
at a time. The solar instruments including SOLSTICE are generally operated
about 90% of the time though due to their low power requirements and to
the scientific need to measure the solar irradiances whenever atmospheric
measurements are being made. This UARS low power mode is expected to continue
for the life of the mission which may last for several more years.