A variety of conditions in Antarctica generally and at the South Pole specifically make the continent a world-class observatory. Since 1988, NSF and NASA
have developed techniques for flying and recovering large balloon payloads
(1,800 kg (2 tons) at altitudes of roughly 37 kilometers (120,000 ft) for extended
periods of approximately 2 weeks. These techniques locate the experiment above
99.7% of the atmosphere. For some experiments this provides scientists with conditions as good as a satellite.
For two reasons, the unique geophysical conditions above Antarctica make
long duration balloon flights possible during the austral summer. Because the balloon is illuminated continuously by sunlight, both directly and by reflection from
the underlying clouds or snow, it does not undergo the large changes in temperature, and therefore in altitude, that are experienced during the normal diurnal cycle
in more temperate regions. There, the daily heating and cooling cycle results in the
loss of helium and also ballast, which severely limits flight times, a situation that
is eliminated above Antarctica. Additionally, each summer for a period of a few
weeks, a nearly circular pattern of gentle east-to-west winds is established in the
Antarctic stratosphere. The circulation is generated by a long- lived high-pressure
area resulting from the constant solar heating of the stratosphere. This allows the
launching and return of a balloon where it can be recovered relatively simply on
land. Over the past decade there have been long duration flights in most Antarctic
research seasons, roughly mid-December through mid- January, with two balloons
often being flown during a single season.
Several geophysical attributes make the Amundsen-Scott South Pole Station an
important and unique observatory. Its location at the Earth’s axis means that any
celestial object can be observed for long periods at the same elevation in the sky.
Most famously, for many years the South Pole facilitated long continuous solar
observations, with some runs lasting over 100 hours. The station is located at an
altitude of approximately 3,000 m (10,000 ft) atop the Antarctic ice sheet. There
the atmosphere is so cold that there is very little water vapor overhead, which is
important because water vapor is the principal cause of atmospheric absorption
and variability in broad portions of the electromagnetic spectrum from the nearinfrared to millimeter radio waves. Many telescopes have exploited this over the
past decade, most notably to chart submillimeter neutral carbon emission in the
galaxy and to measure the anisotropy (the property of a material which allows it
to change or assume different properties in different directions) of the radiation
field of the cosmic microwave background.
U.S. scientific flights from Antarctica are supported by the CSBF, governed by
the NSF USAP staff that provide logistics and administrative support. Because
many flights are controlled by the polar vortex, it is possible to circumnavigate
the continent. Antarctica is the highest, driest, coldest, windiest and brightest of
the seven continents. It is about the size of the U.S. and Mexico together, and is
202 The Balloon World
have developed techniques for flying and recovering large balloon payloads
(1,800 kg (2 tons) at altitudes of roughly 37 kilometers (120,000 ft) for extended
periods of approximately 2 weeks. These techniques locate the experiment above
99.7% of the atmosphere. For some experiments this provides scientists with conditions as good as a satellite.
For two reasons, the unique geophysical conditions above Antarctica make
long duration balloon flights possible during the austral summer. Because the balloon is illuminated continuously by sunlight, both directly and by reflection from
the underlying clouds or snow, it does not undergo the large changes in temperature, and therefore in altitude, that are experienced during the normal diurnal cycle
in more temperate regions. There, the daily heating and cooling cycle results in the
loss of helium and also ballast, which severely limits flight times, a situation that
is eliminated above Antarctica. Additionally, each summer for a period of a few
weeks, a nearly circular pattern of gentle east-to-west winds is established in the
Antarctic stratosphere. The circulation is generated by a long- lived high-pressure
area resulting from the constant solar heating of the stratosphere. This allows the
launching and return of a balloon where it can be recovered relatively simply on
land. Over the past decade there have been long duration flights in most Antarctic
research seasons, roughly mid-December through mid- January, with two balloons
often being flown during a single season.
Several geophysical attributes make the Amundsen-Scott South Pole Station an
important and unique observatory. Its location at the Earth’s axis means that any
celestial object can be observed for long periods at the same elevation in the sky.
Most famously, for many years the South Pole facilitated long continuous solar
observations, with some runs lasting over 100 hours. The station is located at an
altitude of approximately 3,000 m (10,000 ft) atop the Antarctic ice sheet. There
the atmosphere is so cold that there is very little water vapor overhead, which is
important because water vapor is the principal cause of atmospheric absorption
and variability in broad portions of the electromagnetic spectrum from the nearinfrared to millimeter radio waves. Many telescopes have exploited this over the
past decade, most notably to chart submillimeter neutral carbon emission in the
galaxy and to measure the anisotropy (the property of a material which allows it
to change or assume different properties in different directions) of the radiation
field of the cosmic microwave background.
U.S. scientific flights from Antarctica are supported by the CSBF, governed by
the NSF USAP staff that provide logistics and administrative support. Because
many flights are controlled by the polar vortex, it is possible to circumnavigate
the continent. Antarctica is the highest, driest, coldest, windiest and brightest of
the seven continents. It is about the size of the U.S. and Mexico together, and is
202 The Balloon World