POST - A POLAR STRATOSPHERIC TELESCOPE FOR THE ANTARCTIC

The tropopause, typically at 16 to 18 km altitude at the lower latitud es, dips down to only 8 km in the polar regions, allowing access to th e cold, dry and nonturbulent lower stratosphere by tethered aerostats. These can float as high as 12 km, have long operating lifetimes, and are extremely reliable. In contrast to free-flying balloons, they can stay on station for weeks at a time, and payloads can be safely recove red for maintenance and adjustment and relaunched in a matter of hours . We propose to use such a platform, located first near Fairbanks, Ala ska, and later in the Antarctic, to operate a new-technology 4 m teles cope with diffraction-limited performance in the near infrared. Thanks to the low ambient temperature (similar to 200 K), thermal emission f rom the optics is of the same order as that of the zodiacal light in t he 2-3 mu m band. Since this wavelength interval is the darkest part o f the zodiacal light spectrum from optical wavelengths to 100 mu m, th e combination of high-resolution images and a very dark sky make it th e spectral region of choice for observing galaxies, QSOs and clusters of galaxies at the formation epoch of galaxies.