  The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) is a
sub-orbital experiment designed to study the process of star formation in local
galaxies (including the Milky Way) and in galaxies at cosmological distances.
Using a 2-m Cassegrain telescope, BLAST images the sky onto a focal plane,
which consists of 270 bolometric detectors split between three arrays,
observing simultaneously in 30% wide bands, centered at 250, 350, and 500
microns. The diffraction-limited optical system provides a resolution of 30" at
250 microns. The pointing system enables raster-like scans with a positional
accuracy of ~30", reconstructed to better than 5" rms in post-flight analysis.
BLAST had two successful flights, from the Arctic in 2005, and from Antarctica
in 2006, which provided the first high-resolution and large-area (~0.8-200
deg^2) submillimeter surveys at these wavelengths. As a pathfinder for the
SPIRE instrument on Herschel, BLAST shares with the ESA satellite similar focal
plane technology and scientific motivation. A third flight in 2009 will see the
instrument modified to be polarization-sensitive (BLAST-Pol). With its
unprecedented mapping speed and resolution, BLAST-Pol will provide insights
into Galactic star-forming nurseries, and give the necessary link between the
larger, coarse resolution surveys and the narrow, resolved observations of
star-forming structures from space and ground based instruments being
commissioned in the next 5 years.
