  The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) is a
sub-orbital surveying experiment designed to study the evolutionary history and
processes of star formation in local galaxies (including the Milky Way) and
galaxies at cosmological distances. The BLAST continuum camera, which consists
of 270 detectors distributed between 3 arrays, observes simultaneously in
broad-band (30%) spectral-windows at 250, 350, and 500 microns. The optical
design is based on a 2m diameter telescope, providing a diffraction-limited
resolution of 30" at 250 microns. The gondola pointing system enables raster
mapping of arbitrary geometry, with a repeatable positional accuracy of ~30";
post-flight pointing reconstruction to ~5" rms is achieved. The on-board
telescope control software permits autonomous execution of a pre-selected set
of maps, with the option of manual override. In this paper we describe the
primary characteristics and measured in-flight performance of BLAST. BLAST
performed a test-flight in 2003 and has since made two scientifically
productive long-duration balloon flights: a 100-hour flight from ESRANGE
(Kiruna), Sweden to Victoria Island, northern Canada in June 2005; and a
250-hour, circumpolar-flight from McMurdo Station, Antarctica, in December
2006.
