a decade, and will enable assessment of the potential hazard each poses to Earth. It will take a census of some 10,000 of the most primitive bodies in the solar system, located in the Kuiper Belt. It will also contribute to the study of the structure of the universe by observing thousands of supernovae, both nearby and at large redshift, and by measuring the distribution of dark matter through gravitational lensing. LSST will produce a terabyte of data per night, all of which will be accessible to scientists and the public alike through the National Virtual Observatory.

Terrestrial Planet Finder. The main goal of TPF is nothing less than to search for evidence of life on terrestrial planets around nearby stars. The present concept calls for a space-based infrared interferometer of enormous sensitivity, capable of nulling out the light from the host star. TPF’s angular resolution will also enable it to peer into the innermost regions of protoplanetary disks, galactic nuclei, starburst galaxies, and galaxies at high redshift. By a large margin, TPF is the most costly and the most technically challenging mission discussed in this report. Both SIM and NGST involve key technologies that must be successfully demonstrated if TPF as currently envisioned is to go forward. The committee’s recommendation of this mission is predicated on the assumptions that TPF will revolutionize major areas of both planetary and nonplanetary science, and that, prior to the start of TPF, ground- and space-based searches will confirm the expectation that terrestrial planets are common around solartype stars. NASA should pursue a vigorous program of technology development to enable the construction of TPF to begin in this decade.

Single Aperture Far Infrared Observatory. The SAFIR Observatory will take advantage of the technology developed for NGST to study the relatively unexplored region of the spectrum between 30 and 300 µm. It will investigate the earliest stage of star formation and galaxy formation by revealing regions too shrouded by dust to be studied with NGST and too warm to be studied effectively with ALMA. An 8-m-class space-based telescope that is diffraction-limited at 30 µm, it will be more than 100 times as sensitive as SIRTF or the European FIRST mission. It will have the capability of becoming part of an interferometer at a later time.

Telescope System Instrumentation Program. Universities and independent observatories operate the majority of the large optical and infrared