In 1962 he joined the Smithsonian Astrophysical Observatory and the Harvard College Observatory, where he initiated a program in gamma-ray astronomy using balloon-borne and ground-based telescopes He initiated the construction of the 10-meter optical reflector at the F. L. Whipple Observatory, Arizona, to search for ultrahigh-energy cosmic gamma-rays. In the early 1970's he pioneered the development of large balloonborne telescopes for far-infrared astronomical observations above the atmosphere, and for twenty years was Principal Investigator for the 1-Meter Balloon-Borne Far-Infrared Telescope. His current research interests include the development of infrared instrumentation and the use of infrared array cameras on ground-based and space telescopes to observe galaxy formation and evolution in the early Universe, black holes, ultraluminous galaxies, star formation and evolution, brown dwarfs, and asteroids.