NASA's Explorer Program

The Extreme Ultraviolet Explorer, NASA's 70th Explorer mission, is one in a long line of relatively low-cost, small-to-moderately sized missions that traditionally have been devoted to exploring new phenomena or opening up new spectral regions to scientific study. Since the Explorer Program began in 1958, these missions have given scientists worldwide a new understanding of astronomy and astrophysics, providing them with an opportunity to probe nearly every region of the electromagnetic spectrum, from infrared radiation to gamma rays.

NASA's Small Astronomy Satellite-1, named UHURU after it was launched in 1970, carried out the first comprehensive sky survey in X rays and discovered several hundred highly energetic galactic and extragalatic sources.

Data from the still-operational International Ultraviolet Explorer, launched in 1978, revealed a hot gaseous halo surrounding the Milky Way Galaxy and a previously undetected form of sulfur in a comet that swung past the Earth during the mission. The Infrared Astronomical Satellite (IRAS) opened up the fertile field of infrared astronomy in 1983 by carrying out the first all-sky survey of infrared sources. IRAS discovered disks of warm dust and gas in orbit around several nearby stars, which are thought to be planetary systems in the process of formation.

The Cosmic Background Explorer (COBE), launched in 1989, was primarily designed to study the remnant radiation of the Big Bang, the primordial explosion believed to have given birth to the Universe 10 to 20 billion years ago. COBE has provided strong evidence supporting this theory.

Image of COBE (159kbytes)

Through three decades of space exploration, NASA has evolved a proven method for exploring space. Its small satellite program has become the backbone of space astrophysics because it opens frontiers and paves the way for more sophisticated follow-on missions. Though scientists had some inkling of what they would find with the Extreme Ultraviolet Explorer, they also understood a basic precept that has proven true throughout the Explorer Program: open a new spectral range to observation and discoveries are likely to follow.