<title>Development of lightweight mirror technology for the next generation space telescope</title>

Abstract

ABSTRACT In 2009, NASA plans to launch the Next Generation Space Telescope (NGST) to the L2 point, 1.5 million kilometers from Earth. With a 6-meter diameter mirror, NGST is a successor to the Hubble Space Telescope with 5 times the collecting aperture. As part of NASA’s Origins Program, the ten-year observing mission will search for the “first light” of the universe. NGST will provide astronomers with unparalleled light collection, mid-infrared sensitivity, spatial resolution and field of view. Mirror technology is critical to the system’s success. The hard part is solving the problem of how to launch a 6m, 600 kg, mirror into space on a 4-meter diameter rocket. Additionally, high performance is expected at operating temperatures of 50K. This paper reviews the mirror requirements and development efforts. 1.0 NEXT GENERATION SPACE TELESCOPE As part of NASA’s Origins Program, the Next Generation Space Telescope (NGST) will search the heavens for the ‘first light of the universe’ while allowing astronomers to ponder some of the grandest questions in modern cosmology: where did we come from and are we alone. To study the formation of galaxies, stars and heavy elements as well as search for other planetary systems with habitable planets requires a demanding combination of sensitivity (particularly in the mid-infrared), angular resolution and wide field of view. NGST will observe objects which were formed extremely early in the history of the universe and thus have their radiation greatly red shifted towards the infrared. NGST will be capable of detecting radiation in the range of 0.6 to 28 m with optimum performance in the 1-5 m region. Furthermore, NGST must be able to see objects fainter than those currently studied with large ground-based infrared telescopes (such as Keck or Gemini) or space-based infrared telescopes (ISO, NICMOS or SIRTF). And, it must do so with a spatial resolution comparable to the Hubble Space Telescope. To achieve this fundamental science driver, NGST must have a primary mirror collecting area greater than 25 square-meters (approximately 6 meter diameter). Because NGST is a Zodiacal-light limited infrared observatory, the telescope must operate at a temperature between 30 and 50K. Furthermore, because of size limitations, a conventional baffle tube is impractical. Therefore, the entire telescope will be exposed to space and cooled to the desired temperature in the shadow of a sunshield. Additionally, to see the faintest objects, it must be able to follow sky fields continuously over a period of months. Both of these requirements are achieved by locating NGST at the sun-earth/moon Lagrange gravitational L2 point, where NGST will enjoy unsurpassed temperature and mechanical disturbance stability.