An optical/UV space coronagraph concept for the terrestrial planet finder

NASA's current strategic plan calls for the launching of a space observatory, The Terrestrial Planet Finder (TPF), by the middle of the next decade; it will search for terrestrial planets in the habitable zone of roughly 150 nearby stars and characterize them for the potential to harbor life. This paper describes a visible light concept for TPF developed by the Ball Aerospace led TPF study team. This concept consists of a 4 m by 10 m coronagraphic telescope in a deep space orbit. Imaging planets requires overcoming the problem of high contrast between the light from the parent star and from the planet, coupled with their small angular separation. For a coronagraph, the diffraction pattern of the telescope must be suppressed at the planet image location. The high contrast needed can be achieved using optimized pupil shapes that provide the needed 10 billion times suppression as close as 4λ/D to the center of the star. In addition, wavefront errors induced by the mirror deformities will be corrected using deformable mirrors in a novel active optics system that corrects both amplitude and phase errors. The paper describes the baseline design of a visible light telescope and instrument that will meet the mission requirements.