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Optical Planet Discoverer: how to turn a 1.5-m class space telescope into a powerful exo-planetary systems imager

2003; SPIE; Volume: 4860; Linguagem: Inglês

10.1117/12.457646

1996-756X

Bertrand Mennesson, Michael Shao, B. M. Levine, J. Kent Wallace, Duncan T. Liu, Eugene Serabyn, S. C. Unwin, Charles Beichman,

Adaptive optics and wavefront sensing

Optical Planet Discoverer (OPD) is a 1.5m class space telescope concept working as a visible nulling-interferometer imager. It is designed to detect Jupiter-like planets orbiting main sequence stars 10pc away in a few minutes of integration and carry out a low resolution (~20) spectroscopy of their atmosphere. OPD would fit in the budget envelope of a discovery class mission. It would serve as an efficient precursor to a Visible Terrestrial Planet Finder (VTPF), a scaled-up 4m class version based on the same optical scheme and allowing direct detection of 10pc Earthlike planets in a few hours. We detail here OPD's optical principle layout, which is primarily driven by an integrated stellar light attenuation of 1e-6 in the final focal plane. The optical concept is based on a double-shearing nulling interferometer followed by an array of single-mode waveguides. The waveguides array ensures high residual starlight suppression - as already demonstrated at the 1e-6 level by preliminary JPL visible LASER nulling experiments - together with diffraction limited imaging of the circumstellar environment over a 2 arcsec field. During the observations, the telescope is spun around the line of sight to allow for proper detection of fixed planetary signatures against residual off-axis speckle patterns at the 1e-9 level. Use of the single-mode waveguide array to filter out scattered starlight eliminates the requirements for pristine λ/4000 rms wavefronts anywhere in the optical train. With OPD, stringent phase requirements apply only to scales larger than 5 cm - the equivalent size of the pupil regions to be recombined and nulled in a given fiber, so that phase specifications can be met using low order active optics.