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Laser Guide Star for Large Aperture Segmented Space Telescopes

Kerri Cahoy
Massachusetts Institute of Technology

ESI 2016 Cahoy Quad Chart

Astronomers plan to use very large telescopes to take pictures of exoplanets, which are hard to see next to their bright parent stars. High contrast (<10^-10) coronagraph instruments onboard the telescope help by blocking the parent starlight so the exoplanets can be imaged. Exoplanet spectra, images taken over many wavelengths, provide information about the planet’s composition and habitability. To achieve high contrast, wavefront sensing and control techniques need to be used. Natural guide stars nearby the exoplanet system are typically used to set up the wavefront sensing and control, but many natural guide stars do not provide enough signal to run the wavefront control loop fast enough to overcome instabilities and disturbances in the system. We propose to study using a space telescope architecture with external small satellite laser guide stars paired with the large telescopes to act as the reference sources. This would reduce the need design and build large telescopes with picometer stability, which would be needed if only natural guide stars were used. We will study high contrast imaging performance using the external small satellite laser guide star, as we relax the stability requirements on the large telescope.