AO4ELT5 Proceedings
Wavefront sensing for a future HabEx space telescope
Nissen, Joel (Jet Propulsion Laboratory), Martin, Stefan (Jet Propulsion Laboratory)
The next generation of space telescopes such as HabEx and LUVOIR, now being studied, will have stability requirements orders of magnitude more stringent than any previously flown space-based observatory. Many of these requirements arise from the need to implement high contrast imaging of exoplanet systems using coronagraphy as the principal tool. Sensing of starlight rejected from a coronagraph is essential in stabilizing the observatory’s pointing and slow thermally induced wavefront drift, but the control bandwidth is likely insufficient to counter observatory vibrations arising from spacecraft reaction wheels, especially for dim stars. Laser metrology provides a different, complementary sensing method, one that can be used to measure changes in the alignment of the optics at high bandwidth, independent of the magnitude of the host star. Thus, wavefront control can be maintained even during attitude maneuvers such as slews between target stars, thereby avoiding the need to repeat time-consuming speckle suppression. Laser metrology measures changes in the separation of optical fiducial pairs which may be separated by many meters, making it ideal for active control of large structures. The principle of operations is similar to the laser metrology system used in LISA-Pathfinder to measure the on-orbit displacement between two test masses to a precision of ~10 picometers. In closed loop with actuators, laser metrology actively maintains rigid body alignment of the front-end mirrors, thereby eliminating the dominant source of wavefront drift. In the case of a segmented, active primary mirror, laser metrology provides sensing of six degrees of freedom, replacing edge sensors. We evaluate the metrology truss layout for a monolithic space-based telescope design proposed for HabEx, and present the performance requirements necessary to maintain contrast drift below 10^-11
DOI: 10.26698/AO4ELT5.0032- Proceeding PDF
