In-orbit wavefront sensing of wide-field line scan space camera with a co-axial three-mirror system

A method to estimate the wavefront errors of a wide-field line-scan space camera with a coaxial three-mirror anastigmatic optical system is proposed. Zernike polynomial coefficients of 3 fields are obtained through 3 wavefront sensors, after subtracting the design aberrations, the Zernike polynomial coefficients varies with field along a parabolic curve, then Zernike polynomial coefficients of any field can be estimated by interpolating. That the Zernike polynomial coefficient varies with field and the accuracy of the fitting is studied by simulations. Simulations show that the Zernike coefficients of the design error vary with field along a cubic curve or quartic curve. The Zernike coefficients of the wavefront error caused by surface error of the primary mirror, position error of the second mirror, surface error of the second mirror, and surface error of the third mirror vary with field along a line or parabolic curve. So by storing the design errors, only 3 wavefront sensors are needed to estimate the wavefront error of any field. Estimation error of the Zernike coefficients is in the order of 10^-5.