Due to the ability to achieve a wide-diffraction-limited field of view, three-mirror anastigmat (TMA) telescopes are widely used in many applications that demand high imaging quality and detection accuracy, in which polarization aberrations play increasingly important roles. In this paper, polarization properties of on-axis elements and those of off-axis elements are analyzed and compared via polarization aberration theory. Then, an on-axis TMA (OTMA) telescope and an off-axis TMA (FTMA) telescope are designed and optimized to be diffraction-limited systems in parallel. Their constructional parameters and first-order parameters are set to be identical. Via polarization ray tracing, polarization aberrations of the 2 telescopes are obtained and compared in terms of diattenuation map, retardance map, Jones pupil, Pauli pupil, and amplitude response matrix. Results demonstrate that polarization aberrations are closely related to the structural features of mirrors and telescopes. The diattenuation and retardance maps of power mirrors in the OTMA telescope are rotationally symmetric, while those in the FTMA telescope are not. A Maltese cross appears in off-diagonal elements of the Jones pupil of the OTMA telescope and disappears in the FTMA telescope. Amplitude response matrices of polarization crosstalk components in the OTMA telescope are with a four-peak structure, while those in the FTMA telescope are with a two-peak structure. After quantitative comparisons, it is found that diattenuation in the OTMA telescope is smaller than that in the FTMA telescope as well as in the cases of retardance and polarization crosstalk. There are also similarities between the 2 TMA telescopes. Polarization aberrations of secondary mirrors (SM) are greater than those of both primary mirrors (PM) and tertiary mirrors (TM). What is more, polarization aberrations of TM are so small that they can be ignored safely. The numerical sum of Pauli coefficients of PM, SM, and TM is nearly identical to the cumulative Pauli coefficients. Hence, the TMA telescopes can be treated as weak polarization elements. This work compares polarization aberration performance of on- and off-axis TMA telescopes and can provide important references for designing and optimizing telescopes in which polarization aberrations matter.

It is necessary for large aperture space telescopes to achieve high measurement accuracy for mechanical reference mounting surfaces, complex deformation conditions, and difficulty in describing spatial geometric properties. In this manuscript, we propose a measurement method for evaluating the deformation of the trusses structure by fusing multiple sources of data. The multi-source data are obtained from the theodolite, laser tracker, and photogrammetry systems. The datum alignment of the laser tracker and photogrammetry coordinate systems is achieved by establishing the transition coordinate system method of the datum platform, and the alignment accuracy (3σ) is about 8.8″, 5.1″ and 4.2″. Using the laser tracker to establish the relationship between the cubic mirror coordinate system and the geometric coordinate system of the mounting part, the fast and high-precision measurement of the mounting angle of the cubic prism is realized, and the measurement accuracy reaches 2″. The data from multiple sources are fused through datum transfer and alignment to establish a cosine matrix transfer chain between the mechanical characteristic coordinate system of each component and the transition coordinate system of the datum platform, and the Eulerian rotation angle is obtained to describe the angular relationship between the components after solving. Based on the Monte Carlo mathematical error modeling analysis, the datum transfer and alignment simulations were carried out, and related experiments were conducted. The experiments show that the transfer error (3σ) of the XYZ rotation angle is less than 20.6″ after the datum transfer, the maximum error is within 3″ compared to the simulation results, and the deviation of the comparison photographic measurement data is less than 7.6″. The datum transfer method combined with photogrammetry can describe the deformation trend of large-size trusses under different load conditions more objectively and reasonably.