During the machining of large aperture lightweight space mirror, the mirror figure consistency between ground test and space mission is a problem. In order to effectively control the supporting deformation effect on test results in gravity environment, in view of a 1.2-m space mirror with back blind holes, a supporting method for optical axis horizontal test is proposed, with this method, mirror under test is positioned by three center hole surfaces and supported by six external hole surfaces. The effect of deformation caused by different supporting force value, area and position is analyzed by finite element method, the simulation results show that this supporting method can control the mirror supporting deformation within PV0.035λ rms0.005λ. The actual supporting system uses soft expansion mandrel to control the mirror position and pneumatic lever to realize the floating support. In order to ensure that the support force can evenly distribute on the contact surface, a pressure mapping system is adopted to measure the interface pressure between the mirror blind holes and the soft supporting pads for the first time. This method can meet the test requirements of rms=1/40λ mirror and provides a technical support for high precision test of large aperture space mirror with back blind holes.
Aiming at the concave aspheric mirror with large aperture or large relative aperture, catadioptric null compensating test is proposed. To carry out the null compensation test of concave aspheric surface, double lens and single mirror are used. The catadioptric compensator is set in front of curvature center of tested mirror. Based on third-order aberration theory, making spherical aberration coefficient S1=0, the calculating formulas of initial configuration structure parameters are derivated. This novel testing method is studied by design of catadioptirc compensators for the following three situations, the design results and drawings are given: 1) mirrors(F/2, e2=1.05) with different apertures; 2) mirrors(Φ0=2000mm, e2=1.05) with different relative apertures; 3) to design catadioptric compensators for mirror (Φ0=2000mm, e2=1.05, r0=8000mm) with different inner obscuration ratio. The analysis shows that this new method is available to test concave aspheric mirror with large aperture or large relative aperture.
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