| International cooperation project,the Thirty Meter Telescope(TMT),is also known as Giant Steerable Science Mirror(GSSM).The diameter of GSSM is 3.5m ×2.5 m,which is the largest planar mirror in the world.For learning and understanding,a 1:4 prototype(Giant Steerable Science Mirror Prototype GSSMP)was built in the Changchun Institute of Optics,Fine Mechanics and Physics,Chinese Academy of Sciences.For the alignment and metrology of GSSM,the error analysis and budget of GSSM investigated by normalized Point Source Sensitivity(PSSn)was proposed by the TMT team.By researching on the all-frequency domain evaluation properties of PSSn,and the relationship between PSSn and other evaluation indexes,we chose PSSn as the performance specification of GSSM.After that,the GSSM mirror figure testing method,the combination of sparse aperture testing and Ritchey-Common method,was discussed.For GSSM center of gravity(C.G.)measurement,when considering its large size,the static equilibrium method is chosen to estimate its C.G.position.With the laser tracker as the measuring instrument,this paper combines the non-uniform Sphere-Mounted Retro-reflector(SMR)to obtain the GSSM calibration data with higher precision.According to the Jitter measurement requirements,the Jitter's definition,detecting method and analysis method are investigated to realize the Jitter measurement by high-precision accelerometers.Through the dynamical testing of GSSM,the dynamic characteristics of the system are analyzed,and the estimation of the internal vibration of GSSM is obtained by the inversion of the Frequency Response Function(FRF).Firstly,the advantages of PSSn as an all-frequency domain evaluation index are discussed.Then,Zernike polynomials were used for the system static error analysis and the influence of dynamic error was studied by combining the Optical Transfer Function(OTF)and power spectral Density(PSD).Secondly,the error of Ritchey-common sparse aperture testing was studied,and the influence on PSSn was 0.9759 in the GSSMP test.A Warping Harness semi-active correction simulation was carried out,and the sparse sampling PSSn of GSSMP rose from 0.1654 to 0.2548,which was close to the limit of PSSn in this sampling mode.Thirdly,for GSSM C.G.testing,mass of GSSMP is 805.80 kg,and the position of GSSMP C.G.is(-7.169 mm,12.900 mm,526.000 mm).The position accuracy of 0.50 mm.Then,the GSSM pointing error is calibrated by laser tracker.The positioning error of the tilt axis is 1?m,and 4.6?m for rotation axis.After that,the Angle measurement error of two different arrangement SMRs was compared.For GSSMP,the measurement error of single SMR is 23.7".The error of uniform SMR distribution is 11.5",and the error of the four un-uniform SMR is 9.04,"corresponding PSSn is 0.9916.After that,GSSM jitter characteristics were measured by accelerometers For the GSSMP rotation axis,the Jitter is 14.1432 mas and the tilt axis is 20.7475 mas.The corresponding PSSn is 0.9992 and 0.9967.The jitter of the GSSMP were obtained by the frequency domain integration,and then the Jitter was 0.0797?m along the mirror normal line direction,and the corresponding PSSn was 0.9875.Finally,the GSSM dynamical model was studied,and the system FRF under different zenith Angle was obtained.For the declining of system optical relay ability caused by vibration,the numerical method was used.The modal test of GSSMP was carried out by hammer testing.Its first-order modal was 35.2 Hz,and its corresponding mode was the swinging of GSSMP Yoke.With the acceleration sensor and GSSMP FRF,the internal force of GSSMP was tested as 0.0033N(after the filtering).Under the influence of internal vibration,GSSMP PSSn decreased from 0.9995 to 0.9991... |
PDF Full Text Request