Research On The Application Technology Of The Large-Aperture Collimator For Space Optical Remote Sensor Test

With the development of space optical remote sensor continuously, therequirements of technical performance parameters was higher and higher. In order toachieve higher ground resolution, the aperture and focal length of the space opticalremote sensor was increased gradually. A series of new problems of the space opticalremote sensor test and image quality evaluation work have been brought, because thetechnique factors were changed. For example, while the aperture and focal length ofoptical remote sensor were increasing, larger diameter and longer focal lengthcollimators were needed to test and image quality evaluate for optical remote sensor.Collimators of larger aperture and longer focal length also have higher requirementsfor image quality, focal plane position accuracy and environment stability. However,the guarantees included the size of collimator diameter and focal length, collimatorimage quality, collimator focal plane position accuracy and the stability of testenvironment would be difficult to achieve because of the gradual improvement ofspace optical remote sensor technology parameter. Test and image quality evaluation on the ground are the most basic and important work for space optical remote sensor.These works determine whether optical remote sensor can work on-orbit or finishspecified missions for scientific research and military. Therefore, the research on largeaperture collimator related technical problems is great significant for space opticalremote sensor test on the ground.This paper proposes a new research idea that reduced the focal length selectionrequirement of large aperture collimator for high costs for manufacture, adjustment,operation and maintenance of large aperture and long focal length collimator.Traditional selection requirements of collimator parameters were studied, and focallength requirement was analyzed and discussed as emphasis. Using collimators ofdifferent focal length, different wave aberration and different defocusing amount toconduct simulation image quality evaluation experiment. The experimental resultsshow that using collimator which has2times focal length of optical remote sensor totest, the drop of optical image quality results was controlled in2%. It is more effectiveto save cost and realize reasonable configuration of scientific research resourcescompare with using collimator which has3~5times focal length of optical remotesensor.Test environment also can affect the test results of optical remote sensor exceptthe internal factors of collimator, because collimator would has different imagequality in different environment. In order to solve this problem, this paper analyzesand research on several kinds of main environmental factors, and determine that thereason for image quality fluctuation of collimator is air disturbance. And theexperimental results show that the forcible convection method can restrain the airdisturbance effect and make image quality reach average level(λ/25) in vacuumenvironment for collimator. It is effective to guarantee the accuracy of optical testresult for space optical remote sensor.The paper also proposes a new method that applied Zernike polynomial toeliminate wave aberration which imported by collimator in optical test result. Themethod can get the real wavefront of optical system under test, through wavefrontoperation of collimator and whole system. According to the characteristics of the ground optical test for space optical remote sensor, the paper conducted a simulationexperiment in ZEMAX. The experimental results show that optical system simulationwavefront which obtained by using this method had wavefront PV error of0.0032λand wavefront RMS error of0.0003λ compared with the system wavefront under test.Using collimator of150mm diameter,1597mm focal length and lens of50mm focallength to conduct experiment, the results showed that using this method to obtain theoptical system simulation wavefront had wavefront PV error of0.0016λ andwavefront RMS error of0.0009λ compared with the lens under test. This resultconforms to the simulation experiment result. Therefore, this method can effectivelyeliminate wave aberration introduced by large aperture collimator and obtain the realoptical performance of optical remote sensor.Defocusing is most likely to appear and seriously affect optical test result ofoptical remote sensor, except the manufacture and installation error of collimator. Inspace environment simulation experiment, large-aperture collimator is most likely toappear defocusing for the severe changing of temperature and air pressure. This paperproposes a kind of auto-collimation relative test technology based on pentaprism forsolving the problems that the defocusing amount measure in vacuum had somecharacteristics included difficult to test, low accuracy and no real-time. Theimplementation method of this technology was explained in detail. The major systemerror introduced by pentaprism was analyzed and corrected. Using a collimator of18m diameter and700mm focal length to conduct experiment. The result showed thatfocal plane position test precision can reach150μm and verified the focal plane testability of this technology in real time.This paper researched lots of technical problems which were caused by largeaperture collimator in space optical remote sensor ground test, and it was a newattempt to research on collimator application technology.