In this paper, a whole general design and optimization process is detailedly demonstrated by taking the design and optimization of a 55mm diameter variable curvature mirror(VCM) with a cycloid-like thickness distribution as example. The finite-element analysis to the VCM under each change of main structure parameter is done and analyzed to choose the proper parameter value of each structure to obtain the optimum surface figure accuracy. Finally, the designed VCM can achieve 0.386mm central deflection and RMS 82.84nm within the effective aperture 28.4mm.
Phase diversity technique (PD) can jointly estimate the wavefront aberration and the target image of an optical imaging system. The PD technique reconstructs images by acquiring a focal plane image of optical system and one or more images with known aberrations (often selected defocus). Due to the simple construction of the optical system, the ability to detect discontinuous co-phase errors, and its applicability to both point sources and extended targets, The PD technique is uniquely suited for spatial target imaging applications, especially for the detection of multi-aperture piston errors. However, in a spatially low-illumination environment, Poisson noise as the main noise source of the imaging system seriously affects the accuracy of the reconstructed images. In this paper, we propose a method of phase diversity technique based on a fast Non-local Means (NLM) algorithm for reconstructing single-aperture images or multi-aperture images. For the two cases of single-aperture imaging and multi-aperture imaging with piston errors in spatial low illumination conditions, the method is used to solve the sensitivity problem of Poisson noise during image reconstruction. Numerical simulation results show that our method has significant improvement in structural similarity of the recovered images compared with the traditional phase diversity technique, and also is faster than the common non-local mean algorithm. The combination of this fast non-local means algorithm which using integral images and the phase diversity technique greatly reduce the computation time. The field experimental results and simulation results show good agreement. The new method would be useful in the AO system with active Poisson noise.
Synthetic aperture is the mainstream structure of current astronomical telescopes. However, after the synthetic aperture telescope is deployed in orbit, there will remain tilt and piston error between adjacent segments, which will sharply deteriorate the imaging quality of the optical system. The traditional piston error detection method based on dispersed fringe sensor has the question that it is difficult to detect the piston error within one wavelength, and the detection accuracy is restricted by the detection range. The method in this paper constructs multiple monochromatic light channels by opening windows in different areas on the dispersed fringe pattern, calculating and obtaining the feature value in each window to form a feature vector. Then, the convolutional neural network is introduced to distinguish the feature vector to detect piston error. Among them, the training set construction method adopted in this paper only needs raw data in one wavelength to construct a training set covering the entire detection range. Through simulation, the method proposed in this paper achieves the detection range of [-208λ, 208λ] (λ=720nm), and regardless of the presence of noise, the root mean square value of the detection error does not exceed 17.7nm (0.027λmin, λmin=660nm).
Space-based solar observation has severe requirements for resolution, dynamic range, and signal-to-noise ratio of the camera. In order to acquire high-quality solar image data, this paper proposes a high-resolution electronics system based on Gpixel GSENSE6060 image sensor for space-based solar observation. The system uses XILINX XQ5VFX130T as the timing control of the overall system, with DDR SDRAM to cache the image data, which can realize flexible working mode with the windowing mode of the sensor. Firstly, the principle of system parameter selection are given, and the work characteristics of GSENSE6060 are described, then the triggering and termination of event mode are realized by algorithm. The system has high flexibility and reliability, which is suitable for long-time Full-Disk observation and solar eruptions monitoring. During the flare eruption, a high frame rate acquisition with a resolution of 1024 × 1024 can be realized every 4s for the eruption region, which can be used to acquisition the maximum effective data. Experiments show that the system readout noise is better than 6 e-, in Rolling HDR mode can synthesize 16-bit, resolution of 4608 × 4608 and dynamic range larger than 90dB images, to meet the system design index.
In this paper, the deployment systems of a deployable space telescope for CubeSat are proposed. This telescope can achieve a ground resolution less than 1 meter at an orbital altitude of 400 km. Both the primary and secondary mirrors of it can be stowed in 3U volume(100mm×100mm×300mm)during launching period. The functions of the deployment systems include the locking of the primary and secondary mirrors when stowed, the deployment on-orbit, and the active adjustment of the primary mirror segments after deployment. In this paper, firstly, the optical system of deployable telescope is described, then the deployment systems of the telescope are designed. Finally, the modal analysis is carried out using finite element method.
Nowadays, large aperture space-borne optical camera is one important payload used to capture optical images of space targets based on satellite platform, but many factors could prevent space-borne camera from obtaining satisfactory images. Firstly, vibration during launch, moisture absorption, deflation and violent temperature variation and so on could make the focal plane of space-borne camera deviate from its ideal position. Secondly, space targets are usually distant, moving quite fast and especially noncooperative targets may even appear in unknown distances. In this case, frequent, rapid and precise on-orbit focusing mechanism are indispensable to traditional imaging system, but wave-front coded imaging provides another choice. In wave-front coded imaging system, by introducing a suitably designed phase mask, the optical transfer function will become insensitive to defocus and the clear images similar to diffraction limited ones could be obtained through digital restoration. Therefore in this manuscript, the experimental research is carried out to investigate the effectiveness of wave-front coding technique in realizing high-resolution imaging without introducing any focusing mechanisms. By only adding a cubic phase mask to the exit pupil with diameter of approximately 80mm and keeping other optical-mechanical structures of a prototype large aperture camera with focal length of 6000mm and aperture of 600mm unchanged, the extension of depth of focus could be obtained. In the collimator based testing, the depth of focus of that prototype space-borne camera could be extended 8.5x approximately, which provides another way to realize high-resolution imaging of space targets while designing space-borne optical camera in future.
For large aperture and high-resolution space optical cameras, the focusing requirements caused by different resolution requirements, or the requirements for the segmented primary mirror for deployable telescopes or on-orbit assembly space telescopes, the micro- or nano-metric multi degree of freedom adjusting of the primary mirror or the segment mirror is one of the inevitable development trends of the active optical system. According to the different degrees of freedom involved in the primary mirror adjustment, the micro- or nano-metric multi degree of freedom adjusting displacement scaling mechanisms of the monolithic and segmented primary mirror are studied. The development history and structural characteristics of multi degree of freedom adjusting displacement scaling mechanisms including rigid lever type, gear deceleration type, hydraulic mechanism type and compliant hinge type, as well as their research status and application fields, are introduced. The performance characteristics and applications of various displacement scaling mechanisms are analyzed and compared. Finally, according to the application requirements of space telescopes in the future, the development trend of multi degree of freedom (DOF) adjusting displacement scaling mechanism for segmented primary mirror is proposed.
The Space-based multi-band astronomical Variable Objects Monitor (SVOM) project is a dedicated satellite developed at the cooperation of China and France, aim to make prompt multi-band observations of Gamma-Ray Bursts (GRBs), the afterglows and other high-energy transient astronomical events. The Visible Telescope (VT) is one of the four payloads onboard the SVOM. VT is designed to observe the afterglows of GRBs both in the visible and near infrared bands simultaneously. The telescope can reach a limiting magnitude of +22.5Mv and provide the redshift indicators for high-Z (z<4) GRBs. VT is also designed to measure the Relative Performance Errors (RPEs) for the satellite attitude and orbit control system (AOCS), aiming to improve the pointing stability of the platform during observation. VT adopts a Ritchey-Chrétien (RC) catadioptric optical configuration with a 440mm aperture and uses the dichroic prism before the focal plane to split the incident light into blue (visible) and red (near infrared) band. Two Fine Guidance Sensor (FGS) CCDs are mounted beside the main CCD on the blue band focal plane of VT and provide sub-arcsecond pixel resolution. Fiber reinforced plastic (CFRP) composites is selected as the material of VT’s main structure to ensure enough stiffness and strength during launch. The electrical video processing circuit is carefully designed to make the readout noise below 6e-/pix (rms) in 100s exposure time. Active and passive thermal control are used together to ensure the optical performance and thermoelectric cooler (TEC) is adopted to control the main CCDs working temperature below -65°C to reduce the noise. This paper provides a comprehensive overview of the scientific requirements and the key instrument design aspects of optics, main structure, electrics, thermal control, performance test and validation results of VT.
Exploring exoplanets using stellar coronagraph requires coronagraph with a contrast of 10-10 or even lower, because the difference in light intensity between the planet and its parent star is very large. To this end, we optimized the coronagraph imaging system with Four-Quadrant Phase-Mask (FQPM) proposed by D. ROUAN et al in 2000. The FQPM has the advantages of high extinction efficiency for the coherent light from the main source, low sensitivity to atmospheric turbulence and large dynamic range. This paper proposed an apodizer with continuous transmission and a Lyot stop optimized in conjunction with the apodizer for FQPM coronagraph, which enhance the nulling ability of FQPM to achieve a high contrast ratio of 10-12 at 1.25λ/D and a contrast of 10-13 at larger distance. Moreover, this optimization method can optimize the non-circular symmetric mask, that is, the optimization method is two-dimensional, rather than one-dimensional optimization in the case of circular symmetry. Then we compare the joint optimization with the optimization of the apodizer only, the results show that the former has better diffraction suppression and concentrating ability than the latter, which makes the energy more concentrated and the peak signal obtained on the detector is stronger. In the follow-up work, we will continue to complete the FQPM coronagraph system, such as adding adaptive optical to correct wavefront distortion, adding considerations for manufacturing precision of optical components and so on.
Space telescopes are widely used nowadays with the development of space optics and manufacture technologies. Large aperture of telescope means better resolution and observation. However, due to the carrying capacity and outline dimension of rocket, the aperture of telescope cannot be too large. In order to get the large telescope, more and more scientists and engineers are coming to a new idea that assembling the large space telescope on orbit. First of all, the paper makes an introduction about the concepts and types of on-orbit assembly for telescope. Then paper presents some projects which are being conducted and takes one project as an example to introduce specific implementation methods of on-orbit assembly. What’s more, high precision robots are needed in this process. Therefore, paper also introduces technologies about the robots for space assembly. At last, the paper summarizes the features and technical difficulties in on-orbit assembly of large space telescope. Furthermore, the paper points out the development directions about on-orbit assembly telescope in the future, which can give some help or guidance to engineers.
The detection of exoplanets is a hot topic in international astronomy nowadays. The methods of exoplanets detection are mainly divided into indirect detection and direct imaging. Direct imaging of exoplanets is being pursued by a number of research groups around the world. In this paper, the research status of space-based direct imaging technologies for exoplanets detection is reviewed, and the advantages and disadvantages of related technologies are analyzed and summarized. The most advantageous and promising space-based nulling interferometry technologies are described in detail, including some laboratory verification studies based on ground-based astronomical telescopes. With the continuous development of spacecraft micro-Newton propulsion and high-precision positioning control, ultra-high-precision laser measurement, adaptive optics, integrated optics, etc., space-based direct imaging technologies for exoplanets detection will continue to make breakthroughs.
In this paper, a new type of focusing mechanism for space telescope is designed to compensate defocusing caused by alteration of space condition in orbit. The focusing mechanism is driven by a stepping motor and a worm gear reducer, transmitted by a ball screw and output by a flexible hinge. It has advantages of low mass, small overall size and especially high accuracy that is better than 1 micrometer. As one of main parts of focusing mechanism, the flexible hinge is mounted in the focusing shaft and connected to the nuts of ball screw kinematic pair which has mechanical end stops. The focusing shaft is guided by two couples of thin film boards to ensure the precise displacement along optical axis direction. The secondary mirror frame is connected to the shaft to complete focusing. Firstly, the focusing mechanism is designed, and the design scheme is illustrated in this paper. Then a modal analysis with finite element method for the mechanism is completed. The results show that the dynamic stiffness is high enough and meets the requirement.
Linear rolling guide have widely used in precision machinery today, with significant advantages such as high precision, low traction and low wear. Research on the dynamic characteristics of precision linear rolling guide became very important for space applications due to the continuous improvement of the manufacturing level of high-precision equipment. The THK's RSR small precision guide is studied in this research. The model of guide joint is established by optimized tandem damping element with the finite element method to simulate the dynamic stiffness and ball mass of the guide joint. The analytical formula based on Hertzian contact theory is adopted in this research to obtain the dynamic parameters of the guide joint. Accomplishing the the dynamic simulation analysis of the precision guide based on the finite element method by MSC.Patran & Nastran software.
Fourier ptychography (FP) has emerged as a powerful tool to improve spatial resolution. In order to apply FP technique to long-distance imaging for example remote sensing, many factors have to be overcome, such as diffraction, noise, turbulence and so on. In this paper, we mainly aims at studying the influence of atmospheric turbulence on FP technique, and using iterative algorithms to restore high-legible image and eliminating the residual errors, so it will meet or reach the diffraction limit of imaging system. The optical imaging systems which work in atmospheric circumstance will face the problem of imaging through atmospheric turbulence, which causing the blurring of image and badly impact the imaging capability of optical systems. We combine the FP with the theory of adaptive optics to achieve the effective recovery of the long-range target, which is subject to the effect of atmospheric turbulence. In this work, we firstly introduce a Fourier Series (FS) atmospheric phase screen generator to simulate the atmospheric-induced wave front phase distortions and represent the wave front phase as a two dimensional periodic function. Both the spatial and temporal correlations between wave-front phase screens separated by time and/or angle are properly modeled. And using the adaptive optics, we complete the correction of the atmospheric turbulence in large distance imaging through the developed algorithm. Then we propose using laser arrays coupled with coherent illumination as an effective method of improving spatial resolution in long distance images. We emulate a laser arrays realized by optical fiber conduction and also show that appropriate phase retrieval based reconstruction algorithm which can be used to effectively recover the lost high resolution details from the multiple low resolution acquired images. Finally we analyze the effects of the atmospheric turbulence on the reconstructed image quality. The results prove that under the influence of atmospheric turbulence at outer scale of 1-m, inner scale of 0.1-m, Fourier ptychographic reconstruction can obtain good image quality for object 200 meters far away. The spatial resolution is increased six-fold.
Variable curvature mirror (VCM) is a long-history technique used to correct the defocus and spherical aberrations caused by thermal lens effect in solid-state laser. In recent years, the probability of VCM in realizing non-moving element optical zoom imaging has been paid much attention and how to generate a large enough saggitus variation while still maintaining good enough surface figure accuracy is the research hot topic. In this manuscript, two kinds of VCM has been studied and the advantages of pressurization actuation based VCM having variable mirror thickness has been confirmed. Compared with the traditional annular force actuation based VCM with constant mirror thickness, the pressurization actuation based one having variable mirror thickness is capable of providing a saggitus variation of larger than 35um and still maintaining its surface figure accuracy superior to 1/10λ(λ=632.8nm). Besides that, it is found that spherical aberration plays a main role in leading to the degradation of surface figure accuracy and the surface figure accuracy at extreme curvature could be improved to about 1/40λ(λ=632.8nm) by only removing spherical aberration. Therefore, when applying pressurization actuation based VCM to realize non-moving element optical zooming, the wavefront sensing and subsequent digital correction to eliminate the spherical aberration will become a necessary step.
The 470mm lightweight primary mirror of a space telescope is made of ULE, and supported on a titanium hexapod. The hexapod consists of six bond pads, six titanium struts with flexures and three support parts. The hexapod provides a quasi-kinematic mount for the lightweight mirror, and the flexures are used to isolate optical elements from the mechanical and thermal deformations of the support structure, then the surface figure distortion of the mirror is minimized. In this paper, the finite element method is used to analyze the static and dynamic characteristics of the mirror assembly. Then, six pads are bonded to the mirror and the support hexapod is assembly. The vertical optical test of the primary mirror assembly is implemented. Vibration test of the mirror assembly is performed, and the test results are consistent with the results of the finite element analysis.
Space optical remote sensors play an important role in earth observation, space situation awareness and astronomy exploration. The optical resolution of space remote sensing system is constantly improved. Several new techniques for realizing ultra-high resolution of spatial optical remote sensors are reviewed. The research status and application prospects of these new technologies are discussed, mainly including synthetic aperture optical system, Fourier ptychography and intensity correlation imaging. The critical technical problems of these new technologies in spacebased and ground-based optical remote sensing engineering are summed up.
Super-resolution image reconstruction is a process to reconstruct high-resolution images from shifted, low-resolution, degraded observations. In the last two decades, a variety of super-resolution methods have been proposed. These methods are usually very sensitive to their assumed model of data and noise, which limits their utility. This paper reviews some of these methods and addresses their shortcomings. We propose an alternate approach using 1norm minimization and robust regularization based on a bilateral prior to deal with different data and noise models. This computationally inexpensive method is robust to errors in motion and blur estimation and results in images with sharp edges. Experimental results confirm the effectiveness of our method and demonstrate its superiority to other super-resolution methods.
In this paper, a new type of calibration mechanism based on worm drive is presented for a space telescope. This calibration
mechanism based on worm drive has the advantages of compact size and self-lock. The mechanism mainly consists of
thirty-six LEDs as the light source for flat calibration, a diffuse plate, a step motor, a worm gear reducer and a
potentiometer. As the main part of the diffuse plate, a PTFE tablet is mounted in an aluminum alloy frame. The frame is
fixed on the shaft of the worm gear, which is driven by the step motor through the worm. The shaft of the potentiometer is
connected to that of the worm gear to measure the rotation angle of the diffuse plate through a flexible coupler. Firstly, the
calibration mechanism is designed, which includes the LEDs assembly design, the worm gear reducer design and the
diffuse plate assembly design. The counterweight blocks and two end stops are also designed for the diffuse plate assembly.
Then a modal analysis with finite element method for the diffuse plate assembly is completed.
For its compact size and light weight, space telescope with deployable support structure for its secondary mirror is very
suitable as an optical payload for a nanosatellite or a cubesat. Firstly the realization of a prototype deployable space
telescope based on tape springs is introduced in this paper. The deployable telescope is composed of primary mirror
assembly, secondary mirror assembly, 6 foldable tape springs to support the secondary mirror assembly, deployable
baffle, aft optic components, and a set of lock-released devices based on shape memory alloy, etc. Then the deployment
errors of the secondary mirror are measured with three-coordinate measuring machine to examine the alignment accuracy
between the primary mirror and the deployed secondary mirror. Finally modal identification is completed for the
telescope in deployment state to investigate its dynamic behavior with impact hammer testing. The results of the
experimental modal identification agree with those from finite element analysis well.
Ground-based optical detection of low-dynamic vehicles in near-space is analyzed to detect, identify, and track high-altitude balloons and airships. The spectral irradiance of a representative vehicle on the entrance pupil plane of ground-based optoelectronic equipment was obtained by analyzing the influence of its geometry, surface material characteristics, infrared self-radiation, and the reflected background radiation. Spectral radiation characteristics of the target in both clear weather and complex meteorological weather were simulated. The simulation results show the potential feasibility of using visible–near-infrared (VNIR) equipment to detect objects in clear weather and long-wave infrared (LWIR) equipment to detect objects in complex meteorological weather. A ground-based VNIR and LWIR optoelectronic experimental setup is built to detect low-dynamic vehicles in different weather. A series of experiments in different weather are carried out. The experiment results validate the correctness of the simulation results.
In this paper, a new type of lightweight passive deployment mechanism based on the tape spring and the shape memory alloy is presented for the secondary mirror of a deployable space telescope. In this passive deployment mechanism for the secondary mirror, the high elastic potential energy of the folded tape springs is used as driving force when the support structure is extended, and the high stiffness characteristics of the circular arc cross section of the tape spring can be used to achieve structure self-locking after deployment. Then a deployable space telescope combined with lightweight passive deployable mechanism for the secondary mirror is designed for applying to nanosatellite imaging. Furthermore, a lock-release device is designed to achieve the function of locking the folded structure and releasing on orbit by taking advantage of the phase transformation characteristics of shape memory alloy with temperature changing. Finally, the correction method for the deployment error of secondary mirror is discussed. The temperature of the tape springs is controlled respectively to make a required length change. This can achieve the purpose of adjusting the position of the secondary mirror and improve the deployment accuracy.
With the gradual development of micro-satellite technology and the extension of application field of earth observation technology, researchers show more concern and attention on how to obtain high-resolution images with microsatellite platform equipped with space telescope. Such microsatellites require the space telescopes with small volume, low mass, and low cost. Deployable telescope is a good choice to meet these requirements, and it has the same capabilities as the traditional space telescope. We investigate a space telescope with smart self-deployable structure. The telescope is folded before launch, the distance between primary mirror and secondary mirror becomes short and the volume of the telescope becomes small, and the telescope extends to its working configuration after it is in orbit. The deployable structure is one of the key techniques of deployable space telescope, and this paper focuses on the design of a self-deployable structure of the secondary mirror. There are mainly three parts in this paper. Firstly, the optics of the telescope is presented, and a Ritchey-Chretien (RC) type optical system is designed. Secondly, the self-deployable structure is designed and the finite element method (FEM) is used to analyze dynamics of the extended telescope. Thirdly, an adjusting mechanism with six degrees of freedom to correct the misalignment of the secondary mirror is investigated, and the kinematics is discussed.
One space-based astronomy telescope will observe astronomy objects whose brightness should be lower than 23th magnitude. To ensure the telescope performance, very low system noise requirements need extreme low CCD operating temperature (lower than -65°C). Because the satellite will be launched in a low earth orbit, inevitable space external heat fluxes will result in a high radiator sink temperature (higher than -65°C). Only passive measures can’t meet the focal plane cooling specification and active cooling technologies must be utilized. Based on detailed analysis on thermal environment of the telescope and thermal characteristics of focal plane assembly (FPA), active cooling system which is based on thermo-electric cooler (TEC) and heat rejection system (HRS) which is based on flexible heat pipe and radiator have been designed. Power consumption of TECs is dependent on the heat pumped requirements and its hot side temperature. Heat rejection capability of HRS is mainly dependent on the radiator size and temperature. To compromise TEC power consumption and the radiator size requirement, thermal design of FPA must be optimized. Parasitic heat loads on the detector is minimized to reduce the heat pumped demands of TECs and its power consumption. Thermal resistance of heat rejection system is minimized to reject the heat dissipation of TECs from the hot side to the radiator efficiently. The size and surface coating of radiator are optimized to compromise heat reject ion requirements and system constraints. Based on above work, transient thermal analysis of FPA is performed. FPA prototype model has been developed and thermal vacuum/balance test has been accomplished. From the test, temperature of key parts and working parameters of TECs in extreme cases have been acquired. Test results show that CCD can be controlled below -65°C and all parts worked well during the test. All of these verified the thermal design of FPA and some lessons will be presented in this paper.
Benefiting from low cost, light weight and reduced volume in launch, deployable optical telescopes will be extensively applied in microsatellites. As a result of manufactured tolerance and external disturbance, the secondary mirror can’t arrive at designed position precisely after a deployable telescope is unfolded. We investigate an adjustment system with six degrees of freedom based on hexapod structure to solve this problem. There are mainly four parts in this paper. Firstly, the adjustment methods of deployable telescopes for microsatellites are introduced. Generally several kinds of optical components can be adjusted to align a deployed telescope: primary mirror, tip/tilt mirror and secondary mirror. Due to its high sensitivity and convenience, the secondary mirror is chosen to collimate the optical system of the telescope. Secondly, an adjustment system with hexapod structure is designed for a secondary mirror with 85 mm diameter. After comparing the characteristics of step motors, piezo actuators and voice coil motors (VCMs), VCMs are selected as the linear actuators. By using optical gratings as displacement sensors in the system, we can make closed-loop control come true. The hexapod structure mainly consists of 6 VCMs, 6 optical gratings and 6 oblique legs with flexible hinges. The secondary mirror adjustment system is 83 mm in diameter and 55 mm high. It has tip/tilt rotational ranges of ±2.205° with resolution of better than ±0.007°, and translational ranges of ±1.545 mm with resolution of better than ±0.966 μm. Thirdly, the maximum stress and the maximum deformation in the adjustment system are computed with finite element method. At last, the kinematics problems of the adjustment system are discussed.
Signal-to-noise ratio (SNR) is an important parameter of infrared detection system. SNR of infrared detection system is determined by the target infrared radiation, atmospheric transmittance, background infrared radiation and the detector noise. The infrared radiation flux in the atmosphere is determined by the selective absorption of the gas molecules, the atmospheric environment, and the transmission distance of the radiation, etc, so the atmospheric transmittance and infrared radiance flux are intricate parameters. A radiometric model for the calculation of SNR of infrared detection system is developed and used to evaluate the effects of various parameters on signal-to-noise ratio (SNR). An atmospheric modeling tool, MODTRAN, is used to model wavelength-dependent atmospheric transmission and sky background radiance. Then a new expression of SNR is deduced. Instead of using constants such as average atmospheric transmission and average wavelength in traditional method, it uses discrete values for atmospheric transmission and sky background radiance. The integrals in general expression of SNR are converted to summations. The accuracy of SNR obtained from the new method can be improved. By adopting atmospheric condition of the 1976 US standard, no clouds urban aerosols, fall-winter aerosol profiles, the typical spectrum characters of sky background radiance and transmittance are computed by MODTRON. Then the operating ranges corresponding to the threshold quantity of SNR are calculated with the new method. The calculated operating ranges are more close to the measured operating range than those calculated with the traditional method.
Microsatellites will be widely applied as an earth-observing platform in coming future for their low costs. Such satellite
missions require optical payloads with low cost, low mass and small volume. In order to meet these requirements, one
way is to develop deployable telescopes. They not only maintain the capabilities of the traditional non-deployable
telescopes, but also have compacter launch volume and lighter weight. We investigate a telescope with precise
deployable structure based on coilable tensegrity. Before launch, the secondary mirror support structure is coiled, and
when the satellite is in orbit, the secondary mirror is deployed with the elastic strain energy from the coiled longerons.
There are mainly three parts in this paper. Firstly, the telescope optics is presented. A Ritchey-Chretien (RC) type optical
system with 150mm aperture is designed. Secondly, the deployable telescope structure is designed for the RC system.
The deployable structure mainly consists of coilable longerons, batten rings, and diagonal stringers. The finite element
method (FEM) is used to analyze the dynamics of the unfolded telescope structure. Thirdly, the adjusting mechanism for
secondary mirror is discussed. Piezoelectric actuators can be used to achieve remote alignment to improve the
performance of the imaging system.
As one type of the deployable telescope, the deployable space telescope under researching uses tape springs as the
support structure of secondary mirror. Before launch, the support structure of secondary mirror is folded, and when on
orbit the structure is deployed. Usually the secondary mirror is not on the nominal position after deploying, so the
alignment of the secondary mirror is needed. To achieve this we need to obtain the deployment errors. So the measuring
of secondary mirror deployment errors of thus deployable telescope is an important topic. In this paper, we designed an
accurate measuring system based on position sensitive detectors (PSDs) to measure the deployment errors, through
measuring the six-degree-of-freedom motions of the secondary mirror. The measuring system contains 3 twodimensional
PSDs, 3 laser diodes and 3 small mirrors. In order to resolve the deployment errors, the equations linking
the PSD readings and the six-degree-of-freedom displacement of the secondary mirror were deduced. These equations
are solved through a numerical method. Finally, we did measuring experiments on a deployable prototype. The
experimental results show that this deployable prototype has deployment errors about 100um.
A space telescope containing two CCD cameras is being built for scientific observation. The CCD detectors need to
operate at a temperature below -65°C in order to avoid unacceptable dark current. This cooling is achieved through
detailed thermal design which minimizes the parasitic load to 2K×4K array with 13.5 micron pixels and cools this
detector with a combination of thermo electric cooler(TEC).
This paper will describe detailed thermal design necessary to maintain the CCD at its cold operating temperature while
providing the means to reject the heat generated by the TECs. It will focus on optimized techniques developed to manage
parasitic loads including material selection, surface finishes and thermal insulation. The paper will also address analytical
techniques developed to characterize TEC performance. Finally, analysis results have been shown the temperature of key
parts.
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