Starlight navigation technology is widely used in spacecraft. Celestial navigation is designed for star identification and confirmation of satellite attitudes in the space. Sensors of celestial navigation require hardware-in-the-loop simulation system for ground-testing. A new celestial navigation technology is based on dual-star-sensor for the sake of high accuracy and reliability. Hardware-in-the-loop simulation system for ground-testing generates two celestial scenes and projects them into the dual-star-sensors during navigation process by real-time graphics and simulation technologies according to the satellite’s orientation.
With the increase in application of celestial navigation as well as the advances in computer graphics technology, modeling and simulation of celestial background is widely used in ground-testing of celestial navigation.
Celestial navigation is designed for star identification and confirmation of satellite attitudes in the space. A new celestial navigation technology is based on dual-star-sensor for the sake of high accuracy and reliability. Two star-sensors are set on the satellite, and there is an angle between the light axis of these two star-sensors. So these two star-sensors are designed pointed to the different direction in the space.
Modeling and simulation of celestial background which is used in the ground-testing for dual-star-sensor displays two different celestial scenes during navigation process by real-time graphics technology according to the two sensors’ orientation.
The starlight navigation is considered to be one of the most important methods for spacecraft navigation. Starlight simulation system is a high-precision system with large fields of view, designed to test the starlight navigation sensor performance on the ground. A complete hardware-in-the-loop simulation of the system has been built. The starlight simulator is made up of light source, light source controller, light filter, LCD, collimator and control computer. LCD is the key display component of the system, and is installed at the focal point of the collimator. For the LCD cannot emit light itself, so light source and light source power controller is specially designed for the brightness demanded by the LCD. Light filter is designed for the dark background which is also needed in the simulation.
Infrared resistor arrays perform a vital role in the hardware in the loop testing of infrared seekers. Infrared resistor arrays composed of large numbers of suspended resistor elements are commonly used to produce dynamic two-dimensional images of infrared radiation. Due to inconsistencies in the fabrication process of the resistor arrays, the temperature each resistor elements reaches for a given input voltage is variable and this leads to more significant radiance differences, these differences result in spatially-distributed radiance non-uniformity. Therefore, in order to obtain an available infrared image, non-uniformity correction (NUC) is necessary. In this paper, the non-uniformity characters of the infrared resistor arrays are analyzed base on measured data and then an improved sparse grid method for engineering are discussed and analyzed. First of all, the NUC camera has a strong influence on the effectiveness of the infrared resistor arrays NUC procedure. According to the actual fact and the laboratory condition, we presented an alternative method for collecting resistor arrays intended to reduce the influence causing by the NUC camera. Secondly, based on the measured non-uniformity data, we obtain the response characteristics of the infrared resistor arrays. In each gray level, we take two points or several points correction algorithm to calculate the gain data and the offset data, and then the linear look-up table is established. Finally, through MATLAB we develop the correction software, and we can obtain the driving output conveniently. The result shows that the image quality has a remarkable improvement after non-uniformity correction, the non-uniformity correction flow and algorithm preferably satisfies the requirement of the high confidence infrared imaging simulation.
The first and most essential capability a visible scene projection system must have is low background and high contrast during dynamic simulation. A complex visible scene projection system was developed to meet the above requirements. The complex visible scene projection system mainly consists of the optical fiber subsystem, LCD (Liquid Crystal Display) subsystem, multiple focal plane coupler and the collimation objective. The design and build and details of the system characterization of a prototype complex visible scene projector were summarized.
KEYWORDS: Stars, Star sensors, Computer simulations, Visualization, OpenGL, Image sensors, Space operations, Scene simulation, Computing systems, Navigation systems
The star sensor simulation system is uesed to test the star sensor performance on the ground,which is designed for star identification and spacecraft attitude determnation of the spacecraft. The computer star scene based on the astronomical star chat is generated for hardware-in-the-loop simulation of the star sensor simulation system using by openGL.
Resistor array plays a vital role in emulation of the IR control and guide system. However, its serious nonuniformity confines the range of its application. Therefore, in order to obtain an available IR image, nonuniformity correction (NUC)
is necessary. The traditional method is sparse grid and flood which only take the array’s nonuniformity into account. In
this paper we present an improved sparse grid method which considers the whole system which affects the array’s
nonuniformity by dividing the NUC process into different gray levels. In each gray level, we can take two points or several points to calculate the nonuniformity of every block which is divided before correction. After that, we can have several characteristic curves which will be operated with curve fitting. By this means, we will correct the nonuniformity. At last, through the experiment of a number of images, we find the residual nonuniformity associated with random noise
is about 0.2% after the correction.
The Modified Hybrid-Input-Output (MHIO) phase retrieval algorithm is proposed for wavefront sensing. The results show that the MHIO algorithm significantly outperforms the Modified Gerchberg-Saxton algorithm (MGS) in large noise. However its dynamic-range is lower than MGS algorithm. It also shows that if combine the MGS algorithm with MHIO algorithm, which is called MGS+MHIO algorithm, then it can retain the property of MGS’s high dynamic-range and MHIO’s accuracy so that outperforms either MGS or MHIO algorithm. Repeating simulation results show that MGS+MHIO algorithm improves RMS of phase error obviously in high dynamic range and large noise.
In the process of high-resolution astronomical observation and space optical mapping, the wavefront aberrations caused by atmosphere turbulence effect lead to reduced resolution of optical imaging sensor. Firstly, on the base of influence of atmosphere turbulence effect for the optical observation system, this paper investigates and analyses the development and technical characteristics of deformable mirror, which is the key device of optical wavefront control technology. In this part, the paper describes the basic principles of wavefront control and measurement using the current production line of deformable mirror, including micro-electromechanical systems (MEMS) deformable mirror which is one of the most promising technology for wavefront modulation and Shack-Hartmann wavefront sensors. Secondly, a new method based on the technology of optical wavefront control and the data of optical path difference (OPD) for simulating the effect of optical transmission induced by turbulence is presented in this paper. The modeling and characteristics of atmosphere turbulence effect applied for optical imagery detector of astronomical observation and space optical mapping has been obtained. Finally, based on the theory model of atmosphere turbulence effects and digital simulation results, a preliminary experiment was done and the results verify the feasibility of the new method. The OPD data corresponding to optical propagation effect through turbulent atmosphere can be achieved by the calculation based on the method of ray-tracing and principle of physical optics. It is a common practice to decompose aberrated wavefronts in series over the Zernike polynomials. These data will be applied to the drive and control of the deformable mirror. This kind of simulation method can be applied to simulate the optical distortions effect, such as the dithering and excursion of light spot, in the space based earth observation with the influence of turbulent atmosphere. With the help of the optical wavefront control technology, the optical sensor and ability of space optical detection system for correcting the target image blurred by turbulence of atmosphere can be tested and evaluated in the laboratory.
The imaging through atmospheric turbulence is an inevitable problem encountered by infrared imaging sensors working in the turbulence atmospheric environment. Before light-rays enter the window of the imaging sensors, the atmospheric turbulence will randomly interfere with the transmission of the light waves came from the objects, causing the distribution of image intensity values on the focal plane to diffuse, the peak value to decrease, the image to get blurred, and the pixels to deviate, and making image identification very difficult. Owing to the fact of the long processing time and that the atmospheric turbulent flow field is unknown and hard to be described by mathematical models, dynamic simulation for distortion Image with turbulence atmospheric transmission effects is much more difficult and challenging in the world. This paper discusses the dynamic simulation for distortion Image of turbulence atmospheric transmission effect. First of all, with the data and the optical transmission model of the turbulence atmospheric, the ray-tracing method is applied to obtain the propagation path of optical ray which propagates through the high-speed turbulent flow field, and then to calculate the OPD from the reference wave to the reconverted wave front and obtain the point spread function (PSF). Secondly, infrared characteristics models of typical scene were established according to the theory of infrared physics and heat conduction, and then the dynamic infrared image was generated by OpenGL. The last step is to obtain the distortion Image with turbulence atmospheric transmission effects .With the data of atmospheric transmission computation, infrared simulation image of every frame was processed according to the theory of image processing and the real-time image simulation, and then the dynamic distortion simulation images with effects of blurring, jitter and shifting were obtained. Above-mentioned simulation method can provide the theoretical bases for recovering the blur images and analyzing the turbulence atmospheric transmission effects.
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