Search Results (24)

Large-area membrane spacecraft, such as solar sails, must be tightly stowed before launch. However, excessive folding readily induces plastic creases that impede full on-orbit deployment and degrade membrane surface accuracy. To overcome this challenge, this study aims to quantify the mechanical response of Kapton films during folding and to establish a reliable welding process for post-fold sail membranes. Based on the theory of linear elastic engineering, an S-shaped folding model was theoretically simplified to obtain the relationship between the rebound force P of adjacent contact thin films and the thin-film spacing h. Then, the Kapton film folding process was numerically simulated based on the implicit static method by using ABAQUS. The stress–strain curves and mechanical parameters of the thin films measured through uniaxial tensile tests are applied to theoretical and numerical results. It is found that the P-h curves obtained by the theoretical, numerical, and experimental method have good consistency. Step-loaded creep tests show that, after 6 h, the mean spacing reductions Δh are 0.43 mm for 50 µm thin films and 1.05 mm for 125 µm thin films, matching simulation results within 3%. Finally, uniaxial tensile tests are conducted on the welded thin films to measure the strength of the thin-film welds under different welding temperatures and pressures. The tensile force and elongation required to eliminate weld wrinkles are also measured to explore the welding connection of Kapton film. Further, for 50 µm thin films with a 10 mm weld width, eliminating welding-induced wrinkles requires a tensile force of 9.61 N and an elongation of 0.43%. Full article

The on-orbit geometric calibration accuracy of high-resolution space cameras directly affects the application value of Earth observation data. Conventional on-orbit geometric calibration methods primarily rely on ground calibration fields, making it difficult to simultaneously achieve high precision and real-time monitoring. To address this limitation, we, in collaboration with Tsinghua University, propose a high-precision, real-time, on-orbit geometric calibration system based on active optical monitoring. The proposed system employs reference lasers to integrate the space camera and the star tracker into a unified optical system, enabling real-time monitoring and correction of the camera’s exterior orientation parameters. However, during on-orbit operation, the space camera is subjected to a complex thermal environment, which induces thermal deformation of optical elements and their supporting structures, thereby degrading the measurement accuracy of the geometric calibration system. To address this issue, this article analyzes the impact of temperature fluctuations on the focal plane, the reference laser unit, and the laser relay folding unit and proposes athermalization design optimization schemes. Through the implementation of a thermal-compensated design for the collimation optical system, the pointing stability and divergence angle control of the reference laser are effectively enhanced. To address the thermal sensitivity of the laser relay folding unit, a right-angle cone mirror scheme is proposed, and its structural materials are optimized through thermo–mechanical–optical coupling analysis. Finite element analysis is conducted to evaluate the thermal stability of the on-orbit geometric calibration system, and the impact of temperature variations on measurement accuracy is quantified using an optical error assessment method. The results show that, under temperature fluctuations of 5 °C for the focal plane and the reference laser unit, 1 °C for the laser relay folding unit, and 2 °C for the star tracker, the maximum deviation of the system’s measurement reference does not exceed 0.57″ (3σ). This enables long-term, stable, high-precision monitoring of exterior orientation parameter variations and improves image positioning accuracy. Full article

The Joint Polar Satellite System (JPSS) is a collaborative program between NASA and NOAA to provide scientific measurements from multiple polar-orbiting satellites. The development, testing, launch, and operation of the satellites is jointly overseen by NASA and NOAA, with NASA responsible for developing and building instruments, spacecraft, ground systems, and launching into orbit. While three VIIRS instruments are currently on-orbit, spacecraft integration of the two VIIRS instruments planned for launch on the JPSS-3 and -4 spacecraft is ongoing. The latest build in the series, set to be launched on the JPSS-4 platform, recently completed its main ground calibration program at the vendor facility. This program covered a comprehensive series of performance metrics designed to ensure that the instrument can maintain its calibration successfully on-orbit. In this paper, we present the results from the radiometric calibration process, which includes metrics such as dynamic range, signal-to-noise ratio, noise equivalent differential temperature, polarization sensitivity, scattered light response, relative spectral response, response versus scan angle, and crosstalk. All key metrics have met or exceeded their design requirements, with some minor exceptions. Also included are comparisons with previous VIIRS instruments, as well as a description of their expected performance once on-orbit. Full article

This paper describes the benefits of using a microwave radiative transfer model (RTM) to improve the inter-satellite radiometric calibration (XCAL) between two independent satellite microwave radiometers. Because this work was sponsored by the NASA Global Precipitation Mission, the emphasis of this paper is on radiometer channels that are used for atmospheric precipitation retrievals; however, this technique is applicable for microwave remote sensing in general, over a wide range of satellite remote-sensing applications. An XCAL example is presented for the NASA Global Precipitation Mission, whereby the GPM Microwave Imager is used to calibrate another microwave radiometer (TROPICS) within the GPM constellation of satellites. This approach involves intercomparing near-simultaneous measured brightness temperatures from these radiometers viewing a common homogeneous ocean scene. The double difference between observed and theoretical brightness temperature, derived using a radiative transfer model, is used to establish a radiometric calibration offset or bias. On-orbit comparisons are presented for two different approaches, namely, with and without the aid of the RTM. The results demonstrate significant improvements in the XCAL biases derived when using the RTM, and this is especially beneficial when one radiometer produces anomalous brightness temperatures. Full article

The periodic rotation of the Ocean Color and Temperature Scanner (OCTS) introduces jitter errors in the HaiYang-3A (HY-3A) satellite, leading to internal geometric distortion in optical imagery and significant registration errors in multispectral images. These issues severely influence the application value of the optical data. To achieve near real-time compensation, a novel jitter error estimation and correction method based on multi-source attitude data fusion is proposed in this paper. By fusing the measurement data from star sensors and gyroscopes, satellite attitude parameters containing jitter errors are precisely resolved. The jitter component of the attitude parameter is extracted using the fitting method with the optimal sliding window. Then, the jitter error model is established using the least square solution and spectral characteristics. Subsequently, using the imaging geometric model and stable resampling, the optical remote sensing image with jitter distortion is corrected. Experimental results reveal a jitter frequency of 0.187 Hz, matching the OCTS rotation period, with yaw, roll, and pitch amplitudes quantified as 0.905”, 0.468”, and 1.668”, respectively. The registration accuracy of the multispectral images from the Coastal Zone Imager improved from 0.568 to 0.350 pixels. The time complexity is low with the single-layer linear traversal structure. The proposed method can achieve on-orbit near real-time processing and provide accurate attitude parameters for on-orbit geometric processing of optical satellite image data. Full article

The Joint Polar Satellite System 3 (JPSS-3) and -4 (JPSS-4) Visible Infrared Imaging Radiometer Suite (VIIRS) instruments are the last in the series (S-NPP VIIRS launched in October 2011, JPSS-1 VIIRS launched in November 2017, and JPSS-2 VIIRS launched in November 2022) of highly advanced polar-orbiting environmental satellites. Both instruments underwent a comprehensive sensor-level thermal vacuum (TVAC) testing at the Raytheon Technologies El Segundo facility to characterize the spatial, spectral, and radiometric aspects of the VIIRS sensor performance. This paper focuses on the radiometric performance of the 14 reflective solar bands (RSBs) that cover the wavelength range from 0.41 to 2.3 µm. Key instrument calibration parameters such as instrument gain, signal-to-noise ratio (SNR), dynamic range, and radiometric calibration uncertainty were derived from the TVAC measurements for both the primary and redundant electronics at three instrument temperature plateaus: cold, nominal, and hot. This paper shows that all the JPSS-3 and -4 VIIRS RSB detectors have been well characterized, with key performance metrics comparable to the previous VIIRS instruments on-orbit. The radiometric calibration uncertainty of the RSBs is within the 2% requirement, except in the case of band M1 of JPSS-4. Comparison of the radiometric performance to sensor requirements, as well as a summary of key instrument testing and performance issues, is also presented. Full article

With the continuous advancement of high-resolution satellite technology, the impact of thermal deformation on the performance of star cameras is becoming more significant, particularly in relation to installation conditions and orbital environments. To address this challenge, an in-depth investigation of the thermal design of a star camera is conducted in this study. The thermal deformation of this camera is evaluated systematically through simulation analysis, thermal balance tests, and on-orbit temperature measurements. In addition, a simulation analysis is used to identify and quantitatively evaluate the thermal deformation error sources that affect the spatial attitude measurement accuracy of the star camera. The results indicate that thermal deformations of the optical system, the mounting surface of the star camera, and the support significantly impact on-orbit measurement accuracy. Ultimately, the limit error attributable to on-orbit thermal deformation is determined to be 0.62″. In the thermal balance experiments, the maximum absolute difference between the test results and the thermal simulation analysis results is under 1.8 °C. Additionally, analysis of the orbital temperature data reveals that the maximum absolute difference between the orbital results and the thermal simulation results is 1.18 °C, while the attitude accuracy of the star sensor is better than 0.54″. These findings validate the effectiveness of the thermal design and the accuracy of the thermal simulation analysis. The analysis of error sources presented in this paper offers crucial insights for effectively controlling the thermal deformation errors of star cameras and lays the groundwork for optimizing overall thermal design. Full article

The Microwave Radiation Imager (MWRI) onboard the FengYun satellite plays a crucial role in global change monitoring and numerical weather prediction. Estimating and correcting geolocation errors are important to retrieving accurate geophysical variables. However, the instantaneous field of view (IFOV) inter-channel deviation, which is mainly caused by the structure mounting error and measurement error of feedhorns, is less studied. In this present study, we constructed a general theoretical model to automatically estimate the IFOV inter-channel deviations suitable for conical-scanning instruments. The model can automatically detect the along-track and across-track vectors that pass through the land–sea boundary points and are perpendicular to the actual coastlines. Regarding the midpoints of the vectors as the brightness temperature (Tb) inflection points, the IFOV inter-channel deviation is the pixel offset or distance of the maximum gradients of the Tb near the inflection points for each channel relative to the 89-GHz V-pol channel. We tested the model’s operational performance using the FY-3G/MWRI-Rainfall Mission (MWRI-RM) observations. Considering that parameter uploading adjusted the IFOV inter-channel deviations, the model’s validity was verified by comparing the adjustments calculated by the model with the theoretical changes caused by parameter uploading. The result shows that the differences between them for all window channels are less than 100 m, indicating the model’s effectiveness in evaluating the IFOV inter-channel deviation for the MWRI-RM. Furthermore, the estimated on-orbit IFOV inter-channel deviations for the MWRI-RM show that all channel deviations are less than 1 km, meeting the instrument’s design requirement of 2 km. We believe this study will provide a foundation for IFOV inter-channel registration of passive microwave payloads and spatial matching of multiple payloads. Full article

Proper prediction of the temperature variation in a metallic wire mesh for spaceborne large deployable reflector antennas is essential for evaluating the dimensional stability of the antenna under extreme on-orbit thermal environments. However, predicting the temperature of a mesh is difficult because of its complex yarn configuration. To analyze the thermal behavior of the spaceborne mesh antenna reflector, the thermal optical characteristics with various knitting methods of the metallic mesh were obtained experimentally in this study. Subsequently, to analyze the thermal sensitivity of the reflector based on its optical properties, an on-orbit thermal analysis of the mesh reflector was performed based on measurements of the mesh specimen. We also investigated the influence of deployable solar panels on the thermal gradient of the reflector. Full article

Temperature fluctuations affect the performance of high-precision gravitational reference sensors. Due to the limited space and the complex interrelations among sensors, it is not feasible to directly measure the temperatures of sensor heads using temperature sensors. Hence, a high-accuracy interpolation method is essential for reconstructing the surface temperature of sensor heads. In this study, we utilized XGBoost-LSTM for sensor head temperature reconstruction, and we analyzed the performance of this method under two simulation scenarios: ground-based and on-orbit. The findings demonstrate that our method achieves a precision that is two orders of magnitude higher than that of conventional interpolation methods and one order of magnitude higher than that of a BP neural network. Additionally, it exhibits remarkable stability and robustness. The reconstruction accuracy of this method meets the requirements for the key payload temperature control precision specified by the Taiji Program, providing data support for subsequent tasks in thermal noise modeling and subtraction. Full article

To increase the interferometric measurement resolution in the Taiji program, we present a noise suppression method in this paper. Taking the specific micro-force perturbation and temperature fluctuation in the Taiji-1 interferometer as an example, we set up and experimentally verified the corresponding transfer function to quantify the effect of both noise sources on the interferometric results. Consistent results were obtained between the numerical and experimental results for the transfer function. It is instructive to eliminate the micro-force perturbations and temperature fluctuations during on-orbit interferometric measurement for as long as the acquisition of the force or temperature distribution of related surfaces and the corresponding transfer functions. This indicates that the method can be used for noise sensing and more in the field of noise elimination and measurement resolution improvement for future Taiji program interferometers. Full article

Aiming to solve the problem of the high-precision deformation measurement of large-scale satellite structures in manufacturing and testing environments, this paper proposes a measurement method based on the idea of fusing actual measurements with finite element analysis. The digital image correlation (DIC) method is used to obtain the high-precision deformation of the honeycomb panel, and the finite element method (FEM) model is introduced to remove the limitations of existing pure measurement methods. Data fusion based on a machine learning neural network is proposed to fuse high-precision deformation and physical information such as temperature to conduct multi-level training on FEM parameters. Through an interpolation of the analysis and calculation results after training, not only can the accuracy of the finite element be improved, but difference and extrapolation of the digital image correlation measurement results can be performed. In the experiments, the satellite on-orbit temperature data are substituted into the modified finite element model. The testing results shows that the prediction accuracy of the model under different temperature loads can be controlled within 10 μm under an 840 mm × 640 mm scale. A high predictive accuracy can be achieved for the revised model for the complete deformation of large structural sections. Full article

The ZY1-02E satellite carrying a thermal infrared sensor was successfully launched from the Taiyuan Satellite Launch Center on 26 December 2021. The quantitative characteristics of this thermal infrared camera, for use in supporting applications, were acquired as part of an absolute radiometric calibration campaign performed at the Ulansuhai Nur and Baotou calibration site (Inner Mongolia, July 2022). In this paper, we propose a novel on-orbit absolute radiometric calibration technique, based on multiple ground observations, that considers the radiometric characteristics of the ZY1-02E thermal infrared sensor. A variety of natural surface objects were selected as references, including bodies of water, bare soil, a desert in Kubuqi, and sand and vegetation at the Baotou calibration site. During satellite overpass, the 102F Fourier transform thermal infrared spectrometer and the SI-111 infrared temperature sensor were used to measure temperature and ground-leaving radiance for these surface profiles. Atmospheric water vapor, aerosol optical depth, and ozone concentration were simultaneously obtained from the CIMEL CE318 Sun photometer and the MICROTOP II ozonometer. Atmospheric profile information was acquired from radiosonde instruments carried by sounding balloons. Synchronous measurements of atmospheric parameters and ECMWF ERA5 reanalysis data were then combined and input to an atmospheric radiative transfer model (MODTRAN6.0) used to calculate apparent radiance. Calibration coefficients were determined from the measured apparent radiance and satellite-observed digital number (DN), for use in calculating the on-orbit observed radiance of typical surface objects. These values were then compared with the apparent radiance of each object, using radiative transfer calculations to evaluate the accuracy of on-orbit absolute radiometric calibration. The results show that the accuracy of this absolute radiometric calibration is better than 0.6 K. This approach allows the thermal infrared channel to be unrestricted by the limitations of spectrum matching between a satellite and field measurements, with strong applicability to various types of calibration sites. Full article

Outgassing or thruster’s generated contaminants are critical for optical surfaces and optical payloads because scientific measurements and, in general, the performances can be degraded or jeopardized by uncontrolled contamination. This is a well-known issue in space technology that is demonstrated by the growing usage of quartz crystal microbalances as a solution for measuring material outgassing properties data and characterizing the on-orbit contamination environment. Operation in space requires compatibility with critical requirements, especially the mechanical and thermal environments to be faced throughout the mission. This work provides the design of a holding structure based on 3D printing technology conceived to meet the environmental characteristics of space application, and in particular, to face harsh mechanical and thermal environments. A kinematic mounting has been conceived to grant compatibility with a large temperature range, and it has been designed by finite element methods to overcome loading during the launch phases and cope with a temperature working range down to cryogenic temperatures. Qualification in such environments has been performed on a mockup by testing a prototype of the holding assembly between −110 ${}^{\circ }$C and 110 ${}^{\circ }$C and allowing verification of the mechanical resistance and stability of the electrical contacts for the embedded heater and sensor in that temperature range. Moreover, mechanical testing in a random environment characterized by an RMS acceleration level of 500 m/s² and excitation frequency from 20 to 2000 Hz was successfully performed. The testing activity allowed for validation of the proposed design and opened the road to the possible implementation of the proposed design for future flight opportunities, also onboard micro or nanosatellites. Moreover, exploiting the manufacturing technology, the proposed design can implement an easy assembling and mounting of the holding system. At the same time, 3D printing provides a cost-effective solution even for small series production for ground applications, like monitoring the contaminants in thermo-vacuum chambers or clean rooms, or depositions chambers. Full article

The Fengyun-4A/B (FY-4A/B) geostationary satellite carries the Geostationary Interferometric Infrared Sounder (GIIRS). The instrument parameters of the GIIRS on FY-4A and FY-4B are not exactly the same, which is crucial for the atmospheric temperature and humidity measurements. The objective of this paper is to discuss the influence of spectral range on the retrieval for the FY-4A/B GIIRS. Firstly, we performed channel selection to choose the appropriate channels for retrieval. Then, the multiple cycling utilization of the physical retrieval method is proposed and conducted for improving the accuracy, and the retrieval results of FY-4A/B GIIRS are compared. Finally, perturbation analysis is performed to discuss the sensitivity of the retrieval to temperature perturbations due to the difference in spectral range between the two GIIRS. The results show the retrieval method can realize the improvement of the average accuracy by more than 0.9 K for temperature and 3.0% for humidity. As the spectral range widens, the retrieval accuracy of FY-4B GIIRS is superior to that of FY-4A GIIRS from 130 hPa to 400 hPa. Furthermore, perturbation analysis also shows the extension of the spectral range is beneficial to the retrieval. This study could offer the usefulness of current GIIRS instruments with observed on-orbit bias, and a reference for the parameter design of the subsequent instruments. Full article