The Study of In-Orbit Calibration Accuracy of NOAA Satellite Infrared Sounder and Its Effect on Temperature Profile Retrievals

The calibration accuracy of High Resolution Infrared Radiation Sounder Mod. 2 (HIRS / 2) on NOAA-10 satellite is analyzed in this paper. The non-linear effect in the linear calibration curve induces a deviation of 1.5 degrees (k) of brightness temperature in the tenth channel (8.3 um, water vapor absorption) of the HIRS/2 and the non-linear effect affects the other channels to a different extent. Based on analyzing non- linearity in two-point calibration curve, a tri-point calibration equation is given. A numerical test of effects of the linear and non-linear calibration models on the accuracy of atmospheric temperature retrievals is carried out.

Wind speed inversion and in-orbit assessment of the imaging altimeter on Tiangong-2 space station

Imaging altimeter(IALT)is a new type of radar altimeter system.In contrast to the conventional nadir-looking altimeters,such as HY-2 A altimeter,Jason-1/2,and TOPEX/Poseidon,IALT observes the earth surface at low incident angles(2.5°–8°),so its swath is much wider and its spatial resolution is much higher than the previous altimeters.This paper presents a wind speed inversion method for the recently launched IALT onboard Tiangong-2 space station.Since the current calibration results of IALT do not agree well with the well-known wind geophysical model function at low incidence angles,a neural network is used to retrieve the ocean surface wind speed in this study.The wind speed inversion accuracy is evaluated by comparing with the ECMWF reanalysis wind speed,buoy wind speed,and in-situ ship measurements.The results show that the retrieved wind speed bias is about–0.21 m/s,and the root-mean-square(RMS)error is about 1.85 m/s.The wind speed accuracy of IALT meets the performance requirement.

MONTE CARLO SIMULATION FOR MODELING THE EFFECT OF GROUND SEGMENT LOCATION ON IN-ORBIT RESPONSIVENESS OF LEO SUNSYNCHRONOUS SATELLITES

Responsiveness is a challenge for space systems to sustain competitive advantage over al-ternate non-spaceborne technologies.For a satellite in its operational orbit,in-orbit responsiveness is defined as the capability of the satellite to respond to a given demand in a timely manner.In this paper,it is shown that Average Wait Time(AWT) to pick up user demand from ground segment is the ap-propriate metric to evaluate the effect of ground segment location on in-orbit responsiveness of Low Earth Orbit(LEO) sunsynchronous satellites.This metric depends on pattern of ground segment access to satellite and distribution of user demands in time domain.A mathematical model is presented to determine pattern of ground segment access to satellite and concept of cumulative distribution function is used to simulate distribution of user demands for markets with different total demand scenarios.Monte Carlo simulations are employed to take account of uncertainty in distribution and total volume of user demands.Sampling error and standard deviation are used to ensure validity of AWT metric obtained from Monte Carlo simulations.Incorporation of the proposed metric in the ground segment site location process results in more responsive satellite systems which,in turn,lead to greater customer satisfaction levels and attractiveness of spaceborne systems for different applications.Finally,simula-tion results for a case study are presented.

In-Orbit Calibration and Data Analysis of China＇s First Grazing Incidence Focusing X-Ray Pulsar Telescope

The grazing incidence focusing X-ray pulsar telescope(iFXPT), as the main payload of the X-ray Pulsar Navigation Test Satellite(XPNAV-1), will have great significance on China's space scientific exploration and X-ray pulsar navigation. With PSR B0531+21(Crab Pulsar) as the observation target, the pulsar profile has been recovered based on the data obtained by iFXPT, realizing the main objective of "observing" PSR B0531+21 for the first time in China. This payload mainly consists of the Wolter-I X-ray optics, silicon drift detector, magnetic deflector, electronics, high-energy particle shield and high-stability structures. Currently, the iFXPT, with its good in-orbit performance, has obtained a considerable observation data. The effective area, sensitivity and energy response have been calibrated both on ground and in-orbit, demonstrating a high degree of consistency. Meanwhile, the in-orbit observation data and information for pulsar navigation has also been analyzed simultaneously. As a result, the feasibility of the exploration scheme and the performance of the telescope have been fully validated.

Elimination of the Potential Hazard of the Long March 4 Launch Vehicle's In-orbit Breakup

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FY-2F Satellite In-orbit Test Review Passed

The FY-2F satellite recently passed its in-orbit test review and can be put into operational use. Experts from Chinese Academy of Sciences, China Meteorological Administration, CASC, China Electronics Technology Group Corporation, State Administration of Science, Technology and Industry for National Defense,

The In-orbit Application of 25Nms Gyroscope Fills the Gap in Domestic Market

After the successful launch of Yaogan 14, the 25Nms control moment gyroscope onboard the Yaogan 14 satellite successfully finished the attitude maneuver commands to the satellite and operates in a normal state. The successful maiden use of the 25Nms gyroscope fills the gap in the field of small control moment gyroscopes in

In-orbit performance of LE onboard Insight-HXMT in the first 5 years

Purpose The low-energy X-ray telescope(LE)is a main instrument of the Insight-HXMT mission and consists of 96 swept charge devices covering the 1–10 keV energy band.The energy gain and resolution are continuously calibrated by analyzing Cassiopeia A(Cas A)and blank sky data,while the effective areas are also calibrated with the observations of the Crab Nebula.In this paper,we present the evolution of the in-orbit performances of LE in the first 5 years since launch.Methods The Insight-HXMT data analysis software package(HXMTDAS)is utilized to extract the spectra of Cas A,blank sky,and Crab Nebula using different good time interval selections.We fit a model with a power-law continuum and several Gaussian lines to different ranges of Cas A and blank sky spectra to get peak energies of their lines through xspec.After updating the energy gain calibration in CALibration DataBase(CALDB),we rerun the Cas A data to obtain the energy resolution.An empirical function is used to modify the simulated effective areas so that the background-subtracted spectrum of the Crab Nebula can best match the standard model of the Crab Nebula.Results The energy gain,resolution,and effective areas are calibrated every month.The corresponding calibration results are duly updated in CALDB,which can be downloaded and used for the analysis of Insight-HXMT data.Simultaneous observations with NuSTAR and NICER can also be used to verify our derived results.Conclusion LE is a well-calibrated X-ray telescope working in 1–10 keV band.The uncertainty of LE gain is less than 20eV in 2–9 keV band,and the uncertainty of LE resolution is less than 15eV.The systematic errors of LE,compared to the model of the Crab Nebula,are lower than 1.5%in 1–10 keV.

In-orbit performance of ME onboard Insight-HXMT in the first 5 years

Introduction The medium-energy X-ray telescope(ME)is a collimated X-ray telescope onboard the Insight hard X-ray modulation telescope(Insight-HXMT)satellite.It has 1728 Si-PIN pixels readout using 54 low noise application-specific integrated circuits(ASICs).ME covers the energy range of 5–30 keV and has a total detection area of 952cm2.The typical energy resolution of ME at the beginning of the mission is 3 keV at 17.8 keV(full width at half maximum,FWHM),and the time resolution is 255μs.In this study,we present the in-orbit performance of ME in its first 5 years of operation.Methods The performance of ME was monitored using onboard radioactive sources and astronomical X-ray objects.ME carries six 241Am radioactive sources for onboard calibration,which can continuously illuminate the calibration pixels.The long-term performance evolution of ME can be quantified using the properties of the accumulated spectra of the calibration pixels.In addition,observations of the Crab Nebula and the pulsar were used to check the long-term evolution of the detection efficiency as a function of energy.Conclusion After 5 years of operation,742cm2 of the Si-PIN pixelswere stillworking normally.The peak positions of 241Am emission lines gradually shifted to the high-energy region,implying a slow increase in ME gain of 1.43%.A comparison of the ME spectra of the Crab Nebula and the pulsar shows that the E–C relations and the redistribution matrix file are still acceptable for most data analysis works,and there is no detectable variation in the detection efficiency.

In-orbit performance of HE onboard Insight-HXMT in the first 5 years

Purpose The high-energy X-ray telescope(HE),one of the three main payloads of the Insight-HXMT mission,is composed of eighteen NaI(Tl)/CsI(Na)phoswich detectors,where NaI(Tl)serves as the primary detector covering 20–250 keV,and CsI(Na)is used as an active shield detector to suppress the background of NaI(Tl)and also serves as an all-sky gammaray burst monitor covering 0.2–3MeV.In this paper,we review the in-orbit performance of HE in the first 5 years since Insight-HXMT was launched on June 15,2017.Methods The major performances we concern include the gain and energy resolution of NaI(Tl)and CsI(Na)detectors,the performance of pulse shape discriminator(PSD)and system dead time.In this work,we investigate these performances mainly using the data of blank-sky observations and the data when the telescope is in earth occultation.Results The overall performance of HE/NaI(Tl)is very stable in the first 5 years,whereas the gain of HE/CsI(Na)shows a continuously increasing trend and should be calibrated regularly.Conclusion In general,HE is still in good health and well-calibrated status after five-year’s operation.The in-orbit performance of HE has no significant deviation from expectation.HE is expected to be in operation healthily for another several years of extended mission life.

ESGM/INS/GPS/CNS组合导航系统对飞行器定轨精度的影响

针对新一代航天测量船基于静电陀螺监控器（electrostatic gyro monitor，ESGM）的组合导航系统，分析了测量船外测误差模型及对定轨精度的影响。根据误差传播原理对测量船外测误差进行了分析，得到了位置误差的计算公式，为外测数据的使用策略提供依据。结合实测数据对组合导航系统与惯性导航系统的定位误差进行对比分析，结果表明：组合导航系统的定位误差在大部分时间内比惯性导航系统小609／6左右，并且其定位结果更为稳定。

Calibration and brightness temperature algorithm of CE-1 Lunar Microwave Sounder (CELMS)

CE-1 Lunar Microwave Sounder (CELMS) is the first passive microwave radiometer in the world to sound the surface of the Moon in the lunar orbit at altitude of 200 km. The scientific objective of CELMS is to obtain global brightness temperature (TB) of the Moon, to retrieve information on lunar regolith, and to evaluate the distribution of helium-3 on the Moon implanted by solar wind. Before launch of CELMS, a series of experiments were carried out in laboratories to test the performances of the systems, and to calibrate the responses between the input of TB and the output of voltage from the receivers. However, the thermal condition exposed to CELMS is more complicated in lunar orbit than on the Earth, which makes the temperatures of different parts of CELMS wave vary greatly, and the cosmic background is not very clean due to the pointing of cold space antenna to the direction of the satellite running, which brings uncertainties into data-processing of CELMS when the temperature of cold space is used as a calibrator. Furthermore, the lack of knowledge on the lunar ingredients and compositions, distributions of physical temperatures, and properties on lunar microwave radiation leads to difficulties in validating the measurements and retrievals of CELMS. By analyzing the results of ground experiments and the measurements of CELMS in-orbit, along with our knowledge of the properties of lunar surface, here we give algorithms on calibration and antenna pattern correction (APC) of CELMS. We also describe in detail the principle of microwave transfer among the elements of CELMS, and discuss the method on testing calibration parameters of the system. In addition, the theory and model on correction antenna pattern of CELMS are developed by comparing antenna temperatures by CELMS with those simulated by microwave radiative transfer models. The global distribution of TB is given and the features of TB are analyzed. Our results show rich information included in TB on the properties of lunar regolith, especially the thickness and dielectric constant, which are nearly directly reflected by the differences of TB at day and those at night.