Satellite Range Measurements Research Articles

High precision time delay calibration system for range measurement by using phase stabilized optical fiber to eliminate temperature error

A high precision time delay calibration system based on optical fiber switches and fiber coils network for the satellite range measurement system is proposed in this paper. To reach the high time delay precision, the Phase Stabilized Optical Fiber (PSOF), is proposed to use as time delay component instead of the Single Mode Fiber (SMF) to minimize the temperature dependence of transmission delay time. In order to verify the time delay precision, a low coherence interferometry which contains a Michelson interferometer and a Mach-Zehnder interferometer is used to measure the thermal coefficient of delay of the PSOF compared with the SMF from −20 to 60℃. The result showed that by using the PSOF, the temperature error can be decreased by 4.15 times compared with using the standard SMF in the fiber based range measurement system.

Simulation of long-term rotational dynamics of large space debris: A TOPEX/Poseidon case study

Accurate knowledge of the rotational dynamics of a large space debris is crucial for space situational awareness (SSA), whether it be for accurate orbital predictions needed for satellite conjunction analyses or for the success of an eventual active debris removal mission charged with stabilization, capture and removal of debris from orbit. In this light, the attitude dynamics of an inoperative satellite of great interest to the space debris community, the joint French and American spacecraft TOPEX/Poseidon, is explored. A comparison of simulation results with observations obtained from high-frequency satellite range measurements is made, showing that the spacecraft is currently spinning about its minor principal axis in a stable manner. Predictions of the evolution of its attitude motion to 2030 are presented, emphasizing the uncertainty on those estimates due to internal energy dissipation, which could cause a change of its spin state in the future. The effect of solar radiation pressure and the eddy-current torque are investigated in detail, and insights into some of the satellite’s missing properties are provided. These results are obtained using a novel, open-source, coupled orbit-attitude propagation software, the Debris SPin/Orbit Simulation Environment (D-SPOSE), whose primary goal is the study of the long-term evolution of the attitude dynamics of large space debris.

BikeGPS

The past few years have witnessed a rapid growth of stationless bike sharing services. The service allows the bikes to be dropped off freely and to be found through GPS localization. In practice, the bikes are often parked in close proximity to buildings, where GPS accuracy suffers, making bike search a challenging task. This article proposes a novel approach to addressing this problem. Inspired by multi-antenna systems, our method tries to collect GPS signals from multiple distributed bikes, by organizing a group of bikes into a network, called a BikeGPS network. Formed by pedestrian users who opportunistically measure inter-bike distance via radio sensing and step tracking, the generated network permits one to map all the nodes’ satellite range measurements into a single lead node ’s view. By considering both signal and geometry properties of satellite raw measurements, and using an asynchronous coarse time navigation algorithm, the lead node can accurately derive the locations of all the network nodes. Experiments in real-world scenarios show that BikeGPS significantly improves the localization performance, in terms of both accuracy and solution availability, compared with the naive GPS approach and a high-level cooperative localization method.

Applying Standard Digital Map Data in Map-aided, Lane-level GNSS Location

Urban positioning using the Global Positioning System (GPS) is challenging because of multipath. Urban canyons limit open sky visibility, and cause signal reflection and diffraction, resulting in significant satellite range measurement errors. The investigations reported here have been carried out in a French project calledInturb(an acronym derived from integrity and urban positioning). So far, the project has had two phases: first, a simple Three-Dimensional (3D) geometrical city modelling, called “Urban Trench”, has been developed and engineered manually from data sets collected in different cities. Positioning improvement in terms of accuracy was quantified where the model could be applied. Second, this modelling has been automated, based on the standard national BD Topo ® map database for France, with promising results. This geometrical modelling makes it possible to distinguish between line-of-sight satellite signals and those from non-line-of-sight. The latter, apparentlybona fide, signals are caused by strong reflections, usually from buildings with a lot of steel and glass in their construction. A correction of the pseudo-range measurements of the latter is also computed and applied in the position estimator. Positioning accuracy is improved, whilst availability is kept at its maximum. In the study both manual and automatic 3D models are used in extensive experimental campaigns. Results are: first, the possibility to cover entirely any urban area in the country; second, the reduction of the median error in 3D by more than 50% on data collected in Nantes, Paris and Toulouse for a total duration of nearly ten hours; third, the compliance with standards used in most embedded maps and geographical information systems, including an assessment of the trade-off between the model simplicity and the positioning improvement.

다목적실용 위성 2호의 위성 거리 측정 최적 운용 방안 연구

Based on the analyses of satellite range measurement, the optimal operation for satellite range measurement of KOMPSAT II, which operates in the low-earth orbit, was proposed in this paper. The orbital motion of the satellite was analyzed in viewpoints of radial velocity, acceleration and speed of acceleration. Correspondingly the effects for satellite ranging signal due to satellite motion were analyzed in viewpoints of doppler phenomena, which are doppler frequency, doppler rate and speed of doppler rate. The accuracy and ambiguity probability of the satellite range measurement were quantitatively analyzed under various circumstances. The optimal operation parameters for satellite range measurement were also analyzed based on the analyzed results. The analyzed results in this paper can be utilized in design of small-sized ground station for satellite range measurement.

부 반송파를 사용하는 이동형 다목적실용위성 관제국에 대한 하향 링크 채널 설계

This paper describes the downlink design of a transportable small-sized KOMPSAT ground station using sub-carrier signal. Based on the analysis of the transmission modes of satellite real-time telemetry and range measurement signals, the downlink channel design of KOMPSAT ground station using sub-carrier signal was processed. By considering the threshold signal-to-noise ratio of real-time 2 kbps telemetry signal and the required signal-to-noise ratio for satellite range measurement, the small-sized KOMPSAT downlink channel with G/T value of 6.5 dB/K was designed. The real G/T of implemented ground station was proven to be 6.62 dB/K when measured using the Sun. Moreover, through interface test with KOMPSAT, the ground station has shown the required link performance for real-time telemetry acquisition using sub-carrier and was consequently evaluated to be adequate for a transportable small-sized KOMPSAT ground station.

통신해양기상위성의 위성 관제 신호 전송 방식의 최적화 연구

본 연구에서는 다중 변조 방식의 변조 지수에 따른 전력 손실을 위성 관제 전송 모드별로 해석하고, 위성 관제 전송 모드에 대한 필요한 위성 링크 마진을 제시하였다. NRZ/PSK/PM 다중 변조 신호의 전송 신호간 간섭 현상과 위성 관제 수신 신호의 임계값을 기준으로 원격 명령과 원격 측정 신호의 최적 부 반송파 신호를 제안하였다. ESA 거리 측정 방식을 사용하는 위성 관제 모드에서는 12 kHz 또는 14 kHz 의 원격 명령 부 반송파 신호를 그리고, GSTDN 방식을 사용하는 운용 모드에서는 16 kHz 부 반송파를 사용하여 다양한 위성 관제를 할 수 있도록 한다. 또한 원격 측정 신호의 부 반송파는 65.536 kHz를 사용하여 양호한 수신 성능 및 동작 영역을 보장하도록 한다. The power losses due to modulation index for multi-modulation scheme were analyzed under various transmission mode of satellite control and the necessary satellite link margin for transmission mode were proposed in this paper On the basis of the analyses for interference between the transmission signals and threshold of satellite control signal receiver, the optimal subcarrier signals were proposed for satellite range measurement methods, respectively. The subcarrier signal of 12 kHz or 14 kHz is proper for telecommand using the ESA method, and 16 kHz for telecommand signal using the GSTDN method. On the other hand, the telemetry subcarrier of 65.536 kHz is a proper in the viewpoint of receiver threshold value.

Exhaustive global grid search in computing receiver position from modular satellite range measurements

A global grid search algorithm with an application in weak signal satellite positioning is implemented and tested numerically. The algorithm consists of local Gauss-Newton search and a global starting point chooser, and it can be generalized as a global optimization method for functions with an attraction basin of computable minimum radius. The method is shown to .nd the global minimum in a bounded region in predictable time.

Waveform Retracking of Topex/Poseidon Altimeter in China Seas and Its Vicinity

AbstractJust as in the open oceans, the altimeter data in the coastal zone can provide valuable information on wave heights, structure of the geoid and the associated gravity field, and dynamic sea surface topography. Because of this wealth of information, many scientists are seeking to extend the use of altimeter data to the shoreline. There are many different methods described in the literature that are available for re‐tracking altimeter waveform data. All the various re‐tracking algorithms have their own unique advantages and disadvantages, and it is generally accepted that no single algorithm can meet the diverse needs of all altimetry data users. To obtain accurate altimeter data in offshore of China Sea and its vicinity, we have reprocessed the raw Topex/Poseidon altimeter waveform data using more sophisticated algorithms, based on a fit of the waveform to a 5 parameters function. Re‐tracking altimetry data is done by computing the departure of the waveform's leading edge from the tracking gate of altimeter and correcting the satellite range measurement accordingly. On the base of colleagues' experience, reprocessed Topex/Poseidon altimeter waveform data is used to generate a time series of sea surface height. The post‐processed altimeter waveform data is compared with the data from tide gauge station in the China Seas, which close to the ground tracks of satellite. The comparison shows that shallow water areas can be investigated with much more data and closer to the coastal line than the official products.

Potential of Differential Global Positioning System for Category III Operations: Analysis of Flight Test Results

The Federal Aviation Administration is conducting a program to investigate the feasibility of satellite-based navigation to support Category III precision landing applications. Category III (CAT III) refers to zero or nearzero visibility conditions. The program is evaluating the potential of the Differential Global Positioning System (DGPS) for CAT III precision approach and landing. Evaluations include flight tests, satellite simulator tests, and various analyses to supplement these tests.DGPS uses a ground reference station that computes corrections to satellite range measurements and transmits them to the aircraft, where they are used to augment the airborne GPS solution. DGPS can provide position accuracies of a few meters down to a small fraction of a meter, depending on the particular implementation.This paper presents flight test requirements, evaluation methods, and results. Flight test results for two code-based and two carrier-based DGPS systems are given, along with brief descriptions of each design. Code-based systems have the potential for submeter accuracy; carrier-based systems have the potential for subdecimeter accuracy. Results presented include measurements of sensor errors, flight technical errors, total system errors, and touchdown dispersion errors, as well as some assessments of system integrity. These are all measures of precision landing system performance. The results indicate the feasibility of using DGPS for CAT III applications.

Flight Test Evaluation of Precision-Code Differential GPS for Terminal Approach and Landing

A flight test evaluation conducted at the NASA Ames Research Center of precision-code differential GPS for terminal approach and landing is described. Differential corrections to satellite range and range-rate measurements are computed in a stationary ground reference system, uplinked to the test aircraft, and employed to correct corresponding airborne satellite data. Differentially corrected range and range-rate data, combined with inertial data, are then utilized with satellite position and velocity to compute aircraft position and velocity employing an eight-state extended Kalman filter.

Metrologic foundations of laser satellite range measurements

Metrologic foundations of laser satellite range measurements

A formula for computing refraction effects on range measurements

It is shown that models of the troposphere based on a constant temperature lapse rate lead to simple formulas for the computation of corrections to satellite range measurements. This is true for any lapse rate.

Present tectonic-plate motions from lunar ranging

Measurements to determine the motion of the Pacific Plate with respect to North America are planned to start within a few months. The University of Hawaii Lunar Ranging Station on Maui is expected to begin operating, and to achieve an accuracy of 2 or 3 cm soon for a single run. The University of Texas McDonald Observatory has been achieving an accuracy of 8–15 cm on a routine basis since late 1971. Work on further improving the McDonald accuracy is planned. Using data from many runs, an accuracy of 1 cm/yr is expected for the relative motion within the first few years. A transportable lunar-ranging station has been proposed which could be constructed in about eighteen months. The station could observe for 3–6 weeks at a chosen site, and determine the location of the site with respect to the fixed lunar-ranging stations. The accuracy expected is 1–3 cm in each coordinate. If approved, a possible initial itinerary for the station might be as follows: 1. (a) two or three sites in California, including Goldstone, plus one site in Utah; 2. (b) sites in Baja California and Mexico, plus several others in the U.S.; 3. (c) several sites in Central America, the Caribbean, and South America; 4. (d) repeat measurements in California, Utah, and Baja California, plus initial measurements at sites in Africa, India, and the Pacific. It is expected that data on plate motions also will become available from satellite range measurements and VLBI.

Optimal and Suboptimal Methods of Satellite Surveillance for Traffic Control of Transoceanic Flights

Description of a system which uses two synchronous equatorial satellites. Aircraft location is determined by measuring the range of the aircraft to each satellite as well as aircraft altitude, and transmitting this information periodically to a ground station. There, the aircraft's geographic position at the time of transmission is computed. This information is then combined with past position measurements in a suboptimal filter to determine aircraft position and velocity (the velocity being used to estimate aircraft position between transmissions). The suboptimal filter is a simplification of the optimal Kalman filter. Except for altitude information, the system is independent of the aircraft navigation system.

The laser satellite range measurement at ondřejov observatory

An experiment was run at the Ondřejov Observatory to test the fundamental equipment for constructing a satellite laser radar system, to check the assumptions, calculations, and the methods of measurement. Using a modified SBG chamber, a laser of Czechoslovak production was employed to measure the distance to the GEOS B satellite. Good results and a sufficient power reserve of the experiment have thus become the fundamental stepping stone of constructing a satellite laser radar system. The short contribution which follows gives a brief description of the experiment and some of the results obtained.

Geodetic and Geophysical Applications of Laser Satellite Ranging

The Smithsonian Astrophysical Observatory (SAO) uses computed satellite orbits in its geodesy program and for studies of the gravitational field and other parameters of the earth. As the accuracy of these orbits increases, so does their field of application. The measurement of temporal changes, such as continental drift or other crustal motion, is in prospect. Laser systems are providing satellite-range measurements from which orbits are computed with significantly increased accuracy. SAO uses three pulsed ruby-laser systems routinely in its worldwide network of satellite observing stations and cooperates on an international basis with other agencies who have their own systems. The 500-MW laser at Smithsonian's Mt. Hopkins Observatory in Arizona is described. This system uses currently available orbits to position the laser transmitter and receiving telescope in azimuth and altitude. The laser is pulsed at the proper epoch without the satellite's being acquired visually. The accuracy of this method of positioning, its advantages for the present application, and its future potential will be discussed.