Validation of Geostationary Earth Orbit Satellite Ephemeris Generated from Satellite Laser Ranging
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This study presents the generation and accuracy assessment of predicted orbital ephemeris based on satellite laser ranging (SLR) for geostationary Earth orbit (GEO) satellites. Two GEO satellites are considered: GEO-Korea Multi-Purpose Satellite (KOMPSAT)-2B (GK-2B) for simulational validation and Compass-G1 for real-world quality assessment. SLR-based orbit determination (OD) is proactively performed to generate orbital ephemeris. The length and the gap of the predicted orbital ephemeris were set by considering the consolidated prediction format (CPF). The resultant predicted ephemeris of GK-2B is directly compared with a pre-specified true orbit to show 17.461 m and 23.978 m, in 3D root-mean-square (RMS) position error and maximum position error for one day, respectively. The predicted ephemeris of Compass-G1 is overlapped with the Global Navigation Satellite System (GNSS) final orbit from the GeoForschungsZentrum (GFZ) analysis center (AC) to yield 36.760 m in 3D RMS position differences. It is also compared with the CPF orbit from the International Laser Ranging Service (ILRS) to present 109.888 m in 3D RMS position differences. These results imply that SLR-based orbital ephemeris can be an alternative candidate for improving the accuracy of commonly used radar-based orbital ephemeris for GEO satellites.Keywords:
Ephemeris
Satellite laser ranging
Orbit (dynamics)
Orbit Determination
Position (finance)
Satellite launch requirements to acquire the desired orbit, various in-orbit operations such as orbit stabilization, orbit correction and station keeping that are necessary for keeping the satellite in the desired orbit, are discussed in this chapter. In addition to these, the chapter provides a detailed description of major launch vehicle systems and space centres, and other related issues like Earth coverage, eclipses and look angles. It provides a discussion on typical launch sequences employed worldwide for putting satellites in the geostationary orbit, as putting a satellite in a lower circular or elliptical orbit is only a step towards achieving the geostationary orbit. The satellite once placed in its orbit, experiences various perturbing torques that cause variations in its orbital parameters with time. These perturbations are also discussed in the chapter. The chapter is illustrated with mathematics wherever necessary and a large number of solved problems.
Orbit (dynamics)
Medium Earth orbit
Elliptic orbit
Frozen orbit
Ground track
Orbit Determination
Synchronous orbit
Circular orbit
Orbital mechanics
Geocentric orbit
Earth's orbit
Sun-synchronous orbit
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Abstract : This study presents the results of an analysis comparing ephemerides obtained using Satellite Laser Ranging (SLR) derived from a reduced number of ground sites. The study provides insight into the extent to which ephemeris can be determined for an extremely well-specified satellite. The study was conducted to determine the viability of using a single SLR site to provide an independent method of verifying onboard Global Positioning System navigational performance. Computational simulations included varying the number and distribution of sites as well as empirical modeling of nonconservative forces to determine the limitations of this SLR- based reduction strategy.
Ephemeris
Satellite laser ranging
Ranging
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Ephemeris
Orbit Determination
Orbit (dynamics)
Position (finance)
Orbital elements
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Orbit Determination
Orbit (dynamics)
Medium Earth orbit
Ground track
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The state information of GEO satellite can not be easily accepted by the ground-based surveillance system owning to its geostationary observing model.To monitor and catalog all GEO satellites under surveillance,both the structure in observation geometry and constrained effects in dynamic models are strengthened via in-orbit tracking by space platform.High or low-orbit platform and their observation methods were analyzed.The effects of orbit determination caused by measuring errors were studied.Simulation shows that orbit determination precision for GEO satellites is in kilometer level on high or low-orbit platform,but the orbit determination accuracy with low-orbit platform is better than with high-orbit platform.System error is the main source of orbit determination errors.
Orbit (dynamics)
Orbit Determination
Ground track
Medium Earth orbit
Synchronous orbit
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A strategy for geostationary orbit (or geostationary earth orbit [GEO]) surveillance based on optical angular observations is presented in this study. For the dynamic model, precise analytical orbit model developed by Lee et al. (1997) is used to improve computation performance and the unscented Kalman filer (UKF) is applied as a real-time filtering method. The UKF is known to perform well under highly nonlinear conditions such as surveillance in this study. The strategy that combines the analytical orbit propagation model and the UKF is tested for various conditions like different level of initial error and different level of measurement noise. The dependencies on observation interval and number of ground station are also tested. The test results shows that the GEO orbit determination based on the UKF and the analytical orbit model can be applied to GEO orbit tracking and surveillance effectively.
Orbit Determination
Orbit (dynamics)
Medium Earth orbit
Orbital mechanics
Ground track
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This paper describes the use of recently collected Satellite Laser Range (SLR) data in assessing the accuracy of the Global Positioning System (GPS) ephemeris produced by the National Imagery and Mapping Agency (NIMA). The SLR data were collected by the National Aeronautics and Space Administration (NASA) during October-December 1996. At that time, NASA launched an intensive tracking campaign for the two GPS satellites which carry laser retro-reflectors. The satellites, Satellite Vehicle Numbers (SVN) 35 and 36, were to be tracked on a higher than normal priority level with nineteen NASA affiliated tracking stations for the duration of the campaign. There was less uniformity in the geographic coverage of the data than was hoped for. However, the campaign still afforded an excellent opportunity to assess the accuracy of the NIMA ephemerides. This was done by utilizing ephemerides provided by the international GPS Service (IGS) to form a baseline. The IGS provides GPS ephemerides that are considered to be accurate to better than ten centimeters. In addition, ephemerides from the Jet Propulsion Laboratory (JPL) was also examined, because the JPL ephemerides are used in the production of the IGS ephemerides and could provide another point in the baseline. NASA "quick-look" normal point data, the principal NASA SLR data product, were obtained from the NASA Crustal Dynamics Data Information System (CDDIS). Normal point data have better than centimeter accuracy and were used here to calculate SLR residuals from the NIMA, the JPL and the IGS ephemerides. The RMS values, for the SLR residuals over the three month study period, were seven centimeters for the IGS, eight centimeters for the JPL and twelve centimeters for the NIMA ephemerides. The IGS and the JPL ephemerides have a small negative bias for both SVN35 and SVN36, while the NIMA results are mixed, with SVN36 having the same negative bias but SVN35 having a small positive bias. One possible explanation for this bias could be a change in the satellite's center of mass, CM, which might have occurred since the launch date. Solving for the center of mass, when calculating the SLR residuals for each organization, removes the bias and gives an RMS of less than five centimeters for the IGS, less than five centimeters for the JPL and less than ten centimeters for the NIMA ephemerides.
Ephemeris
Satellite laser ranging
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Orbit Determination
Orbit (dynamics)
Satellite laser ranging
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This paper describes the use of Satellite Laser Range
(SLR) data in assessing the accuracy of the Global
Positioning System (GPS) precise ephemerides produced
by the Department of Defense (DoD) and civilian
organizations. The SLR data were collected by the
National Aeronautics and Space Administration (NASA)
during 1996, 1997, and 1998. During the three month
period October-December, 1996, NASA launched an
intensive tracking campaign for the two GPS satellites
which carry laser retro-reflectors. The satellites, Satellite
Vehicle Numbers (SVN) 35 and 36, were to be tracked on
a higher than normal priority level with nineteen NASA
affiliated tracking stations, Figure 1B, for the duration of
the campaign. The campaign afforded an excellent
opportunity to assess the accuracy of the GPS ephemerides
and establish a baseline from which future ephemeris
improvements could be measured. The procedure utilized
ephemerides provided by the International GPS Service
(IGS), the Air Force GPS Operational Control Segment
(OCS), and the National Imagery and Mapping Agency
(NIMA). Data in the form of NASA quick-look normal
points, the principal NASA SLR data product, were
obtained from the NASA Crustal Dynamics Data
Information System (CDDIS). The normal point data have
better than centimeter accuracy and were used here to
calculate SLR residuals. SLR Residuals were computed
from the NIMA and the IGS ephemerides during the three
month campaign period in 1996. During a subsequent three
month period (December, 1997 - February, 1998), SLR
residuals were calculated from the OCS, NIMA, and IGS ephemerides. The Mean and RMS values for the SLR
residuals over each three month tracking period are provided.
Ephemeris
Satellite laser ranging
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This paper describes the use of recently collected Satellite Laser Range (SLR) data in assessing the accuracy of the Global Positioning System (GPS) ephemeris produced by the National Imagery and Mapping Agency (NIMA). The SLR data were collected by the National Aeronautics and Space Administration (NASA) during October-December 1996. At that time, NASA launched an intensive tracking campaign for the two GPS satellites which carry laser retro-reflectors. The satellites, Satellite Vehicle Numbers (SVN) 35 and 36, were to be tracked on a higher than normal priority level with nineteen NASA affiliated tracking stations forthe duration of the campaign. There was less uniformity in the geographic coverage of the data than was hoped for. However, the campaign still afforded an excellent opportunity to assess the accuracy of the NlMA ephemerides. This was done by utilizing ephemerides provided by the International GPS Service (IGS) to form a baseline. The IGS provides GPS ephemerides that are considered to be accurate to better than ten centimeters. In addition, ephemerides from the Jet Propulsion Laboratory (JPL) was also examined, because the JPL ephemerides are used in the production of the IGS ephemerides and could provide another point in the baseline. NASA “quick-look” normal point data, the principal NASA SLR data product, were obtained from the NASA Crustal Dynamics Data Information System (CDDIS). Normal point data have better than centimeter accuracy and were used here to calculate SLR residuals from the NIMA, the JPL and the IGS ephemerides. The RMS values, for the SLR residuals over the three month study period, were seven centimeters for the IGS, eight centimeters for the JPL and twelve centimeters for the NlMA ephemerides. The IGS and the JPL ephemerides have a small negative bias for both SVN35 and SVN36, while the NIMA results are mixed, with SVN36 having the same negative bias but SVN35 having a small positive bias. One possible explanation for this bias could be a change in the satellite‘s center of mass, CM, which might have occurred since the launch date. Solving for the center of mass, when calculating the SLR residuals for each organization, removes the bias and gives an RMS of less than five centimeters for the IGS, less than five centimeters for the JPL and less than ten centimeters for the NlMA ephemerides. lNTRODUCTlON
Ephemeris
Satellite laser ranging
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