scholarly journals Reference system origin and scale realization within the future GNSS constellation “Kepler”

2020 ◽  
Vol 94 (12) ◽  
Author(s):  
Susanne Glaser ◽  
Grzegorz Michalak ◽  
Benjamin Männel ◽  
Rolf König ◽  
Karl Hans Neumayer ◽  
...  
Keyword(s):  
Time Synchronization ◽  
Solar Radiation Pressure ◽  
Terrestrial Reference Frame ◽  
Low Earth Orbit ◽  
Global Navigation Satellite Systems ◽  
Earth Orbit ◽  
Present System ◽  
Satellite Systems ◽  
The Future ◽  
German Aerospace

AbstractCurrently, Global Navigation Satellite Systems (GNSS) do not contribute to the realization of origin and scale of combined global terrestrial reference frame (TRF) solutions due to present system design limitations. The future Galileo-like medium Earth orbit (MEO) constellation, called “Kepler”, proposed by the German Aerospace Center DLR, is characterized by a low Earth orbit (LEO) segment and the innovative key features of optical inter-satellite links (ISL) delivering highly precise range measurements and of optical frequency references enabling a perfect time synchronization within the complete constellation. In this study, the potential improvements of the Kepler constellation on the TRF origin and scale are assessed by simulations. The fully developed Kepler system allows significant improvements of the geocenter estimates (realized TRF origin in long-term). In particular, we find improvements by factors of 43 for the Z and of 8 for the X and Y component w. r. t. a contemporary MEO-only constellation. Furthermore, the Kepler constellation increases the reliability due to a complete de-correlation of the geocenter coordinates and the orbit parameters related to the solar radiation pressure modeling (SRP). However, biases in SRP modeling cause biased geocenter estimates and the ISL of Kepler can only partly compensate this effect. The realized scale enabling all Kepler features improves by 34% w. r. t. MEO-only. The dependency of the estimated satellite antenna phase center offsets (PCOs) upon the underlying TRF impedes a scale realization by GNSS. In order to realize the network scale with 1 mm accuracy, the PCOs have to be known within 2 cm for the MEO and 4 mm for the LEO satellites. Independently, the scale can be realized by estimating the MEO PCOs and by simultaneously fixing the LEO PCOs. This requires very accurate LEO PCOs; the simulations suggest them to be smaller than 1 mm in order to keep scale changes below 1 mm.

Position and velocity estimation with a low Earth orbit regional navigation satellite constellation

2021 ◽  
pp. 095441002110313
Author(s):  
Tomer Shtark ◽  
Pini Gurfil
Keyword(s):  
Low Earth Orbit ◽  
Velocity Estimation ◽  
Global Navigation Satellite Systems ◽  
Dynamical Model ◽  
Earth Orbit ◽  
Navigation Satellite ◽  
Satellite Systems ◽  
Satellite Constellation ◽  
Leo Satellites ◽  
Order Of Magnitude

Position and velocity estimation using Global Navigation Satellite Systems (GNSS) has been widely studied and implemented. In contrast to existing GNSS, the idea of using low Earth orbit (LEO) satellites for position and velocity determination is relatively new. On one hand, the launch to LEO is more affordable compared to GNSS orbits. On the other hand, LEO satellites provide reduced coverage and suffer from orbit determination uncertainties. In this article, we study position and velocity estimation for an aerial platform using signals from a LEO satellite constellation, designed to produce a relatively long coverage duration, while minimizing the geometric dilution of precision. We determine the receiver’s position by using the trilateration method and the velocity by using Doppler estimation, and improve the accuracy thereof by utilizing an Extended Kalman Filter (EKF). We suggest a solution for the trilateration initialization problem, which arises for LEO navigation satellites, which relies on averaging the Earth projection of all the satellites within sight. We examine two scenarios, one wherein the EKF’s dynamical model matches the reference dynamical model, and another with a model mismatch. When the dynamical model is approximated, the EKF reduces the position and velocity errors considerably. When the dynamical model is known, the position and velocity errors can be reduced by an order of magnitude.

Millimeter-accuracy SLR bias determination using independent multi-LEO DORIS and GNSS-based orbits

2021 ◽  
Author(s):  
Daniel Arnold ◽  
Alexandre Couhert ◽  
Eléonore Saquet ◽  
Heike Peter ◽  
Flavien Mercier ◽  
...  
Keyword(s):  
Center Of Mass ◽  
Global Scale ◽  
Terrestrial Reference Frame ◽  
Low Earth Orbit ◽  
Global Navigation Satellite Systems ◽  
Laser Ranging ◽  
Bias Estimation ◽  
Satellite Systems ◽  
Leo Satellites ◽  
Orbit Errors

<p>Satellite Laser Ranging (SLR), i.e., the optical distance measurement to satellites equipped with laser retro-reflectors, has become an invaluable core technique in numerous geodetic applications. For instance, SLR measurements to spherical geodetic satellites, such as LAGEOS-1/2 or Etalon-1/2, form an essential contribution for the determination of geocenter coordinates and global scale in the International Terrestrial Reference Frame (ITRF) realizations.</p><p>SLR measurements to active satellites in Low Earth Orbit (LEO) are, on the other hand, up to now mostly used for an independent validation of orbit solutions, usually derived by microwave tracking techniques based on Global Navigation Satellite Systems (GNSS) or <span>Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS). This allows for the analysis of systematic orbit errors (e.g., originating from poorly known satellite center of mass locations or sensor offsets) not only in radial direction, but in t</span><span>h</span><span>ree dimensions. A high level of radial orbit reliability is, e.g., key to satellite altimetry applications.</span></p><p><span>For many of these geodetic SLR applications a mm accuracy and 0.1 mm/year stability is required or at least desired. Unavoidable SLR station biases are a major error source and obstacle to reach the aforementioned accuracy and stability goals. Among the stations of the International Laser Ranging Service (ILRS) there is a large diversity of biases and measurement qualities, and the calibration of these biases for all stations is key to further exploit SLR data for present and future geodetic applications.</span></p><p><span>In this presentation we demonstrate that the analysis of SLR data to active LEO satellites equipped with GNSS or DORIS receivers is a promising means to analyze SLR biases and their stability. </span><span>Using three independent selections of Earth observation missions in LEOs with three different SLR analysis software packages (Bernese GNSS Software, Zoom, Napeos), we estimate SLR range biases for all involved tracking stations on a yearly basis. We find that for many of the stations the three independently estimated sets of biases agree on a few-mm level</span><span> and that the inclusion of satellites from multiple missions allows to render the bias estimation more robust and in particular less prone to geographically correlated orbit errors. This shows that microwave-derived orbits of active LEO satellites, nowadays of very high quality due to numerous advances in modeling and an</span><span>alysis</span><span> techniques, can serve as interesting source</span><span>s</span><span> for SLR station calibration in </span><span>demanding</span><span> geodetic applications like, e.g., future ITRF realizations.</span></p>

scholarly journals GNSS RTK Positioning Augmented with Large LEO Constellation

2019 ◽  
Vol 11 (3) ◽  
pp. 228 ◽  
Author(s):  
Xingxing Li ◽  
Hongbo Lv ◽  
Fujian Ma ◽  
Xin Li ◽  
Jinghui Liu ◽  
...  
Keyword(s):  
Low Earth Orbit ◽  
Global Navigation Satellite Systems ◽  
Convergence Time ◽  
Current Status ◽  
Initial Assessment ◽  
Satellite Systems ◽  
Long Baseline ◽  
Leo Satellites ◽  
Global Navigation Satellite ◽  
Long Baselines

It is widely known that in real-time kinematic (RTK) solution, the convergence and ambiguity-fixed speeds are critical requirements to achieve centimeter-level positioning, especially in medium-to-long baselines. Recently, the current status of the global navigation satellite systems (GNSS) can be improved by employing low earth orbit (LEO) satellites. In this study, an initial assessment is applied for LEO constellations augmented GNSS RTK positioning, where four designed LEO constellations with different satellite numbers, as well as the nominal GPS constellation, are simulated and adopted for analysis. In terms of aforementioned constellations solutions, the statistical results of a 68.7-km baseline show that when introducing 60, 96, 192, and 288 polar-orbiting LEO constellations, the RTK convergence time can be shortened from 4.94 to 2.73, 1.47, 0.92, and 0.73 min, respectively. In addition, the average time to first fix (TTFF) can be decreased from 7.28 to 3.33, 2.38, 1.22, and 0.87 min, respectively. Meanwhile, further improvements could be satisfied in several elements such as corresponding fixing ratio, number of visible satellites, position dilution of precision (PDOP) and baseline solution precision. Furthermore, the performance of the combined GPS/LEO RTK is evaluated over various-length baselines, based on convergence time and TTFF. The research findings show that the medium-to-long baseline schemes confirm that LEO satellites do helpfully obtain faster convergence and fixing, especially in the case of long baselines, using large LEO constellations, subsequently, the average TTFF for long baselines has a substantial shortened about 90%, in other words from 12 to 2 min approximately by combining with the larger LEO constellation of 192 or 288 satellites. It is interesting to denote that similar improvements can be observed from the convergence time.

The Contribution of LARES to Global Climate Change Studies With Geodetic Satellites

2015 ◽  
Author(s):  
Giampiero Sindoni ◽  
Claudio Paris ◽  
Cristian Vendittozzi ◽  
Erricos C. Pavlis ◽  
Ignazio Ciufolini ◽  
...  
Keyword(s):  
Reference Frame ◽  
Earth Science ◽  
Global Climate ◽  
Temporal Variations ◽  
Terrestrial Reference Frame ◽  
Global Navigation Satellite Systems ◽  
Satellite Systems ◽  
Long Baseline ◽  
Geophysical Processes ◽  
Global Navigation Satellite

Satellite Laser Ranging (SLR) makes an important contribution to Earth science providing the most accurate measurement of the long-wavelength components of Earth’s gravity field, including their temporal variations. Furthermore, SLR data along with those from the other three geometric space techniques, Very Long Baseline Interferometry (VLBI), Global Navigation Satellite Systems (GNSS) and DORIS, generate and maintain the International Terrestrial Reference Frame (ITRF) that is used as a reference by all Earth Observing systems and beyond. As a result we obtain accurate station positions and linear velocities, a manifestation of tectonic plate movements important in earthquake studies and in geophysics in general. The “geodetic” satellites used in SLR are passive spheres characterized by very high density, with little else than gravity perturbing their orbits. As a result they define a very stable reference frame, defining primarily and uniquely the origin of the ITRF, and in equal shares, its scale. The ITRF is indeed used as “the” standard to which we can compare regional, GNSS-derived and alternate frames. The melting of global icecaps, ocean and atmospheric circulation, sea-level change, hydrological and internal Earth-mass redistribution are nowadays monitored using satellites. The observations and products of these missions are geolocated and referenced using the ITRF. This allows scientists to splice together records from various missions sometimes several years apart, to generate useful records for monitoring geophysical processes over several decades. The exchange of angular momentum between the atmosphere and solid Earth for example is measured and can be exploited for monitoring global change. LARES, an Italian Space Agency (ASI) satellite, is the latest geodetic satellite placed in orbit. Its main contribution is in the area of geodesy and the definition of the ITRF in particular and this presentation will discuss the improvements it will make in the aforementioned areas.

Performance of Low Earth Orbit Satellite Systems with a Gaussian Mixtures Traffic Distribution

Frequenz ◽  
2002 ◽  
Vol 56 (3-4) ◽  
Author(s):  
Hebatallah M. Mourad ◽  
Abd El-Aziz M. El-Basioni ◽  
Sherief S. Emam ◽  
Emad K. Al-Hussaini
Keyword(s):  
Low Earth Orbit ◽  
Earth Orbit ◽  
Gaussian Mixtures ◽  
Satellite Systems ◽  
Traffic Distribution ◽  
Orbit Satellite ◽  
Low Earth Orbit Satellite

scholarly journals Study the Effect of Solar Radiation Pressure at Several Satellite Orbits

2013 ◽  
Vol 10 (4) ◽  
pp. 1253-1261 ◽  
Author(s):  
Baghdad Science Journal
Keyword(s):  
Solar Radiation ◽  
Radiation Pressure ◽  
Jacobian Matrix ◽  
Solar Radiation Pressure ◽  
Equation Of Motion ◽  
Low Earth Orbit ◽  
Earth Orbit ◽  
Satellite Orbits ◽  
Orbit Satellite ◽  
Low Earth Orbit Satellite

The effects of solar radiation pressure at several satellite (near Earth orbit satellite, low Earth orbit satellite, medium Earth orbit satellite and high Earth orbit satellite ) have been investigated. Computer simulation of the equation of motion with perturbations using step-by-step integration (Cowell's method) designed by matlab a 7.4 where using Jacobian matrix method to increase the accuracy of result.

Co-location of SLR and GNSS techniques onboard Galileo and GLONASS satellites

2021 ◽  
Author(s):  
Grzegorz Bury ◽  
Krzysztof Sośnica ◽  
Radosław Zajdel ◽  
Dariusz Strugarek ◽  
Urs Hugentobler
Keyword(s):  
Orbital Plane ◽  
Terrestrial Reference Frame ◽  
Global Navigation Satellite Systems ◽  
Navigation Systems ◽  
Local Ties ◽  
Satellite Systems ◽  
The Impact ◽  
Space Ties ◽  
Gnss Observations

<p>All satellites of the Galileo and GLONASS navigation systems are equipped with laser retroreflector arrays for Satellite Laser Ranging (SLR). SLR observations to Global Navigation Satellite Systems (GNSS) provide the co-location of two space geodetic techniques onboard navigation satellites.</p><p>SLR observations, which are typically used for the validation of the microwave-GNSS orbits, can now contribute to the determination of the combined SLR+GNSS orbits of the navigation satellites. SLR measurements are especially helpful for periods when the elevation of the Sun above the orbital plane (β angle) is the highest. The quality of Galileo-IOV orbits calculated using combined SLR+GNSS observations improves from 36 to 30 mm for β> 60° as compared to the microwave-only solution. </p><p>Co-location of two space techniques allows for the determination of the linkage between SLR and GNSS techniques in space. Based on the so-called space ties, it is possible to determine the 3D vector between the ground-based co-located SLR and GNSS stations and compare it with the local ties which are determined using the ground measurements. The agreement between local ties derived from co-location in space and ground measurements is at the level of 1 mm in terms of the long-term median values for the co-located station in Zimmerwald, Switzerland.</p><p>We also revise the approach for handling the SLR range biases which constitute one of the main error sources for the SLR measurements. The updated SLR range biases consider now the impact of not only of SLR-to-GNSS observations but also the SLR observations to LAGEOS and the microwave GNSS measurements. The updated SLR range biases improve the agreement between space ties and local ties from 34 mm to 23 mm for the co-located station in Wettzell, Germany.</p><p>Co-location of SLR and GNSS techniques onboard navigation satellites allows for the realization of the terrestrial reference frame in space, onboard Galileo and GLONASS satellites, independently from the ground measurements. It may also deliver independent information on the local tie values with full variance-covariance data for each day with common measurements or can contribute to the control of the ground measurements as long as both GNSS and SLR-to-GNSS observations are available.</p>

Sign in / Sign up

Export Citation Format

Share Document