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Geodetic network infrastructure has evolved with increasing pace the past decade with remarkable additions of modern hardware, replacing aging, ‘80s vintage equipment throughout the globe. SLR needs however more than updating the network to deliver the accuracy required today. New and improved design “targets” must also be used that support the required “1-mm accuracy”. LAGEOS was conceived and built in the early ‘70s with a ~5 mm accuracy in mind [Pearlman et al., 2019]. This limitation forced analysts to develop approaches of data analysis to ensure that even with such data one can reach the required 1-mm accuracy [Luceri et al., 2019]. Along with the network updates a parallel effort was thus initiated to modernize the space segment as well. Initially with the design and launch of LARES in 2012 [Pavlis et al., 2015] and following that, the design of LARES-2 [Ciufolini et al., 2017, Paolozzi et al., 2019], which was successfully launched on July 13, 2022 [https://www.nature.com/articles/d41586-022-02034-x]. The new mm-accurate target was quickly acquired first by the Italian station at Matera, only three days after launch and although very early in the mission, the data were of remarkably high quality and insignificant bias. This prompted a quick evaluation and a test inclusion of this target in the limited list of SLR targets supporting the ITRF development. With an orbit nearly identical to LAGEOS (with supplementary inclination), taking full advantage of all the appropriate models designed and applied to LAGEOS, we achieved 7-day orbital fits of 3-5 mm even without a tuned target signature correction. Using the approach described in [Kuzmicz-Cieslak, M. et al., 2022] and along with data from the other geodetic spheres, we have generated preliminary combination products for the development of the ITRF. We will present an overview of this initial analysis of LARES-2 data focusing on comparing these results to contemporaneously taken data from the standard four geodetic spheres only, (LAGEOS 1 & 2 and Etalon 1 & 2).Pearlman et al. J Geod 93, 2181–2194 (2019). https://doi.org/10.1007/s00190-019-01228-yLuceri et al. J Geod 93, 2357–2366 (2019). https://doi.org/10.1007/s00190-019-01319-wPavlis et al. EEEIC (2015), pp. 1989-1994. https://doi.org/10.1109/EEEIC.2015.7165479Paolozzi et al. J Geod 93, 2437–2446 (2019). https://doi.org/10.1007/s00190-019-01316-zCiufolini et al. Eur. Phys. J. Plus 132, 336 (2017). https://doi.org/10.1140/epjp/i2017-11635-1Kuzmicz-Cieslak, M. et al. (2022). https://doi.org/10.22541/essoar.167214343.32185093/v

The ILRS contributed to the development of ITRF2020 via the combined products submitted to ITRS. The combined products were the result of the combination of individual AC contributions where a new approach in handling systematic errors at the stations was implemented. A set of a priori estimated mean biases was considered for the main period 1993-2020 that includes data from LAGEOS, LAGEOS-2 and the Etalons, whereas an adjusted 15-day average bias at each station for the 1983-1993 period was considered to accommodate systematic and target signature errors, if a priori mean biases were missing. The implementation of ITRF2020/SLRF2020 in SLR operational products required an extended version of the SSEM model, SSEM-X, which led to the finalization of a new DH file. Considering this updated set of long-term mean biases, all ACs produced a solution set based on models used for REPRO2020 and SLRF2020 as input to a combined product intended for the IERS RS/PC at USNO. These EOP series will be used for the calibration of EOP biases prior to the release the final version of the new Bulletin A. The new bias model SSEM-X will be publicly available and maintained current over the coming years.

The member ACs of the ILRS Analysis Standing Committee—ASC, evaluated the preliminary release of ITRF2020—ITRF2020P. For the most part, this evaluation is based on the reanalysis of part or all of the SLR data from geodetic spherical targets in the model; in particular, we focused on the two LAGEOS and two Etalons from 1993 to the end of 2020, extended by one year of data NOT included in the model: all of 2021. The evaluation report was submitted to ITRS for consideration in the finalization of the ITRF2020 model. Some ACs used additional data that do not contribute to ITRF development for testing. The reanalysis used the same improved modeling that was used for the development of the ILRS contribution to ITRF2020.We will focus on the implementation of the new approach in handling systematic errors at the stations and how users will need to adapt their data analysis procedures to benefit the most from the new model. The 2021 ILRS contribution to ITRF2020 minimized the scale difference between SLR and VLBI below 2 mm (ITRF2014 ~9 mm). The reanalysis incorporates an improved “target signature” model (CoG) for better separation of true systematic errors from errors in describing the target’s signature. This model will be periodically updated from now on, so that it represents accurately the state of operations at all sites in the ILRS network of tracking stations. SLR data users should make sure from now on to use each ITRF model with the appropriate (consistent) Data Handling file and “target signature” model.The presentation will provide an overview of the analysis procedures and models, and it will demonstrate the level of improvement with respect to the previous ILRS product series, focusing especially on the Core ILRS sites.

The satellite laser ranging (SLR) technique has the potential to make extremely precise measurements to retroreflector arrays on orbiting satellites, with normal point range precision at a level of 1 mm for the core tracking stations of the International Laser Ranging Service (ILRS). The main limitation to achieving a similar level of range accuracy is the presence of uncorrected systematic errors, which can be attributed to various sources at the stations (e.g., calibration and/or synchronization procedures, hardware malfunctioning, nonlinearities in the time-of-flight measurement devices), as well as to modeling deficiencies, especially in the ability to refer the range measurements to the center of mass of the spacecraft. The ILRS has always been active in adopting rigorous procedures to detect and remove systematic errors from the data: a group of ILRS analysis centers routinely performs data quality control a few hours after data acquisition; the ILRS Analysis Standing Committee (ASC) is in charge of long-term monitoring and characterization of systematic errors in the observations used for the ILRS products; a Quality Control Board was established in 2015 to address SLR systems’ biases and other data issues. In particular, the ASC is devoting efforts on an investigation of an alternative approach whereby a simultaneous estimation of site coordinates and range biases provides station positions that are in principle free of systematic errors. Results using this approach have shown a significant impact on the realization of the TRF, in particular by reducing the existing scale offset between the VLBI and SLR solutions and reaching a closer agreement with the ITRF2014 scale. This paper outlines the work that continues to be done to improve these products and in particular focuses on new research to evaluate rigorously any impact on the strength of coordinate solutions and geophysical inferences when systematic range errors are determined simultaneously with reference frame parameters. Future procedures for handling systematic errors will be informed by the outcome of the current investigations.

NASA’s legacy Satellite Laser Ranging (SLR) network produces about one-third of the global SLR data to support space geodesy. This network of globally distributed stations has been using Time Interval Units (TIU) for range measurements for the last 25 + years. To improve the reliability of the SLR network and satisfy the need for stable millimeter precision data, a phased replacement of the TIUs in the network with picosecond-precise Event Timer Modules was initiated in 2015. This scheme allowed the time of flight and laser transmit epoch measurement to one picosecond resolution. For a network with global scientific impact, transitioning to a new data generation metrological scheme requires significant data scrutiny and long-term science data validation. Any long-term testing/measurement has the potential to interrupt the station’s daily operational data flow to the International Laser Ranging Service (ILRS) as the station under test will have to put its test data into quarantine. We have demonstrated a very effective way to test and implement the new device without removing the old hardware and without the need for the orbit analysis. This operationally noninvasive scheme performed concurrent test measurements enabling uninterrupted operational data flow to the users, while allowing simultaneous test data capture for short- and long-term systematics and stability analysis. Extensive analysis of the test data was performed by the NASA SLR engineering team and the ILRS Analysis Standing Committee, to uncover biases and any dependencies on the satellite ranges (for nonlinear scale issues). Multi-ETM comparison was also performed at two of the SLR stations through the interchange of hardware to establish the inter-device range biases and stability. Such benchmarked hardware was subsequently sent to the remaining stations to allow traceability and normalize the network performance. The range bias intercomparison performed using the multiyear SLR data analysis agreed well with the engineering changes, thus validating the approach to flush out station-specific ranging systematics affecting precise orbit determination. Such an improvement and rebalancing of the current network will allow an orderly transition of the current NASA SLR network operating at a maximum rate of 10 Hz to the NASA next generation Space Geodesy Satellite Laser Ranging (SGSLR) network operating at 2 kHz (McGarry et al. in J Geod, 2018. https://doi.org/10.1007/s00190-018-1191-6; Merkowitz et al. in J Geod, 2018. https://doi.org/10.1007/s00190-018-1204-5).

LARES 2 is an Italian Space Agency (ASI) satellite designed for testing with unprecedented accuracy frame-dragging, a fundamental prediction of general relativity, for other tests of fundamental physics and to contribute to space geodesy with a precision higher than any other satellite presently in orbit. The choice of the material for the body of LARES 2 satellite determines, along with its dimensions, the surface-to-mass ratio minimization, which is the main requirement for the satellite. The paper will report the studies conducted for the fulfillment of the above-mentioned requirement and the tests performed to qualify the materials for construction of the satellite.

The International Laser Ranging Service (ILRS) was established by the International Association of Geodesy (IAG) in 1998 to support programs in geodesy, geophysics, fundamental constants and lunar research, and to provide the International Earth Rotation Service with data products that are essential to the maintenance and improvement in the International Terrestrial Reference Frame (ITRF), the basis for metric measurements of changes in the Earth and Earth–Moon system. Other scientific products derived from laser ranging include precise geocentric positions and motions of ground stations, satellite orbits, components of Earth’s gravity field and their temporal variations, Earth Orientation Parameters, precise lunar ephemerides and information about the internal structure of the Moon. Laser ranging systems are already measuring the one-way distance to remote optical receivers in space and are performing very accurate time transfer between remote sites in the Earth and in Space. The ILRS works closely with the IAG’s Global Geodetic Observing System. The ILRS develops (1) the standards and specifications necessary for product consistency, and (2) the priorities and tracking strategies required to maximize network efficiency. The service collects, merges, analyzes, archives and distributes satellite and lunar laser ranging data to satisfy a variety of scientific, engineering, and operational needs and encourages the application of new technologies to enhance the quality, quantity, and cost effectiveness of its data products. The ILRS works with (1) new satellite missions in the design and building of retroreflector targets to maximize data quality and quantity, and (2) science programs to optimize scientific data yield. Since its inception, the ILRS has grown to include forty laser ranging stations distributed around the world. The ILRS stations track more than ninety satellites from low Earth orbit (LEO) to the geosynchronous orbit altitude as well as retroreflector arrays on the surface of the Moon. Applications have been expanded to include time transfer, asynchronous ranging for targets at extended ranges, free space quantum telecommunications, and the tracking of space debris. Laser ranging technology is moving to lower energy, higher repetition rates (kHz), single-photon-sensitive detectors, shorter pulse widths, shorter normal point intervals for faster data acquisition, and increased pass interleaving, automated to autonomous operation with remote access, and embedded software for real-time updates and decision making. An example of pass interleaving is presented for the Yarragadee station (see Fig. 4); tracking of LEO satellites is often accommodated during break in LEO and GNSS passes. New satellites arrays provide more compact targets and work continues on the development of lighter less expensive arrays for satellites and the moon. The service now provides operational ITRF products including daily/weekly station positions and daily resolution Earth orientation products; the flow of weekly combination of satellite orbit files for LAGEOS/Etalon-1 and -2 has recently been established. New products are under testing through a pilot project on systematic error monitoring currently underway. The article will give an overview of activities underway within the service, paths forward presently envisioned, and current issues and challenges.

The International Laser Ranging Service (ILRS) contribution to ITRF2020 has been prepared after the re-analysis of the data from 1993 to 2020, based on an improved modeling of the data and a novel approach that ensures the results are free of systematic errors in the underlying data. This reanalysis incorporates an improved “target signature” model (CoM) that allows better separation of true systematic error of each tracking system from the errors in the model describing the target’s signature. The new approach was developed after the completion of ITRF2014, the ILRS Analysis Standing Committee (ASC) devoting almost entirely its efforts on this task. The robust estimation of persistent systematic errors at the millimeter level permitted the adoption of a consistent set of long-term mean corrections for data collected in past years, which are now applied a priori (information provided by the stations from their own engineering investigations are still taken into consideration). The reanalysis used these corrections, leading to improved results for the TRF attributes, reflected in the resulting new time series of the TRF origin and especially in the scale. Seven official ILRS Analysis Centers computed time series of weekly solutions, according to the guidelines defined by the ILRS ASC. These series were combined by the ILRS Combination Center to obtain the official ILRS product contribution to ITRF2020.The presentation will provide an overview of the analysis procedures and models, and it will demonstrate the level of improvement with respect to the previous ILRS product series; the stability and consistency of the solution are discussed for the individual AC contributions and the combined SLR time series.

The International Laser Ranging Service (ILRS) is improving its services through network expansion and continuous upgrades of its modeling and analysis approaches. New ground stations are being deployed with higher repetition rate systems, more efficient detection, and increased automation; new technologies are also being adopted at some of its legacy stations. In addition, the roster of tracking missions is rapidly expanding. The top priority for the Service continues to be its contribution to the reference frame development, but of increasing importance is also the tracking of GNSS satellites, including the anticipated deployment of the new GPS III constellation over this decade. These requirements are being reflected in new system designs and updates. Stations are also being adapted to accommodate ground and space-time synchronization. A few stations continue with their lunar laser ranging activities while several others have begun testing their ability to do lunar ranging in the future. About a dozen stations are active in space-debris tracking for studies of orbital dynamics and reentry predictions. New tools and procedures have been implemented to improve the quality of SLR data and derived products, and to expedite the resolution of engineering issues. Work also continues on the design and building of improved retroreflector targets to maximize data quality and quantity. This paper will give an overview of activities underway within the Service, paths forward and presently envisioned, and current issues and challenges.

The International Laser Ranging Service (ILRS) Analysis Standing Committee (ASC) plans to complete the re-analysis of the SLR data since 1983 to end of this year by early 2021. This will ensure that the ILRS contribution to ITRF2020 will be available to ITRS by February 2021, as agreed by all space geodetic techniques answering its call. In preparation for the development of this contribution, the ILRS completed the re-analysis of all data (1983 to present), based on an improved modeling of the data and a novel approach that ensures the results are free of systematic errors in the underlying data. The new approach was developed after the completion of ITRF2014, the ILRS ASC devoting almost entirely its efforts on this task. A Pilot Project initially demonstrated the robust estimation of persistent systematic errors at the millimeter level, leading us to adopt a consistent set of a priori corrections for data collected in past years. The initial reanalysis used these corrections, leading to improved results for the TRF attributes, reflected in the resulting new time series of the TRF origin and scale. The ILRS ASC will now use the new approach in the development of its operational products and as a tool to monitor station performance, extending the history of systematics for each system that will be used in future re-analysis. The new operational products form a seamless extension of the re-analysis series, providing a continuous product based on our best knowledge of the ground system behavior and performance, without any dependence whatsoever on a priori knowledge of systematic errors (although information provided by the stations from their own engineering investigations are always welcome and taken into consideration). The presentation will demonstrate the level of improvement with respect to the previous ILRS product series and give a glimpse of what is to be expected from the development of a preliminary version of the ITRF2020.

The GGOS Bureau of Networks and Observations works with the IAG Services (IVS, ILRS, IGS, IDS, IGFS, and PSMSL) to advocate for the expansion and upgrade of space geodesy networks for the maintenance and improvement of the reference frame and other applications, as well as for the integration with other techniques, including absolute gravity and sea level measurements from tide gauges. New sites are being established following the GGOS concept of “core” and co-location sites, and new technologies are being implemented to enhance performance in data yield as well as accuracy. The Bureau continues to meet with organizations to discuss possibilities, including partnerships, for new and expanded participation. The GGOS Network continues to grow as new stations join every year.The Bureau holds meetings frequently, providing the opportunity for representatives from the services to meet and share progress and plans, and to discuss issues of common interest. It also monitors the status and projects the evolution of the network based on information from the current and expected future participants. Of particular interest at the moment is the integration of gravity and tide gauge networks and the forthcoming establishment of the new absolute gravity reference frame. The IAG Committees and Joint Working Groups play an essential role in the Bureau activity. The Standing Committee on Performance Simulations and Architectural Trade-offs (PLATO) uses simulation and analysis techniques to project future network capability and to examine trade-off options. The Committee on Data and Information is working on a strategy for a GGOS metadata system for data products and a more comprehensive long-term plan for an all-inclusive system. The Committee on Satellite Missions is working to enhance communication with the space missions, to advocate for missions that support GGOS goals and to enhance ground systems support. The IERS Working Group on Site Survey and Co-location (also participating in the Bureau) is working to enhance standardization in procedures, outreach and to encourage new survey groups to participate and improve procedures to determine systems’ reference points, a crucial aid in the detection of technique-specific systematic errors. We will give a brief update on the status and projection of the network infrastructure of the next several years, and the progress and plans of the Committees/Working Group in their critical role in enhancing data product quality and accessibility to the users.

Satellite laser ranging (SLR) is an important technique that contributes to the determination of terrestrial geodetic reference frames, especially to the realization of the origin and the scale of global networks. One of the major limiting factors of SLR-derived reference frame realizations is the datum accuracy which significantly suffers from the current global SLR station distribution. In this paper, the impact of a potential future development of the SLR network on the estimated datum parameters is investigated. The current status of the SLR network is compared to a simulated potential future network featuring additional stations improving the global network geometry. In addition, possible technical advancements resulting in a higher amount of observations are taken into account as well. As a result, we find that the network improvement causes a decrease in the scatter of the network translation parameters of up to 24%, and up to 20% for the scale, whereas the technological improvement causes a reduction in the scatter of up to 27% for the translations and up to 49% for the scale. The Earth orientation parameters benefit by up to 15% from both effects.

LARES (LAser RElativity Satellite) developed by the Italian Space Agency (ASI) is a laser-ranged satellite successfully launched in February 2012 by ESA (European Space Agency). A second ASI laser-ranged satellite, LARES 2, is scheduled for launch by ESA at the end of 2019. Here we describe the main scientific objectives achieved and achievable by LARES and LARES 2, both in General Relativity and in space geodesy and geodynamics. Among the main tests achieved by LARES is a 5% test of frame-dragging, a fundamental and intriguing prediction of General Relativity. The LARES 2 satellite together with the laser-ranged satellite LAGEOS of NASA, is aimed to provide a 0.2% test of frame-dragging together with other relevant tests and determinations in fundamental physics, space geodesy and geodynamics.

Special issue Satellite Laser Ranging.-- 11 pages, 7 figures, 1 table, NASA maintains and operates a global network of Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), and Global Navigation Satellite System ground stations as part of the NASA Space Geodesy Program. The NASA Space Geodesy Network (NSGN) provides the geodetic products that support Earth observations and the related science requirements as outlined by the US National Research Council (NRC in Precise geodetic infrastructure: national requirements for a shared resource, National Academies Press, Washington, 2010. http://nap.edu/12954, Thriving on our changing planet: a decadal strategy for Earth observation from space, National Academies Press, Washington, 2018. http://nap.edu/24938). The Global Geodetic Observing System (GGOS) and the NRC have set an ambitious goal of improving the Terrestrial Reference Frame to have an accuracy of 1 mm and stability of 0.1 mm per year, an order of magnitude beyond current capabilities. NASA and its partners within GGOS are addressing this challenge by planning and implementing modern geodetic stations colocated at existing and new sites around the world. In 2013, NASA demonstrated the performance of its next-generation systems at the prototype next-generation core site at NASA¿s Goddard Geophysical and Astronomical Observatory in Greenbelt, Maryland. Implementation of a new broadband VLBI station in Hawaii was completed in 2016. NASA is currently implementing new VLBI and SLR stations in Texas and is planning the replacement of its other aging domestic and international legacy stations. In this article, we describe critical gaps in the current global network and discuss how the new NSGN will expand the global geodetic coverage and ultimately improve the geodetic products. We also describe the characteristics of a modern NSGN site and the capabilities of the next-generation NASA SLR and VLBI systems. Finally, we outline the plans for efficiently operating the NSGN by centralizing and automating the operations of the new geodetic stations

We report the improved test of frame-dragging, an intriguing phenomenon predicted by Einstein's General Relativity, obtained using 7 years of Satellite Laser Ranging (SLR) data of the satellite LARES (ASI, 2012) and 26 years of SLR data of LAGEOS (NASA, 1976) and LAGEOS 2 (ASI and NASA, 1992). We used the static part and temporal variations of the Earth gravity field obtained by the space geodesy mission GRACE (NASA and DLR) and in particular the static Earth's gravity field model GGM05S augmented by a model for the 7-day temporal variations of the lowest degree Earth spherical harmonics. We used the orbital estimator GEODYN (NASA). We measured frame-dragging to be equal to 0.9910 +/- 0.02, where 1 is the theoretical prediction of General Relativity normalized to its frame-dragging value and +/- 0.02 is the estimated systematic error due to modelling errors in the orbital perturbations, mainly due to the errors in the Earth's gravity field determination. Therefore, our measurement confirms the prediction of General Relativity for frame-dragging with a few percent uncertainty., Comment: Submitted on September 27, 2019; accepted for publication on October 8, 2019 and published on October 23, 2019 in The European Physical Journal C: Eur. Phys. J. C (2019) 79:872 https://doi.org/10.1140/epjc/s10052-019-7386-z

International audience; Satellite Laser Ranging (SLR) began in the mid-1960s on satellites of opportunity with retro-reflectors intended as a part of intercomparison tests of satellite tracking techniques. Shortly thereafter, data from these satellites began to work their way into geodetic solutions and dedicated geodesy experiments. By early 1970s when future requirements for centimeter accuracy were envisioned, planning began for dedicated, spherical retro-reflector geodetic satellites. Built with high mass-to-area ratios, these satellites would have important applications in gravity field modeling, station geolocation and fiducial reference systems, Earth rotation, and fundamental physics. Early geodetic satellites were Starlette, launched in 1975 by Centre National d’Etudes Spatiales (CNES), and LAGEOS in 1976 by the National Aeronautics and Space Administration (NASA). Recent geodetic satellites include LARES, launched in 2012, and LARES-2 under development, both by the Italian Space Agency (ASI). Today, a complex of these ‘geodetic satellites’ from low to high altitude Earth orbits supports many space geodesy requirements. This paper will discuss the evolution of the geodetic satellites from the early days, through current programs and out to future needs as we approach our goal for millimeter accuracy.

Quality control systems for satellite laser ranging (SLR) observations have been developed at a number of analysis institutes worldwide, using various software packages of precise orbit determination and data analysis. Satellite laser range observations, primarily from the two LAGEOS satellites but also from other satellites in low-Earth orbits and up to GNSS altitude, are being processed on a sub-daily to weekly basis. The generated quality control reports are widely used to detect various kinds of problems and quickly provide anomalous information to laser ranging stations. They have been effective in shortening the time to return to normal operations when anomalous data are detected and in quantifying the performance of laser ranging stations. Consequently, a rapid feedback loop has now been incorporated in the modern SLR operation.

In 2016, we published "A test of general relativity using the LARES and LAGEOS satellites and a GRACE Earth gravity model. Measurement of Earth's dragging of inertial frames [1]", a measurement of frame-dragging, a fundamental prediction of Einstein's theory of General Relativity, using the laser-ranged satellites LARES, LAGEOS and LAGEOS 2. The formal error, or precision, of our test was about 0.2% of frame-dragging, whereas the systematic error was estimated to be about 5%. In the 2017 paper "A comment on "A test of general relativity using the LARES and LAGEOS satellites and a GRACE Earth gravity model by I. Ciufolini et al." "by L. Iorio [2] (called I2017 in the following), it was incorrectly claimed that, when comparing different Earth gravity field models, the systematic error in our test due to the Earth's even zonal harmonics of degree 6, 8, 10 could be aslarge as 15%, 6% and 36%, respectively. Furthermore, I2017 contains other, also incorrect, claims about the number of necessary significant decimal digits of the coefficients used in our test (claimed to be nine), in order to eliminate the largest uncertainties in the even zonals of degree 2 and 4, and about the non-repeatability of our test. Here we analyze and rebut those claims in I2017., Comment: Published on The European Physical Journal C 78, no. 11 (2018): 880

Increasing numbers of Geostationary Earth Orbit satellites have led to the requirement of accurate station keeping and precise orbit prediction to avoid collision between satellites. In the case of ground-based optical observation, angular resolution is better than other tracking systems, such as radar systems; however, the observation time of optical observation is limited by weather or lighting conditions. To develop an effective optical observation strategy, the optical observation campaign from January to February 2014 for Communication, Ocean and Meteorological Satellite (COMS) was conducted. Because COMS is a controlled satellite with station keeping manoeuvres performed twice a week, the observation results for 1- and 2-day observations were analysed. Sparse and sporadic cases for the sequential observation of multiple satellites and a dense case for the intensive observation of specific targets were assumed for the experiments. In the 1-day arc observation experiment, the estimated orbits for dense observation cases over 10% of the orbital period showed that the maximum difference was less than 40 km (station keeping area) for 7-day propagation compared to the estimation result using the whole 1-day measurement. For the 2-day arc observation, the orbit estimation difference could be maintained within 2 km using a more frequent observation than the 1-h interval for 13 h that was used in the sparse case. Additionally, the longitudinal and latitudinal positions via the estimation result using the optical observation were compared with the Two-Line Elements (TLEs) and operator’s data. Through this study, an adequate optical tracking strategy was studied, and the possibility of cooperation with other systems was also validated.

Earth rotation, besides external actions due to other bodies in the solar system, is influenced by internal mass redistributions, including its atmospheric and water envelope. EI Nifio-Southern Oscillation (ENSO) is one such event characterized by sea level change in the eastern part of the Pacific Ocean due to an increase of the temperature by about 2°C. ENSO is manifested with irreguIar periodicity and with different strength. SateIIite Laser Ranging (SLR) to orbiting satellites such as LAGEOS and LARES in conjunction with the other geodedic techniques, such as GNSS and Very Long Baseline Interferometry (VLBI), allow very accurate determination of the center of mass and rotation vector of the Earth. The paper will report on the experimental vaIues of the Earth orientation parameters and in particuIar of the center of mass and the Iength of the day with particuIar reference to signatures due to last ENSO event ended in 2016.

We introduce the LARES 2 space experiment recently approved by the Italian Space Agency (ASI). The LARES 2 satellite is planned for launch in 2019 with the new VEGA C launch vehicle of ASI, ESA and ELV. The orbital analysis of LARES 2 experiment will be carried out by our international science team of experts in General Relativity, theoretical physics, space geodesy and aerospace engineering. The main objectives of the LARES 2 experiment are gravitational and fundamental physics, including accurate measurements of General Relativity, in particular a test of frame-dragging aimed at achieving an accuracy of a few parts in a thousand, i.e., aimed at improving by about an order of magnitude the present state-of-the-art and forthcoming tests of this general relativistic phenomenon. LARES 2 will also achieve determinations in space geodesy. LARES 2 is an improved version of the LAGEOS 3 experiment, proposed in 1984 to measure frame-dragging and analyzed in 1989 by a joint ASI and NASA study., 16 pages

In the previous paper we have introduced the LARES 2 space experiment. The LARES 2 laser-ranged satellite is planned for a launch in 2019 with the new VEGA C launch vehicle of the Italian Space Agency (ASI), ESA and ELV. The main objectives of the LARES 2 experiment are accurate measurements of General Relativity, gravitational and fundamental physics and accurate determinations in space geodesy and geodynamics. In particular LARES 2 is aimed to achieve a very accurate test of frame-dragging, an intriguing phenomenon predicted by General Relativity. Here we report the results of Monte Carlo simulations and covariance analyses fully confirming an error budget of a few parts in one thousand in the measurement of frame-dragging with LARES 2 as calculated in our previous paper., 15 pages and 6 figures. arXiv admin note: text overlap with arXiv:1310.2601

We present a test of General Relativity, the measurement of the Earth's dragging of inertial frames. Our result is obtained using about 3.5 years of laser-ranged observations of the LARES, LAGEOS and LAGEOS 2 laser-ranged satellites together with the Earth's gravity field model GGM05S produced by the space geodesy mission GRACE. We measure $\mu = (0.994 \pm 0.002) \pm 0.05$, where $\mu$ is the Earth's dragging of inertial frames normalized to its General Relativity value, 0.002 is the 1-sigma formal error and 0.05 is the estimated systematic error mainly due to the uncertainties in the Earth's gravity model GGM05S. Our result is in agreement with the prediction of General Relativity.

The use of satellite laser ranging in combination with other space geodetic techniques allows us to determine Earth's motion with unprecedented accuracy, which is not as simple as usually described in basic textbooks. Besides rotation and revolution there is a wobble of the rotation axis that can be derived by the torque free case in rigid body dynamics. The presence of gravitational perturbations complicates the motion and considering Earth as non-rigid introduces even more variations in the basic Earth motion theory. What is interesting is that also the mass redistribution of air and water on the planet can affect the motion of Earth's rotational axis. Thanks to the millimetre accuracy achievable today, it is possible to correlate very small anomalous rotational axis displacements with global environmental changes such the change in ice melting. The paper will show the experimental motion of the Earth rotation axis and interpret it with the use of the Euler rigid body equations of motion, outlining also the effects of the gravitational perturbations of other bodies in the solar system and of the global climate changes on the Earth rotational axis.

We summarize a laser-ranged satellite test of frame-dragging, a prediction of General Relativity, and then concentrate on the estimate of thermal thrust, an important perturbation affecting the accuracy of the test. The frame dragging study analysed 3.5 years of data from the LARES satellite and a longer period of time for the two LAGEOS satellites. Using the gravity field GGM05S obtained via the Grace mission, which measures the Earth's gravitational field, the prediction of General Relativity is confirmed with a 1-$\sigma$ formal error of 0.002, and a systematic error of 0.05. The result for the value of the frame dragging around the Earth is $\mu$ = 0.994, compared to $\mu$ = 1 predicted by General Relativity. The thermal force model assumes heat flow from the sun (visual) and from Earth (IR) to the satellite core and to the fused silica reflectors on the satellite, and reradiation into space. For a roughly current epoch (days 1460 - 1580 after launch) we calculate an average along-track drag of -0.50 $pm/s^{2}$., Comment: 6 pages, multiple figures in Proceedings of Metrology for Aerospace (MetroAeroSpace), 2016 IEEE

The Earth Orientation Parameters (EOP), i.e. the spin axis of the Earth, is influenced by the mass redistribution inside and on the surface of the Earth. On the Earth surface, global ice melting, sea level change and atmospheric circulation are the prime contributors. Recent studies have unraveled the majority of the mysteries behind the Chandler wobble, the annual motion and the secular motion of the pole. The differences from the motion of a pole for a rigid Earth is indeed due to the mass redistribution and transfer of angular momentum among the atmosphere, the oceans and solid Earth. The technique of laser ranging and the use of laser ranged satellites such as LARES along with other techniques such Very Long Baseline Interferometry (VLBI) allow to measure the EOP with accuracies at the level of ~200 μas which correspond to few millimeters at the Earth’s surface, while the use of Global Navigation Satellite System (GNSS) data can reach an accuracy even below 100 μas. At these unprecedented high levels of accuracy, even tiny anomalous behavior in EOP can be observed and thus correlated to global environmental changes such as ice melting on Greenland and the polar caps, and extreme events that involve strong ocean-atmosphere coupling interactions such as the El Nino. The contribution of Satellite Laser Ranging (SLR) data such as from the LARES mission and similar satellites to this area is outlined in this paper.

The ILRS EOP Time Series Since 2004, ILRS has been providing on a weekly basis combined SSC/EOP solutions from 7-day arcs to support IERS for EOP computation and reference frame maintenance. At present, eight Analysis Centers and two Combination Centers contribute to the weekly official ILRS combined solution from which the main SLR contribution to the IERS EOP reference series is derived. The most recent work performed jointly by all ILRS Analysis Centers (AC) was the generation of a contribution to the next ITRF, extending the time-span coverage of the 7-day arcs combined solution to 1983-2008. In another effort we try to improve the ILRS products' latency and to minimize the delay of the SLR contribution to the IERS EOP estimation, by increasing the product generation frequency (pre-operational daily product), to once per day.

For Precise Orbit Determination of altimetry missions, we have computed a data set of DORIS station coordinates defined for specific time intervals called DPOD2005. This terrestrial reference set is an extension of ITRF2005. However, it includes all new DORIS stations and is more reliable, as we disregard stations with large velocity formal errors as they could contaminate POD computations in the near future. About 1/4 of the station coordinates need to be defined as they do not appear in the original ITRF2005 realization. These results were verified with available DORIS and GPS results, as the integrity of DPOD2005 is almost as critical as its accuracy. Besides station coordinates and velocities, we also provide additional information such as periods for which DORIS data should be disregarded for specific DORIS stations, and epochs of coordinate and velocity discontinuities (related to either geophysical events, equipment problem or human intervention). The DPOD model was tested for orbit determination for TOPEX/Poseidon (T/P), Jason-1 and Jason-2. Test results show DPOD2005 offers improvement over the original ITRF2005, improvement that rapidly and significantly increases after 2005. Improvement is also significant for the early T/P cycles indicating improved station velocities in the DPOD2005 model and a more complete station set. Following 2005 the radial accuracy and centering of the ITRF2005-original orbits rapidly degrades due to station loss.

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.Copyright © 2015 by ASME

The LARES satellite was successfully launched in 2012 for tests of General Relativity and gravitational physics including the accurate measurement of frame-dragging. It is currently very well observed all over the world by the stations of the International Laser Ranging Service. Its preliminary orbital analyses show that LARES behaves as the best artificial massive test particle today available in the solar system, providing an optimal approximation to the time-like geodesic motion of General Relativity. Furthermore, on the basis of a test using almost three years of observations of LARES, we concluded that LARES, together with the LAGEOS and LAGEOS 2 satellites, provides excellent preliminary results for testing General Relativity.

LAser RElativity Satellite (LARES) is an Italian Space Agency mission that started operations on February 2012 after a successful launch on ESA's VEGA qualification flight. The satellite is covered with retroreflectors that allow accurate laser ranging tracking from the stations of the International Laser Ranging Service. Data of laser ranged satellites are publicly available for scientific analysis and in the case of LARES are being used mainly for testing general relativity and in particular the Lense-Thirring effect due to the rotation of Earth. Although designed for fundamental physics, the LARES mission is also very useful for geodesy and geodynamics and it will provide, among other things, improvement of the International Terrestrial Reference Frame. After a description of the scientific objectives and of the satellite, the paper will focus on the operations required to run the mission.

LARES is the latest laser ranged geodetic satellite launched in orbit. It is an Italian Space Agency mission devoted mainly to test fundamental physics. However, it will be shown in the present paper that it will also contribute significantly to Earth science. The use of LARES together with the constellation of the other geodetic satellites will provide improvements in the measurement of the gravity field of Earth including its temporal variation measurements. In particular the latter carries signatures of mass redistribution due to several phenomena including global atmospheric and oceanic circulation, useful not only for monitoring global climate change but also to provide a means for climate model validation.

LARES is an Italian Space Agency satellite specifically designed, built and launched to test general relativity. It is a passive satellite covered with Cube Corner Reflectors that reflect laser pulses from tracking stations, thus allowing accurate measurement of the distance. That in turn enables accurate orbit reconstruction that is a key ingredient to allow the measurement of the tiny Lense-Thirring effect predicted by general relativity. The International Space Time Analysis Research Center provides the International Laser Ranging Service-ILRS, the orbital predictions for LARES for pointing of the tracking telescopes toward the target. The paper describes the technical aspects of generating the orbital predictions.

Satellite Laser Ranging (SLR) data have been fundamental over the past three decades for the realization of the International Terrestrial Reference Frame (ITRF), which is based on an inter-technique combination of the geodetic solutions obtained from an intra-technique combination strategy performed at each IERS Technique Centre. This approach provides an opportunity to verify the internal consistency for each technique and a comparison of Analysis Center (AC) adherence to internal procedures and adopted models.

LARES is an Italian Space Agency mission designed to test General Relativity in the weak field of Earth. In particular, the satellite will be able to measure frame-dragging with an accuracy of about 1%. The difficulty of the measurement is mainly due to the perturbations acting on the satellite and the relatively tiny size of the effect, amounting to about 118 milliarcseconds/year. LARES will also provide data to geodesists and it will contribute to GNSS by improving the origin definition of the International Terrestrial Reference Frame. The mission was designed and the satellite subsystems built and tested in less than four years. The short time to launch and the very limited budget of the LARES mission, raised doubts whether LARES could be, as expected by design, one of the best satellite laser ranging targets. The best way to confirm the success of the mission is to look at the range residuals from the primary stations of the International Laser Ranging Service (ILRS). In the paper it will be shown that from the majority of these stations LARES behaves as the best target.

In this paper, we provide a detailed description of our recent analysis and determination of the frame-dragging effect obtained using the nodes of the satellites LAGEOS and LAGEOS 2, in reply to the paper "On the reliability of the so-far performed tests for measuring the Lense-Thirring effect with the LAGEOS satellites" by L. Iorio, Added: the precise references to the the ArXiv papers of L. Iorio: gr-qc/0411024 v9 19 Apr 2005 and gr-qc/0411084 v5 19 Apr 2005, explicitly containing his proposal to use the mean anomaly

A space mission, OPTIS, has been proposed for testing the foundations of special relativity and post-Newtonian gravitation in the field of the Earth. The constraints posed on the original OPTIS orbital geometry would allow for a rather wide range of possibilities for the final OPTIS orbital parameters. This freedom could be exploited for further tests of post-Newtonian gravity. In this paper, we wish to preliminarily investigate if it would be possible to use the orbital data from OPTIS together with those from the existing geodetic passive laser-ranged LAGEOS and LAGEOS II satellites in order to perform precise measurements of the Lense Thirring effect. With regard to this possibility, it is important to note that the drag-free technology which should be adopted for the OPTIS mission would yield a lifetime of many years for this satellite. It turns out that the best choice would probably be to adopt the same orbital configuration as the proposed LAGEOS-like LARES satellite and, for testing, select a linear combination including the nodes of LAGEOS, LAGEOS II and OPTIS and the perigee of OPTIS. The total systematic error should be of the order of 1%. The LARES orbital geometry should not be too much in conflict with the original specifications of the OPTIS mission. However, a compromise solution could also be adopted. A comparison with the new perspectives of measuring the Lense Thirring effect with the existing laser-tracked satellites opened by the new gravity models from CHAMP and, especially, GRACE is made. It turns out that an OPTIS/LARES mission would still be of great significance because the obtainable accuracy would be better than that offered by a reanalysis of the currently existing satellites.

As early as the 15th century Swedes noticed that rocks in their harbors were slowly rising out of the sea [Ekman, 1991]. These local observations were not sufficient to distinguish whether the rocks were rising or the sea level falling. Later, it was realized that Fennoscandia was still rebounding from the last Ice Age. This historical observation is still relevant today. How can you know whether a point on the Earth's surface is slowly moving up, down, or horizontally? One must relate local measurements to a stable and accurate reference frame, one whose scale is much larger than the problem at hand. We remain concerned with sea-level variations, but present-day studies recognize that change must be measured from a global point of view and with respect to a globally well-defined reference frame. Thus, the regional and national geodetic datums developed over the past 200 years are inappropriate for studying global-level problems.

The WEGENER group has promoted the development of scientific space-geodetic activities in the Mediterranean and in the European area for the last fifteen years and has contributed to the establishment of geodetic networks designed particularly for earth science research. WEGENER currently has three scientific objectives which are related to plate-boundary processes, sea-level and height changes, and postglacial rebound. In a full exploitation of the space-geodetic techniques, namely SLR, VLBI and GPS, the individual scientific projects do not only pursue these objectives but also contribute to improving and developing the observation techniques as well as the modelling theories. In the past, particularly SLR observations within WEGENER-MEDLAS have provided a fundamental contribution to determine the regional kinematics of the tectonic plates in the Mediterranean with high precision. With GPS, spatially denser site distributions are feasible, and in several WEGENER projects detailed studies of tectonically active areas were possible on the basis of repeated episodic GPS observations. Current projects associated with WEGENER are successful in separating crustal movements and absolute sea-level variations as well as in monitoring postglacial rebound. These tasks require high-precision height determinations, a problem central to all of the present WEGENER activities. In these projects, continuously occupied GPS sites are of increasing importance. Time series of heights observed with continuous GPS can be determined with a few centimeters RMS error thus enabling the reliable estimates of vertical rates over relatively short time intervals. Regional networks of continuous GPS sites are already providing results relevant, for example, for the study of postglacial rebound. The Mediterranean area is an extraordinary natural laboratory for the study of seismotectonic processes, and the wealth of observations acquired in previous WEGENER projects together with new space-geodetic observations will allow the test of geophysical hypotheses linking three-dimensional deformations of the Earth's surface to the dynamics of the Earth's interior. In particular, it is anticipated that WEGENER projects will aim at a test of the slab-detachment hypothesis. The complex investigations on sea-level fluctuations presently carried out at basin scale from the Strait of Gibraltar to the Black Sea make it possible to study the present and recent past interactions of ocean, atmosphere and solid Earth, as well as to develop appropriate models to assess future aspects.

The last two Global Positioning System (GPS) spacecraft launched on August 30, 1993 and March 10, 1994 carried identical laser retroreflector arrays that allow laser ranging from ground stations. Tracking of these targets is a low priority for most of the ground stations due to the present mandatory support of missions with no alternative tracking. The available data is sparse and concentrated primarily on the first of the two spacecraft, GPS-35 (PRN 5). Despite this, analysis of this data set indicates that there is great potential for engineering and scientific experiments in a synergistic application of Satellite Laser Ranging (SLR) and radiometric GPS techniques.

In this paper we respond to the criticisms of "Phenomenology of the Lense-Thirring effect in the Solar System" by lorio et al. about the general relativistic phenomena of gravitomagnetism and frame-dragging. The claims of the paper by lorio et al. are not reproducible in any of our independent analyses. (C) 2011 Elsevier B.V. All rights reserved.