Satellite Laser Ranging System Research Articles

NASA's Satellite Laser Ranging Systems for the 21st Century.

For over 40 years, NASA's global network of satellite laser ranging (SLR) stations has provided a significant percentage of the global orbital data used to define the International Terrestrial Reference Frame (ITRF). The current NASA legacy network is reaching its end-of-life and a new generation of systems must be ready to take its place. Scientific demands of sub-millimeter precision ranging and the ever-increasing number of tracking targets give aggressive performance requirements to this new generation of systems. Using lessons learned from the legacy systems and the successful development of a prototype station, a new network of SLR stations, called the Space Geodesy Satellite Laser Ranging (SGSLR) systems, is being developed. These will be the state-of-the-art SLR component of NASA's Space Geodesy Project (SGP). Each of SGSLR's nine subsystems has been designed to produce a robust, kilohertz laser ranging system with 24/7 operational capability and with minimal human intervention. SGSLR's data must support the aggressive goals of the Global Geodetic Observing System (GGOS), which are 1 millimeter (mm) position accuracy and 0.1 mm per year stability of the ITRF. This paper will describe the major requirements and accompanying design of the new SGSLR systems, how the systems will be tested, and the expected system performance.

Time and laser ranging: a window of opportunity for geodesy, navigation and metrology.

Recent progress in the domain of time and frequency (T/F) standards requires important improvements of existing time distribution links. Among these, the accuracy of time transfer is actually an important part of the concerns in order to establish and maintain time & space references from ground and/or space facilities. Several time transfers by laser link projects have been carried out over the past 10 years with numerous scientific and metrological objectives. Satellite Laser ranging (SLR) has proven to be a fundamental tool, offering a straightforward, conceptually simple, highly accurate and unambiguous observable. Depending on the mission, LR is used to transmit time over two-way or one-way distances from 500 to several millions of km. The following missions and their objectives employed this technique: European Laser Timing (ELT) at 450 km, Time Transfer by Laser Link (T2L2) at 1,336 km, Laser Time Transfer (LTT) at 36,000 km, Lunar Reconnaissance Orbiter (LRO) at 350,000 km, and MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) at tens of million km. This article describes the synergy between SLR and T/F technologies developed on the ground and in space and as well as the state of the art of their exploitation. The performance and sources of limitation of such space missions are analyzed. It shows that current and future challenges lie in the improvement of the time accuracy and stability of the time for ground geodetic observatories. The role of the next generation of SLR systems is emphasized both in space and at ground level, from the point of view of GGOS and valuable exploitation of the synergy between time synchronization, ranging and data transfer.

角反射器形状效应对卫星激光测距系统测距精度的影响

角反射器形状效应对卫星激光测距系统测距精度的影响

基于激光大气传输特性的卫星激光测距系统的最大探测距离

基于激光大气传输特性的卫星激光测距系统的最大探测距离

Identification and calibration of one-way delays in satellite laser ranging systems

We are reporting on identification and calibration of one-way delays in satellite laser ranging systems. Satellite Laser Ranging (SLR) is a standard technique to measure the distance of satellites as a function of time with millimeter precision and a few millimeters accuracy. For one-way laser ranging, laser time transfer ground to space and for bi- and multi-static laser ranging to space objects identification and measurement of system delays related separately to transmitting and receiving parts of the system are needed. The epochs of transmission and reception of optical signals have to be referred to the coordinated time scale with the accuracy reaching one nanosecond level or better for one-way ranging and space debris multi-static ranging. For transponder ranging and laser time transfer an even higher accuracy of 50ps or better is needed. These accuracy requirements are by several orders of magnitude higher in comparison to standard SLR applications. A new procedure of calibration of one-way delays related to the SLR systems has been developed and tested. The necessary hardware components needed for calibration measurements were designed and developed in a form of a Calibration Device. It consists of a photon counting detector, an epoch timing device and a dedicated signal cable. The signal propagation delays of these components were determined with an accuracy of better than 20ps. The signal propagation delay stability of the Calibration Device is on a level of units of picoseconds over days of operation. The Calibration Device and calibration procedure were tested in real measurements at the SLR site in Graz, Austria. The time needed to complete a calibration of one-way delays of the SLR system is less than two days. The one-way system delays were determined with the accuracy better than 50ps. The measurement principle, Calibration Device and the first results are presented.

고반복율 인공위성 레이저추적을 위한 운영 소프트웨어 개발

한국천문연구원은 인공위성 정밀궤도 결정, 우주측지 및 인공위성 자세역학 연구를 위해서 2kHz 반복율을 가지는 SLR 시스템을 운영하고 있다. 그러나 측지위성의 회전속도를 보다 정밀히 결정하고 거리 측정 정밀도 향상을 위해서 고반복율의 SLR 관측 데이터가 요구된다. 따라서 고반복율 시스템 구현을 위해 운영 소프트웨어 및 레인지 게이트 생성기를 개발하여 최대 10kHz 반복율로 레이저추적이 가능한 HSLR-10(High repetition-rate Satellite Laser Ranging-10kHz) 시스템으로 개선하였다. 본 연구에서는 10kHz 반복율을 가지는 HSLR-10 시스템의 운영 소프트웨어 개발 방법, 구성 및 검증 결과를 제시한다. Korea Astronomy and Space Science Institute (KASI) has been operating SLR (Satellite Laser Ranging) system with 2kHz repetition rate for satellite precise orbit and spin determination as well as space geodesy. But the SLR system was improved to be capable of laser ranging with high repetition rate, up to 10kHz by developing new operation software and novel range gate generator, called HSLR-10. The HSLR-10 will contribute to the accurate spin rate determination of geodetic satellites and geodetic research due to its largest repetition rate in the world. In this study, the development methodology and configuration of operation software are addressed, and its validation results are also presented.

First successful satellite laser ranging with a fibre-based transmitter

Satellite laser ranging (SLR) is an established technology used for geodesy, fundamental science and precise orbit determination. This paper reports on the first successful SLR measurement from the German Aerospace Center research observatory in Stuttgart. While many SLR stations are in operation, the experiment described here is unique in several ways: The modular system has been assembled completely from commercial off-the-shelf components, which increases flexibility and significantly reduces hardware costs. To our knowledge it has been the first time that an SLR measurement has been conducted using an optical fibre rather than a coudé path to direct the light from the laser source onto the telescope. The transmitter operates at an output power of about 75mW and a repetition rate of 3kHz, and at a wavelength of 1064nm. Due to its rather small diameter of only 80μm, the receiver detector features a low noise rate of less than 2kHz and can be operated without gating in many cases. With this set-up, clear return signals have been received from several orbital objects equipped with retroreflectors. In its current configuration, the system does not yet achieve the same performance as other SLR systems in terms of precision, maximum distance and the capability of daylight ranging; however, plans to overcome these limitations are outlined.

Confirmation of gravitationally induced attitude drift of spinning satellite Ajisai with Graz high repetition rate SLR data

The high repetition rate Satellite Laser Ranging system Graz delivers the millimeter precision range measurements to the corner cube reflector panels of Ajisai. The analysis of 4599 passes measured from October 2003 until November 2014 reveals the secular precession and nutation of Ajisai spin axis due to the gravitational forces as predicted by Kubo (1987) with the periods of 35.6years and 116.5days respectively. The observed precession cone is oriented at RA=88.9°, Dec=−88.85° (J2000) and has a radius of 1.08°. The radius of the nutation cone increases from 1.32° to 1.57° over the 11years of the measurements. We also detect a draconitic wobbling of Ajisai orientation due to the ‘motion’ of the Sun about the satellite’s orbit.The observed spin period of Ajisai increases exponentially over the investigated time span according to the trend function: T=1.492277·exp(0.0148388·Y) [s], where Y is in years since launch (1986.6133), RMS=0.412ms. The physical simulation model fitted to the observed spin parameters proves a very low interaction between Ajisai and the Earth’s magnetic field, what assures that the satellite’s angular momentum vector will remain in the vicinity of the south celestial pole for the coming decades.The developed empirical model of the spin axis orientation can improve the accuracy of the range determination between the ground SLR systems and the satellite’s center-of-mass (Kucharski et al., 2015) and enable the accurate attitude prediction of Ajisai for the laser time-transfer experiments (Kunimori et al., 1992).

Design and Development of High-Repetition-Rate Satellite Laser Ranging System

Copyright © The Korean Space Science Society http://janss.kr plSSN: 2093-5587 elSSN: 2093-1409 Received Aug 6, 2015 Revised Sep 7, 2015 Accepted Sep 7, 2015 †Corresponding Author E-mail: eunjung@kasi.re.kr, ORCID: 0000-0003-3637-2028 Tel: +82-42-865-3275, Fax: +82-42-865-3358 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http:// creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Technical Paper J. Astron. Space Sci. 32(3), 209-219 (2015) http://dx.doi.org/10.5140/JASS.2015.32.3.209

Attitude and Spin Period of Space Debris Envisat Measured by Satellite Laser Ranging

The Environmental Satellite (Envisat) mission was finished on April 8, 2012, and since that time, the attitude of the satellite has undergone significant changes. During the International Laser Ranging Service campaign, the Satellite Laser Ranging (SLR) stations have performed the range measurements to the satellite that allowed determination of the attitude and the spin period of Envisat during seven months of 2013. The spin axis of the satellite is stable within the radial coordinate system (RCS; fixed with the orbit) and is pointing in the direction opposite to the normal vector of the orbital plane in such a way that the spin axis makes an angle of 61.86 $^{\circ}$ with the nadir vector and 90.69 $^{\circ}$ with the along-track vector. The offset between the symmetry axis of the retroreflector panel and the spin axis of the satellite is 2.52 m and causes the meter-scale oscillations of the range measurements between the ground SLR system and the satellite during a pass. Envisat rotates in the counterclockwise (CCW) direction, with an inertial period of 134.74 s (September 25, 2013), and the spin period increases by 36.7 ms/day.

Performance Analysis of the First Korean Satellite Laser Ranging System

The first Korean satellite laser ranging (SLR) system, Daedeok SLR station (DAEK station) was developed by Korea Astronomy and Space Science Institute (KASI) in 2012, whose main objectives are space geodesy researches. In consequence, Korea became the <TEX>$25^{th}$</TEX> country that operates SLR system supplementing the international laser tracking network. The DAEK station is designed to be capable of 2 kHz laser ranging with precision of a few mm both in daytime and nighttime observation of satellites with laser retro-reflector array (LRA) up to the altitude of 25,000 km. In this study, characteristics and specifications of DAEK station are investigated and its data quality is evaluated and compared with International Laser Ranging Service (ILRS) stations in terms of single-shot ranging precision. The analysis results demonstrated that the DAEK station shows good ranging performance to a few mm precision. Currently, the DAEK station is under normal operations at KASI headquarters, however, it will be moved to Sejong city in 2014 to function as a fundamental station for space geodesy researches in combination with other space geodesy systems (GNSS, VLBI, DORIS, etc.).

Two-Color Satellite Laser Ranging Measurements at 10 Hz and 100 Hz at TIGO

In this paper, a detailed comparative performance analysis of the two-color satellite laser ranging (SLR) systems of the Transportable Integrated Geodetic Observatory (TIGO) is presented. The study is based on four years of continuous measurement data and a comparison of two different layouts of the laser system. The focus lies on a quantitative analysis of measurement precision, range accuracy, and data production for the two laser system layouts. Main findings include a significant gain in temporal stability due to removal of active elements in the oscillator, an improvement of range measurement accuracy by a factor of 2, and an important increase in data productivity. The analysis presented here provides a valuable input for the design of future SLR systems, as well as related topics such as time transfer applications and optical communications to satellites.

Spin parameters of High Earth Orbiting satellites Etalon-1 and Etalon-2 determined from kHz Satellite Laser Ranging data

The high repetition rate Satellite Laser Ranging (SLR) system developed in Graz, Austria, measures ranges to the High Earth Orbiting satellites Etalon-1 and Etalon-2 with the millimeter accuracy. The 2kHz repetition rate of the laser and the relatively high return rates allow to use the SLR data to calculate the spin parameters of the Etalon satellites. The analysis of the 10years (October 2003–September 2013) of the SLR data gives trends of the spin axes orientation (J2000 Inertial Reference Frame):Etalon-1: RA=−11.39·Y+432.341 [°], Dec=−0.0402979·Y+10.154 [°],Etalon-2: RA=−12.7871·Y+328.144 [°], Dec=0.0141925·Y+1.563 [°],where Y is in years since launch (Etalon-1: 1989.02489, Etalon-2: 1989.41193).The frequency signal obtained from the SLR data indicates that the satellites rotate counter-clockwise about the spin axes with a period of:Etalon-1: T=60.843·exp(0.00319710·Y) [s], Etalon-2: T=58.958·exp(0.00695744·Y) [s],where Y is in years since launch.The spin model built upon the derived trends shows that the Etalons are losing rotational energy with the lowest rate among the geodetic satellites (8 satellites compared). It takes 170.9years for the spin period of Etalon-1 to double, and 82.24years for Etalon-2.The complete spin trends presented in this paper can help to model the acceleration pattern of the spacecrafts, and thus improve accuracy of the precise orbit determination of Etalon-1 and Etalon-2.

Key technologies implementation of high-repetition-rate satellite laser ranging

Satellite laser ranging (SLR) is one of the major space geodetic instruments, which has various applications in earth science. In this paper, we introduce several issues regarding the key technology implementation of high-repetition-rate SLR system. Compared with traditional technology, using kHz and 8 ps pulse width laser component, the data quantity and quality of high-repetition-rate satellite laser ranging (SLR) can be significantly improved. The characteristics of high-repetition-rate laser ranging and the key technologies are presented, including the event timer with the precision of picosecond, the generation of range gate signal, and so on. All of them are based on the Field Programmable Gate Arrays (FPGA) and tested on China mobile SLR system-TR0Sl000. Finally, the observations of satellite Beacon-C are given.

Design and experiment of onboard laser time transfer in Chinese Beidou navigation satellites

High-precision time synchronization between satellites and ground stations plays the vital role in satellite navigation system. Laser time transfer (LTT) technology is widely recognized as the highest accuracy way to achieve time synchronization derived from satellite laser ranging (SLR) technology. Onboard LTT payload has been designed and developed by Shanghai Astronomical Observatory, and successfully applied to Chinese Beidou navigation satellites. By using the SLR system, with strictly controlling laser firing time and developing LTT data processing system on ground, the high precise onboard laser time transfer experiment has been first performed for satellite navigation system in the world. The clock difference and relative frequency difference between the ground hydrogen maser and space rubidium clocks have been obtained, with the precision of approximately 300ps and relative frequency stability of 10E−14. This article describes the development of onboard LTT payload, introduces the principle, system composition, applications and LTT measuring results for Chinese satellite navigation system.

인공위성 레이저추적 시스템(ARGO-M) 개발 현황

KASI (Korea Astronomy and Space Science Institute) has developed an SLR (Satellite Laser Ranging) system since 2008. The name of the development program is ARGO (Accurate Ranging system for Geodetic Observation). ARGO has a wide range of applications in the satellite precise orbit determination and space geodesy research using SLR with mm-level accuracy. ARGO-M (Mobile, bistatic 10 cm transmitting/40 cm receiving telescopes) and ARGO-F (Fixed stationary, about 1 m transmitting/receiving integrated telescope) SLR systems development will be completed by 2014. In 2011, ARGO-M system integration was completed. At present ARGO-M is in the course of system calibration, functionality, and performance tests. It consists of six subsystems, OPS (Optics System), TMS (Tracking Mount System), OES (Opto-Electronic System), CDS (Container-Dome System), LAS (Laser System) and AOS (ARGO Operation System). In this paper, ARGO-M system structure and integration status are introduced and described.

HIGH-PRECISION STEERING AND POINTING CONTROL OF A LUNAR/SATELLITE LASER RANGING TELESCOPE

The establishment of a new fundamental space geodetic station in South Africa has been proposed. A Satellite Laser Ranging System (SLRS) utilising a 1 m optical telescope enhanced for Lunar Laser Ranging (LLR) will form part of the geodetic instrumentation to be located at the new fundamental space geodetic station. The Tracking and Mount Control (T&MC) subsystem of the ranging system will require development of high-precision steering and pointing control for the telescope. A working model using National Instruments (NI) LabVIEW and an NI CompactRIO interface will be developed. We present an overview of this component of the ranging system and sketch the way forward. Envisaged outcome of this project is to achieve arc-second accurate steering and pointing of the telescope.

Optical response of nanosatellite BLITS measured by the Graz 2 kHz SLR system

The nanosatellite BLITS (Ball Lens In The Space) is the first object designed as a passive, spherical retroreflector of the Luneburg type, dedicated for Satellite Laser Ranging (SLR). The optical response of BLITS has been measured by the Graz 2 kHz SLR station and compared with the response of the classical retroreflector arrays (RRA) of the Low Earth Orbiting satellites such as ERS-2 and Stella. This work demonstrates that the optical response of BLITS is flat and featureless, comparable with the signature of a point-source or a flat target, and suggests that this innovative design will deliver a higher normal point (NP) accuracy (2.55 mm) than any other SLR target currently in orbit. The high reflectivity of the glassy BLITS (about 60% of the return rate from the multi-reflector Stella) is found to be decreasing by about 30% per year, probably due to the solar irradiation. Detailed analysis of the reflective half-shell demonstrates that a high return rate of SLR measurements can be achieved regardless of the incident angle of the laser beam, thus making the spherical lens a perfect successor of the classical RRA panels mounted on active satellites such as CHAMP, GOCE and GRACE.

KHz repetition Satellite Laser Ranging system with high precision and measuring results

kHz repetition Satellite Laser Ranging (kHz SLR) with the advantages of fast target acquisition,large amount of returns,high measuring accuracy and high normal point data density,has become the trend of international laser ranging technology.For kHz Satellite Laser Ranging system,using kHz repetition laser with picosecond's pulse-width and high-precision Event Timer,designing nanosecond accuracy of Range Gate Generator with event mode and back-scattering avoiding circuit,developing real-time control software and data pre-processing software,Shanghai Astronomical Observatory (CAS) has established the kHz repetition laser ranging system with the ability to track routinely the LEO/HEO satellites at nighttime and daylight laser ranging for LEO satellites at the precision of 7-12 mm and become the first station to range to GEO satellite with kHz repetition rate laser.By comparing with low repetition laser ranging,the returns and data density per normal points are greatly increased.The ranging precision is also improved obviously.

Atmospheric range correction for two-frequency SLR measurements

It has been widely known that the use of two-frequency Satellite Laser Ranging (SLR) system is limited by stringent precision requirements of the range measurements and the proper atmospheric model. Owing to the stringent requirements, this SLR system is impractical for the current requirement of SLR measurements within the framework of global geodetic observing system (GGOS). If in the future this stringent requirement could be met, this SLR system would be an attractive tool to reduce atmospheric propagation effects of SLR and would be of great benefit for the next generation of GGOS design. To anticipate possible future developments of the two-frequency SLR systems, we have developed a new atmospheric correction formula for the two-frequency SLR measurements. The new formula eliminates the total atmospheric density effect including its gradient and provides two terms to calculate the curvature effect and the water vapor distribution effect. While the curvature effect can be calculated by an accurate model, the required information about the water vapor distribution along the propagation path can be calculated using previous developments of optical delay modeling or alternatively using results from microwave measurements. Theoretical simulations using the two-frequency systems of the Graz and TIGO-Concepcion stations shows that the new formula completely reduces all propagation effects at any elevation angle above 3° with an accuracy better than 1 mm. However, the required precision for the difference of the two-frequency SLR measurements, i.e. better than 45 μm for a single epoch, exceeds the capability of the current state of the art SLR systems.