Current Trends in Satellite Laser Ranging

G13C-07 Michael Pearlman Graham Appleby Georg Kirchner Jan Mcgarry Tom Murphy Carey Noll Erricos Pavlis Francis Pierron Harvard-Smithsonian Center for Astrophysics NERC Space Geodesy Facility Space Research Institute, Austrian Academy of Sciences Code 694, NASA GSFC University of California San Diego Code 690.1, NASA GSFC GEST, UMBC OCA/CERGA Cambridge, MA, USA Hailsham, East Sussex, United Kingdom Graz, Austria Greenbelt, MD, USA La Jolla, CA, USA Greenbelt, MD, USA Baltimore, MD, USA Grasse, France Current Trends in Satellite Laser Ranging [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] Abstract Current SLR/LLR Network Satellite Laser Ranging (SLR) techniques are used to accurately measure the distance from ground stations to retroreflectors on satellites and the moon. SLR is one of the fundamental techniques that define the International Terrestrial Reference Frame (ITRF), which is the basis upon which we measure many aspects of global change over space, time, and evolving technology. It is one of the fundamental techniques that define at a level of precision of a few mm the origin and scale of the ITRF. Laser Ranging provides precision orbit determination and instrument calibration/validation for satellite-borne altimeters for the better understanding of sea level change, ocean dynamics, ice budget, and terrestrial topography. Laser ranging is also a tool to study the dynamics of the Moon and fundamental constants. Many of the GNSS satellites now carry retroreflectors for improved orbit determination, harmonization of reference frames, and in-orbit co-location and system performance validation. The GNSS Constellations will be the means of making the reference frame available to worldwide users. Data and products from these measurements support key aspects of the GEOSS 10-Year Implementation Plan adopted on February 16, 2005. The ITRF has been identified as a key contribution of the IAG to GEOSS and the ILRS makes a major contribution for its development since its foundation. The ILRS delivers weekly additional realiza- tions that are accumulated sequentially to extend the ITRF and the Earth Orientation Parameter (EOP) series with a daily resolution. Additional products are currently under development such as precise orbits of satellites, EOP with daily availability, low-degree gravitational harmonics for stud- ies of Earth dynamics and kinematics, etc. SLR technology continues to evolve toward the next generation laser ranging systems as programmatic requirements become more stringent. Ranging accuracy is improving as higher repetition rate, narrower pulse lasers and faster detectors are imple- mented. Automation and pass interleaving at some stations is already expanding temporal coverage. Web-based safety keys are allowing the SLR network stations to range to optically vulnerable satellites. Some stations are experimenting with two-wavelength operation as a means of better understanding the atmospheric refraction and with very low power laser to improve eye-safety conditions. New retroreflector designs are improving the signal link and enable daylight ranging. Dramatic improvements have also been made with lunar ranging with the new APOLLO Site in New Mexico, USA and the upgraded lunar station “MEO” in Grasse, France. We will discuss many of these laser ranging activities and some of the current challenges that the SLR network currently faces. The Laser Ranging Technique and Science/Applications of SLR The laser ranging technique consists of a precise range measurement between an SLR ground SLR and the Terrestrial Reference Frame Need for SLR measurements on the GNSS Constellations station and a retroreflector-equipped satellite using ultrashort laser pulses corrected for refraction, satellite center of mass, and the internal delay of the ranging machine. The global net- • SLR is one of the key space technologies that contribute to the devel- Geoscience work of SLR stations has supported more than sixty space missions supported since 1970; five of opment of the ITRF: • Improve the Terrestrial Reference Frame (co-location of techniques these missions have been rescued in the last decade by laser ranging measurements. - An accurate, stable set of station positions and velocities. in space) Concept: • The unique contribution of SLR to ITRF is the link of its origin to the • Improve LEO POD based on GNSS tracking of SLR-calibrated GNSS • Simple measurement of range from accurate time inter- Satellite center of mass of the Earth system orbits val counters Corner Cube • SLR contributes also in maintaining a stable scale for the ITRF, in equal Reflector • Space segment is passive Laser Ranging parts with VLBI GNSS World • Accurate atmospheric delay correction (independent of Station • The ITRF Requirements of GGOS are: • Provide independent quality assurance: water vapor) - <1 mm reference frame accuracy - GNSS orbit accuracy cannot be directly validated from the GNSS • Night/Day Operation - < 0.1 mm/yr stability data itself • Near real-time global data availability Transmit/Receive Optical Arrangement • The primary science driver is the • Assure interoperability amongst GPS, GLONASS, Galileo, COMPASS, • Satellite altitudes from below 300 km to synchronous measurement of sea level change QZSS, etc. Pulse Laser Photon Detector satellites, and the Moon START STOP • The GGOS goal requires a factor of • Ensure realization of constellation-dependent reference frames Measurement of round • Unambiguous centimeter accuracy orbits trip time of laser pulse Time Interval Unit 10-20 improvement over current ITRF (WGS84 , GTRF, etc.) are consistent with ITRF • Long-term stable time series of positions, low degree performance demonstrated below for Station coordinate and satellite orbit GPS Satellite Constellation GIOVE-B spherical harmonics, orbital elements, and others determination relative to Earth’s center ITRF2008 Measurements: ITRF2008 Origin and Scale Variations from SLR • Precision Orbit Determination (POD) • Time history of station positions and motions • Low degree gravitational harmonics and GM COMPASS-M1 SLR Site ESA • Tidal harmonics, planetary Love numbers, etc. CSNPC SLR/LLR Site SLR/LLR products contributing to: QZSS • Terrestrial reference frame (Center of mass and scale) GNSS Site • Plate tectonics and crustal deformation VLBI Site • Static and time-varying gravity field DORIS Site • Earth orientation and rotation (polar motion, length of day) • Orbits and calibration of altimetry missions (oceans, ice) TerraSAR-X and TanDEM-X: SLR provides • Total Earth mass distribution calibration and validation of onboard systems and supports POD GFZ GLONASS Galileo New Technology and Developments JAXA • Space science (tether dynamics, etc.) ESA • Relativity measurements and lunar science • The Russian Blits satellite with a novel Luneberg Lens, a single corner cube reflector whose center of mass correction can be very accu- LRO Laser Ranging (LRO-LR) Spin Rate Measurements The International Laser Ranging Service and its Support of Missions through Laser Ranging rately computed independent of aspect angle resulting in very pre- Transmit 532nm laser pulses at 28 Hz to LRO Graz kHz SLR station measures the spin cise ranging measurements. Time stamp departure and arrival times period of Ajisai with accuracy of 80µs. Chart 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 CryoSat-2 A shows the spin period measurements of IPIE The International Laser Ranging Service (ILRS), founded by the International NPOESS Ajisai (years 2003.8-2009). Chart B shows Association of Geodesy (IAG) in 1998, organizes and coordinates Satellite Galileo IOV • Stations with kHz repetition laser systems provide ranging measure- Receiver telescope on High Gain An- the spin period change during arbitrary se- SARAL tenna System (HGAS) routes LR signal lected 163 days. Chart C shows spin period Laser Ranging (SLR) and Lunar Laser Ranging (LLR) to support programs in TODAY QZS-1 ments that show details of retroreflector geometry and can measure RadioAstron to LOLA residuals to the spin period trend function ESA spin rate on spherical geodetic satellites. At this time, four stations geodetic, geophysical, and lunar research and provides the International KOMPSAT-5 for the selected data set. The distribution of Moon Satellites equipped with retroreflectors have been Tandem-X SRI/AAS Earth Rotation and Reference Frame Service (IERS) with products important to NASA ETS-8 in the ILRS network operate at kHz rates. the residuals is correlated with the percent- tracked by laser systems since 1965. Satellite laser CryoSat-2 age of the Ajisai orbit illuminated by the the maintenance of an accurate International Terrestrial Reference Frame Starlette PROBA-2 ranging supports a variety of geodetic, Earth sens- Blits Sun. The spin period is increasing faster (ITRF). • NASA supports the development of the Next Generation SLR (NGSLR) LOLA channel 1 detects when the full orbit is exposed to the solar ing, navigation, and space science applications. ANDE-Castor ANDE-Pollux system, a prototype automated SLR system for replication and de- LR signal irradiation. The minimum percentage of Ajisai orbit in the Sun is about 75% - this corre- LRO-LR The ILRS produces quality-assured scientific results

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