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Missions Supported by Laser Ranging

CryoSat

Geodetic Satellites

Geodetic satellites are designed to look and act as point-mass objects in order to allow for the most precise computation of their orbits. Big or small, cannonball-shaped, with as small an area-to-mass ratio as possible (to minimize the effect of non-conservative forces), they are passive objects studded with corner-cube retroreflectors (CCRs). Used as targets by Satellite Laser Ranging (SLR) ground systems, these satellites with their very precise orbits, provide very accurate, unambiguous distance measurements. They contribute to geodesy with positioning, determining the shape and size of Earth; and the variations of the terrestrial gravity field. The Lageos satellites are the basis of the ILRS contribution to the International Terrestrial Reference Frame (ITRF). Other geodetic satellites such as Etalon, Starlette, Stella etc are now being added to further strengthen the reference frame.

Remote Sensing Missions

Remote sensing satellites carry payloads that measure structure and ongoing processes on the Earth using electronic and optical sensors (altimeters, gradiometers, satellite to satellite tracking, etc.) These systems measure the environment and monitor change on a global basis. Altimeters measure the topography of the ocean and ice surface to monitor changes on sea level and ice volume. Gravity field measurements help us understand the structure and dynamic processes within the Earth including changes surface hydrology, mass shifts, etc. Atmospheric and Ionospheric sensors help us understand the structure of these media and the dynamic process within. SLR is used to calibrate, validate, and monitor many of these systems and is a contributor to POD. SLR has also provided full POD in several cases when the radio systems have failed.

Global Navigation Satellite Systems (GNSS)

GNSS satellites are launched in constellations to provide accurate positioning and velocity for land, sea, air and space applications. Ground surveys today are based on GNSS and nearly every vehicle has or will have GNSS to monitor its motion and plan its future path. Science has adopted GNSS as a fundamental tool for measuring ground motions, Earth rotation, ionospheric and atmospheric structure (using occultation), and a host of other uses. SLR is used to calibrate the GNSS orbits and the combination of GNSS and SLR will be used to distribute the reference frame for users worldwide. Retroreflectors have been placed on satellites in the GPS, GLONASS, Compass, and Galileo (GIOVE) constellations. The apparent trend is to place arrays on many more. New complexes underway in India and Japan will also include arrays.

Experimental Satellites

Experimental satellites are a catchall for demonstration payloads that do not fit easily in any one of the other mission classifications. These satellites can often be in relatively low altitude orbits. RadioAstron is an exception. Some of these satellites have only SLR for tracking to save space and power. These satellites are often small in size and weight, irregularly shaped, and low cost. Some examples include TIPS, Starshine, Reflector, LRE, ANDE, and RadioAstron. The ILRS has thus established a CCR array standard which provides guidance in designing the correct array for each application.

Recent News

ESA Lunar Pathfinder mission to include Lunar Laser Ranging - The European Space Agency (ESA) announced that a test version of a unique satellite navigation receiver has been delivered for the Lunar Pathfinder spacecraft, scheduled for launch in 2024. The receiver will receive GNSS signals from the Galileo and GPS constellations for position, navigation and timing in orbit around the Moon. In addition the Lunar Pathfinder spacecraft will carry a laser retroreflector array for lunar laser ranging, and an X-Band radio transponder for ranging and communications.

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GGOS Coordinating Office Develops Film to Promote Geodesy - The Global Geodetic Observing System (GGOS) coordinating office has helped to organize a general ∼8 minute video that explains geodesy, the geodetic observations and products that are available from the different IAG services, and the benefits of geodesy to science and society. The GGOS video so far is available in English, Spanish, German, French & Japanese. Check out the videos on YouTube:

https://www.youtube.com/watch?v=Jwqz097N2IY&list=PLIIfsJS7iAuxXGqq0YLAUO_m_06za9vqr

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The IERS ITRS Center at the IGN (Institut Géographique National, France) announced the availability of the ITRF2020 solution - On April 15, 2022, the IERS ITRS Center at the IGN (Institut Géographique National, France) announced the availability of the ITRF2020 solution at their dedicated web site:

https://itrf.ign.fr/en/solutions/ITRF2020

The new reference frame realization includes the contributions of all the IAG Geodetic Services (IVS, ILRS, IDS, IGS) and their Analysis Centers and Combination Centers. The ILRS contribution was based on a reprocessing of SLR data to the LAGEOS, LAGEOS-2 & the two Etalon satellites from 1993.0 to 2020.0 and to LAGEOS only from 1983.0 to 1993.0.

The ILRS ASC is working on an ILRS extended version, the SLRF2020, which will include the SLR stations that were not part of the ITRF2020 solution and will provide instructions on how to get the highest accuracy results when implementing this extended model in SLR data analysis.

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New ILRS Station Izaña (7701, IZ1L) in Tenerife (Canary Islands, Spain) is now Operational - Izaña (7701) has completed the requirements to be an operational station in the ILRS network and its data has been released from quarantine. The Analysis Standing Committee has approved the release of data collected since 2021-11-28.

We thank our station colleagues Andrea Di Mira, Jens Steinborn for their efforts, and congratulate them on this achievement!

ILRS Stations Participate in Tracking Campaign for the IRNSS Satellites - From April 17- 30, 2022 at the request of ISRO (Indian Space Research Organization), the ILRS Central Bureau is organizing a tracking campaign for IRNSS, the Indian constellation of GNSS satellites. The objective is for the network to provide an even distribution of SLR normal points around the orbit, for the satellites that are the focus of the campaign. The IRNSS satellites are located in geosynchronous (24-hr) orbits over the Indian Ocean region and their ground track makes a 'figure-8' on the surface of the Earth.

During the current campaign (April 17- 30, 2022) ILRS stations in the Eastern Region of the Indian Ocean (Asia, Australia) will track IRNSS 1C plus IRNSS -1D. ILRS stations in the Western Region of the Indian Ocean (Europe, Africa) will track IRNSS 1C plus IRNSS- 1I. The IRNSS tracking data from the campaigns will be used to assess the performance of these IRNSS satellites, in a similar way to that used to validate the performance of other GNSS constellations such as Galileo.

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Definitions of Pass, Pass-Segment, and Session - The CDDIS, EDC, and NASA DOC provide statistics for the ILRS community including the monthly report cards, verification counts, and statistics for presentations and reports. These groups have worked together to standardize their definitions of a pass and a pass-segment.

The following definitions have been agreed to:

A pass is defined as all tracking that lasts less than a full satellite period. For geosynchronous satellites, the duration is capped at 24 hours; this is the standard product.
A pass-segment is another term for a session (interval of continuous data) which is a reflection of how the data was taken at the station and submitted to the data centers. A single pass-segment/session is counted from one H1 to H8.

A pass includes all data taken on a satellite during one transit over the station. The pass-segment is just a magnification of how the data was taken and submitted.

Call for Papers for IAG REFAG2022 Meeting - The primary scope of REFAG 2022 is to address today's theoretical concepts of reference systems and their practical implementation by space geodetic techniques and their combination. Contributions for the meeting may include, global reference frames by individual space geodetic techniques and their combination; space geodetic measurements and mitigation of their systematic errors; geocenter motion and non-tidal loading effects; terrestrial and space geodetic ties for multi-technique combination; regional reference frames and related applications; Celestial reference frames; comparison and combination of Earth Orientation parameters; and use and challenges of geodetic reference frames for Earth science applications. The scientific program of the symposium will also cover initiatives and projects that endorse the role of geodetic reference frames for scientific exploration, sustainable development, climate monitoring, and satellite navigation.

Key Dates:

June 20, 2022 (Abstract deadline)
July 25, 2022 (Early registration deadline)

For more information, check the URL for the meeting: www.refag2022.org

CPF v1 format discontinued - On March 1, 2022, the ILRS officially discontinued predictions in the CPF v1 format and have switched to the CPF v2 format. Please find the most recent predictions available at https://cddis.nasa.gov/archive/slr/cpf_predicts_v2/current/

IAG Statement on Ukraine - The International Association of Geodesy, a parent organization of the IVS/ILRS, has posted a statement on Ukraine. Read the statement.