September 30, 2005

NASA Satellite Laser Ranging (SLR) Program Site Connecting via HPWREN

The NASA Satellite Laser Ranging (SLR) Program has recently become a collaborator of the High Performance Wireless Research and Education Network (HPWREN). The NASA SLR Program is conducted through the Goddard Space Flight Center, and consists of a network of eight SLR systems located in the continental US and throughout the world. The eight station network consists of five Mobile Laser Ranging Systems (MOBLAS 4 through 8), two Transportable Laser Ranging Systems (TLRS 3 and 4), and the McDonald Laser Ranging System (MLRS). These NASA stations are located at Monument Peak, California (MOBLAS-4), Yarragadee, Australia (MOBLAS-5), Hartebeesthoek, South Africa (MOBLAS-6), Greenbelt, Maryland at the Goddard Space Flight Center (MOBLAS-7 and TLRS-4), Tahiti, French Polynesia (MOBLAS-8), Arequipa, Peru (TLRS-3), and near Ft. Davis, Texas (MLRS). The NASA SLR Network is part of the larger, international SLR network of stations, the International Laser Ranging Service (ILRS - http://ilrs.gsfc.nasa.gov/).

SLR involves the precise, time-of flight measurement of a short pulse of laser energy from a ground based station to earth orbiting manmade and natural satellites. Each time-of-flight measurement is converted into range information which universities, scientists, and engineers use to develop millimeter precision satellite orbits, Earth gravitational models, Earth and Lunar orientation parameters, fundamental physical constant, as well as to calibrate space based altimeters, and to define and maintain the Terrestrial Reference System. The NASA SLR Network tracks approximately 25 different retroreflector equipped satellites in both the daytime and nighttime hours as long as some clear sky is available. Most NASA site operations are conducted 24 hours/5 days per week, Monday through Friday, by a crew of three persons on a single person per shift basis. The data collected is automatically processed on the station, compressed, and then automatically sent on an hourly basis to the Crustal Dynamics Data Information System (CDDIS - http://cddis.gsfc.nasa.gov/) at the NASA Goddard Space Flight Center (GSFC).

The MOBLAS-4 system is located on Mt. Laguna, California at a NASA GSFC site, in cooperation with the California Cleveland National Forest Service. This is a remote site situated about one hour east of San Diego with limited communications and self sufficient metropolitan services. The MOBLAS-4 compound is also home to other scientific observational systems such as the Scripps Orbit and Permanent Array Center (SOPAC - http://sopac.ucsd.edu/) permanent Global Positioning System station, the soon to be upgraded EarthScope geophysical station (http://www.earthscope.org/), and the soon to be constructed Doppler Orbitography and Radiopositioning Integrated by Satellite Precise orbit determination and location system (DORIS - http://ids.cls.fr/welcome.html).

Previously, the MOBLAS-4 system used a commercial 56 kilobit data communications line to transmit an average of 120 kilobytes of tracking data per hour, with an approximate peak of 265 kilobytes, using File Transfer Protocol (FTP). Each hour, the Lynx based data processing computer automatically transmits satellite laser ranging data. This data communications line is also used by the three person crew to send text based system status reports once per shift, monitor weather conditions every few hours for several minutes, communicate with NASA SLR Headquarters in Greenbelt, Maryland, communicate with other SLR systems throughout the world using electronic mail, and to maintain the MOBLAS-4 site via a Windows based desktop computer. The NASA SLR Program engineering staff in Greenbelt, Maryland uses the communication line, via FTP and Telnet, to troubleshoot software anomalies, investigate hardware problems, and upgrade system software. The engineering staff communicates with the data processing computer mentioned above as well as the controller computer. Unfortunately, the commercial communications service had been relatively slow with network connections intermittent. The service is many times interrupted during data communications and system functions, requiring repeated data transmissions and delayed system operations. The 56 kilobit service is also used by the MOBLAS-4 crew to periodically communicate with the sponsors of the other geophysical experiments taking place at the MOBLAS-4 site, such as SOPAC, EarthScope, and DORIS.

The NASA MOBLAS-4 site is home to several other geophysical experiments, one of which is already part of the HPWREN alliance, EarthScope.

The following are pictures of the MOBLAS 4 during daytime and can be seen in the view of the HPWREN Mt. Laguna West camera.

Mobile Laser Ranging System 4 (MOBLAS 4) Daytime Operations MOBLAS 4 daytime

MOBLAS 4 nighttime
Mobile Laser Ranging System 4 (MOBLAS 4) Nighttime Operations

David L. Carter, NASA Satellite Laser Ranging Networks Manager
NASA Goddard Space Flight Center

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