Powerful SLR Facility Established to Determine Precise Position of Satellites

6/17/1996 - 57-96r
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In a joint effort, the Naval Research Laboratory (NRL), the USAF Phillips Laboratory, and NASA have established a new Satellite Laser Ranging (SLR) station at the USAF Starfire Optical Range (SOR) in Albuquerque, New Mexico. Returns have been obtained from satellites as low as 370 km and as high as 20,200 km overhead (NAVSTAR GPS).

Dr. G. Charmaine Gilbreath, NRL's SLR Project Manager and Principal Investigator says, "The new capability has been developed for precise determination of satellites and for onboard spacecraft system performance verification. This is an experimental facility and runs in a `campaign' mode. Specifically, data on geodetic satellites will be obtained at intermittent times of the year coincident with special experiments."

NRL designed, integrated, and operates the transmit/receive system at SOR. This powerful new system presents an energy/receiver aperture-to-area Figure-of-Merit of 2886 mJ-m2. The USAF designed the optical train through the 3.5-meter telescope and provides tracking and acquisition for the effort. The processing and analysis of scientific data are performed by NRL. NASA provides technical assistance as required.

The system comprises a 10 Hz, 300 mJ doubled Nd-YAG laser, with a 250 ps pulse width. The beam divergence is on the order of 70 to 100 microradians through the 3.5-meter telescope.

"Non-terminator assisted and daytime ranging can be performed; however, we are limited to ranging 1.5 hours before sunset to 1.5 hours after sunrise at this time due to direct sunlight restrictions on the telescope itself," says Dr. Gilbreath.

The 3.5-meter telescope combined with the Micro-Channel Plate-enhanced photomultiplier tube used for photon detection, and 300 mJ of energy enables the system to obtain returns from enhanced spacecraft at 22,000 km or higher.

The receiver subsystem also has 1 GHz and 4 GHz oscilloscopes for waveform detection and signature analysis. A GPS-steered rubidium clock serves as the master

clock for the telescope and the Tx/Rx system, which includes externally triggering the laser.

Officially, the site has been assigned 7884 for a pad marker, 66 for the SLR station ID, occupation 01. The reference point on the 3.5 Meter telescope is: x: 1483442.808 (m); y: -5019625,640 (m); z: 3635692.076 (m). This position was derived from range data obtained from LAGEOS-1 and is in ITRF-95 epoched 49875.

Dr. Gilbreath adds, "During May and June 1995, NRL conducted SLR operations at SOR on the satellites LAGEOS-1, LAGEOS-2, TOPEX, GPS-36, ETALON-1, ETALON-2 and GFZ-1 from the facility. Data for these satellites have been released to the international network. The data are available via anon.ftp on cddis.gsfc.nasa.gov."

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