Recent and future operation of Helwan-SLR station Makram Ibrahim, Khalil I. Khalil, and A. T. Roman National Research Institute of Astronomy and Geophysics (NRIAG), Helwan, Cairo, Egypt. Abstract We concerned on the recent Satellite Laser Ranging (SLR) from the Helwan station. The recent equipments used for the operation of the Helwan SLR-station are described. A new Laser Radar Control (LRC) system had been tested theoretically and will apply during august, 2011 to the Helwan station. The results and the analysis of the data obtained recently using the cpf-formats are given. The future operation of the Helwan-SLR station which is expected to improve after the upgrading with the LRC, is also discussed. 1. The description of the present Helwan SLR-station The tracking of the artificial earth satellites from the Helwan has started in the year 1974. A lot of modifications and upgrading have been applied to the Helwan-SLR station in order to improve its accuracy and performance (Hamal, K. , 1978, Jelinkova, H., 1984, Prochazka, I. , 1989, Tawadros, M. et. al, 2000, Ibrahim, M. ,2005). For this end, a brief description of the H-SLR station is given. The mount configuration is Azimuth/Elevation with a coude system of mirrors for the transmitted beams as shown in fig. 1(a). The movement drive is consisting of 2 step drive motors, and the maximum tracking rate is 2 deg./sec. The guiding of the mount is a computer controlled. The receiving system of the mount is a spherical mirror lens of diameter 40 cm, and optical filter of 6 nm with 80 % transmission. The type of the detector is a Photomultiplier (PMT) manufactured by Hamamatsu model H6533. The quantum efficiency of this PMT is 10 % at 532 nm and of normal gain equal 5.6 million. The mode of the PMT is single photoelectron detection (Cech, M., et.al, 1998). The laser transmitter (as shown in fig.1b ) is composed of Nd: YAG oscillator, Pulse selector, three amplifiers system and a Second Harmonic Generator (SHG); it produces a semi train of pulses. The wavelength of the laser is 0.53µm with output energy of 80 millijoule, the pulse width is 20 psec and its repetition rate is nearly 5 Hz. The divergence of the laser beam is adjustable and can reach to 0.1 mill radians. The laser transmitter is placed outside the mount and then the laser beam is directed to the satellite through the mount via a four coude of mirrors. The ranging electronics of the system consists of a time interval counter of type a Stanford SR620 of resolution equal 4 ps. The time and frequency system, is GPS Time/Frequency standard, manufactured by Helwlett-Packard of model 58503B, and it measures the time with accuracy below than 110 nsec. The meteorological station (MET-3) is installed to improve temperature, humidity and atmospheric pressure s' measurements. The pressure sensor model is a Digiquartz MET3 and it measures with accuracy of 0.1 mbar. The temperature sensor model is Platinum resistance temperature probe and it measures with accuracy ~ 0.5 deg C. As for the model of the humidity sensor, it is a capacitance probe and its accuracy is 2 % at 25 deg C. The Laser Radar Control (LRC) unit used at the Helwan station is used since 20 years and will replace by a new one as explained in section3. (a) (b) Fig1. The mount of the H-SLR Station in (a) and the used Nd:YAG laser transmitter in (b) 2. Recent satellites tracking The data obtained from satellite tracking is the distance between the satellite under observation and the station. The most recent data of the satellites tracked from Helwan SLR station has been obtained during the years 2008 and 2009. The observations are carried out for low orbit satellite only; by the way during 2007 we started observation of the satellites using the CPF-formats as a prediction of their positions (Blazej, J. et al, 2008). The analysis of the data is based on calculating the difference between the observed and the predicted ranges of the satellites. To analyze and remove the noise of the Helwan satellite laser ranging data, a procedure has been used. The principal phases of the analysis as explained (Tawadros, M. et al, 2000 , Ibrahim, M., 2005).