This paper describes a new low cost method implemented in Bremen university ground station for correcting Doppler measurements based on GPS techniques. The facilities of the tracking ground station to determine the one-way Doppler shift of the NOAA weather satellites are described. Using an open source GPS platform, frequency bias in the measurement and receiving devices was measured. The performance of the low cost instruments with antennas, rotor controller, receiver, frequency counter and open source GPS terminal will be explained. This station is a reassembly of the same ground station used previously in 1994 to support the BREM-SAT mission, with the addition of the GPS terminal in order to measure the reference oscillator's error. Incorporating all the processed measurements, a corrected Doppler shift curve will result which differs from the original measured Doppler curve by the fact that the frequencies now are the absolute values. The results are compared with the expected nominal predictions. Finally, the least square algorithm was implemented for orbit determination using the uncorrected and corrected measurements. Nomenclaturec = speed of light f d = Doppler frequency f 0 = nominal frequency f synth = synthesizer frequency f measured = measured frequency H = transition matrix R = covariance matrix x, y, z = coordinates of state vector ρ = range ρ = range rate ρ ′ = estimated range rate
A small European geostationary platform (SGEO) for communications applications is being developed under OHB's lead management. Initiated by OHB, it has been established as a separate component of the long-term ESA schedule under the ARTES-11 program. The technical specifications for SGEO are based on a proposal submitted by OHB-System AG. What sets the SGEO platform apart is its modular structure. As a result, the satellite can be fitted individually in accordance with the customer's specific requirements without any major modifications to the satellite bus. SGEO has been developed as an optimum platform for communications payloads. With its modular design, however, SGEO also provides a costefficient basis for other applications such as earth observation or meteorology. The first SGEO mission based on the new satellite platform will be launched with a payload for the Spanish satellite operator HISPASAT as "HISPASAT Advanced Generation 1". HISPASAT AG1 will be placed in a geostationary orbit, where it will supply Spain, Portugal, the Canary Islands and South America with multimedia services. The paper presents an overview of the satellite modular design and main features together with a brief description of the new payload technologies that will fly onboard the mission. The operational concept behind the mission is described by going through the details of the ground segment design together with the operability requirements and solutions that fulfill those requirements, also the highlights of the different mission phase operations including preparation, LEOP, payload and platform IOT, and on-station. Two scenarios are discussed regarding the transfer strategy: a geo-stationary transfer approach and a super-synchronous transfer approach. And finally an overview of mission timeline is presented.
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