Results of the earth station and RadioAstron compatibility tests show that the VIRK 8 GHz band timing system performs well with the earth station. An overnight 16 hour phase test showed phase residuals similar to those logged from the VSOP satellite. However, the wide band data link at 15 GHz appears to have modulation problems. No acceptable data error rates were achievable in field tests with the earth station despite good results achieved over the identical path with the NRAO satellite simulator. Time prohibited further tests to identify the problem.
Several problems need to be resolved with the VIRK module. The stability of the downlink phase signal in the 8 GHz band needs to be improved so that jumps in the timing residuals are eliminated. The VIRK needs to be completed so that valid bit error rate measurements can be made. It is strongly suggested that the Russian equipment be brought back to Green Bank in the future to perform valid bit error rate measurements and to also verify compatibility of the data modulation with the earth station once these improvements have been made.
Also of concern is the 3-5 minute response time of the VIRK before it produces valid residual timing information once an uplink has been established. A clean signal source (not the current 14.71 MHz oscillator) is needed for the VIRK once it is integrated into the spacecraft.
These test proved to be valuable to the earth station. We were able to debug our software so that valid links could be established with the future RadioAstron satellite. The major tasks left for the earth station before we are ready for the RadioAstron mission is properly handling the RadioAstron downlink telemetry data.
Pictures of the Russian visit, including setup views, some spectrum
analyzer and scope displays from the tests, and off-site activities, are