MGS UPLINK ARRAYING EXPERIMENT (2/25/06)
Arraying of receiving antennas for downlink reception is the subject of several ongoing efforts, and 34-m antennas have already been arrayed previously to enhance reception performance of Galileo downlink signals. However, uplink arraying to deep-space has not been demonstrated before, hence calibration and tracking concepts for uplink arraying must be developed and validated with spacecraft operating under realistic conditions.
The objectives of the MGS Uplink Arraying Experiment are as follows:
- Demonstrate far-field maximization of uplink array signal power at the spacecraft
- Show that uplink power at the spacecraft increases by 6 dB when equal powers are transmitted
- Demonstrate differential phase-ramp optimization algorithms designed to estimate the required phase offsets based on spacecraft AGC measurements
- Determine the degradation in received power due to uncompensated phase drift
- Attempt to maintain phase alignment of the two uplink signals using active phase control on the ground
The uplink arraying functions demonstrated and evaluated during this experiment include:
- Removal of differential Doppler from the transmitted X-band uplink carriers;
- Differential phase ramping of transmitted X-band carriers;
- Spacecraft configuration to record AGC readings at predetermined intervals and rates;
- AGC readings obtained in real-time from downlink telemetry and processing of engineering data to extract the sequence of AGC readings;
- Real-time analysis of spacecraft data to estimate the optimum uplink array differential phase;
- Application of optimum differential phase to the uplink signals; and
- Near real-time monitoring of phase drifts in the ground equipment.
