Measurements on an autonomous wireless payload at 635 km distance using a sensitive radio telescope

The Delfi-C3 spacecraft carries the first autonomous wireless payload in space. This payload is a wireless sun sensor developed by TNO in the Netherlands. The data captured by the sensor is wirelessly transported to the central computer system inside the spacecraft. Since no additional power supply is needed, this sensor is fully autonomous. The radio link is a FSK link at 915 MHz using a standard Nordic Chipset. At the Delfi C3 spacecraft two of these autonomous sun sensors are mounted. Unfortunately only one is operational. Using the Westerbork Synthesis Radio Telescope we tried to detect the 915 MHz signal from the sun sensor to the internal receiver. Before the measurements could be done, the effects of the shielding of the spacecraft case were measured using a spare spacecraft. The final obtained link budget showed a 10 dB SNR when using a 25 meter single dish telescope. Measurements were performed at the WSRT by using multiple radio telescopes placed in the orbit direction. The downlink signal of Delfi C3 was detected, but the 915 MHz signal was not as it should be. We conclude that the sun sensor is malfunctioning.