Measurement of Station Delay at DSS-25

— This article discusses a measurement of the station delay at the Deep Space Network’s DSS-25 antenna in support of the Juno Gravity Science investigation. Calibration of the station delays in radiometric measurements is crucial in the computation of spacecraft trajectories and gravitational fields. Due to the high dynamics experienced by the Juno spacecraft, the accuracy of the Doppler measurements is more sensitive to small errors in the calibration. To support the Juno Gravity Science investigation, a test was conducted in November 2018 to measure the phase delay from the transmitter to the DSS-25 antenna and back to the receivers along three signal paths: X-up/X-down, X-up/Ka-down, and Ka-up/Ka-down. Both the uplink signal generation equipment and the receiver equipment are located at the Goldstone Signal Processing Center, approximately 10 kilometers direct line-of-sight away from the DSS-25 antenna. The previous estimate of the station delay at DSS-25 is 77 microseconds one-way (154 microseconds round-trip). Here we present results that the measured round-trip X-up/ X-down and X-up/Ka-down delay is fairly close to the previous estimate with a delay of 151 microseconds, but the Ka-up/Ka-down delay is 24 microseconds longer and is attributable to the Ka-band uplink. We recommend new values to be used for station delay at DSS-25.