Citation
Abstract
In August 1989, Voyager 2 flew by the planet Neptune. Due to a faulty trackingloop capacitor in the spacecraft’s transponder, the last 25 minutes before ingress| the most critical period for obtaining coherent Doppler for gravity field analysis| had to be performed with the spacecraft assigned to the less-frequency-stable (but more reliable) noncoherent mode. The noncoherent downlink reduced the accuracy of the higher-order (J2 and J4) gravity terms [1]. However, a weak side tone, generated by the coherent oscillator feeding across the transponder mode switch, offered the possibility of extracting a coherent downlink from the noncoherent data. This article presents the results of synthesizing coherent Doppler from the Voyager feedthrough side tone. Furthermore, it shows how to form a linear combination of the two Doppler data sets that displays a lower noise level (30 to 50 percent at time scales of 300 seconds and above) for measuring the gravity field of Neptune.
Details
- Volume
- 42-131
- Published
- November 15, 1997
- Pages
- 1–19
- File Size
- 519.2 KB