Citation
Abstract
Precision Doppler tracking of deep-space probes is central to spacecraft navigation and many radio science investigations. The most sensitive Doppler observations to date have been taken using the NASA/JPL Deep Space Network (DSN) antenna DSS 25—a 34-m-diameter beam-waveguide station especially instrumented with simultaneous X-band (≈8.4-GHz) and Ka-band (≈32-GHz) links and tropospheric scintillation calibration equipment—tracking the Cassini spacecraft. These Cassini observations achieved Doppler fractional frequency stability (Doppler frequency fluctuation divided by center frequency, ∆f/f ) of ≈3×10−15 at τ = 1000 s o integration. In those very-high-sensitivity tracks, the leading disturbance was antenna mechanical noise: time-dependent unmodeled physical motion of the ground antenna’s phase center caused by antenna sag as the elevation angle changed, unmodeled subreflector motion, wind loading, bulk motion of the antenna as it rolled over irregularities in the supporting azimuth ring, differential thermal expansion of the structure, etc. This noise has seemed irreducible at reasonable cost, since it is unclear how to build a practical, large, moving, steel structure having mechanical stability significantly better than that of current tracking stations. Here we show how the mechanical noise of a large tracking antenna can effectively be removed when two-way Doppler tracking data from an existing DSN antenna are suitably combined with simultaneous tracking data using an ancillary (smaller and stiffer) antenna. Using our method, the mechanical noise in the final Doppler observable can be reduced, substantially, to that of the stiffer antenna.
Details
- Volume
- 42-165
- Published
- May 15, 2006
- Pages
- 1–6
- File Size
- 92.7 KB