Precise Cassini Navigation During Solar Conjunctions Through Multifrequency Plasma Calibrations

Odyssey: a solar system mission

“…In fact, (1 − γ ) measures the deviation from general relativity of competing theories. This deviation has been shown to be smaller than 2 × 10 −5 by the Cassini relativity experiment performed at solar conjunctions [43,44]. But there exist theoretical models [49][50][51][52][53][54] which suggest that this deviation might have a natural value in the range 10 −6 as a consequence of a damping of the scalar contribution to gravity during cosmological evolution.…”

“…One of the two channels (either X or Ka) would be the standard radio link for commands and telemetry; the others are specific to radio science and the associated instrumentation is therefore considered as payload. This approach has been used for the Cassini [43,44] and BepiColombo [58] spacecraft, but the calibration of the plasma noise is only possible for Doppler observables and is baselined for Odyssey. The crucial component of the plasma noise cancellation system is a Kaband radio link (34 GHz uplink, 32.5 GHz downlink) originally developed for Cassini radio science experiments.…”

“…This objective justifies the optional embarkment of laser equipment which would lead to a measurement of γ with an accuracy of 10 −7 , a factor of 200 beyond the current best result obtained by Cassini [43,44]. A VLBI optional equipment is also proposed for improving the resolution of navigation on the celestial sky.…”

Experimental validation of a dual uplink multifrequency dispersive noise calibration scheme for Deep Space tracking

“…[3] The full multifrequency link configuration proposed in Bertotti et al [1993] was successfully tested for the first time using Cassini's tracking data acquired during the cruise phase radio science experiments [Tortora et al, 2002[Tortora et al, , 2004Bertotti et al, 2003;Armstrong et al, 2003], showing a dramatic improvement in data stability, if compared to the raw X band and Ka-band observables for data acquired at low solar elongations angles (or SEP, Sun-Earth-Probe angle). The residuals obtained by the calibrated observables using a simple orbital model (the six parameter fit, described by Bertotti et al [1995] based upon the Doppler formulation introduced by Curkendall and McReynolds [1969]) showed a fractional frequency stability (the fluctuation of the received sky frequency around the carrier reference frequency, in terms of Allan standard deviation, ASDEV) compatible with the one achieved during solar oppositions, a benign scenario for interplanetary plasma noise.…”

“…Despite its simplicity, this calibration scheme is extremely effective in terms of link stability and allows eliminating almost entirely its dependency upon the S/C SEP angle, as shown by Tortora et al [2003Tortora et al [ , 2004. The spectrum of solar plasma noise is strongly dependent on the SEP, because it represents the solar wind velocity component perpendicular to the carrier optical path, that is the main source of the phase scintillation [Armstrong et al, 1979;Asmar et al, 2005].…”