Cassini radio science investigations will be conducted both during the cruise (gravitational wave and conjunction experiments) and the Saturnian tour of the mission (atmospheric and ionospheric occultations, ring occultations, determinations of masses and gravity fields). New technologies in the construction of the instrument, which consists of a portion on-board the spacecraft and another portion on the ground, including the use of the Ka-band signal in addition to that of the S-and X-bands, open opportunities for important discoveries in each of the above scientific areas, due to increased accuracy, resolution, sensitivity, and dynamic range.

The first four sets of radio occultations of the Titan's ionosphere were obtained by the Cassini spacecraft between March 2006 and May 2007. These occultations occurred at middle and high latitudes, at solar zenith angles from about 86° to 96°. The main ionospheric peak was seen, as expected from modeling and previous observations, near 1200 km, with a density of about 1–3 × 103 cm−3. A consistent ledge near 1000 km was also seen, and one of the polar observations found a significant (∼3 × 103 cm−3) layer in the region of 500–600 km. This layer also is seen in other observations with a density varying from about 0.7 to 1.7 × 103 cm−3, suggesting a variable production source (or sources) for this peak.

The Ultra Stable Oscillator aboard the Cassini spacecraft failed in late 2011, which means that all radio occultations after that date have to be done in two‐way mode, using a ground‐based signal transmitted to the spacecraft as the frequency reference. Here we present the numerical technique we use to analyze the data from the two‐way atmospheric radio occultations of both Saturn and Titan that have occurred since the Ultra Stable Oscillator (USO) failure, along with the theoretical reasons behind this technique. Since our two‐way technique is based upon our earlier one‐way technique which used the USO as the frequency reference, we also present our one‐way technique which we used for Saturn occultations prior to the loss of the USO.

Abstract.Six radio occultation experiments were conducted with the Galileo orbiter in 1997, yielding detailed measurements of the distribution and motion of plasma surrounding Io. This distribution has two components. One is highly asymmetric, consisting of a wake or tail that appears only on the downstream side and extends to distances as large as 10

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