George W. Null

Pioneer saturn celestial mechanics experiment.

During the Pioneer Saturn encounter, a continuous round-trip radio link at S band (∼ 2.2 gigahertz) was maintained between stations of the Deep Space Network and the spacecraft. From an analysis of the Doppler shift in the radio carrier frequency, it was possible to determine a number of gravitational effects on the trajectory. Gravitational moments ( J2 and J4) for Saturn have been determined from preliminary analysis, and preliminary mass values have been determined for the Saturn satellites Rhea, Iapetus, and Titan. For all three satellites the densities are low, consistent with the compositions of ices. The rings have not been detected in the Doppler data, and hence the best preliminary estimate of their total mass is zero with a standard error of 3 x 10–6 Saturn mass. New theoretical calculations for the Saturn interior are described which use the latest observational data, including Pioneer Saturn, and state-of-the-art physics for the internal composition. Probably liquid H2O and possibly NH3 and CH4 are primarily confined in Saturn to the vicinity of a core of approximately 15 to 20 Earth masses. There is a slight indication that helium may likewise be fractionated to the central regions.

Gravity Field of Jupiter from Pioneer 11 Tracking Data

Significantly improved values of the zonal gravity harmonic coefficients J39 J4, and J6 of Jupiter have been obtained from a preliminary analysis of Pioneer 11 spacecraft Doppler data taken while the spacecraft was near Jupiter. The new results, which will have an important application as boundary conditions for theoretical models of Jupiters interior. are consistent with a planet in hydrostatic equilibrium.

Gravitational parameters of the jupiter system from the Doppler tracking of pioneer 10.

Preliminary analyses of Doppler data from Pioneer 10 during its encounter with Jupiter indicate that the mass of Io is about 20 percent greater than previously thought and that Ios mean density is about 3.5 grams per cubic centimeter. A determination of the dynamical flattening of Jupiter (a - b)/a (where a is the semimajor axis and b is the semiminor axis) is found to lie in the neighborhood of 0.065, which agrees with the value determined from satellite perturbations.

The challenges of deep impact autonomous navigation

On July 4, 2005 at 05:44:34 UTC the Impactor spacecraft (s/c) impacted comet 9P/Tempel 1 with a relative speed of more than 10 km/s. The Flyby s/c captured the impact event, using both the medium resolution imager and the high resolution imager, and tracked the impact site for the entire observing period following impact. The objective of the Impactor s/c was to impact in an illuminated area viewable from the Flyby s/c and telemeter high-resolution context images of the impact site prior to impact. The Flyby s/c had two primary objectives: (1) capture the impact event in order to observe the ejecta plume expansion dynamics and (2) track the impact site for at least 800 s to observe the crater formation and capture high-resolution images of the fully developed crater. All of these objectives were met by estimating the trajectory of each spacecraft relative to 9P/Tempel 1 using the autonomous navigation system, precise attitude information from the attitude determination and control subsystem, and allowing each spacecraft to independently select the same impact site. This paper describes the challenges of targeting and tracking comet 9P/Tempel 1.

THE EVALUATION OF CERTAIN PHYSICAL CONSTANTS FROM THE RADIO TRACKING OF MARINER II

Statistical formulas, doppler residuals, and equations of condition are used to obtain certain physical constant data from the radio tracking of mariner ii