The Dawn Gravity Investigation at Vesta and Ceres

Abstract

The objective of the Dawn gravity investigation is to use high precision X-band Doppler tracking and landmark tracking from optical images to measure the gravity fields of Vesta and Ceres to a half-wavelength surface resolution better than 90-km and 300-km, respectively. Depending on the Doppler tracking assumptions, the gravity field will be determined to somewhere between harmonic degrees 15 and 25 for Vesta and about degree 10 for Ceres. The gravity fields together with shape models determined from Dawn's framing camera constrain models of the interior from the core to the crust. The gravity field is determined jointly with the spin pole location. The second degree harmonics together with assumptions on obliquity or hydrostatic equilibrium may determine the moments of inertia.

The case of the missing Ceres family

“…Although gravity measurements are expected to be similar in fidelity to those at Vesta (Konopliv et al, 2012), the presence and depth of a strongly Fig. 2.…”

Dawn completes its mission at 4 Vesta

“…This understanding was used to develop a payload for the mission consisting of a framing camera (Sierks et al 2011); a visible and infrared mapping spectrometer, dubbed VIR (De Sanctis et al 2011); and a gamma ray and neutron spectrometer, called GRaND ). These instruments were supplemented by the telemetry system that was used to obtain radiometric tracking data to define the gravitational field (Konopliv et al 2011a). The framing camera was used to obtain observations of the surface from different viewing directions that were used to reconstruct the topography of the surface using stereophotogrammetry and stereophotoclinometry Jaumann et al 2012;Preusker et al 2012).…”

Precise Orbit Determination of MEX Flyby Phobos Using Simulated Radiometric and Image Data

“…In the conventional two-way or three-way measurement mode, as the Earth-Sun-spacecraft angle approaches 180°, the spacecraft is blocked by the Sun, making it impossible for ground stations to receive these measurements. Moreover, as the Sun-Earth-spacecraft angle approaches 0°, the radio tracking data of the spacecraft will be significantly influenced by solar plasma, so the accuracy of orbit determination is reduced when these tracking data are used in orbit determination of spacecraft [ 10 , 11 ]. Radiometric data are also subject to the scheduling availability of tracking stations that typically support different missions simultaneously.…”

“…Images from spacecraft have been used to improve orbit knowledge on many deep space exploration missions [ 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ]. In Near Earth Asteroid Rendezvous (NEAR) and Dawn missions, the gravity field and mass of the target body, the orbit of the target body around the Sun, the orientation and spin of the target, the location of the optical landmarks on the surface of the target, and orbits of spacecraft were jointly determined using earth-based tracking and optical landmark tracking data in a global estimation procedure [ 11 , 12 , 13 ].…”