Gravity, Geodesy and Fundamental Physics with BepiColombo’s MORE Investigation

open40siThe Mercury Orbiter Radio Science Experiment (MORE) of the ESA mission BepiColombo will provide an accurate estimation of Mercury’s gravity field and rotational state, improved tests of general relativity, and a novel deep space navigation system. The key experimental setup entails a highly stable, multi-frequency radio link in X and Ka band, enabling two-way range rate measurements of 3 micron/s at nearly all solar elongation angles. In addition, a high chip rate, pseudo-noise ranging system has already been tested at 1-2 cm accuracy. The tracking data will be used together with the measurements of the Italian Spring Accelerometer to provide a pseudo drag free environment for the data analysis. We summarize the existing literature published over the past years and report on the overall configuration of the experiment, its operations in cruise and at Mercury, and the expected scientific results.openIess L.; Asmar S.W.; Cappuccio P.; Cascioli G.; De Marchi F.; di Stefano I.; Genova A.; Ashby N.; Barriot J.P.; Bender P.; Benedetto C.; Border J.S.; Budnik F.; Ciarcia S.; Damour T.; Dehant V.; Di Achille G.; Di Ruscio A.; Fienga A.; Formaro R.; Klioner S.; Konopliv A.; Lemaitre A.; Longo F.; Mercolino M.; Mitri G.; Notaro V.; Olivieri A.; Paik M.; Palli A.; Schettino G.; Serra D.; Simone L.; Tommei G.; Tortora P.; Van Hoolst T.; Vokrouhlicky D.; Watkins M.; Wu X.; Zannoni M.Iess L.; Asmar S.W.; Cappuccio P.; Cascioli G.; De Marchi F.; di Stefano I.; Genova A.; Ashby N.; Barriot J.P.; Bender P.; Benedetto C.; Border J.S.; Budnik F.; Ciarcia S.; Damour T.; Dehant V.; Di Achille G.; Di Ruscio A.; Fienga A.; Formaro R.; Klioner S.; Konopliv A.; Lemaitre A.; Longo F.; Mercolino M.; Mitri G.; Notaro V.; Olivieri A.; Paik M.; Palli A.; Schettino G.; Serra D.; Simone L.; Tommei G.; Tortora P.; Van Hoolst T.; Vokrouhlicky D.; Watkins M.; Wu X.; Zannoni M

Orbital effects of a monochromatic plane gravitational wave with ultra-low frequency incident on a gravitationally bound two-body system

We analytically compute the long-term orbital variations of a test particle orbiting a central body acted upon by an incident monochromatic plane gravitational wave. We assume that the characteristic size of the perturbed two-body system is much smaller than the wavelength of the wave. Moreover, we also suppose that the wave's frequency is much smaller than the particle's orbital one. We make neither a priori assumptions about the direction of the wavevector nor on the orbital geometry of the planet. We find that, while the semi-major axis is left unaffected, the eccentricity, the inclination, the longitude of the ascending node, the longitude of pericenter and the mean anomaly undergo non-vanishing long-term changes. They are not secular trends because of the slow modulation introduced by the tidal matrix coefficients and by the orbital elements themselves. They could be useful to indepenedently constrain the ultra-low frequency waves which may have been indirectly detected in the BICEP2 experiment. Our calculation holds, in general, for any gravitationally bound two-body system whose characteristic frequency is much larger than the frequency of the external wave. It is also valid for a generic perturbation of tidal type with constant coefficients over timescales of the order of the orbital period of the perturbed particle.Comment: LaTex2e, 24 pages, no figures, no tables. Changes suggested by the referees include

MORE: An advanced tracking experiment for the exploration of Mercury with the mission BepiColombo

Precise microwave tracking of interplanetary spacecraft has been a crucial tool in solar system exploration. Range and range rate measurements, the main observable quantities in spacecraft orbit determination and navigation, have been widely used to refine the dynamical model of the solar system and to probe planetary interiors. Thanks to the use of Ka-band and multifrequency radio links, a significant improvement in microwave tracking systems has been demonstrated by the radio science experiments of the Cassini mission to Saturn. The Cassini radio system has been used to carry out the most accurate test of general relativity to date. Further developments in the radio instrumentation have been recently started for the Mercury Orbiter Radio Experiment (MORE), selected for the ESA mission to Mercury, BepiColombo. MORE addresses the mission\u2019s scientific goals in geodesy, geophysics and fundamental physics. In addition, MORE will carry out a navigation experiment, aiming to a precise assessment of the orbit determination accuracies attainable with the use of the novel instrumentation. The key instrument is a Ka/Ka band digital transponder enabling a high phase coherence between uplink and downlink carriers and supporting a wideband ranging tone. The onboard instrumentation is complemented by a ground system based upon the simultaneous transmission and reception of multiple frequencies at X- and Ka-band. The new wideband ranging system is designed for an end-to-end accuracy of 20cm using integration times of a few seconds. Two-way range rate measurements are expected to be accurate to 3m/s, thanks to nearly complete cancellation or calibration of the propagation noise from interplanetary plasma and troposphere. We review the experimental configuration of the experiment and outline its scientific goals and expected results

Precision of Radio Science Instrumentation for Planetary Exploration

Radio Science techniques have been used for planetary exploration, space physics, and experiments addressing aspects of relativity on many deep space missions. Various Radio Science experiments are also planned for many future missions. This paper presents the noise processes in the Radio Science data acquired by the Deep Space Network and provides a detailed noise model for Doppler radio science experiments. The most sensitive instrumentation and experiments to date achieve fractional frequency fluctuation noise of 3E-15 at an integration time of 1000 seconds, corresponding to better than 1 micron per second velocity noise. Our noise model focuses on the Fourier range in the millihertz to 1 Hz, but we briefly discuss noise in lower frequency observations. We identify phenomena limiting current Doppler sensitivity and discuss prospects for significant sensitivity improvements

The Determination of the Gravity Fields of the Saturnian Satellites With Cassini

During the first two years of its tour of the Saturn system, Cassini has been flying-by some of the most interesting icy satellites. Gravity field results obtained from the orbital fit of radiometric data acquired during these close encounters with Phoebe, Iapetus, Enceladus, Hyperion, Dione and Rhea are presented. These results were then used to infer information about the internal structure of these bodies. This paper describes the technique used for the short-arc orbit determination process, the data calibration and analysis procedure, and the mass and gravity field results, emphasizing the advantages offered by Cassini\u2019s advanced deep-space tracking system

Mass and interior of Enceladus from Cassini data analysis

Gravity results are available from radio Doppler data acquired by the Deep Space Network during the encounter of the Cassini spacecraft with Enceladus in February 2005. We report the mass of Enceladus to be (1.0798\ub10.0016) 7 10^20 kg, which implies a density of 1608.9\ub14kg*m^−3. For a core made of hydrated silicates with a density of 2500kg*m^−3 the core radius is about 190 km and the quadrupole moment C22 = 1.4 710^−3. If Enceladus is in hydrostatic equilibrium, the larger than previously anticipated density implies that the recently proposed secondary spin\u2013orbit resonance cannot be present. Therefore, the source of endogenic activity of Enceladus remains unexplained

Cassini\u2019s Determination of the Gravity Fields of the Saturnian Satellites

The determination of the gravity fields of the Saturnian satellites is one of the main scientific goals and responsibilities of the Cassini Radio Science team. Radiometric tracking data were acquired during the flybys of Phoebe, Enceladus, Dione, Rhea, Hyperion, and Iapetus, allowing an accurate determination of the masses of these satellites as well as the gravity quadrupole field of Rhea. Our technique consists of using X-band and Ka-band coherent, two-way Doppler data and fit them in JPL\u2019s Orbit Determination Program in short data arcs. Doppler data are fitted using a spacecraft dynamical model that includes the gravitational accelerations from all Saturn system bodies, as well as non-gravitational accelerations from the spacecraft Radioisotope Thermoelectric Generators and from solar radiation pressure. Calibrations of the noise introduced by the Earth troposphere, using an Advanced Media Calibration system, and charged particles in the solar corona and the Earth ionosphere are applied. The paper will describe the technique used for the short-arc orbit determination process and the data calibration and analysis procedure, emphasizing the advantages offered by Cassini\u2019s advanced deep-space tracking system

Interiors of Enceladus and Rhea

Measurement method and data set: Gravity field parameters determined by means of range rate measurements over multiple arcs across flyby. Optical imaging not required when reliable a priori estimates of spacecraft state vector are available. Interior of Enceladus: Density of 1605 +/-14 kg/cu m, higher than pre-Cassini estimates, requires a substantial amount of rock to warmer interior to enhance likelihood of differentiation of water from rock-metal. Assume no porosity. Assuming Io s mean density for the rock-metal component, one finds its fractional mass to be 0.52+/-0.06. There is evidence that Enceladus may be differentiated: a) Areas devoid of craters must be geologically young. b) Systems of ridges, fractures, and groove indicate that the surface has been tectonically altered. c) Viscous relaxation of craters has occurred, and d) The plumes near the South pole indicate venting of subsurface volatiles

Gravity field and interior of Rhea from Cassini data analysis

The Cassini spacecraft encountered Rhea on November 26, 2005. Analysis of the Doppler data acquired at and around closest approach yields the mass of Rhea and the quadrupole moments of its gravity field with unprecedented accuracy. We obtained GM = 153.9395 +/- 0.0018 km(3) s(-2) which corresponds to a density of 1232.8 +/- 5.4 ka m(-3). Our results for J(2) and C-22 are (7.947 +/- 0.892) x 10(-4),and (2.3526 +/- 0.0476) x 10(-4) respectively. These values are consistent with hydrostatic equilibrium. From the value of C22, we infer the non-dimensional moment of inertia C/MR2 = 0.3721 +/- 0.0036. Our models of Rhea's interior based on the gravity data favor an almost undifferentiated satellite. A discontinuity between a core and a mantle is possible but not required by the data. Models with a constant silicate mass fraction throughout the body cannot account for the determined quadrupole coefficients. The data exclude fully differentiated models in which the core would be composed of unhydrated silicates and the mantle would be composed of pure ice. If the mantle contains 10% in mass of silicates, the core extends to 630 km in radius and has a silicate mass fraction of 40%. A continuous model in which the silicates are more concentrated toward the center of the body than in the outer layers is allowed by the gravity data but excluded by thermal evolution considerations. The one model that fits the gravity data and is self-consistent when energy transport and ice melting are qualitatively considered is an "almost undifferentiated" Rhea, in which a very large uniform core is surrounded by a relatively thin ice shell containing no rock at all. (C) 2007 Elsevier Inc. All rights reserved