P. J. S. Gil

Quantum Physics Exploring Gravity in the Outer Solar System: The SAGAS Project

We summarise the scientific and technological aspects of the Search for Anomalous Gravitation using Atomic Sensors (SAGAS) project, submitted to ESA in June 2007 in response to the Cosmic Vision 2015–2025 call for proposals. The proposed mission aims at flying highly sensitive atomic sensors (optical clock, cold atom accelerometer, optical link) on a Solar System escape trajectory in the 2020 to 2030 time-frame. SAGAS has numerous science objectives in fundamental physics and Solar System science, for example numerous tests of general relativity and the exploration of the Kuiper belt. The combination of highly sensitive atomic sensors and of the laser link well adapted for large distances will allow measurements with unprecedented accuracy and on scales never reached before. We present the proposed mission in some detail, with particular emphasis on the science goals and associated measurements and technologies.

Thermal Analysis of the Pioneer Anomaly: A Method to estimate radiative momentum transfer

We present a methodology based on pointlike Lambertian sources that enables one to perform a reliable and comprehensive estimate of the overall thermally induced acceleration of the Pioneer 10 and 11 spacecraft. We show, by developing a sensitivity analysis of the several parameters of the model, that one may achieve a valuable insight into the possible thermal origin of the so-called Pioneer anomaly.

Odyssey: A Solar System Mission

The Solar System Odyssey mission uses modern-day high-precision experimental techniques to test the laws of fundamental physics which determine dynamics in the solar system. It could lead to major discoveries by using demonstrated technologies and could be flown within the Cosmic Vision time frame. The mission proposes to perform a set of precision gravitation experiments from the vicinity of Earth to the outer Solar System. Its scientific objectives can be summarized as follows: (1) test of the gravity force law in the Solar System up to and beyond the orbit of Saturn; (2) precise investigation of navigation anomalies at the fly-bys; (3) measurement of Eddington’s parameter at occultations; (4) mapping of gravity field in the outer solar system and study of the Kuiper belt. To this aim, the Odyssey mission is built up on a main spacecraft, designed to fly up to 13 AU, with the following components: (a) a high-precision accelerometer, with bias-rejection system, measuring the deviation of the trajectory from the geodesics, that is also giving gravitational forces; (b) Ka-band transponders, as for Cassini, for a precise range and Doppler measurement up to 13 AU, with additional VLBI equipment; (c) optional laser equipment, which would allow one to improve the range and Doppler measurement, resulting in particular in an improved measurement (with respect to Cassini) of the Eddington’s parameter. In this baseline concept, the main spacecraft is designed to operate beyond the Saturn orbit, up to 13 AU. It experiences multiple planetary fly-bys at Earth, Mars or Venus, and Jupiter. The cruise and fly-by phases allow the mission to achieve its baseline scientific objectives [(1) to (3) in the above list]. In addition to this baseline concept, the Odyssey mission proposes the release of the Enigma radio-beacon at Saturn, allowing one to extend the deep space gravity test up to at least 50 AU, while achieving the scientific objective of a mapping of gravity field in the outer Solar System [(4) in the above list].

On spiral coordinates with application to wave propagation

We introduce a possibly new system of orthogonal curvilinear coordinates, whose coordinate curves are logarithmic spirals in the plane, supplemented by a cylindrical coordinate for three dimensions. It is shown that plane spiral coordinates form a one-parameter family, with equal scale factors along the two orthogonal coordinate curves, and constant Christoffel symbols. The equations of magnetohydrodynamics, which include those of fluid mechanics, are written in spiral coordinates and used to find a state of magnetohydrostatic equilibrium under a radial gravity field and spiral magnetic field, and to solve the equation of non-dissipative Alfven waves in a spiral magnetic field in terms of Bessel functions. This exact solution specifies the evolution of wave perturbations (velocity and magnetic field) and energy variables (kinetic and magnetic energy densities and energy flux) with distance, for waves of arbitrary frequency. Both the frequency and the spiral angle are varied in plots of the waveforms, which show the effect on Alfven wave propagation of three simultaneous effects : change in the mass density of the medium and in the strength and direction of the external magnetic field.

Simulations of Quasi-Satellite Orbits Around Phobos

DOI: 10.2514/1.44434 In this work, quasi-synchronous orbits around Phobos are studied from a preliminary mission design point of view. Addressed issues include stability of the orbits, possible choices of specific suitable orbits, and their impact on the design of a mission to Phobos (eclipses, observation conditions, etc.). An exploration of the phase space is performed to assess the precision requirements on the initial conditions of the spacecraft state vector for insertion into these orbits. The possibility of using an orbit outside the orbital plane of Phobos around Mars is also explored. Nomenclature e = second primary (usually Phobos) orbit eccentricity in the three-body problem hmax,hmin = maximum and minimum altitudes, relative to Phobos, reached by a quasi-satellite orbit, km RPh = mean radius of Phobos, km TPh = mean sidereal period of revolution of Phobos vx,vy,vz = spacecraft velocity Cartesian components in the synodic reference frame, m=s x,y,z = spacecraft position vector Cartesian components in the synodic reference frame, km � ,� ,� ,� , = parameters defining the quasi-satellite orbit geometry � = second primary mass, divided by the total mass, in the three-body problem

TESTING THE FLYBY ANOMALY WITH THE GNSS CONSTELLATION

We propose the concept of a space mission to probe the so called flyby anomaly, an unexpected velocity change experienced by some deep-space probes using earth gravity assists. The key feature of this proposal is the use of GNSS systems to obtain an increased accuracy in the tracking of the approaching spacecraft, mainly near the perigee. Two low-cost options are also discussed to further test this anomaly: an add-on to an existing spacecraft and a dedicated mission.

Modeling the nongravitational acceleration during Cassini’s gravitation experiments

In this paper we present a computation of the thermally generated acceleration of the Cassini probe during its solar conjunction experiment, obtained from a model of the spacecraft. We build a thermal model of the vehicle and perform a Monte Carlo simulation to find a thermal acceleration with a main component of

Hyperbolic orbits of Earth flybys and effects of ungravity-inspired conservative potentials

(3.01 \pm 0.33) \times 10^{-9} {\rm m/s^2}

On the Reflection of Alfvén Waves in the Inhomogeneous Solar Wind

. This result is in close agreement with the estimates of this effect performed through Doppler data analysis.

Quasi-Synchronous Orbits Around Phobos in the Context of a Phobos Sample Return Mission

In this work we take a critical look at the available data on the flyby anomaly and on the current limitations of attempts to develop an explanation. We aim to verify how conservative corrections to gravity could affect the hyperbolic trajectories of Earth flybys. We use ungravity-inspired potentials as illustrative examples and show how the resulting orbital simulations differ from the observed anomaly. We also get constraints on the model parameters from the observed flyby velocity shifts. The conclusion is that no kind of conservative potential can be the cause of the flyby anomaly.