We present a methodology based on point-like 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 on the possible thermal origin of the so-called Pioneer anomaly.
The anomalous time depending blueshift, the so-called "Pioneer anomaly", that was detected in the radio-metric data from Pioneer 10/11, Ulysses and Galileo spacecraft may not result from a real change of velocity. Rather, the Pioneer anomaly may be understood within the framework of general relativity as a time depending gravitational frequency shift accounting for the time dependence of the density of the dark energy when the latter is identified with quintessence. Thus, instead of being in conflict with Einstein equivalence principle, the main Pioneer anomaly appears merely as a new validati…
A methodology based on point-like sources is discussed, enabling a reliable estimate of the acceleration of the Pioneer 10 and 11 probes caused by thermal effects. A sensitivity analysis of the several parameters of the model allows for a clear indication of the possible thermal origin of the so-called Pioneer anomaly.
Recently, Brownstein and Moffat proposed a gravitational mechanism to explain the Pioneer anomaly based on their scalar-tensor-vector (STVG) metric theory of gravity. In this paper we show that their model, fitted to the presently available data for the anomalous Pioneer 10/11 acceleration, is in contrast with the latest determinations of the perihelion extra-rates of Jupiter, Saturn and Uranus.
Analysis of the radio-metric data from Pioneer 10 and 11 spacecrafts has indicated the presence of an unmodeled acceleration starting at 20 AU, which has become known as the Pioneer anomaly. The nature of this acceleration is uncertain. In this paper we give a description of the effect and review some relevant mechanisms proposed to explain the observed anomaly. We also discuss on some future projects to investigate this phenomenon.
In this paper we test the hypothesis that the Pioneer anomaly can be of gravitational origin by comparing the predicted model-independent shifts Delta a/a for the semimajor axis of Uranus and Neptune with the Voyager 2 radio-technical distance measurements performed at JPL-NASA. As in the case of other tests based on different methods and data sets (secular perihelion advance, right ascension/declination residuals over about one century), the orbits of the investigated planets are not affected by any anomalous acceleration like that experienced by the Pioneer 10/11 spacecraft.
Precision navigation of spacecraft requires accurate knowledge of small forces, including the recoil force due to anisotropies of thermal radiation emitted by spacecraft systems. We develop a formalism to derive the thermal recoil force from the basic principles of radiative heat exchange and energy-momentum conservation. The thermal power emitted by the spacecraft can be computed from engineering data obtained from flight telemetry, which yields a practical approach to incorporate the thermal recoil force into precision spacecraft navigation. Alternatively, orbit determination can be used to …
Recently, Jaekel and Reynaud put forth a metric linear extension of general relativity which, in the intentions of its proponents, would be able, among other things, to provide a gravitational mechanism for explaining the Pioneer anomaly without contradicting either the equivalence principle or what we know about the planetary motions. In this paper we perform an independent test of such an hypothesis by showing that the planets' orbits are, in fact, affected by the suggested mechanism as well and comparing the resulting effects with the latest observational determinations. It turns out that t…
In order to satisfy the equivalence principle, any non-conventional mechanism proposed to gravitationally explain the Pioneer anomaly, in the form in which it is presently known from the so-far analyzed Pioneer 10/11 data, cannot leave out of consideration its impact on the motion of the planets of the Solar System as well, especially those orbiting in the regions in which the anomalous behavior of the Pioneer probes manifested itself. In this paper we, first, discuss the residuals of the right ascension αand declination δof Uranus, Neptune and Pluto obtained by processing various data sets wi…
In this paper we use the ratio of the corrections to the standard Newtonian/Einsteinian secular precessions of the longitudes of perihelia of Jupiter and Saturn, recently estimated by the Russian astronomer E.V. Pitjeva by fitting almost one century of data with the EPM ephemerides, to make an independent, planetary-based test of the hypothesis that the Pioneer anomaly (PA), as it is presently known in the 5-10 AU region, is of gravitational origin. Accounting for the errors in the determined apsidal extra-rates and in the values of the PA acceleration at the orbits of Jupiter and Saturn the a…
In this paper we analyze the impact on the orbital motions of the outer planets of the solar system from Jupiter to Pluto of some velocity-dependent forces recently proposed to phenomenologically explain the Pioneer anomaly, and compare their predictions (secular variations of the longitude of perihelion \varpi or of the semimajor axis a and the eccentricity e) with the latest observational determinations by E.V. Pitjeva with the EPM2006 ephemerides. It turns out that while the predicted centennial shifts of a are so huge that they would have been easily detected for all planets with the excep…
We report on a \lessim 1% test of the Lense-Thirring effect with the Mars Global Surveyor (MGS) spacecraft and on certain features of motion of Uranus, Neptune and Pluto which contradict the hypothesis that the Pioneer anomaly can be caused by some gravitational mechanism.
In this paper we put on the test the new mechanism of gravitational origin recently put forth by Jaekel and Reynaud in order to explain the Pioneer anomaly in the framework of their post-Einsteinian metric extension of general relativity. According to such a proposal, the secular part of the anomalous acceleration experienced by the twin spacecraft of about 1 nm s^-2 could be caused by an extra-potential δΦ_P=c^2χr^2, with χ=4 10^-8 AU^-2, coming from the second sector of the considered model. When applied to the motion of the planets of the Solar System, it would induce anomalous secular peri…
NASA's first two deep space missions, Pioneers 10 and 11, have been travelling through the outer solar system for three decades. A slight deviation from their calculated trajectories presents an as yet unsolved scientific mystery. The use of recently recovered Doppler and telemetry data may help us develop a better understanding of this anomaly, and decide whether or not it is due to a force of on-board origin.
The Pioneer 10/11 spacecraft yielded the most precise navigation in deep space to date. However, their radio-metric tracking data received from the distances between 20--70 astronomical units from the Sun has consistently indicated the presence of a small, anomalous, Doppler frequency drift. The drift is a blue frequency shift that can be interpreted as a sunward acceleration of a_P = (8.74 +/- 1.33) x 10^{-10} m/s^2 for each particular spacecraft. This signal has become known as the Pioneer anomaly; the nature of this anomaly remains unexplained. Recently new Pioneer 10 and 11 radio-metric Do…
One noticed a numerical coincidence between the Pioneer spacecrafts deceleration anomaly and $(γ-1)$, with $γ$ the Lorentz factor. The match is not only for distances larger than 20 AU, but even for the observed slop between 10 and 20 AU. Such numerical link may eventually lead to a scientific hypothesis for future theoretical investigations.
Some features of the Pioneer anomaly are discussed in context of author's explanation of this effect as a deceleration of the probes in the graviton background. It is noted that if the model is true then the best parameter of the anomalous acceleration should be not the distance to the Sun but a cosine of the angle between a velocity of the probe and its radius-vector.
Analysis of the radio-metric tracking data from the Pioneer 10 and 11 spacecraft at distances between 20--70 astronomical units from the Sun has consistently indicated the presence of an anomalous, small, and constant Doppler frequency drift. The drift is a blue-shift, uniformly changing at the rate of (5.99 +/- 0.01) x 10^{-9} Hz/s. The signal also can be interpreted as a constant acceleration of each particular spacecraft of (8.74 +/- 1.33) x 10^{-8} cm/s^2 directed toward the Sun. This interpretation has become known as the Pioneer anomaly. We provide a problem set based on the detailed inv…
Considering an expanding locally anisotropic (ELA) metric with the Sun as central mass and the heuristic ansatz for the dimensionless functional exponent parameter 'alpha=3+alpha_2(r_1)(1-U_Sun)^2' with a linear ansatz 'alpha_2(r_1)=alpha_2^(2.0)+alpha_2^(2.1) r_1' above 20 AU the pioneer anomaly is fully accounted for as due to the blue-shift of the background space-time. For compatibility with orbital motion within the Solar system it is further considered a branch ansatz for which α_2(r_1)=0 below 20 AU. This construction reduces the physical acceleration correction above 20 AU down to ~10^…
In this paper we investigate the effects that an anomalous acceleration as that experienced by the Pioneer spacecraft after they passed the 20 AU threshold would induce on the orbital motions of the Solar System planets placed at heliocentric distances of 20 AU or larger as Uranus, Neptune and Pluto. It turns out that such an acceleration, with a magnitude of 8.74\times 10^-10 m s^-2, would affect their orbits with secular and short-period signals large enough to be detected according to the latest published results by E.V. Pitjeva, even by considering errors up to 30 times larger than those r…
We investigate the possibility that the anomalous acceleration of the Pioneer 10 and 11 spacecraft is due to the recoil force associated with an anisotropic emission of thermal radiation off the vehicles. To this end, relying on the project and spacecraft design documentation, we constructed a comprehensive finite-element thermal model of the two spacecraft. Then, we numerically solve thermal conduction and radiation equations using the actual flight telemetry as boundary conditions. We use the results of this model to evaluate the effect of the thermal recoil force on the Pioneer 10 spacecraf…
For over 20 years NASA has struggled to find an explanation to the Pioneer anomaly. Now it becomes clear the solution to the riddle is that they have uncovered evidence that c, the speed of light, is not quite a universal constant. Using J. C. Cure s hypothesis that the index of refraction is a function of the gravitational energy density of space and straightforward Newtonian mechanics, NASA s measurements provide compelling evidence that the speed of light depends on the inverse of the square root of the gravitational energy density of space. The magnitude of the Pioneer anomalous accelerati…
The present work describes the investigation of the navigation anomaly of Pioneer 10 and 11 probes which became known as the Pioneer Anomaly. It appeared as a linear drift in the Doppler data received by the spacecraft, which has been ascribed to an approximately constant sunward acceleration of about $8.5 \times 10^{-13} km/s^2$. Since then, the existence of the anomaly has been confirmed independently by several groups and a large effort was devoted to find its origin. The present study consists of two main parts: thermal modeling of the spacecraft throughout its trajectory, and orbit determ…
We work out the impact that the recently determined time-dependent component of the Pioneer Anomaly (PA), interpreted as an additional exotic acceleration of gravitational origin with respect to the well known PA-like constant one, may have on the orbital motions of some planets of the solar system. By assuming that it points towards the Sun, it turns out that both the semi-major axis a and the eccentricity e of the orbit of a test particle experience secular variations. For Saturn and Uranus, for which modern data records cover at least one full orbital revolution, such predicted anomalies ar…
This paper reports the results of an analysis of the Doppler tracking data of Pioneer probes which did show an anomalous behaviour. A software has been developed for the sake of performing a data analysis as independent as possible from that of J. Anderson et al. \citep{anderson}, using the same data set. A first output of this new analysis is a confirmation of the existence of a secular anomaly with an amplitude about 0.8 nms$^{-2}$ compatible with that reported by Anderson et al. A second output is the study of periodic variations of the anomaly, which we characterize as functions of the azi…
If the Pioneer Anomaly (PA) was a genuine dynamical effect of gravitational origin, it should also affect the orbital motions of the solar system's bodies moving in the space regions in which the PA manifested itself in its presently known form, i.e. as a constant and uniform acceleration approximately directed towards the Sun with a non-zero magnitude APio = (8.74 +/- 1.33) x 10^-10 m s^-2 after 20 au from the Sun. In this paper we preliminarily investigate its effects on the orbital motions of the Neptunian satellites Triton, Nereid and Proteus, located at about 30 au from the Sun, both anal…
We present an improved method to compute the radiative momentum transfer in the Pioneer 10 & 11 spacecraft that takes into account both diffusive and specular reflection. The method allows for more reliable results regarding the thermal acceleration of the deep-space probes, confirming previous findings. A parametric analysis is performed in order to set an upper and lower-bound for the thermal acceleration and its evolution with time.
A method for the computation of the radiative momentum transfer in the Pioneer 10 & 11 spacecraft due to the diffusive and specular components of reflection is presented. The method provides a reliable estimate of the thermal contribution to the acceleration of these deep space probes and allows for a Monte-Carlo analysis from which an estimate of the impact of a possible variability of the parameters. It is shown that the whole anomalous acceleration can be explained by thermal effects. The model also allows one to estimate the expected time evolution of the acceleration due to thermal effect…
Applying Newtonian dynamics in five dimensions rather than four, to a universe that is closed, isotropic and expanding,suggests that under certain circumstances an additional and previously unidentified acceleration, a_A, can arise affecting the four dimensional motion of spacecraft. The two cases of this acceleration being either real or virtual are considered. In the real case, simple estimates of a_A are shown to be in partial agreement with reported acceleration anomalies from several Earth flybys and from the Pioneer spacecraft. However, these estimates do not fully reconcile with radio D…
Residual accelerations due to thermal effects are estimated through a model of the New Horizons spacecraft and a Monte Carlo simulation. We also discuss and estimate the thermal effects on the attitude of the spacecraft. The work is based on a method previously used for the Pioneer and Cassini probes, which solve the Pioneer anomaly problem. The results indicate that after the encounter with Pluto there is a residual acceleration of the order of $10^{-9}~\mathrm{m/s^2}$, and that rotational effects should be difficult, although not impossible, to detect.
