63 research outputs found
Testing General Relativity with the Radio Science Experiment of the BepiColombo mission to Mercury
The relativity experiment is part of the Mercury Orbiter Radio science Experiment (MORE) on-board the ESA/JAXA BepiColombo mission to Mercury. Thanks to very precise radio tracking from the Earth and accelerometer, it will be possible to perform an accurate test of General Relativity, by constraining a number of post-Newtonian and related parameters with an unprecedented level of accuracy. The Celestial Mechanics Group of the University of Pisa developed a new dedicated software, ORBIT14, to perform the simulations and to determine simultaneously all the parameters of interest within a global least squares fit. After highlighting some critical issues, we report on the results of a full set of simulations, carried out in the most up-to-date mission scenario. For each parameter we discuss the achievable accuracy, in terms of a formal analysis through the covariance matrix and, furthermore, by the introduction of an alternative, more representative, estimation of the errors. We show that, for example, an accuracy of some parts in 10â6 for the Eddington parameter ÎČ and of 10â5 for the Nordtvedt parameter η can be attained, while accuracies at the level of 5 Ă 10â7 and 1 Ă 10â7 can be achieved for the preferred frames parameters α1 and α2, respectively
On the Juno Radio Science Experiment: models, algorithms and sensitivity analysis
Juno is a NASA mission launched in 2011 with the goal of studying Jupiter.
The probe will arrive to the planet in 2016 and will be placed for one year in
a polar high-eccentric orbit to study the composition of the planet, the
gravity and the magnetic field. The Italian Space Agency (ASI) provided the
radio science instrument KaT (Ka-Band Translator) used for the gravity
experiment, which has the goal of studying the Jupiter's deep structure by
mapping the planet's gravity: such instrument takes advantage of synergies with
a similar tool in development for BepiColombo, the ESA cornerstone mission to
Mercury. The Celestial Mechanics Group of the University of Pisa, being part of
the Juno Italian team, is developing an orbit determination and parameters
estimation software for processing the real data independently from NASA
software ODP. This paper has a twofold goal: first, to tell about the
development of this software highlighting the models used, second, to perform a
sensitivity analysis on the parameters of interest to the mission.Comment: Accepted for publication in MONTHLY NOTICES of the Royal Astronomical
Society 2014 October 31. Received 2014 July 28; in original form 2013 October
New Tools for the Optimized Follow-Up of Imminent Impactors
The solar system is populated with, other than planets, a wide variety of minor bodies, the majority of which are represented by asteroids. Most of their orbits are comprised of those between Mars and Jupiter, thus forming a population named Main Belt. However, some asteroids can run on trajectories that come close to, or even intersect, the orbit of the Earth. These objects are known as Near Earth Asteroids (NEAs) or Near Earth Objects (NEOs) and may entail a risk of collision with our planet. Predicting the occurrence of such collisions as early as possible is the task of Impact Monitoring (IM). Dedicated algorithms are in charge of orbit determination and risk assessment for any detected NEO, but their efficiency is limited in cases in which the object has been observed for a short period of time, as is the case with newly discovered asteroids and, more worryingly, imminent impactors: objects due to hit the Earth, detected only a few days or hours in advance of impacts. This timespan might be too short to take any effective safety countermeasure. For this reason, a necessary improvement of current observation capabilities is underway through the construction of dedicated telescopes, e.g., the NEO Survey Telescope (NEOSTEL), also known as âFly-Eyeâ. Thanks to these developments, the number of discovered NEOs and, consequently, imminent impactors detected per year, is expected to increase, thus requiring an improvement of the methods and algorithms used to handle such cases. In this paper we present two new tools, based on the Admissible Region (AR) concept, dedicated to the observers, aiming to facilitate the planning of follow-up observations of NEOs by rapidly assessing the possibility of them being imminent impactors and the remaining visibility time from any given station
Constraining the Nordtvedt parameter with the BepiColombo Radioscience experiment
BepiColombo is a joint ESA/JAXA mission to Mercury with challenging
objectives regarding geophysics, geodesy and fundamental physics. The Mercury
Orbiter Radioscience Experiment (MORE) is one of the on-board experiments,
including three different but linked experiments: gravimetry, rotation and
relativity. The aim of the relativity experiment is the measurement of the
post-Newtonian parameters. Thanks to accurate tracking between Earth and
spacecraft, the results are expected to be very precise. However, the outcomes
of the experiment strictly depends on our "knowledge" about solar system:
ephemerides, number of bodies (planets, satellites and asteroids) and their
masses. In this paper we describe a semi-analytic model used to perform a
covariance analysis to quantify the effects, on the relativity experiment, due
to the uncertainties of solar system bodies parameters. In particular, our
attention is focused on the Nordtvedt parameter used to parametrize the
strong equivalence principle violation. After our analysis we estimated
which is about 1~order of magnitude
larger than the "ideal" case where masses of planets and asteroids have no
errors. The current value, obtained from ground based experiments and lunar
laser ranging measurements, is .
Therefore, we conclude that, even in presence of uncertainties on solar system
parameters, the measurement of by MORE can improve the current precision
of about 1~order of magnitude
Addressing some critical aspects of the BepiColombo MORE relativity experiment
The Mercury Orbiter radio Science Experiment (MORE) is one of the experiments
on-board the ESA/JAXA BepiColombo mission to Mercury, to be launched in October
2018. Thanks to full on-board and on-ground instrumentation performing very
precise tracking from the Earth, MORE will have the chance to determine with
very high accuracy the Mercury-centric orbit of the spacecraft and the
heliocentric orbit of Mercury. This will allow to undertake an accurate test of
relativistic theories of gravitation (relativity experiment), which consists in
improving the knowledge of some post-Newtonian and related parameters, whose
value is predicted by General Relativity. This paper focuses on two critical
aspects of the BepiColombo relativity experiment. First of all, we address the
delicate issue of determining the orbits of Mercury and the Earth-Moon
barycenter at the level of accuracy required by the purposes of the experiment
and we discuss a strategy to cure the rank deficiencies that appear in the
problem. Secondly, we introduce and discuss the role of the solar
Lense-Thirring effect in the Mercury orbit determination problem and in the
relativistic parameters estimation.Comment: 29 pages, 5 figures. Presented at the Seventh International Meeting
on Celestial Mechanics, San Martino al Cimino (Viterbo, Italy), 3-9 September
201
A test of gravitational theories including torsion with the BepiColombo radio science experiment
The Mercury Orbiter radio Science Experiment (MORE) is one of the experiments
on-board the ESA/JAXA BepiColombo mission to Mercury, to be launched in October
2018. Thanks to full on-board and on-ground instrumentation performing very
precise tracking from the Earth, MORE will have the chance to determine with
very high accuracy the Mercury-centric orbit of the spacecraft and the
heliocentric orbit of Mercury. This will allow to undertake an accurate test of
relativistic theories of gravitation (relativity experiment), which consists in
improving the knowledge of some post-Newtonian and related parameters, whose
value is predicted by General Relativity. This paper focuses on two critical
aspects of the BepiColombo relativity experiment. First of all, we address the
delicate issue of determining the orbits of Mercury and the Earth-Moon
barycenter at the level of accuracy required by the purposes of the experiment
and we discuss a strategy to cure the rank deficiencies that appear in the
problem. Secondly, we introduce and discuss the role of the solar
Lense-Thirring effect in the Mercury orbit determination problem and in the
relativistic parameters estimation
The relativity experiment of MORE: global full-cycle simulation and results
BepiColombo is a joint ESA/JAXA mission to Mercury with challenging objectives regarding geophysics, geodesy and fundamental physics. In particular, the Mercury Orbiter Radioscience Experiment (MORE) intends, as one of its goals, to perform a test of General Relativity. This can be done by measuring and constraing the post-Newtonian (PN) parameters to an accuracy significantly better than current one. In this work we perform a global full-cycle simulation of the BepiColombo Radio Science Experiments (RSE) in a realistic scenario, focussing on the relativity experiment but solving simultaneously for all the parameters of interest for RSE in a global least squares fit within a constrained multiarc strategy. The results on the achievable accuracy for each PN parameter will be presented and discussed
Dynamical properties of the Molniya satellite constellation: long-term evolution of orbital eccentricity
The aim of this work is to analyze the orbital evolution of the mean
eccentricity given by the Two-Line Elements (TLE) set of the Molniya satellites
constellation. The approach is bottom-up, aiming at a synergy between the
observed dynamics and the mathematical modeling. Being the focus the long-term
evolution of the eccentricity, the dynamical model adopted is a doubly-averaged
formulation of the third-body perturbation due to Sun and Moon, coupled with
the oblateness effect on the orientation of the satellite. The numerical
evolution of the eccentricity, obtained by a two-degree-of-freedom model
assuming different orders in the series expansion of the third-body effect, is
compared against the mean evolution given by the TLE. The results show that,
despite being highly elliptical orbits, the second order expansion catches
extremely well the behavior. Also, the lunisolar effect turns out to be
non-negligible for the behavior of the longitude of the ascending node and the
argument of pericenter. The role of chaos in the timespan considered is also
addressed. Finally, a frequency series analysis is proposed to show the main
contributions that can be detected from the observational data
The BepiColombo MORE gravimetry and rotation experiments with the ORBIT14 software
open6noopenG. Schettino, S. Di Ruzza, S. CicalĂČ, G. Tommei;
A. Milani Comparetti; E.M. AlessiSchettino, G.; DI RUZZA, Sara; CicalĂČ, S.; Tommei, G.; Milani Comparetti, A.; Alessi, E. M
The Hera Radio Science Experiment at Didymos
Hera represents the European Space Agency's inaugural planetary defence space
mission, and plays a pivotal role in the Asteroid Impact and Deflection
Assessment international collaboration with NASA DART mission that performed
the first asteroid deflection experiment using the kinetic impactor techniques.
With the primary objective of conducting a detailed post-impact survey of the
Didymos binary asteroid following the DART impact on its small moon called
Dimorphos, Hera aims to comprehensively assess and characterize the feasibility
of the kinetic impactor technique in asteroid deflection while conducting
in-depth investigation of the asteroid binary, including its physical and
compositional properties as well as the effect of the impact on the surface
and/or shape of Dimorphos. In this work we describe the Hera radio science
experiment, which will allow us to precisely estimate key parameters, including
the mass, which is required to determine the momentum enhancement resulting
from the DART impact, mass distribution, rotational states, relative orbits,
and dynamics of the asteroids Didymos and Dimorphos. Through a multi-arc
covariance analysis we present the achievable accuracy for these parameters,
which consider the full expected asteroid phase and are based on ground
radiometric, Hera optical images, and Hera to CubeSats InterSatellite Link
radiometric measurements. The expected formal uncertainties for Didymos and
Dimorphos GM are better than 0.01% and 0.1%, respectively, while their J2
formal uncertainties are better than 0.1% and 10%, respectively. Regarding
their rotational state, the absolute spin pole orientations of the bodies can
be recovered to better than 1 degree, and Dimorphos spin rate to better than
10^-3%. Dimorphos reconstructed relative orbit can be estimated at the sub-m
level [...
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