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| Titel |
Influence of the observational noise and the parameters of spacecraft dynamical model on the Phobos mass estimations: Viking 1 and MEX flybys |
| VerfasserIn |
Maria Kudryashova, Pascal Rosenblatt, Jean-Charles Marty |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250092699
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| Publikation (Nr.) |
 EGU/EGU2014-7057.pdf |
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| Zusammenfassung |
| The mass of Phobos (GM more precisely) estimated by different authors based on diverse
data-sets and methods, varies more than 1 -Ïă error. The most complete list of GM values is
presented in the work of R.Jacobson and includes the estimations in the interval
[5.87 - 8.5] * 105[m3-sec2]. Furthermore, even the comparison of the estimations coming
from the same estimation procedure applied to the consecutive flybys of the same spacecraft
shows big variations in GMs. The indicated behavior is very pronounced in the GM
estimations stemming from the Viking1 flybys in February 1977 (as well as from MEX
flybys, though in a slightly smaller degree) and in this work we made an attempt to figure out
its roots.
The GM estimations are very sensitive to the Phobos ephemeris, accuracy of a spacecraft
orbit (particularly, how well we can model non-gravitational forces acting on a spacecraft),
radio-tracking measurements quality (noise and coverage), geometry (i.e. relative position
between a spacecraft, Phobos and an Earth’s tracking station) and distance of flyby.
Inaccuracies in all those elements will result in the errors of GM. Thus, in the present work
we tested the impact of most of those factors by means of simulations as well as by
changing certain parameters of the spacecraft dynamical model while fitting real
observations.
Neither distances of flybys nor a priori ephemerides show clear correlation with the
GMPhobos estimations and their formal errors. In the same time, analysis of the post-fit
Doppler residuals revealed that our observations are not very sensitive to the the
errors in GMPhobos. In other words, changes of the spacecraft velocities due to
ΔGMPhobos = 105[m3-sec2] are at the level of 0.06 mm/sec in case of Viking1 flybys.
Decreasing in the value of the noise of observations diminish the GM formal errors and
bringing the values of GM themselves closer to one another. Thus, we could conclude that the
noise of real Viking 1 measurements is bigger than the sensitivity of those observations to the
GM variations.
The similar studies of radio-science data acquired during MEX flybys in 2006, 2008 and
2010 will be presented as well. |
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