Using range data of spacecrafts and radar
observations for improvement of orbital elements
of planets and parameters of mars rotation
E.V. Pitjeva
Institute of Applied Astronomy of the Russian Academy of
Sciences, 8 Zhdanov St., 197042, St.Peterburg, Russia
We have used the extremely precise observations of spacecrafts VIK-
ING-1, VIKING-2(1972-82), MARINER-9 (1971-72) for improvement of or-
bital elements of Mars and Earth and parameters of Mars rotation.
The ranging observations near conjunctions were corrected for the
solar corona with simultaneous determinations of parameters of a coro-
na model. These range data were combined with radar observations made
at Haystack, Arecibo and Goldstone in 1971-73 (corrected for topogra-
phy of Mars) to improve orbital elements of Mars and Earth. The preci-
sion of the least squares estimates is rather high, for example formal
standard deviations of semi-major axis of Mars and Earth were
0.000002 (arcsec) for da(M)/a(M) and 0.000001 (arcsec) for da(E)/a(e).
Tracking data from planet landers allow to study precession-nutati-
onal motion of the spin axis that would provide a better understanding
of planet geophysics. In the present work the rate of Mars rotation
(V), the mean node (Q), inclinations of the martian equator upon the
mean orbit (I), their variations and Mars precession constant (p)
were improved from VIKING Landers observations:
V = 350.89198959 ! 0.00000038 (deg/day)
Q = 35.32462 ! 0.00037 (deg)
dQ = 0.102 ! 0.014 (deg/cy)
I = 25.19022 ! 0.00018 (deg)
dI = 0.0102 ! 0.0080 (deg/cy)
p = -750 ! 36 (arcsec/cy)
We expect that including into our processing new data from planned
american (project MESUR) and russian Mars landers would improve essen-
tially the estimate of the Mars precession constant and make it pos-
sible to determine amplitudes of the dominant short periodic nutations.
As shown by our computations the inclusion of data within a year from
the MESUR lander yields the estimate of the Mars precession constant
with a standard error of 10-15 arcsec/cy. But if the duration of the
MESUR mission is only one month the improvement of this estimate will
be insignificant. The possible locations of MESUR lander (limited a
latitudinal band centered on 15 deg N latitude and to regions with
below the 0-km-elevation reference datum), for example the south of
Chryse Planitia or Isidis Planitia, will not have an influence on a
precision of the solution for astronomical parameters.
In this paper we present results of the first stage of our investi-
gation when range data of spacecrafts were processed simultaneously
with radar ranging observations of Mars made in 1971-73. Now we are
going to combine them with the data set of more 10000 planet radar ob-
servations (1961-1992, both Soviet and American ones) that have been
already used for constructing our original planet ephemerides and to
obtain new estimates of variability of the gravitational constant and
parameters of PPN formalism.