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.