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The problem of determination of the orbital velocity of an astrometricsatellite from its own observational data is studied. It is well known thatdata processing of microarcsecond-level astrometric observations imposes verystringent requirements on the accuracy of the orbital velocity of the satellite(a velocity correction of 1.45 mm/s implies an aberrational correction of 1$\mu$as). Because of a number of degeneracies the orbital velocity cannot befully restored from observations provided by the satellite. Seven constraintsthat must be applied on a velocity parameterization are discussed andformulated mathematically. It is shown what part of velocity can be recoveredfrom astrometric data by a combined fit of both velocity parameters andastrometric parameters of the sources. Numerical simulations show that, withthe seven constraints applied, the velocity and astrometric parameters can bereliably estimated from observational data. It is also argued that the idea toimprove the velocity of an astrometric satellite from its own observationaldata is only useful if the a priori information on the orbital velocityjustifies the applicability of the velocity constraints. The proposed modeltakes into account only translational motion of the satellite and ignores anysatellite-specific parameters. Therefore, the results of this study are equallyapplicable to both scanning missions similar to Gaia, and pointing ones likeSIM, provided that enough sources were observed sufficiently uniformly.

Determination of the barycentric velocity of an astrometric satellite using its own observational data