Construction of the intermediate HIPPARCOS astrometric catalogue

The data analysis methods for the determination of the astrometric parameters from observations by the Hipparcos satellite as used in FAST and NDAC consortia for the construction of intermediate 18-month and 30-month solutions are presented. The quality of the results depends upon calibrations of the instrumental parameters, examples of which are given. Results for the 18 and 30 month reductions are presented: these include histograms of the rms errors of each astrometric parameters, the FAST-NDAC differences as a function of coordinate, magnitude or colour index and results of a first attempt at combining the two solutions. The actual and pre-launch accuracy predictions are compared and discussed.