Summary of the Scientific Goals

The following goals were those adopted at the time of, or in the case of the Tycho experiment soon after, the formal adoption of the project by ESA (i.e., around 1980).

Main Experiment:

Number of stars	100 000
Limiting magnitude	V = 12.4 mag
Complete to	V = 7.3 - 9.0 mag (*)
Positional accuracy	0.002 arcsec (B="9" mag)
Parallax accuracy	0.002 arcsec (B="9" mag)
Proper motion accuracy	0.002 arcsec per year (B="9" mag)
Systematic errors	<0.001 arcsec

Tycho Experiment:

Number of stars	>400 000
Limiting magnitude	B = 10 - 11 mag
Positional accuracy	0.03 arcsec (B="10" mag)
Photometric accuracy	0.05 mag in B and V (per observation)
Observation per star	approx. 100

*depending on galactic latitude and spectral type

Additional results on photometry, variability and double and multiple stars, not foreseen in detail at the time of the mission's acceptance, also appear as part of the final mission products.

The actual results (published as The Hipparcos and Tycho Catalogues) achieved by the mission in all case supersede these expected performances. The properties of the Catalogues are summarised here.