Gaia's scanning law

During its five year mission Gaia will observe the sky from an orbit around the L2 Lagrange point of the Sun and Earth-Moon system. In this location the satellite will perform a continuous spinning motion about its principal symmetry axis (the satellite spin axis). The spin rate is constant at 60 arcsec/s, so one full revolution will take 6 hours. In this time the two astrometric viewing directions (Line of sight 1 and Line of sight 2) which are perpendicular to the spin axis and separated from each other by a 'basic angle' of 106.5 degrees, scan one great circle on the sky.

The orientation of the spin axis is not constant but instead precesses about the satellite-Sun vector with a period of 63.12 days while the angle between the spin axis and the Sun direction is kept at a constant value of 45 degrees.

These two independent motions constitute the so-called Nominal Scanning Law. Its free parameters (angles, revolving periods) have been chosen in order to achieve optimal sky coverage during the mission's lifetime.

(See also the information sheet on the Scanning Law.)

[High resolution image available]

[Published: 08/12/2003 | Updated: 16/06/2010]