EXPLOITATION OF DOPPLER DATA DURING THE REACTIVATION OF GIOTTO

In February 1990, contact was re-established with the ESA cometary spa cecraft, Giotto, but the signal was too weak for telemetry and only Do ppler data provided information on the status and dynamics of the spac ecraft. These data showed that the orbit prediction had been accurate and were used to determine the spacecraft spin-rate. After several bli nd major reconfigurations of the spacecraft, the Doppler analyses prov ed that the High-Gain Antenna (HGA) had been despun and an attitude ma neuver successfully performed. The Doppler change allowed the attitude to be reconstructed and eventually enabled normal communications via the HGA. Subsequently, the orbit was regularly determined from Doppler and range measurements and Giotto made the first ever Earth swing-by on July 2, 1990.