On July 2, 1985, 11:23 UTC (Universal Time Coordinated), the Giotto spacecraft, the European Space Agency (ESA) contribution to the international effort to study Halley's comet in situ, was successfully launched. The spacecraft was placed by an Ariane I launcher into a geostationary transfer orbit (GTO). About 32 h later, on July 3, 1985, 19:24 UTC, during its fourth perigee passage, the built-in solid propellant transfer propulsion system (TPS) was fired, and Giotto was injected into its escape trajectory from the earth's gravitational influence in order to encounter the comet on March 13, 1986. The TPS firing was so precise that even without further orbit correction maneuvers, Giotto would miss the comet by only 50,000 km. On July 6, 1985, the high-gain antenna was despun, i.e., set rotating in the opposite sense relative to Giotto's spin so that it maintains a constant direction toward the earth. The spacecraft spin rate was set to the nominal 15 rpm. Experiment switch on is scheduled for September 2, 1985, onward, in time for the Comet Giacobini-Zinner encounter of the National Aeronautics and Space Administration's International Cometary Explorer spacecraft.