The 'launch window' that opened on 6 October 1997 would last until the end of the month. The hope of dispatching the mission on the first day was foiled when an air conditioner damaged a piece of the Huygens probe's thermal insulation, so the launch was rescheduled for 13 October, on which date the window ran from 04:55 to 07:15 local time. However, unacceptably high winds at altitude prompted a 'scrub' and a two-day recycle. Watched by a large number of project members, including several hundred Europeans, Cassini-Huygens lifted off at 04:43 on 15 October from the Air Force's Cape Canaveral facility, its plume lighting up the pre-dawn sky.

Even the Centaur stage was incapable of sending the heavy spacecraft straight to Jupiter, whose gravitational field serves as the 'doorway' to the outer Solar System, so, like the Galileo mission, Cassini was to fly a complex interplanetary cruise which began with the spacecraft heading sunward. Consequently, the Centaur's escape burn acted against the energy bestowed by the Earth's orbital motion around the Sun and when Cassini separated from the expired stage 43 minutes after launch, it headed inside the Earth's orbit. Ten minutes later, the spacecraft made contact with the Deep Space Network facility at Tidbinbilla, near Canberra in Australia, and reported that its systems were operating normally. ''I can't recall a launch as perfect as this one,'' said Chris Jones, the Cassini spacecraft development manager. The launch vehicle's performance was ''right on the money'', announced a delighted Spehalski. Indeed, the energy imparted was accurate to within 1 part in 5,000 and, at better than 0.004 degree, the deviation in the trajectory was ''insignificant''. The flight plan allowed for an early trajectory correction of up to 26 metres per second, but tracking indicated that a mere 1-metre-per-second adjustment would be required. Propellant saved by not making corrective manoeuvres would be put towards extending the spacecraft's Saturnian tour, so the mission was already ahead of nominal. Once safely on its way, Cassini transmitted the telemetry that it had recorded in its solid-state memory during the launch, so that the engineers could assess whether any of its systems had been damaged. There were no anomalies. ''The spacecraft is extremely clean,'' noted Ronald Draper, the deputy program manager, ''and mission operations are proceeding in an excellent manner''.

Over the next few days, Cassini turned to face its 4-metre-diameter dish antenna towards the Sun, so that it would act as a parasol to protect the rest of the structure from the increased insolation of the inner Solar System; it also released latches that secured instrument covers and other deployable devices. On 23 October, power was directed to the Huygens probe, which the Operations Center in Darmstadt declared healthy. Several days later, the Langmuir probe of the Radio and Plasma Wave Spectrometer was deployed to measure the electron density in the space in which the spacecraft was travelling, and the 10-metre antennas were deployed to monitor the electric and magnetic fields. It was not often that a deep space mission got off to such a flawless start. ''The spacecraft is operating beautifully,'' confirmed Draper on 29 October.

On 15 October 1997, the Cassini-Huygens spacecraft was successfully launched from the US Air Force's Launch Complex 40 by a Titan IV-B/Centaur.

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