2.2 Billion Miles and Counting: Riding High with Cassini-Huygens

Working with three major project contractors on Cassini-Huygens, software coded with DDC-I tools is successfully orbiting Saturn

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Burning the twilight Cape Canaveral sky, a Titan IV-B/Centaur launch vehicle lifted the Cassini-Huygens spacecraft toward the stars on October 15, 1997, covering the first miles of a 2.2-billion-mile-long “slingshot” ride through the solar system toward Saturn. Too large a mass to shoot straight at the ringed planet, four separate gravity-assisted “turns” hurled the spacecraft along its interplanetary trajectory, passing Venus (twice), the Earth and Jupiter before approaching Saturn in mid-2004.

Cassini-Huygens is the most complex interplanetary spacecraft ever built; it represents the best technical efforts of the United States and 17 European nations involved in the mission. Onboard the dual-mission craft, consisting of the JPL-built Cassini orbiter and an ESA-built Huygens probe destined for the surface of Saturn’s largest moon Titan, is embedded systems software coded by American and European engineers using DDC-I software developments tools.

Space missions define the outer performance envelope of well-used industry terms like “mission-critical,” and Cassini’s systems have performed flawlessly since lift-off. Cassini and the Galileo spacecraft were used in concert to study Jupiter between October 2000 and March 2001, taking advantage of their dual vantage points to observe the shape of the magnetosphere and the effects of solar wind. On July 1, 2004, the main engine fired and Cassini-Huygens was captured by Saturn. Angling through a gap between Saturn’s F and G rings, the craft made its closest arc around the planet to begin the first planned orbit of a four-year primary mission.

Bolted to Cassini in “sleep mode” – and awakened once every six months for a three-hour instrument and engineering checkup — the Huygens probe was released before reaching Titan’s atmosphere, on December 24, 2004. Umbilical cut, Huygens spun gently away from Cassini on a ballistic trajectory toward Titan. Two days later, Cassini adjusted course to miss Titan and setup optimal signal reception for telemetry streaming back during the probe’s descent.

The Cassini-Huygens mission will answer fundamental questions about the evolution of planets through extensive study of Saturn, its rings, magnetosphere, Titan and other icy moons. The Saturn system represents a laboratory – the equivalent of a miniature solar system — where scientists can seek answers to fundamental questions about the physics, chemistry and evolution of planets and the conditions that give rise to life. Saturn may contain much of the primordial cloud’s gases not trapped by the Sun. The largest moon Titan is thought to harbor organic compounds important in the chain of chemistry that led to life on Earth. Too cold to support life now, it is a “frozen vault” that may show what the early Earth was like.

On January 14, 2005, Huygens entered Titan’s atmosphere at 13,500 miles per hour. Designed to withstand the extreme cold of space (about -330F) and the intense heat of atmospheric entry (over 2,700F), the probe used atmospheric drag to reduce speed until a series of parachutes began deploying at 870 miles per hour. During the descent, instruments sampled the physical properties at different levels in the atmopshere and captured the first images of the moon’s surface.

An exotic world with geophysical processes similar to Earth operating under alien conditions, many of Earth’s familiar forms occur on Titan, but the chemistry involved is quite different. Instead of liquid water, Titan has liquid methane. Rather than silicate rocks or dirt, Titan has hydrocarbon particles settling out of the atmosphere. On Titan volcanoes spew ice. Huygens touched down in liquid methane mud – and quickly took more samples. Thirty minutes later, Cassini’s antenna would be out of range.

Cassini’s planned tour of the Saturn system includes 52 close encounters with seven of Saturn’s 31 known moons. Gravity-assist flybys of Titan, as close as 590 miles, will permit high-resolution radar mapping of Titan’s surface to produce vivid topographic maps, as well as providing “slingshot” propulsion. Each orbital path is a mission: the imaging of Titan, fly-bys of selected icy moons, occultations in Saturn’s rings and crossings of the ring plane. Fly-bys will be made of other major moons and Saturn’s polar regions and equatorial zone. The prime mission officially concludes on June 30, 2008, four years after Saturn arrival and 33 days after the final Titan flyby on May 28 aims Cassini for a follow-on Titan flyby one month later, ready to proceed with additional missions if resources allow. A few remarkable scientific discoveries and several billion miles from now, DDC-I will still be flying high among the rings of Saturn.