The Huygens Mission to Saturn's Moon, Titan

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features > > mission to Saturn > > Huygens

The Huygens Moon Lander

Launched on October 15, 1997 from the Kennedy Space Center in Florida, the Cassini-Huygens probe took a very long and indirect path to reach Saturn. This path was necessitated by the heavy weight of the probe - over six tons, including propellant. Lacking a strong enough booster, NASA devised a tricky flight path that utilized the gravitational forces of Venus, Jupiter, and the Earth to create a series of "slingshots" to generate the necessary velocity to reach Saturn. After a nearly seven-year journey covering 3.5 billion kilometers (2.2 billion miles), Cassini-Huygens arrived at Saturn on July 1, 2004.

The 320 kilograms (705 pounds) Huygens lander was built by the European Space Agency, and designed to enter and brake in Titan's atmosphere and parachute a fully instrumented robotic laboratory down to the surface. It was named after the Dutch 17th century astronomer Christiaan Huygens.

Huygens probe descent diagram, courtesy of NASA

After spring-powered ejection away from the Cassini orbiter on December 25, 2004, the probe accelerated under the force of Titan's gravity toward the moon for 22 days. As atmospheric friction built up, the probe decelerated to about Mach 1.5, whereupon the aft cover was pulled off by a 2.6 meter diameter pilot chute. An 8.3 meter diameter main parachute was then deployed to ensure a slow and stable descent. The main parachute slowed the probe and allowed the heat shield to fall away when it was released. To limit the duration of the descent to a maximum of 2.5 hours, the main parachute was then jettisoned and replaced by a smaller 3.0 m diameter drogue chute for the remainder of the descent.

The Huygens probe was designed to photograph and perform much of its scientific analysis during this 2.5 hour descent. The duration of the observations and studies was constrained by two factors: (1) battery life, and (2) the time window within which the Cassini orbiter would be within range to receive and retransmit Huygens' findings to Earth. (Cassini would not come back into radio range for another 32 days). In addition to cameras, key study instrumentation included:

Aerosol Particle Collector - to analyze the chemical makeup of the atmosphere
Descent Imager and Spectral Radiometer - to measure optical properties of the atmosphere
Doppler Wind Experiment - to study Titan's winds
Gas Chromatograph and Mass Spectrometer - another study of the atmosphere's composition
Huygens Atmospheric Structure Instrument - atmospheric density studies
Surface Science Package - to measure the physical properties of Titan ’s surface

On January 14, 2005, the Huygens probe successfully descended to the surface of Titan. During its 2.5 hour descent, and almost 1.5 hours on the surface, the probe transmitted the results of its experiments back to Earth via the Cassini orbital spacecraft. Amazing photographs and telemetry data will be analyzed for years to come.

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