The Huygens Descent Module consists of a Fore Dome, Experiment Platform, Top Platform and Aft Cone. The 2.7-metre-diameter conical Front Shield will protect it from the heat of the plasma generated during the deceleration phase of penetrating Titan's atmosphere. The Descent Module and its parachute systems are enclosed by the Back Cover. Huygens is attached to the side of the Cassini spacecraft by the ring of the Probe Support Equipment (PSE). Apart from its bi-annual functionality checks, the probe will remain dormant during the interplanetary cruise. As Titan looms, Cassini will adopt the proper orientation, charge the probe's batteries, perform a final check, load its 'coast timer' with the time at which it should activate the sequencer, and release it.
The Entry Subsystem works as the probe is released, and during the subsequent atmospheric entry. It consists of the Spin-Eject Device, the Front Shield and the
Back Cover. Activating the Spin-Eject Device severs the bolts attaching the probe to the PSE. As a trio of springs ease the probe away, a curved track and roller system will spin it up to 7 revolutions per minute in order to stabilise it during its several-week ballistic 'fall' to Titan. The spacecraft's attitude at the moment of release will ensure that the probe will contact the moon's atmosphere at the correct angle to penetrate safely. The Thermal Regulation Subsystem will utilise a variety of passive controls to protect the probe from the extremes of temperature to which it will be subjected on the protracted interplanetary cruise. As the probe will chill down upon being released by Cassini, it will be protected by a multiple-layer insulation blanket whose low emissivity will retard radiative cooling, and 1-watt radioisotope heater units strategically situated to ensure that its internal equipment does not freeze. The insulation blanket will be burned off early in the deceleration phase of entering Titan's atmosphere. Aerospatiale in France supplied the Front Shield, which uses Space Shuttle-style silica tiles. As the thermal stress on the Back Cover will be less intense, its shielding is a spray-on silica foam. Nevertheless, at just over 100 kilograms the thermal protection system contributes almost one-third of the probe's mass. The Inner Structure Subsystem comprises two aluminium-honeycombed platforms and an aluminium shell. It is connected to the Front Shield and Back
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