Titan

What made the Huygens landing interesting, besides being the first landing on an outer solar system body, is the parachute system chosen for landing. Huygens was to gather data of Titan's atmosphere, this meant that the requirements on the parachute system were not just a safe landing, it had to fly slowly through the atmosphere. This lead to an Entry Descent and Landing phase that lasted for about 2.5 hours.

Entry, Descent and Landing

Entry occurred at 11:13 CET at an altitude of 1270 km above the atmosphere of Titan. The frontal heat shield slowed the capsule to 400 m/s, where the pilot chute was activated. This parachute removed the back thermal protection system allowing for the deployment of the 8.3 m main parachute. Forty-two seconds after the pilot chute actuated, the frontal thermal protection system was released. This allowed the instruments to be exposed to the atmosphere. This occurs at about 160 km altitude. At about 125 km the main parachute was cut away, and a smaller drogue parachute was deployed. This increased the velocity of the vehicle from about 40 m/s to 100 m/s just before drogue parachute deployment. This was done as Huygens did not have sufficient battery power for the slow descent. The fear was that if the main parachute were not cut away, there would not be enough power for surface measurements. However, as the atmosphere of Titan is about 1.25 the earth atmosphere, and the mass of the capsule was only 318 kg, it still landed with about 5 m/s. Huygens did not have a dedicated landing system but was designed to land on many types of surfaces, including liquid and solid surfaces. 

In order to study Titan more intensively, a new mission is proposed. This mission, called Dragonfly is a rotorcraft that will study multiple locations on Titan. The mission is planned to launch in 2027 and land on Titan in 2036. The rotorcraft will descent through the Titan atmosphere using a 3.75m diameter aeroshell to protect the rotorcraft from the heat and re-entry loads. The thermal protection system is similar to the one used on the perseverance rover and is made out of PICA.

Two parachutes are then used to make sure Dragonfly has a soft landing. First, at 134km above the surface, at Mach 1.5 a 4.5m diameter Disk-Gap Band (DGB) supersonic parachute is deployed. Because of the atmosphere, the drogue parachute phase lasts up to 80min. At 4km the drogue parachute pulls out a 13.4m DGB which is used for approximately 20min until at 1.2km the lander is released. After which the rotorcraft descends on its own for the remainder until touchdown [2].