The design of the Titan Orbiter would be Cassini-like, although somewhat scaled down in capability. All instruments would be body fixed (no articulated instrument platform); however the telecommunication antenna would be articulated to allow decoupling of communications from observations. It would have a payload capability of 70-80 kg (goal 100 kg). It could deliver as much as 400 kg of in situ elements into Titan atmosphere.
The Titan Orbiter (TO) would perform Saturn system science observations once in orbit around Saturn and later be placed in orbit around Titan with the instruments located on the nadir pointed face. The trajectory around Saturn would likely be designed to include Enceladus flybys. Propulsion options being investigated include chemical and inner solar system solar electric propulsion. Orbiter electrical power would be provided by Multi-Mission Radioisotope Thermoelectric Generators (MMRTG's).
The in situ elements to be studied include a hot air balloon (Montgolfiere) and descent probes/landers. The Montgolfiere appears to be the most appropriate type of balloon for Titan, as its thick and cold atmosphere is the most favourable of all Solar System planetary atmospheres for balloon flight. Initial concepts of a Titan Montgolfiere studied by CNES look very promising. The combined heat source for the local gas of the atmosphere and also the electrical source for the Montgolfiere would be an MMRTG which would be provided by NASA (to be confirmed).
The Montgolfiere would be released from an entry aeroshell after traverse through the atmosphere (much like Huygens parachute was deployed); it would then inflate during descent and reach full inflation above 10 km. Following inflation, the Montgolfiere would float around Titan's globe carried by the winds. At mid-latitudes, it would circle the globe in about 6 months. The Montgolfiere would be designed for a lifetime of at least one year (two circumnavigations of Titan's globe) but could live much longer. The altitude of the Montgolfiere would be autonomously adjusted/controlled by using a vent valve in the top of the balloon and on-board software fed by attitude and altitude sensors. Payload options to be studied for the Montgolfiere range in mass from 10 to 30 kg.
Descent probes/landers would provide in situ atmospheric and surface measurements in locations not deemed safe or optimal for the Montgolfiere, especially at high latitudes. The TandEM proposal has put forward mini-probes concepts derived from Huygens design and also inspired by Beagle-2 miniaturisation technology. Heritage from ExoMars will also be available, especially for the surface phase.
Science objectives to be addressed by the probes require that they be designed for a lifetime on the surface of at least two Titan days/Titan orbital periods around Saturn, i.e. 32 Earth days. A combination of primary batteries (for the high-power descent and initial surface phase) and secondary battery/low-power radioisotope-based thermoelectric generators will be studied. Payload options to be studied for the probes range in mass from 5 to 15 kg.