Titan Saturn System Mission (TSSM) was a joint

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...

–

ESA , owners = , headquarters = Paris, Île-de-France, France , coordinates = , spaceport = Guiana Space Centre , seal = File:ESA emblem seal.png , seal_size = 130px , image = Views in the Main Control Room (1205 ...

proposal for an

exploration of Saturn The exploration of Saturn has been solely performed by crewless probes. Three missions were flybys, which formed an extended foundation of knowledge about the system. The ''Cassini–Huygens'' spacecraft, launched in 1997, was in orbit from 2004 ...

and its moons Titan and

Enceladus Enceladus is the sixth-largest moon of Saturn (19th largest in the Solar System). It is about in diameter, about a tenth of that of Saturn's largest moon, Titan. Enceladus is mostly covered by fresh, clean ice, making it one of the most refle ...

, where many complex phenomena were revealed by '' Cassini''. TSSM was proposed to launch in 2020, get

gravity assist In orbital mechanics and aerospace engineering, a gravitational slingshot, gravity assist maneuver, or swing-by is the use of the relative movement (e.g. orbit around the Sun) and gravity of a planet or other astronomical object to alter the p ...

s from Earth and Venus, and arrive at the Saturn system in 2029. The 4-year prime mission would include a two-year Saturn tour, a 2-month Titan aero-sampling phase, and a 20-month Titan orbit phase. In 2009, a mission to Jupiter and its moons was given priority over ''Titan Saturn System Mission'', although TSSM will continued to be assessed for possible development and launch.

Origin and status

The Titan Saturn System Mission (TSSM) was officially created in January 2009 by the merging of the ESA's Titan and Enceladus Mission (TandEM) with NASA's Titan Explorer (2007) study, although plans to combine both concepts date at least back to early 2008. TSSM was competing against the

Europa Jupiter System Mission Europa may refer to: Places * Europe * Europa (Roman province), a province within the Diocese of Thrace * Europa (Seville Metro), Seville, Spain; a station on the Seville Metro * Europa City, Paris, France; a planned development * Europa Clif ...

(EJSM) proposal for funding, and in February 2009 it was announced that NASA/ESA had given EJSM priority ahead of TSSM. TSSM continued to be studied for a later launch date, near the 2020s. Detailed assessment reports of the mission elements as well as a specific concept for a lake-landing module for Titan's lakes called

Titan Mare Explorer Titan Mare Explorer (TiME) is a proposed design for a lander for Saturn's moon Titan. TiME is a relatively low-cost, outer-planet mission designed to measure the organic constituents on Titan and would have performed the first nautical exploratio ...

(TiME) with the potential of becoming a part of the TSSM have been proposed in February and October 2009, respectively. In 2014 it was thought the TSSM might have been revived for a launch on the SLS super-heavy-lift rocket.

Mission overview

The TSSM mission consists of an

orbiter A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, pl ...

and two Titan exploration probes: a

hot air balloon A hot air balloon is a lighter-than-air aircraft consisting of a bag, called an envelope, which contains heated air. Suspended beneath is a gondola or wicker basket (in some long-distance or high-altitude balloons, a capsule), which carries p ...

("Montgolfier" type) that will float in Titan's clouds, and a lander that will splash down on one of its

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Eart ...

seas. Both probes’ data are to be relayed to a Titan orbiter. They will be equipped to study Titan's features with instruments for imaging,

radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...

profiling, and surface as well as atmospheric sampling, much more complete than done by the

Cassini–Huygens ''Cassini–Huygens'' ( ), commonly called ''Cassini'', was a space research, space-research mission by NASA, the European Space Agency (ESA), and the Italian Space Agency (ASI) to send a space probe to study the planet Saturn and its system, i ...

mission. The spacecraft will use several

flybys of other planets to enable it to reach Saturn. The baseline design envisaged a September 2020 launch, followed by four gravity assists (

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

–

Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never fa ...

–Earth–Earth), and arrival at Saturn 9 years later in October 2029. This is one of several available Earth-to-Saturn transfer options from the year 2018 through 2022. Current NASA plans do not give the TSSM a priority, however, and it is unlikely any of the proposed launch dates can be met. Upon Saturn arrival, in October 2029, the orbiter's chemical propulsion system would place the flight system into orbit around Saturn, followed by a two-year Saturn Tour Phase, characterized by the deployment of the ''in situ'' elements, and including a minimum of seven close Enceladus flybys and 16 Titan flybys. During this period, repeated satellite

s and manoeuvres will reduce the energy needed to insert into Titan's orbit. As the craft completes its flyby by Enceladus, the orbiter will analyze the unusual

cryovolcanic A cryovolcano (sometimes informally called an ice volcano) is a type of volcano that erupts volatiles such as water, ammonia or methane into an extremely cold environment that is at or below their freezing point. The process of formation is known ...

plumes at the moon's south pole. The montgolfière, a hot air balloon, would be released on approach to the first Titan flyby for ballistic entry into Titan's atmosphere for its six Earth months’ mission from April 2030 to October 2030. Based on Cassini–Huygens discoveries, the montgolfière should be able to circumnavigate Titan at least once during its nominal lifetime at its deployment

latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pol ...

of about 20°N, 10 kilometers above Titan's surface.

Lake lander

Numerous proposals have been brought forward with respect to the lake-lander concept. One of the most detailed plans so far is the so-called

(TiME), which had originally been proposed as a separate scout mission, but might eventually be postponed and included in the TSSM. If approved, TiME would be released by the orbiter on its second Titan flyby. Due to Titan's haze layer and its distance to the Sun, the lander cannot be powered by solar panels and it would rely on the new Advanced Stirling Radioisotope Generator (ASRG), which is a prototype meant to provide availability of long-lived power supplies for landed networks and other planetary missions. The lander will target

Ligeia Mare Ligeia Mare is a lake in the north polar region of Titan, the planet Saturn's largest moon. It is the second largest body of liquid on the surface of Titan, after Kraken Mare. Larger than Lake Superior on Earth, it is mostly composed of liquid ...

, a northern polar sea of

liquid hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and Hydrophobe, hydrophobic, and their odors are usuall ...

s at about 79°N. The probe will descend by parachute, like the

Huygens probe ''Huygens'' ( ) was an atmospheric entry robotic space probe that landed successfully on Saturn's moon Titan in 2005. Built and operated by the European Space Agency (ESA), launched by NASA, it was part of the ''Cassini–Huygens'' mission and ...

of 2005. During the 6 hours of descent it will analyze the atmosphere and then splashdown on the liquid surface. The plutonium-powered craft's principal function is to sample and analyze organics on the surface for a period of about 3 to 6 months; this would be the first floating exploration of an extraterrestrial sea.

Science goals and objectives

The major goals of the TSSM mission can be summarized under four categories: *Explore Titan as a system *Study Titan's organic inventory and astrobiological potential *Constrain Titan's origin and evolution models *Recover information on Enceladus and Saturn's

magnetosphere In astronomy and planetary science, a magnetosphere is a region of space surrounding an astronomical object in which charged particles are affected by that object's magnetic field. It is created by a celestial body with an active interior dynam ...

At Titan, the science goals would be to provide information on such aspects as the composition of the surface and the geographic distribution of the various organic constituents; on the

cycle and the methane reservoirs; on the ages of the surface features, and in particular on whether

cryovolcanism A cryovolcano (sometimes informally called an ice volcano) is a type of volcano that erupts volatiles such as water, ammonia or methane into an extremely cold environment that is at or below their freezing point. The process of formation is know ...

and

tectonism Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building, the growth and behavior of the strong, old cores of continents ...

are actively ongoing or are relics of a more active past; on the presence or absence of

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...

, of a

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...

and of a sub-surface ocean; on the chemistry that drives complex ion formation in the upper atmosphere; and on a large altitude range in the atmosphere, from 400–900 km, which remains poorly explored after Cassini. In addition, much remains to be understood about seasonal changes of the atmosphere at all levels, and the long-term escape of constituents to space.

TiME Time is the continued sequence of existence and events that occurs in an apparently irreversible succession from the past, through the present, into the future. It is a component quantity of various measurements used to sequence events, to ...

lander would

splashdown Splashdown is the method of landing a spacecraft by parachute in a body of water. It was used by crewed American space capsules prior to the Space Shuttle program, by SpaceX Dragon and Dragon 2 capsules and by NASA's Orion Multipurpose Crew ...

, a

sea on Titan's northern hemisphere. It is believed that Titan's methane cycle is analogous to Earth's

hydrologic cycle The water cycle, also known as the hydrologic cycle or the hydrological cycle, is a biogeochemical cycle that describes the continuous movement of water on, above and below the surface of the Earth. The mass of water on Earth remains fairly const ...

, with meteorological working fluid existing in liquid and gas phase. TiME would directly discern the methane cycle of Titan and help understand its similarities and differences to the hydrologic cycle on Earth. However, questions about the sources of re-supply of methane to the atmosphere remain to be answered. This world is built by organic activities which still operate and Cassini–Huygens findings suggest a world with a balance of geologic and atmospheric processes that is the solar system's best analogue to

. Moreover, an interior ocean discovered by Cassini, deep underneath Titan's dense atmosphere and surface is thought to be largely composed of liquid water. TSSM would be the first mission in the 50 years of space exploration where an extensive and interdisciplinary in situ survey of active organic chemistry and climate on the land, on the sea, and in the air of another world will take place.

References

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