. Distance from Sun: 1,427,000,000 km (9.54 AU)
. Periapsis                        1,186,680 km
. Apoapsis                         1,257,060 km
. Semimajor axis                   1,221,870 km
. Eccentricity                           0.0288
. Orbital inclination     0.34854° (to Saturn's equator)
. Orbital period (Titanic day) 15.95 Earth days
. Rotation Period                  Synchronous 
. Mean radius                          2,576 km
. Mass                       1/45 that of Earth
. Average density                   1.881 times
. liquid water Surface temp      94 K (–180 °C)
. Atmospheric pressure at surface (~1.5 times Earth's)
. Atmospheric composition: Nitrogen (N2) 94.2%, methane (CH4) 5.6%, argon (Ar) 34 ppm, ethane, Hydrogen (H2) 0.1%. 
.Surface gravity             1.352 m/s2 (0.14g)


The mission architecture had included two Venus flybys, that obligate protection against high solar heat. So, the spacecraft was designed to tolerate, not only the cold temperature of Titan, but also very not of Venus. To make a perfect protection, although the probe was partially protected by shadow of the high–gain antenna (HGA), we had included a multilayer insulation that burned off during the atmospheric entry.
For thermal control, the probe used multiple layers of insulation and about 35 W of radioisotope heater units. Prior the separation, all power to the probe was provided by the Cassini orbiter. However, the probe’s thermal subsystem (THSS) maintained all experiments and subsystem units within their allowed temperature ranges during all mission phases. In space, the THSS partially insulated the Probe from the Orbiter, ensuring only small variations in its internal temperatures, despite the incident solar flux varying from 3800 W/m2 (near Venus) to 17 W/m2 (approaching Titan after 22 days of the coast phase following orbiter separation).

• MLI covering all external surfaces, except for the small “thermal window” of the Front Shield,
• 35 radioisotope heater units (RHUs) continuously providing about 1 W each even when the probe is dormant, and
• A white–painted 0.17 m2 thin aluminum sheet on the front shield’s forward face acting as a controlled heat leak (about 8 W during cruise) to reduce the sensitivity of thermal performances to MLI efficiency.
. The installation of the MLI layer is shown below. It was burned and torn away during entry in Titan atmosphere, leaving temperature control to the AQ60 high–temperature tiles on the front shield’s front face, and to Prosial on the front shield’s aft surface and on the back cover. .During the descent phase, thermal control was provided by foam insulation and gas–tight seals, preventing convection cooling by Titan’s cold atmosphere (70K at 45 km altitude) and therefore thermally decoupling the instruments from the cold aluminum shells.
. Thermal Protection System The 79 kg, 2.7 m diameter, 60◦ half–angle coni–spherical front shield was designed to decelerate the probe in Titan’s upper atmosphere from about 6 km/s at entry to a velocity equivalent to Mach 1.5 by 160 km altitude. Tiles of AQ60 ablative material, a felt of silica fibers reinforced by phenolic resin, provided protection against the entry’s 1 MW/m2 thermal flux. These AQ60 tiles were attached with CAF/730 adhesive to the honeycomb shell forming the front shield supporting structure. Prosial, a suspension of hollow silica spheres in silicon elastomer, was sprayed directly onto the aluminium structure of the front shield rear surfaces. Thermal fluxes at the front surface exceeded those at the rear by a factor of ten. After entry, the front shield was jettisoned.
. The back cover protected the descent module during entry, ensured depressurisation during launch, and carried multilayer insulation (MLI) for the cruise and coast phases. Since it did not have to meet stringent aero-thermodynamic requirements, it was constructed of a stiffened aluminum shell of minimal mass (11.4 kg) protected by Prosial (5 kg). The back cover included an access door for late access during integration and for forced–air ground cooling of the probe, a break–out patch through which the first drogue parachute was fired, and a labyrinth sealing joint with the front shield, providing a non-structural thermal and particulate barrier.
Attention was drawn to the exploration of liquid environments on Titan after the discovery of seas in the North Polar Region by Cassini’s radar instrument in 2006 (the northern region was then in winter darkness) and the later mapping of these seas.

Beginning on November 30, 2016, the Cassini spacecraft will repeatedly climb high above Saturn's north Pole, then plunge to a point just outside the narrow F ring, completing about 20 such orbits. 
The Grand Finale will beginning in April 22, 2017, where Cassini will leap over the rings to start its final series of daring dives between the planet and the inner edge of the rings. (see below picture) Each of these orbits take six days to complete. When done, the spacecraft will plunge into the upper atmosphere of the planet and it will burn up like a meteor, ending the epic mission to the Saturn system. 

NASA's Cassini spacecraft will make 22 orbits of Saturn during its Grand Finale, exploring a totally new region between the planet and its rings. Image credit: NASA/JPL-Caltech
The next and finale mission will come when Cassini plunges past Saturn during the Grand Finale. In that time, it will collect some information, as detailed maps of Saturn’s gravity and magnetic fields, which can reveal how the inside's planet is arranged and, possibly, solving the mystery of just how fast the interior is rotating. And, without limit of knowledge, its cameras will take amazing, ultra-close images of Saturn’s rings and clouds.
No other mission has ever explored this unique region so close to the planet. What we learn from these activities will help to improve our understanding of how giant planets – and families of planets everywhere – form and evolve. And at the end of its final orbit, as it falls into Saturn’s atmosphere, Cassini completes its 20-year mission by ensuring the biologically interesting worlds Enceladus and Titan could never be contaminated by hardy microbes that might have stowed away and survived the journey intact. It’s inspiring, adventurous and romantic – a fitting end to this thrilling story of discovery.
Why End the Mission?  By 2017, Cassini will have spent 13 years in orbit around Saturn, following seven years of “cruise” on its way outward from Earth. The spacecraft is beginning to run low on rocket fuel. If left unchecked, this situation would eventually prevent mission operators from controlling the course of the spacecraft. 
Two moons of Saturn, Enceladus and Titan, have captured news headlines over the past decade as Cassini data revealed the moons’ potential to contain habitable – or at least "pre-biotic” – environments.
In order to avoid the unlikely possibility of Cassini someday colliding with one of these moons and contaminating them with any hardy Earth microbes that might have survived on the spacecraft, NASA has chosen to safely dispose of the spacecraft in the atmosphere of Saturn.
* This text is a short resume of the Original one. See Full Text and more by clicking below


When the Cassini–Huygens spacecraft was launched, the probe was mated onto the side of the orbiter. With this conception, the orbiter provided electrical power, command, and data through an umbilical connection to the probe. In its seven–year journey to Saturn, Huygens was subjected to 16 in–flight checkouts to monitor the health of its subsystems and scientific instruments.
The first link test make by the European Space Agency (ESA) was in 2000 who they discover a flaw in the design of the Huygens telemetry receiver on-board the orbiter Cassini. This flaw would have resulted in the loss of the probe’s scientific data during the mission at Titan.


Huygens's Probe beginning its descent through Titan's hazy cloud layers from an altitude of about 1,270 km. First, it had to decelerate from 18,000 to 1,400 km per hour with the following sequence of parachutes, which slowed it down to less than 300 km per hour. At an altitude of about 160 km, every thing were exposed to its atmosphere. When the Probe reached about 120 km, it replaced the main parachute by a smaller one to complete the 2.25 hour descent. 
At an altitude of 700 meters above the surface, the descent lamp was activated. This lamp was not to illuminate the landing site because the light levels on the surface of Titan are roughly 1,000 times less than sunlight and 1,000 times stronger than a full moon. Its purpose is to provide a monochromatic light source, which enable scientists to accurately determine the reflectivity of the surface. 
All in all, the surface mission lasted 1 hour and 10 minutes - considerably longer than had been anticipated, and no damage was done to the Huygens's Probe.
The first link test make by the European Space Agency (ESA) was in 2000 who they discover a flaw in the design of the Huygens telemetry receiver on-board the orbiter Cassini. This flaw would have resulted in the loss of the probe’s scientific data during the mission at Titan.
Because an inappropriate parameters encoded into the Probe Support Avionics (PSA) firmware, the Cassini receiver could not accommodate a large Doppler shift in the signal received from Huygens. (see top-right section for detail) After redesigned the mission's architecture, ESA decided to decrease the Doppler shift by increasing Cassini’s altitude to 60,000 km at closest approach, rather than 1,200 km. That resulted to replacing the first two planned orbits by three shorter ones. The Huygens mission was then executed in the third orbit, rather than the first.
The new trajectory allowed early observations of Titan’s upper atmosphere in order to validate the atmospheric engineering model well before the probe release. Better improvements in the structure and composition of the upper atmosphere, had proved that the argon concentration and the methane was not in sufficient quantity to affect the entry.


The probe Huygens was designed as a Descent Module placed in a shell of a 2.75 m diameter heat shield, with a back cover. This cover is to protect him from the radiative and convective heat fluxes generated during the entry into Titan’s methane–rich and nitrogen atmosphere.

The Huygens probe nestled in its descent module. Image Credit and Copyright: European Space Agency

The European Space Agency's Huygens Probe was a unique, advanced spacecraft and a crucial part of the overall Cassini mission to explore Saturn. The probe was about 9 feet wide (2.7 meters) and weighed roughly 700 pounds (318 kilograms). It was built like a shellfish: a hard shell protected its delicate interior from high temperatures during the a two hour and 27 minute descent through the atmosphere of Saturn's giant moon Titan.

The Descent Module have an aluminum inner shell containing the scientific instruments and servicing subsystems. These instruments and all the electronic equipment are distributed on two platforms: the main platform support most of the instruments, and the top platform, support the container for both the main and the stabilizer chutes, the probe radio transmission antennae, and the mortar that deploy the pilot chute and then remove the back cover.
The inner structure is coated with thick foam blankets to minimize convective cooling during the descent. The fore dome of the descent module include a set of 36 spin vanes that use the aerodynamic interaction with the gas flow to force the probe to spin. The descent module was gas–tight, except for a single 6 cm2 hole to equalize pressure during launch and descent to Titan’s surface.
Beside the Descent Module,the probe include a Heat Shield that acte as a brake and thermal protection, and the Entry Assembly Module, who carrie the equipment to control Huygens after separation from Cassini.
In January 14, 2005, the Huygens Probe land on Titan. After the release from the Orbiter, the Probe Support Equipment (PSE) remain attached to him. This Support contain the electronics necessary to track the probe, recover the data gathered during its descent and process and deliver the data to the Orbiter. When complete, the data is transmit to Earth.
The Huygens probe payload have six scientific instruments, each designed to perform different function as the probe descended through Titan's murky atmosphere.

Scientific instruments in the Huygens Probe. The distributed battery system is shown in the bottom side. (Courtesy of ESA)

Huygens Probe Scientific's Instruments

. Descent imager and spectral radiometer made a range of imaging and spectral observations using several sensors and fields of view. By measuring the upward and downward flow of radiation, the radiation balance (or imbalance) of the thick Titan atmosphere was measured.
..Solar sensors measured the light intensity around the Sun due to scattering by aerosols in the atmosphere. This permitted the calculation of the size and number density of the suspended particles. One visible and one infrared image observed the surface during the latter stages of the descent and, as the probe slowly rotated, built up a mosaic of pictures around the landing site. There was also a side-view visible image that obtained a horizontal view of the horizon and the underside of the cloud deck.
..For spectral measurements of the surface, a lamp switched on shortly before landing that augmented the weak sunlight.
.Huygens atmospheric structure instrument, by a suite of sensors, measured the physical and electrical properties of Titan's atmosphere. ..Accelerometers measured forces in all three axes as the probe descended through the atmosphere. Since the aerodynamic properties of the probe were already known, it was possible to determine the density of Titan's atmosphere and detect wind gusts. Had the probe landed on a liquid surface, this instrument would have been able to measure the probe motion due to waves. ..Temperature and pressure sensors also measured the thermal properties of the atmosphere.
.. The Permittivity and Electromagnetic Wave Analyzer component measured the electron and ion (positively charged particle) conductivities of the atmosphere and searched for electromagnetic wave activity. On the surface of Titan, the conductivity and permittivity (i.e., the ratio of electric flux density produced to the strength of the electric field producing the flux) of the surface material was measured.
. Gas chromatograph and mass spectrometer (GCMS) was a versatile gas chemical analyzer that identified and measured chemicals in Titan's atmosphere. It was equipped with samplers that were filled at high altitude for analysis.
..The mass spectrometer built a model of the molecular masses of each gas, and a more powerful separation of molecular and isotopic species was accomplished by the gas chromatograph. During descent, the GCMS analyzed pyrolysis products (samples altered by heating) passed to it from the Aerosol Collector Pyrolyser. Finally, the GCMS measured the composition of Titan's surface in the event of a safe landing. This investigation was made possible by heating the GCMS instrument just prior to impact in order to vaporize the surface material upon contact.
.Aerosol collector pyrolyzer drew in aerosol particles from the atmosphere through filters, then heated the trapped samples in ovens (the process of pyrolysis) to vaporize volatiles and decompose the complex organic materials. The products were then flushed along a pipe to the GCMS instrument for analysis. Two filters were provided to collect samples at different altitudes.
.Surface science package contained a number of sensors designed to determine the physical properties of Titan's surface at the point of impact. These sensors also determined whether the surface was solid or liquid. An acoustic sounder, activated during the last 100 meters (328 feet) of the descent, continuously determined the distance to the surface, measuring the rate of descent and the surface roughness (e.g., due to waves). During descent, measurements of the speed of sound provided information on atmospheric composition and temperature, and an accelerometer accurately recorded the deceleration profile at impact, providing information on the hardness and structure of the surface. A tilt sensor measured any pendulum motion during the descent and indicated the probe attitude after landing
.Doppler wind experiment measure the wind speed during descent through Titan's atmosphere by observing changes in the carrier frequency of the probe due to the Doppler effect. This measurement could not be done from space because of a configuration problem with one of Cassini's receivers. However, scientists were able to measure the speed of these winds using a global network of radio telescopes. 


Huygens separated from the Cassini spacecraft on December 25, 2004, using the spring– loaded separation mechanism, called the spin eject device. This device provided a nominal relative separation velocity of 33 cm/s and a nominal spin of 7.5 rpm to provide inertial stability during the ballistic trajectory and atmospheric entry. Following release, the probe had no maneuvering capability and functioned autonomously. After 20 days, Huygens arrived at the 1,270-km interface altitude on the predicted trajectory, triggering the sequence to turn on the batteries, the onboard computers, and the sensors and instruments according to the preprogrammed sequence.
The probe was not guaranteed to survive its impact on what was unknown terrain, but included instruments for characterizing any liquid medium in which it landed. Because of large uncertainties in the lateral distances the probe would cover during its descent under parachute, the coordinates of the predicted landing site were uncertain by several hundred kilometers.
Three parachutes controlled the descent of the probe through Titan’s atmosphere, requiring knowledge of the aerodynamic conditions for deployment. The probe on-board computers processed the measurements from the accelerometers monitoring the probe’s deceleration, autonomously determining the correct instant for parachute deployment.

The probe descended for 2 h 27 min 50 s, within the predicted duration of 2 h 15 min ±15 min. Initially, the probe followed the nominal chronological sequence, with instrument operations defined by commands in the on-board mission time-line. Later, the on-board computers filtered measurements from two radar altimeters, providing redundancy to exclude erratic measurements at high altitude and provide reliable measured altitude information to the payload instruments. This allowed for optimization of the measurements during the last part of the descent.
During entry, telemetry could not be transmitted by the probe until its back cover was removed. Ultimately, the probe landed safely with a vertical speed of about 5 m/s and continued thereafter to transmit data for at least another 3 h 14 min, as determined by monitoring the probe’s 2.040 GHz carrier signal by the Earth–based radio telescopes. It is thought that the probe continued to function until the batteries were exhausted.
The landing site was found to have a sponge–like consistency, and data from the Huygens probe indicated that the surface of Titan likely has some liquid methane and heavier hydrocarbons (tholins) in the form of aerosols and/or rain, providing clearly seen river channels. The probe lasted several hours beyond its 2–hour post-landing mission design.
After The GRAND FINALE, the Next Titan's Mission will may be in 2038 with a Cryogenic Submarine in the Kraken Mare, methane-ethane Lakes discover by Cassini-Huygens Spacecraft  

Credit: Phase I Titan Submarine, July 2015, NASA
Titan is the largest moon of Saturn and the only natural satellite known to have a dense atmosphere.  And, since Cassini discovery, it was established that is the only object, other than Earth, with clear evidence of stable bodies of surface liquid.
The atmosphere is largely nitrogen with clouds of methane and ethane. The climate—including wind and rain—creates surface features similar to those of Earth, such as dunes, rivers, lakes, seas and deltas, and is dominated by seasonal weather patterns as on Earth.
The submarine design faced many challenges. Pressures in depth sea-lakes in a liquid ethane is about 60 percent the density of water on Earth. Also, the smaller world of Titan give ~20% Earth’s gravity, which  meant that even at the maximum design depth of 1,000 m (3,281 ft) for the Cryogenic Sub provide a pressure of 1/10th  (10%) of that a terrestrial sub would encounter. That mean, the titan's sub would need to endure only ~10 bar of pressure at maximum depth, not as the 100 bar (10 MPa) pressure in Earth’s oceans.
For NASA, important things about Submarine Design Approach must be driven by science. That is, the Traceability to Decadal Survey, the Astrobiology side about Evolution of hydrocarbons in universe, the Geology, who study atmosphere/sea exchange, surface, shore, waves and heat transfer.
To conceive the Submarine, it is necessary to have a High Level System for Operation in cryogenic sea (93K). Also, the Sub need to be Autonomous, with a Max Speed of 1 m/s and a Range of about 3000 km / 1 year. And, because the distance, a reliable DTE communication system.

Credit. Titan Submarine: Exploring the Depths of Kraken Mare / 26th Space Cryogenic Workshop June 25, 2015
Because the Submarine will be Submerged during 8 hours, the Surface Communications duration will be 16 hours. The possible depth in the sea must be up to 1 km, where the Pressurize sub reach ~150psi and 5-g axial loads, 2-g for lateral loads.
Many options exist to exploring the world of Titan. NASA focus on submarine because it provides more efficient, in-situ science system and, that is, give a very long range and maneuverability.
Briefly, Titan Submarine will be cylinder shapes with a pound of 1200 kg 6m long x 1.1m wide x 2m high, as: 



Cassini-Huygens is one of the most ambitious missions ever launched into space. Loaded with an array of powerful instruments and cameras, the spacecraft is capable of taking accurate measurements and detailed images in a variety of atmospheric conditions and light spectra.
The mission of Cassini’s Orbiter consisted of delivering the ESA Huygens probe to Titan, and remaining in orbit around Saturn for detailed geophysical studies of the planet, its rings, and satellites, particularly Titan. 

With its 5150 km diameter, Titan is the 2nd-largest planetary satellite in theMilky Way after Ganymede, at 5276 km.


An orbit is an elliptical path around a celestial body (like Earth around the Sun). The point on an orbit which is closest to the orbited body is called the periapsis and the furthest point is the apoapsis
. The orbital eccentricity of an astronomical object (Titan) is a parameter that determines the amount by which its orbit around another body (Saturn) deviates from a perfect circle. A value of 0 is a circular orbit, values between 0 and 1 form an elliptical orbit, 1 is a parabolic escape orbit, and greater than 1 is a hyperbola
The orbital period is the time taken by a object (Titan) to make one complete orbit around another object (Saturn).  Can be applied in astronomy to mostly either planets or asteroids orbiting the Sun, moons orbiting planets, exoplanets orbiting other stars, or binary stars
. AAstronomical Unit (AU) is the average distance between Earth and the Sun, which is about 93 million miles or 150 million kilometers. Astronomical units are usually used to measure distances within our Solar System
The methane gas, at room temperature and standard pressure, is a colorless and odorless. Methane has a boiling point of −161 °C (−257.8 °F) at a pressure of one atmosphere and it is flammable over a range of concentrations (5.4–17%) in air at standard pressure. Generally, its melting point is −182.5 °C (−296.4 °F; 90.7 K) and its boiling point −161.49 °C (−258.68 °F; 111.66 K)
. The surface gravity, g, of an astronomical object is the gravitational acceleration experienced at its surface
. The average density of an object equals its total mass divided by its total volume
Atmospheric pressure is the pressure exerted by the weight of air in the atmosphere of a planet. As elevation increases, less overlying atmospheric mass provide atmospheric pressure to decreases . The pressure is caused by the planet's gravitational attraction on the atmospheric gases above the surface. It depend also of the mass ofthe planet, the radius of the surface, and the amount of gas and its vertical distribution in the atmosphere. Finally, it is modified by the planetary rotation and local effects such as wind velocity, density variations
. Liquid nitrogen is a colorless clear cryogenic fluid in a liquid state at an extremely low temperature. Its melting or fusion point is 63 K ((−210 °C; −346 °F) and the Boiling point, 77.355 K ​(−195.795 °C, ​−320.431 °F)
. At standard temperature and pressure, ethane is a colorless and odorless gas. It has a boiling point of −88.5 °C (−127.3 °F; 184.6 K) and melting point of −182.8 °C (−297.0 °F; 90.4 K). After methane, ethane is the second-largest component of natural gas.
. Argon has approximately the same solubility in water as oxygen and is 2.5 times more soluble in water than nitrogen. Argon is colorless, odorless, non-flammable and nontoxic as a solid, liquid or gas. Its melting point     is 83.81 K ​(−189.34 °C, ​−308.81 °F) and its boiling point 87.302 K ​(−185.848 °C, ​−302.526 °F)

The actual sound recording from the Huygens Probe as it descends through the methane atmospheres of Titan, to land on the surface of this moon of Saturn. This is the sound of the landing on another body in our solar system most distant from the earth. Professor Carolin Crawford, Gresham Professor of Astronomy, introduces the recording, describing the 2 1/2 hour descent through the methane winds blowing at 6 to 7 km per hour. She then goes on to explain why we haven't yet been able to hear the sound of the atmosphere of Mars, and how we might be able to soon.

This is an extract from a free public lecture by Carolin Crawford, Gresham Professor of Astronomy: 'The Sounds of the Universe'. The transcript and downloadable versions of the full hour-long lecture are available from the Gresham College website:

Following on from the first pictures ever received of Saturn's moons, a probe is sent out to Titan to get a better picture. Fascinating space film from BBC Worldwide.

It's a voyage of exploration like no other - to Titan, Saturn's largest moon and thought to resemble our own early Earth. For a small team of British scientists this would be the culmination of a lifetime's endeavour - the flight alone, some 2 billion miles, would take a full seven years. This is the story of the space probe they built, the sacrifices they made and their hopes for the landing. Would their ambitions survive the descent into the unknown on Titan's surface?

A missing data stream and bad weather could lead to mission disaster - will they be able to receive any data from the probe? Fascinating space clip from BBC.

. Cassini-Huygens spacecraft voyage
. Scientific's Instrument - Cassini
. Scientific's Instrument - Huygens
. Communication's System
. General Spacecrafts' Classification,
. Suite of The Cassini-Huygens Spacecraft discoveries
. The Huygens Probe Mission
. Some of the most promises futures missions' Scenarios on Moon's Titan, like New Spacecraft and/or Balloons and/or Submarine in Titan's Lakes... AND OTHERS 
. Japan's Hayabusa 2 mission to Asteroid 1999 JU3... and more
. Why  Spacecrafts' Missions are Extended?
. Psyche: Journey to a Metal World