C.R.O.N.U.S: The Titan Project

Cronus was the youngest and the leader of the Titans of ancient Greek Mythology...

CRONUS is an exploration mission concept for a Capable Reconnaissance Operation and Navigation with a UAV System for use on Saturn’s largest moon, Titan. The mission is to fly a UAV with an instrumented science payload through Titan's lower atmosphere to survey Titan's surface. The goal of this mission is to definitively prove the existence of liquid surface lakes on the moon and to obtain scientific data to better understand the patterns of Titan’s atmosphere. If liquid surface lakes are found, an inspection of the liquids composition and characteristics could open research interests in prebiotic molecules which were also the source of early life on Earth.Titan’s low-gravity of 1.352 m/s2 (roughly one-eighth of Earth’s) and high-atmospheric density, about 5.3 kg/m3 at the surface, or more than four times that of Earth, make it ideal for aircraft flight. In this flight-friendly environment CRONUS could be more successful than NASA’s Cassini-Huygens mission because it has the ability to travel greater distances and collect more data. Despite a flight-friendly environment, the UAV faces various unique challenges to structure and payload. The surveillance is proposed to cover a 500 km2 range above 70° N latitude line in the lower troposphere where the only considerable predictable weather effect is extreme cold in the range of 90-100 K, leading to design concerns of structural integrity and payload ability. Other prominent constraints are the packaging of a UAV with a wing-span of 6 meters into an aeroshell of diameter 2.75 meters as well as the deployment from the aeroshell.

Mission Relevance

Some researchers have proposed the existence of a global hydrocarbon ocean,but radar observations, near IR observations, and HST imagesshow that the surface is heterogeneous. These images are stillconsistent with the presence of shallow lakes, particularly near the north pole. Itis proposed that these lakes form by an accumulation of liquids, like methane, in the bottom of crater basins.The empirical evidence, although consistent, is still uncertaindue to unknown details of the dynamics of Titan’s troposphere. The difficulty in observing the troposphere level is the dense haze in the upper atmosphere. This haze is formed when ultraviolet light rays and energy particles from Saturn’s environment interact with and break down the hydrocarbons (nitrogen and methane) in Titan’s upper atmosphere. These organic molecules form a thick, orange-brown haze that surrounds Titan. After the breakdown of the hydrocarbons, the organic molecules are known to sediment onto Titan’s surface, and if they interact with transient water they can form more complex, prebiotic molecules, such as amino acids. The likely composition for the surface liquids includes simple hydrocarbons as opposed to water. However, there is a significant portion of Titan’s mass that is water ice. The Cassini-Huygens mission profiled a few impact craters that are believed to have discharged an amount of liquid water. For these reasons, Titan could be the model for understanding the beginnings of life.

The importance of probing tropospheric dynamics for understanding Titan’s atmosphere goes beyond just the origin of life. Titan’s troposphere contains approximately 90% of the atmospheric mass, yet it has been largely unexamined due to the global haze.The use of UAV’s as flying data-collection platforms presents the opportunity to traverse larger areas and provide a much higher data return than a stationary probe such as Cassini-Huygens or an alternative ground-based locomotion exploration.The scientific instruments were carefully chosen to take advantage of the capability of flight. In this manner, not only can things like the haze layer and cloud cover be penetrated but it can directly be measured in a way that has not been done before. The scientific payload consists of:one high-resolution gimbaled IR camera with full rotation to maximize the target area imaged, a gas chromatograph and neutral mass spectrometer to measure the constituents of the atmosphere as well as a potential liquid probing objective, an atmospheric suite to measure troposphere details, an aerosol density sensor to measure the thick layer of haze, and a radar altimeter.

Flight Environment

Flight on Titan poses many unique challenges, and the aircraft must demonstrate the capability to operate across a wide range of environmental conditions.Titan is the largest moon of Saturn and the second largest moon of the solar system (after Ganymede of Jupiter). It has a very cold, dense atmosphere that is composed of hydrocarbons, primarily nitrogen (97%) and methane (2%). When ultraviolet light rays and energy particles from Saturn’s environment interact with the hydrocarbons in Titan’s atmosphere, the hydrocarbons break down and produce a thick, orange-brown, hazy layer of organic molecules. This layer prohibits us from seeing Titan’s surface from space. While the methane in Titan’s atmosphere may condense to form rain near the surface (at temperatures around 94K), the methane would form clouds of ice crystals at altitudes of 10-20 km. Therefore, conducting the mission at an altitude of 4 km is necessary. Data on winds in this region is scarce, but in Titan’s lower troposphere the winds are believed to be similar to those on Venus, so wind velocities of 5-10 meters/sec are expected. In addition to temperatures of 90-94K, the UAV will be required to fly in an atmosphere at 1.5 bar, a gravity constant of 1.352 m/s2, a density of 5.3 kg/m3, and a kinematic

Mission Profile

Time frame: 7 years (from launch to end of mission).
Target Area Imaged: 1,600 km2
Payload: TASE200 imaging system, CASI, gas chromatograph and neutral mass spectrometer, SSP, radar altimeter, ADS
Landing: Splashdown

Airfoil Selection

Because of Titan’s low gravity and high atmospheric density, airfoils of moderate thickness (with thickness as a percentage of the chord between 8 - 13%) were examined. With such airfoils, the flow will separate at the leading edge at lower angles of attack, but immediately reattach itself. The S4110 airfoil was selected because its theoretical Cd0 is low, its in-flight characteristics were congruent with what is desired, and because it has been used on previous high-range, high-endurance aircraft. It has a thickness of 8.4%, a L/D ratio of 76.84, a stall angle of 8.5°, and a maximum lift-coefficient of 1.278.

Conclusion

Ultimately, no conclusions of the success of this mission can be made without the mission being attempted or completed. However, results of design can be compared to initial goals in an objective manner. The desired ranges of surveillance and area imaged can be achieved given the power system and performance of our aircraft. The aircraft is capable of fitting within the aeroshell when the wings have been folded and the tail boom is reduced by the telescoping system. These theoretical comparisons show the successful adaptation to design constraints, but do not determine the mission to be a success. The success of the mission rests on the absolute proof of surface liquids existing on Titan. The range of the UAV based on its time of flight is 644 km which is under the requirement, the duration of flight is 20 hours which is also under the requirement and the area imaged is 1300 km2 which exceeded the requirement.

Team Contact Information:Jeremy Smith: Project Manager, Materials Lead, Flight Systems; jsmit221@slu.edu

Lyell Brown: Archivist, Aerodynamics Lead; lbrown68@slu.edu ,

Cody Francis: Project Manager, Flight Systems Lead, Propulsions Lead sfranci9@slu.edu

Yi Chen: Webmaster, Flight Systems; ychen33@slu.edu

Lihao Zhou: Recorder, Stability and Control Lead; lzhou4@slu.edu

Jacob May: Modeling; jmay11@slu.edu

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