Dragonfly (spacecraft)

Dragonfly is a proposed spacecraft and mission that would send a mobile robotic rotorcraft lander to Titan, the largest moon of Saturn, in order to study prebiotic chemistry and extraterrestrial habitability at various locations where it would perform vertical-takeoff and landings (VTOL).

Titan is unique in having an abundant, complex, and diverse carbon-rich chemistry on the surface of a water-ice-dominated world with an interior water ocean, making it a high-priority target for astrobiology and origin of life studies. The mission was proposed in April 2017 to NASA's New Frontiers program by the Johns Hopkins Applied Physics Laboratory, and it was selected as one of two finalists (out of twelve proposals) in December 2017 to further refine the mission's concept.

Overview
Dragonfly is a proposal for an astrobiology mission to Titan to assess its microbial habitability and study its prebiotic chemistry at various locations. If selected for launch, Dragonfly would perform controlled flights and vertical-takeoff and landings between locations, while powered by a radioisotope-powered generator. The mission would involve flights to quite different locations on the surface, which allows sampling diverse regions and geological contexts.

Titan is a compelling astrobiology target because its surface contains abundant complex carbon-rich chemistry and because both liquid water and liquid hydrocarbons can occur on its surface, possibly forming a prebiotic primordial soup.

History
The initial Dragonfly conception took place over a dinner conversation between scientists Jason W. Barnes (Department of Physics, University of Idaho) and Ralph D. Lorenz (Johns Hopkins University Applied Physics Laboratory) and it took 15 months to make it a detailed mission proposal. The Principal Investigator is Elizabeth Turtle, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory.

The Dragonfly mission concept builds on several earlier studies of Titan mobile aerial exploration, including the 2007 Titan Explorer Flagship study, which advocated a Montgolfière balloon for regional exploration, and an airplane concept considered for the Discovery program AVIATR. The concept of a rotorcraft lander that flew on battery power, recharged during the 8-Earth-day Titan night from a radioisotope power source, was proposed by Lorenz in 2000. . More recent discussion has included 2014 Titan rotorcraft study by Larry Matthies, at NASA's JPL that would have a small rotorcraft deployed from a lander or a balloon. The hot-air balloon concepts would have used the heat from a radioisotope thermoelectric generator (RTG).

Leveraging proven rotorcraft systems and technologies, Dragonfly would use a multi-rotor vehicle to transport its instrument suite to multiple locations to make measurements of surface composition, atmospheric conditions, and geologic processes.

NASA plans to select one of two proposals (Dragonfly or CAESAR) in July 2019 to build and launch in 2024 or 2025 as the New Frontiers program Mission 4.

Funds and development
The CAESAR and Dragonfly missions will receive $4 million (USD) funding each through the end of 2018 to further develop and mature their concepts. NASA plans to select one of these proposals in July 2019 to build and launch in 2024 or 2025. The selected mission will be the fourth in NASA's New Frontiers portfolio, a series of principal investigator-led planetary science investigations that fall under a development cost cap of approximately $850 million.

The Penn State Vertical Lift Research Center of Excellence is responsible for rotor design and analysis, rotorcraft flight-control development, scaled rotorcraft testbed development, ground testing support, and flight performance assessment.

Science objectives
In 2005, the European Space Agency's Huygens lander acquired some atmospheric and surface measurements on Titan. It detected tholins, which are a mix of hydrocarbons (organic compounds) in the atmosphere and on the surface. Because Titan's atmosphere obscures the surface at many wavelengths, the specific compositions of solid hydrocarbon materials on Titan's surface remain essentially unknown. Measuring the compositions of materials in different geologic settings will reveal how far prebiotic chemistry has progressed in environments that provide known key ingredients for life, such as pyrimidines (bases used to encode information in DNA) and amino acids, the building blocks of proteins.

Areas of particular interest are sites where extraterrestrial liquid water in impact melt or potential cryovolcanic flows may have interacted with the abundant organic compounds. Dragonfly would provide the capability to explore diverse locations to characterize the habitability of Titan's environment, investigate how far prebiotic chemistry has progressed, and search for biosignatures indicative of water-based and even hydrocarbon-based life.

Robert Zubrin has also pointed out that Titan possesses an abundance of all the elements necessary to support microbial life, saying "In certain ways, Titan is the most hospitable extraterrestrial world within our Solar System for human colonization." The atmosphere contains plentiful nitrogen and methane, and strong evidence indicates that liquid methane exists on the surface. Evidence also indicates the presence of liquid water and ammonia under the surface, which are delivered to the surface by volcanic activity.

Design and construction
Dragonfly would be a rotorcraft lander, much like a large quadcopter with double rotors, an octocopter. Such rotor configuration would be able to tolerate the loss of at least one rotor or motor. Each rotor would be about 1 m in diameter. The aircraft would travel at about 10 m/s or 36 km/h and climbs up to 4 km altitude would be desired for best scientific value.

The power required to hover a given mass on Titan is 38 times less than that required on Earth, due to Titan's denser atmosphere and lower gravity. The atmosphere is about four times as thick as Earth's, but local gravity (15 percent of Earth's) would make it easier to fly, although cold temperatures and lower light must be contended with. The rotorcraft could travel significant distances, powered by a battery that would be recharged by a Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) during the night. MMRTGs convert the heat from the natural decay of a radioisotope into electricity, although increased mass and surface area might sacrifice control. The rotorcraft would be able to travel tens of kilometers on every battery charge and stay aloft for a few hours each time. The vehicle would use sensors to scout new science targets, returning to the original site until new landing locations are verified as safe by analysis by mission controllers.

Preliminary studies and modeling contemplate a baseline 450 kg mass for the rotorcraft packed in a 3.7 m diameter heatshield. Samples would be obtained by two sample acquisition drills and hoses, one on each landing skid, for delivery to the mass spectrometer instrument.

The craft would remain on the ground during the Titan nights, which last about 8 Earth days or 192 hours. Activities during the night would include sample collection and analysis, seismological studies, meteorological monitoring, and local microscopic imaging using LED illuminators as flown on Phoenix lander and Curiosity rover. The craft will communicate directly to Earth with a high-gain antenna.

Proposed scientific payload

 * DraMS (Dragonfly Mass Spectrometer) is a mass spectrometer to identify chemical components, especially those relevant to biological processes, in surface samples
 * DraGNS (Dragonfly Gamma-Ray and Neutron Spectrometer), is a set of a Gamma-ray spectrometer and a neutron spectrometer to identify the composition of surface and air samples
 * DraGMet (Dragonfly Geophysics and Meteorology Package) is a suite of meteorological and geophysical sensors to document atmospheric conditions and probe subsurface structure and activity
 * DragonCam (Dragonfly Camera Suite) are a set of microscopic and panoramic camera s to image Titan's terrain and scout for scientifically interesting landing sites.