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A Landing Site for Dragonfly

Rotorcraft have certainly been in the news lately, with Ingenuity, the Mars helicopter, commanding our attention. The Dragonfly mission to Titan involves a far more complex rotorcraft capable of visiting numerous destinations on the surface. In fact, Dragonfly makes use of eight rotors and depends upon an atmosphere more helpful than what Ingenuity has to work with on Mars. Titan’s atmosphere is four times denser than what we have on Earth, allowing Dragonfly to move its entire science payload from one location to another as it examines surface landing zones while operating on a world whose gravity is but one-seventh that of Earth.

I want to call your attention to the publication of the science team that just appeared in the Planetary Science Journal, because it lays out the rationale for the various decisions made thus far about operations on and above Titan’s surface. It’s a straightforward, interesting read, and makes clear how much work we have to do here. Yes, we had Cassini for a breathtaking tour that lasted 13 years, with repeated flybys and investigations on Titan using radar, but while we know a lot about structures like lakes and mountains on the surface, we know all too little about their composition.

In fact, as Alex Hayes points out, we didn’t know at the time Cassini launched whether the Huygens probe would find a global ocean at Titan or a solid surface of ice and organics. Because of the uncertainty, the Huygens science experiments were primarily atmospheric, meant to function during the descent phase. Hayes (Cornell University) is a co-investigator for Dragonfly. He adds:

“The science questions we have for Titan are very broad because we don’t know much about what is actually going on at the surface yet. For every question we answered during the Cassini mission’s exploration of Titan from Saturn orbit, we gained 10 new ones.”

Image: What we do know. This is Figure 1 from the paper. Caption: Dragonfly will image from the surface to provide context for sampling and measurements, as well as in flight to identify sites of interest at a variety of locations. (Left) Huygens image of Titan’s surface; cobbles are 10–15 cm across and may be water ice (Tomasko et al. 2005; Keller et al. 2008; Karkoschka & Schröder 2016a). (Right) Huygens aerial view of terrain akin to the diverse equatorial landscapes that Dragonfly will traverse and image at higher resolution. Credit: NASA/ESA/Barnes et al.

Dragonfly’s 2.7 year mission, starting upon arrival at Titan in 2034 during winter in the northern hemisphere, will commence at a landing site that was chosen for its safety factors (broad, relatively flat terrain) as well as its proximity to nearby interesting scientific targets. The goal is to set down at the equatorial dune fields called Shangri-La, which NASA notes are similar to the dunes found in Namibia on Earth. A series of short flights will explore this area before longer flights of up to eight kilometers begin, the beauty of the design being that Dragonfly will be able to sample interesting surface areas along the route to its destination, the Selk impact crater.

As the mission now stands, the lander should log on the order of 175 kilometers across Titan enroute to Selk. The latter is an interesting place because there is evidence here of past liquid water as well as organics, complex molecules containing carbon, along with hydrogen, oxygen and nitrogen. Methane rain and a snow of organics keep Titan’s weather systems complex amidst a landscape containing the building blocks of life.

But let’s get back to that landing site. The paper refers to Shangri-La as an “organic sand sea,” with the touchdown site located 134 kilometers south of Selk Crater, and approximately 175 kilometers north-northwest of the Huygens Landing Site. The image below is Figure 7 from the paper, giving the landing site in context.

Image: Dragonfly landing site. Credit: Barnes et al.

As the paper notes, a ‘sand sea’ is only partially sand. Dunes can be separated by flat sand-free areas called ‘interdunes,’ a feature likewise common to Namibia, where the Namib sand sea is covered only 40 percent by sand. The interdunes that make up the balance are primarily gravel. Cassini was able to resolve Titan’s interdunes to reveal their predominantly icy character, one that matches the spectral properties at the Huygens landing site. The authors find the correlation interesting because it implies the Shangri-La interdunes will include water-ice gravels, “potentially a fine-grained layer damp with condensed methane,” and thus offering a chance for Dragonfly to sample both Titan’s organic sands and materials with a water ice component.

Image: This illustration shows NASA’s Dragonfly rotorcraft-lander approaching a site on Saturn’s exotic moon, Titan. Taking advantage of Titan’s dense atmosphere and low gravity, Dragonfly will explore dozens of locations across the icy world, sampling and measuring the compositions of Titan’s organic surface materials to characterize the habitability of Titan’s environment and investigate the progression of prebiotic chemistry. Credit: NASA/JHU-APL

The path to Selk Crater should take in a variety of terrain with different compositions, which will include the edge of the crater’s ejecta deposits. From Cassini data, the authors believe this material is similar in composition to the Huygens landing site, representing an area likely to feature water ice. Selk itself is 80 kilometers in diameter. Cassini data along with the Dragonfly team’s modeling show the spectral signature of organic sand in the interior and water-ice around the edges of the crater floor.

As you can see, the astrobiological examinations Dragonfly will engage in are both water-based and hydrocarbon-based, meaning a potential biosignature is possible from impact melt deposits or interactions with the interior ocean — this would be life as we know it — or from a form of life we have yet to discover that draws on liquid hydrocarbons within Titan’s lakes, seas and aquifers. The mission is designed around the ability to seek out both, as the paper explains:

We designed the science of Dragonfly around the themes of prebiotic chemistry, habitability, and the search for biosignatures, with an explicit consideration of both water and hydrocarbon solvents. To address prebiotic chemistry, we will determine the inventory of prebiotically relevant organic and inorganic molecules and reactions on Titan. In the realm of habitability, we will determine the role of Titan’s tropical atmosphere and shallow subsurface reservoirs in the global methane cycle, determine the rates of processes modifying Titan’s surface and rates of material transport, and constrain what physical processes mix surface organics with subsurface ocean and/or melted liquid-water reservoirs. Our search for biosignatures will entail a broad-based search for signatures indicative of past or extant biological processes.

The paper is Barnes et al., “Science Goals and Objectives for the Dragonfly Titan Rotorcraft Relocatable Lander,” Planetary Science Journal Vol. 2, No. 4 (full text).


Comments on this entry are closed.

  • Alex Tolley August 17, 2021, 14:19

    The paper outlines a very ambitious, but exciting science mission. If successful, it will generate a huge number of journal papers.

    I was surprised by the assumption that liquid water could only exist on the surface as transients from impacts, rather than any connection to the possible subsurface ocean, although I can see that this is conservative based on the possible thickness of the ice crust and the lack of any obvious features that suggest cryo-volcanism, geysers, etc. As a laboratory for prebiotic chemistry, Titan must be the premier site in the solar system and the potential for a large range of complex molecules, protected by the low temperatures, to be detected is very interesting indeed.

    I just hope every test imaginable is done to test Dragonfly working in Titan’s environment to guard against unexpected failure. It would be heartbreaking if the probe failed soon after entry due to some unexpected condition.

    In the future, a ballon to carry the science payload and energy generation might be the best way to traverse the planet, with drones that are released to take samples on the surface and return them to the balloon for analysis. With RTGs to supply energy with battery storage, such a mission could last for decades, with the surface being mapped in high resolution as an extra benefit.

    • Geoffrey Hillend August 19, 2021, 18:16

      The problem with a balloon is that it can’t land, but dragonfly can land. The remote sensing instrument payload is impressive as well as the drone which uses radar. It has a gamma ray neutron spectrometer which is used to identify the surface chemistry when it lands on the ground. It also has a mass spectrometer to identify the atmospheric chemistry and more: https://dragonfly.jhuapl.edu/News-and-Resources/docs/34_03-Lorenz.pdf

      • Alex Tolley August 19, 2021, 20:30

        You will note that I said the balloon carries drones that can take samples [from the surface]. Because the drones need not carry the science instruments, they can be small and have redundancy in numbers in case of failure. All the mass of equipment is supported by a lighter than air ship (balloon or dirigible) which has considerable range.

        • Geoffrey Hillend August 21, 2021, 16:50

          Small drones need the redundancy, but not dragonfly, and small drones can’t have a good instrument payload. The balloon idea was also planned for Mars, but Mars has a very thin atmosphere so drones have to be small, but Titan’s atmosphere is thicker than Earth’s so we can make a large drone with a lot of remote sensing capabilities and now our technology has improved in the last fifteen years.

          • Alex Tolley August 21, 2021, 21:34

            Redundancy vs “all eggs in one basket”. r vs k strategy.

            I was watching an old BBC “Sky at Night” with Sir Patrick Moore interviewing 2 of astronomers about the Cassini-Huygens mission that had just released the probe onto Titan’s surface. The idea of a balloon was raised there, but with the proviso that the balloon land to take samples – so definitely a Dragonfly precursor.

            But clearly, any single craft must be made meticulously to circumvent any possible failures. In contrast, having lots of simpler devices allows for failures, particularly for the more hazardous sample collection. We got an example of that with the failure of the Philae lander from Rosetta. It had one shot to succeed but it failed and chance killed its recovery. What if Rosetta had carried several smaller, simpler landers, each with a probability of success, but with a joint (Binomial) probability that at least one would succeed being higher?

            • Mike Serfas August 23, 2021, 8:04

              The uncertainty of the terrain seems worrisome. I imagine some unlikely scenarios: what if some source of oxidized compounds has created a peroxide “land mine” waiting for something warm and heavy to press down on it? What if the ice gravel can undergo liquefaction when disturbed, dropping the probe into liquid hydrocarbon? I think it could be an exciting mission.

            • Geoffrey Hillend August 23, 2021, 20:17

              The problem with the smaller landers is the science payload. With a large lander we can really put inside a lot of cutting edge sensitive remote sensing and large cameras with infra red, and, a large amount of power that would not be as good in a smaller lander. I would like to see what the power options are including solar panels. New Horizons had a radioisotope thermoelectric generator. Maybe With a large drone, there can be more than one computer checking each other so redundancy can be built inside. We should make it just for the complexity and innovation needed. I wonder if dragonfly can fly through the methane rain without getting dirty. Although it has radar for ground topography, I wonder it the cameras lenses could get dirty from the particulates in the atmosphere and how they could be cleaned.

            • Geoffrey Hillend August 23, 2021, 20:42

              Also there is nothing wrong with making a large drone because Titan’s gravity is even lower than Mars and if it is built right, there should be no problem since it is easier to land on a planet with a thick atmosphere with a parachute and a lot of atmospheric drag for re entry.

              I thought the same thing about NASA’s last two Mars rovers, Curiosity and Perseverance that they were too large. Before Curiosity landed, I thought it needs just too many steps and things to have a successful landing due to the fact it is such a heavy rover, but I now see my mechanical physics knowledge was not adequate to understand correctly it’s high probability of success being designed and made so well, so I was wrong and too pessimistic. If dragonfly is built and designed right for the environmental conditions and it looks like it is, it should work and I wonder how long it’s batteries can last and what is the estimate of time for it’s useful working life.

              The amount of scientific information dragonfly could give us would be large. It is an ambitious project and cutting edge idea. I hope it becomes a reality.

  • charlie August 17, 2021, 17:10

    a Methane river – exciting !

  • James Essig August 17, 2021, 19:18

    Awesome! A drone om Titan will be fascinating. Truly we are coming of age in the solar system. The stars will be next.

  • Deanna Shaw August 18, 2021, 17:13

    All good stuff and exciting…. hope I live to see it! …..but how is this craft to be powered? RTG?

    • Andrei August 19, 2021, 8:00

      Yes Dragonfly will be nuclear powered, by one MMRTG to be exact, which charge up one lithium battery during night time.
      With the low gravity and thick atmosphere flying will be easier than on Mars, where a drone like craft is used right now as a scout.
      But drag and the risk of tar like rain will pose a risk for the craft while the instruments most likely can be kept clean by the heat, the rotor blades might get covered. This is one of the reasons the mission is planned for safer but less interesting areas near the equator which got frozen snow dunes of organics. I still look forward to and hope I will be around when this craft reach the destination, the two spectrometers on the craft might find chemistry that is similar to the what might have been found on Earth when life got started.

      • charlie August 19, 2021, 17:19

        “Yes Dragonfly will be nuclear powered, by one MMRTG to be exact, which charge up one lithium battery during night time.”

        means its range will be limited …

        • Alex Tolley August 19, 2021, 20:39

          I don’t see your logic. Which component will limit the range? The MMRTG last many years, even decades. Lithium batteries are highly reliable with a warranty on an electric car that is at least 8 years and will likely last at least a decade or more. The Lithium battery in a family 2006 Prius is still working fine after 15 years.



          • charlie August 20, 2021, 14:21

            simple. distance is limited by Lithium batteries energy content. range is limited to batteries max energy/2; beyond that range – won’t make it back.

            • Alex Tolley August 20, 2021, 19:41

              But the batteries are being recharged by the RTG. Isn’t that point of the RTG?

            • Andrei August 21, 2021, 11:48

              charlie: “….won’t make it back.”

              Make it back to where? The MMRTG is safely bolted to the rear of Dragonfly. And unless something extraordinary is found after analysing data sent back to Earth, the craft is unlikely to visit any place more than once.

              • charlie August 22, 2021, 19:31

                “The MMRTG is safely bolted to the rear of Dragonfly.”

                I wasn’t clear that the MMRTG was attached to Dragonfly.

  • torque_xtr August 18, 2021, 17:35

    Sadly it won’t see any lakes, except maybe it gets some really extended mission…

    Well, if it flies northward ten kilometers each Titanean day, then it will reach the lakes by mid-century. But Curiosity roves Mars for more than four times it’s designed lifespan now, and it has reached only the base of sulfate-bearing unit – at best, half-way through the young Mars records. So, with all the inevitable delays and detours, more like 2070. Still quite within RTG’s lifetime, but possibly not mine unless some real biotech kicks in. =]

    It’s like we already entered the ant’s crawl of milti-generational space projects in this age.

    • Wojciech David Jacyk August 20, 2021, 2:56

      I share your sentiment, it seems that proposed missions and timelines are starting to get very out of sync with expected progress in space launches and abilities of new launch systems. I guess we could be facing a major review of proposed missions in a decade or so if the capabilities are going to expand as much as it is envisioned.

  • Jeff Wright August 19, 2021, 4:07

    Titan is Sols service station, ISRU wise. Now we have seen chains fountaining up out of containers. Imagine spinning fibers out as tethers Saturn pulls on and we can remove hydrocarbons in one chain pull.

    • Alex Tolley August 19, 2021, 10:36

      Not sure what you are thinking about exactly with the plastic tethers, but Titan is definitely the best source of hydrocarbons and nitrogen in the solar system. Ceres would be the best water supply.

      What I am not sure about in this extractive model, is why we need hydrocarbons. If we just need carbon, why not use the more readily available CO2 in the Venusian atmosphere, and combine it with water to via chemistry and biology to create all the carbon compounds we might want? The supply chain from Titan is long.

  • Kamal Ali August 20, 2021, 2:03

    Hugely exciting! I read elsewhere that a mission to the Titan’s North pole was sadly precluded because the N. pole will be in winter at Dragonfly’s arrival. Since Saturn’s year is 30 Earth years, we’ll have to wait another 15 or more years before Dragonfly’s successor can fly to the North pole to interact with Titan’s lakes and rivers.

    • torque_xtr August 23, 2021, 18:30

      The polar night is much less a problem on Titan than on Earth. First, southern shores of Kraken Mare are at 59 degrees north, somewhat below the polar circle. “Magic islands” in Ligeia are at 79 deg N, and polar night lasts there from about 2027 to 2037. But on Titan, there is a really strong atmospheric scattering due to which even the poles are never truly dark. There is an article about twilight conditions on Titan, https://iopscience.iop.org/article/10.3847/1538-3881/aae519/pdf. The zones of “civil”, nautical and astronomical twilight are several times wider than on Earth. Most of lakes experience considerable periods of “civil twilight” even at the winter solstice itself, and with sensitive cameras, this lighting is enough for imaging and navigation. As it is said in the article, illumination in the red band is comparable to full-Moon night on Earth when the Sun is 30 degrees below the horizon! And it never gets this low at the Titanean poles, with axial tilt of 26 degrees. Above polar circles, the “white nights” begin even before the sun rises in spring, creating long periods of “continuous twilight”.

      In addition, Titanean atmosphere has near-infrared windows. The photo of Sun glinting off a lake was made in one of these, with Sun near the horizon; it’s rays made double-pass to the ground and back without much scattering. In some infrared bands, the sky on Titan is as clear as on Earth on a fair day, and with a combination of visible and near-infrared cameras, there is absolutely no need for the Sun to be high in the sky!

      • charlie August 24, 2021, 13:50

        The only problem that I see here is what you just said. That at the depth of the Titan winter nights the sun will appear to be near the horizon. I imagine without doing any detailed calculations that the earth might not be in the best proximity to receive transmissions directly from Lander. That of course is contingent on whether or not there is an orbiter around Titan which can serve as a link. Additionally, transmission in the infrared I imagine would not be quite as easy as you might think from the standpoint of communications-better find an expert!

        • torque_xtr August 24, 2021, 15:48

          Dragonfly needs to be highly autonomous because of long signal roundtrip times. So the only thing it should not do is to fly into the polar night. For the navigation updates by conventional downlink, the Sun rising just a bit above the horizon in the mid-day is enough. More complicated for data transmission, of course. But anyway, southern Kraken is outside polar circle, and by late 2030-s, most of the lakes will see at least some daylight.

  • David Harrison August 24, 2021, 14:20

    To revisit the balloon comment: I believe this is a valid approach – but only if it’s a hybrid design in which the rotors are used to bring the craft DOWN to the surface for sampling missions and then as the rotors spin down the balloon buoyancy would lift the craft back up. The rotors would also provide directional control.

    This would provide two benefits: the mission could cover more surface area when its at it neutral buoyancy altitude, and secondly if/when the rotors stop working the craft can still provide data as it drifts in the wind. It’s always good to design for failure modes.

    The balloon could be inflated and maintained with hydrogen cracked from the local atmosphere, this would provide some additional altitude control if desired or the craft needs to ascend over terrain features.

    The winds encountered by Huygens near the surface were a gentle .3m/sec suggesting that the craft could survive for an extended period of time.

    • Alex Tolley August 24, 2021, 15:59

      I like that idea of using the props to descend, Given the low wind speed at the surface, I would even prefer the balloon to be a dirigible so that it could propel itself in certain directions until the props failed and it became a balloon again.

  • Brian Altmeyer August 31, 2021, 6:16

    I’m again galled and baffled by a mind-bogglingly timid proposal being touted as “bold”.

    Without diminishing the difficulty and risk of reaching a destination like Titan, let’s be clear that after all that technology, time, money, and effort have been invested, they’re proposing to carefully avoid the seas, lakes, and rivers that make Titan a potentially revolutionary topic, and instead place it in an equatorial dune field.

    In other words, the equivalent of traveling to an exotic and historic destination, getting a postcard from the airport gift shop, and then spending the entire rest of the trip hiding in a hotel room while reading Wikipedia articles about the region.

    I take it if we were seeking to explore the Amazon basin, this approach would suggest landing a craft in the Atacama desert on the off chance of discovering fossilized particles of biological material on a grain of sand. This should nauseate anyone with even an ounce of instinctive curiosity.

    There is, and has been for a long time, a startling lack of urgency or hunger for exploration in the design of these missions. I don’t know if it’s a product of the soul-draining bureaucratic process they go through to win funding, or if these fields are actually so afraid of throwing their own subject matter into flux with direct exploring, but it’s incredible to see.

    To travel over a billion kilometers in search of a world of lakes, rivers, and storms, just so that you can land in a dune field and toy with dry gravel because it *might* indirectly imply something about places you refuse to go.

    I’m honestly at a loss.

    One gets the sense some institutional researchers view data from nature as “interference” in their work rather than the entire point of it, and would prefer to keep its channels of input nice and limited.

    Engineering demonstrations are great, but if you’re going that far, you might as well actually explore the place you’re landing.

    • charlie September 1, 2021, 18:13

      “To travel over a billion kilometers in search of a world of lakes, rivers, and storms, just so that you can land in a dune field and toy with dry gravel because it *might* indirectly imply something about places you refuse to go.”

      Probably don’t want to splash down an sink in a methane lake.

      • Brian Altmeyer September 3, 2021, 13:20

        “Probably don’t want to splash down and sink in a methane lake.”

        I’m not suggesting trying to land in a fjord bank or some Canadian Shield-type nightmare terrain. But near at least *some* of the features that are the purpose of the mission would simply be rational.

        If you’re going to spend a billion dollars and over a decade organizing a trip to explore somewhere, it would be pretty insane if the proposal was to limit the zone of exploration to places a thousand miles from anything even resembling it.

        There is just something seriously wrong with how these missions are being planned. Laudably ambitious engineering, but aimed at increasingly trivialized scientific objectives.

        It’s honestly a little creepy. I despise the term “Kafka-esque,” but it does seem like institutions think themselves in circles to some extent, to the detriment of science.

        Having absolutely no idea what you’ll find would be a dream come true to curious minds, but a lot of tenured professors in the sciences would go pale with dread at the thought of being responsible for such a mission.

        It makes my head ache to see, but academia prefers its scientific questions answered in multiple-choice form. They’re scared of the open-ended version of science: The inductive, pioneering model where any idea you come up with is probably a bad joke within a year because so much new information is always coming in.

        But we need that. And NASA probe exploration should get back to that kind of open-ended veil-breaking, and away from this weak-willed textbook-highlighting that the community has convinced itself is “exploration”. If the textbook is still relevant at all, you didn’t actually explore.

        This solar system is colossal and mysterious beyond our current imagining, and we’ve been hiding from that fact for too long.