In this special edition Check 6 Tech Talk in conjunction with IAC 2020 we speak to Elizabeth Turtle, the principal investigator of NASA’s upcoming Dragonfly mission, which seeks to explore the surface of Titan with a rotorcraft.
Dragonfly’s unique dual-quadcopter will land at multiple sites over a nearly three-year baseline mission, assessing the mysterious Saturnian moon’s past and present habitability. Recently delayed by one year due to COVID-related budget pressures, Dragonfly is expected to launch in 2027.
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Transcript:
Jefferson Morris:
Hello and welcome to this special Aviation Week Check 6 tech talk. I'm your host, Jeff Morris, the editor in chief of Aerospace Daily and Defense Report. And today we're joined by Dr. Elizabeth Turtle of the Johns Hopkins University Applied Physics Laboratory. She's the principal investigator of NASA's upcoming Dragonfly mission, which seeks to explore the surface of Saturn's haze shrouded moon, Titan, with a novel Rotorcraft Lander.
Over a nearly three year baseline mission, Dragonfly will explore Titan's chemistry, atmosphere and geology, sampling materials and determining surface composition in a number of different locations on Titan's surface. The goal is to characterize Titan's habitability, assess the evolution of its prebiotic chemistry and search for telltale chemical evidence of life. Dragonfly is scheduled to launch in 2027 and arrive at Titan several years later. Dr. Turtle, Titan has long fascinated scientists. What will Dragonfly tell us about Titan that Cassini Huygens, which sent a lander down to the surface in 2005, couldn't tell us?
Elizabeth Turtle:
Dragonfly is designed to explore the surface of Titan in detail, and it is a mobile lander. It is a rotorcraft, or an X8 octocopter, and so this will allow us to really get to multiple sites on the surface, to be able to make in-situ measurements of Titan's chemistry and to measure its atmosphere over dozens of Titan days, and to explore the geology of Titan's equatorial region.
Morris:
I'm glad you call it an octocopter because that was actually one of my questions, I saw it described as a dual quadcopter and I thought, well, why not octocopter?
Turtle:
Yes, we use the dual quadcopter term sometimes because of the X8 configuration. And sometimes when you say ‘octocopter’ people envision eight arms, and it has four arms with two rotors on each. And so sometimes we refer to it as a dual quadcopter, but yes, technically its octocopter.
Morris:
Right. When NASA announced the mission, Administrator Jim Bridenstine said Dragonfly would have been, quote, "Unthinkable." just a few years ago. Why is that? What are the advances that have made this mission feasible now?
Turtle:
There's been a revolution, really, in drone technology and in the technology of navigation. Autonomous navigation in particular which is what we'll need to use on Titan. The roundtrip light time to Titan can be a couple hours. So, Dragonfly will need to be able to identify landing sites and navigate on its own. So just the amount of technological development that has occurred in the past decade regarding drone technology, rotorcraft capability and navigation really enabled this mission. We're not inventing a new technology, what we're doing is innovating by applying this technology that is now so mature for applications here on Earth to exploring Titan.
Morris:
Now, I know there have been other mission proposals for planetary aircraft and it's been hard for them to gain traction. There were some Mars concepts such as ARES and Kitty Hawk that never came together. What sold NASA on flying an aircraft on Titan for science return?
Turtle:
Titan's atmosphere is much more conducive to flight than the Martian atmosphere. The Martian atmosphere is quite thin, and so flying in that atmosphere is definitely a technological challenge. And the Perseverance Rover has with it the Ingenuity helicopter that will be demonstrating that technology on Mars. But for Titan, we have an atmosphere that's four times denser than the atmosphere here on Earth. And the surface gravity is also lower by a factor of about seven. So it's physically much easier to fly on Titan than it is here on Earth, actually. And in fact, a person could put wings on and be able to soar over the surface of Titan, which is quite tantalizing. So it's a very practical way of exploring Titan. Rather than trying to drive on an unknown surface we can fly above the surface. And that, of course, provides a lot of other opportunities to be able to study the atmosphere and to do aerial imaging of the surface and to scout out future landing sites.
Morris:
So you can simulate thinner atmospheres with high-altitude tests on Earth, but how do you simulate a denser atmosphere like Titan's for the purpose of testing your concept?
Turtle:
Right. So there are a lot of different facilities that NASA has that we will be able to do some testing in. And some are capable of doing overpressure—of stimulating the Titan environment. But we'll actually be building a couple of chambers here at APL that will specifically have that capability to overpressure as opposed to going down to the lower pressure or a vacuum that we’re used to testing to for space exploration.
Morris:
So now you briefly mentioned the Ingenuity technology demonstrator, which I guess is actually supposed to be the first powered flight in the atmosphere of another world. That demonstrator is on its way to Mars right now as part of the Perseverance Rover. So in the spring of 2021, Ingenuity is going to be deployed for about 30 days of technology demonstrations on the surface. What lessons do you hope your team is going to be able to glean from Ingenuity's experience?
Turtle:
There have already been lessons gleaned, and a lot of the lessons that we can learn regarding Ingenuity is related to the development of Ingenuity. And we can take those lessons into our development. And so, we certainly have been able to talk with people involved in the development. There's a lot of commonality in that sense. And it will be fascinating to see how Ingenuity does and the data that it's able to send back from Mars. We're all very much looking forward to that.
Morris:
Now, outer planet mission timescales, of course, are notoriously long. I know a whole career can encompass just one mission or maybe two missions. How long is the transit to Titan actually going to take?
Turtle:
It will take several years. It depends on the launch vehicle that we end up using, and NASA is responsible for selecting the launch vehicle and that hasn't happened yet. That's something that will happen at a later stage in the mission development. So, the transfer time specifically will depend on that, the launch vehicle. But it will be several years, it's definitely further away.
Morris:
Yes. Now what does the team plan on doing during those years? Is there science you can do along the way?
Turtle:
There isn't, actually. Dragonfly is fairly unique in that respect. Often when we are sending missions to the outer planets, you can do a flyby of another planet, for example, you can do observations. But Dragonfly is always buttoned up inside the aeroshell, inside the entry vehicle. So, there is no way to observe anything outside of the aeroshell during cruise, so it will be a pretty quiet cruise in terms of the spacecraft operations. The science team, however, will be busy planning our observation sequence, practicing the operations, et cetera. So there will still be plenty of things for the science team to be working on.
Morris:
Sure. So let's say we've arrived at Titan sometime in the 2030s, I guess. Can you walk us through, in broad strokes, the stages of the deployment, getting the rotorcraft into Titan's atmosphere?
Turtle:
Right. We do direct entry into the atmosphere upon arrival at Titan, there's no go into orbit Saturn or Titan. It's direct entry into the atmosphere. And Titan's atmosphere is very extended. Most of Cassini's flybys, for example, were up at about 1,000 km altitude. Because even at that altitude, there was substantial drag on the spacecraft. So the entry into Titan's atmosphere is actually a fairly long event. People talk at Mars about the seven minutes of terror, because it's such a quick entry. For Titan, we actually have a couple hours over which to space out all of those activities. And so, it's a fairly standard entry until about a kilometer altitude, where we actually will, once the heat shield drops off, we'll spin up the rotors and drop off of the backshell. And Dragonfly will actually fly to its first landing site.
Morris:
What are some of the science payloads that are on the vehicle?
Turtle:
So we have an instrument suite designed to focus on understanding Titan's chemistry, specifically the prebiotic chemistry of Titan. Because we know that Titan has all of the ingredients necessary for life as we know it, a very similar chemical environment to what would have been present here on the early Earth in terms of organic material and liquid water available at the surface in the past on Titan. So the primary focus is to understand the chemistry. And then we have a suite of instruments to provide information on the context of the Titan environment, the atmosphere, the geology, and even some aspects of the subsurface.
So there's a mass spectrometer, which is fed by two drills, one on each side of the lander. And so with this, we'll be able to sample and ingest solid material from the surface of Titan to understand its detailed chemical composition. And then we also have a gamma-ray and neutron spectrometer. This instrument allows us to get at the bulk elemental composition of the surface beneath the lander. So this gives us more context of a broader area than the very specific sites that will be sampled by the drills for the mass spectrometer.
And then we have a suite of meteorological and geophysical sensors to be able to measure the pressure, temperature, wind speed on Titan. As well as a seismometer that will listen for ‘Titanquakes’ to understand just how active, how seismically active, Titan might be. And of course we have a suite of cameras. We actually have eight science cameras. There are two cameras that will do very high-resolution imaging of the sites of the two samplers, the two drills. And then we have cameras that can image the area under the lander and in front of the lander.
The lander has a deployable high-gain antenna, and it’s deployable because, of course, we actually have to worry about aerodynamics, which we don't usually have to worry about for space exploration. But we fold it down to be able to improve the aerodynamics when we're flying. So, because that's already articulated, we also have two cameras mounted on the top of the high-gain antenna, and we'll be able to pan around to build up a image of the terrain all around the lander as well.
Morris:
What is that terrain initially going to look like? Sort of a desert, sand dunes, what do you expect?
Turtle:
Exactly. So Titan’s equatorial region is actually covered in sand dunes. The difference being that on Titan, the surface temperature is very low. It's 94 Kelvin, which is negative 290 Fahrenheit. And so the bedrock on Titan is water ice and the sand dunes are actually native, organic sand particles. So we'll be landing in the inter-dune regions, between these organic sand dunes. And that's important scientifically because it gives us access in the immediate landing area to two different types of materials with very different histories. The inter-dune areas can have a water ice component. And the dunes themselves, of course, are this organic sand and may be very widely sourced from across Titan, collecting in the equatorial region. So the initial landing site will look actually probably fairly similar to some of the dune fields we have on Earth, like the Namib desert, except that the dunes are very dark colored because of the organic component.
Morris:
How many locations do you plan to visit and are all of those locations determined in advance? I mean, to what extent are you able to change the route on the fly?
Turtle:
Right. Yes, we will absolutely. As we've experienced with in-situ mobile exploration of Mars, the plan is always changing and adapting to the discoveries one makes along the way. The area that we've targeted Dragonfly to land in is the equatorial dunes. And in particular, a region just south of a large impact crater. This impact crater's about 80 kilometers in diameter and it's of particular interest because the energy of the impact will have melted the target, will have melted the crust just at the surface of Titan, providing an opportunity, perhaps, for liquid water to have mixed with the organic material that is so abundant on the surface of Titan. And so from a chemical, especially a prebiotic chemistry perspective, this provides a really fascinating opportunity to understand how far organic synthesis can progress, or has progressed, on Titan. When we know we've had this environment that is conducive to the kind of organic chemistry that might've happened before life developed here on Earth. So depending on where we land in the landing ellipse, we will traverse across the landing ellipse, across the organic sand dunes in the Shangri-La Sand Sea, toward this impact crater, over the ejecta blanket and then possibly down into the interior of the impact crater. So how far we traverse depends a lot on where we land in the landing ellipse. But we could traverse up to 150 to 180 km or so, is the capability we have in the nominal mission.
Morris:
Now, the nominal mission, as I understand, is almost three years. It's 2.7 years. Now, I remember the Mars Exploration Rovers way back when, Spirit and Opportunity, they only had a baseline mission of 90 days, which of course they wildly exceeded. Maybe I'm just out of date, but it felt to me like anticipating three years operating within the atmosphere and on the surface of another planet, seems like a long time for a baseline mission. What gives you confidence that it will operate that long?
Turtle:
That is the design lifetime. So we are building the lander to that specification. The Titan day is quite long, so the Titan day is 16 days long. And we will also be spacing out the flights. So we actually fly probably once every other Titan day. So that's about once a month for each flight in the nominal scenario. So we want to have enough time to be able to explore each site before we move on to the next site. And that's part of what drives the mission timeline, to be able to traverse the distance, to be able to explore the impact crater deposits in detail.
Dragonfly's designed to be powered by a MMRTG (Multi-Mission Radiosotope Thermoelectric Generator). This is the same power source for MSL, for the Curiosity Rover and the Perseverance Rover on its way to Mars now. And so the longevity is supported by the power output from the MMRTG, which we actually use to charge a battery, and then we do all the high-energy activities off of the battery.
Morris:
Sure. So given that you've got a radioisotope thermal generator, I mean, how long could it last, optimistically? In theory, how long could this thing operate?
Turtle:
The limiting factor is actually thermal. An MMRTG puts out a lot of heat and it's typically referred to as waste heat. But on Titan, in this very cold, 94 Kelvin environment, that heat is actually a critical component of our thermal design. Because we can use the heat output from the MMRTG to keep the interior of the Dragonfly lander warm. And so, that really becomes the life-limiting factor. Once the output of the MMRTG, in terms of heat, is low enough that we can no longer keep the interior warm the temperature will drop too low for the rotorcraft to continue to operate. But that's several years, based on the decay of plutonium.
Morris:
So let's bring it back to earth before we wrap things up. What's the next major milestone, just in the development program here? You did mention that the launch vehicle has not yet been selected?
Turtle:
Right, that's right. So NASA selects the launch vehicle and we're working with them as part of that selection process. In terms of the milestones for the mission development, we just had our internal system requirements review, just this past summer. And our next milestone review is the preliminary design review. So we're working toward that now, based on the feedback we got in our review this summer. And continuing to do technology development and testing along the way as we get ready for our preliminary design review.
Morris:
Now I imagine a lot of these schedules have shifted recently. Because of course, NASA announced a one-year delay in the launch readiness date for the program, from 2026 to 2027. What was your reaction to that? Is it heartbreak or is it, "Well now we've got another year to make things perfect"? How did you react?
Turtle:
We're still going to Titan, we're still going to be able to do the same science and explore Titan. And so we're all just excited to be continuing work on this project, moving toward flying on Titan. It does mean that there's additional work right now, in terms of replanning and looking at the schedule that we'll need to work to accommodate NASA's request to launch in 2027 as a result of the impact of the COVID-19 pandemic on the funding available in the next fiscal year. But we have plenty of work to do, and that's what we're focusing on. And like I said, everyone's just excited, moving ahead toward exploring Titan.
Morris:
All right. Well, that's about all the time we have for today. Join us again next week for another edition of Check 6, which is available for download on iTunes, Stitcher, and Google Play. Also, if you like what you're listening to, please give us a positive review. We'd love to hear your feedback. So thank you for listening and take care.
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