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NASA plans to launch a spacecraft to Titan (theatlantic.com)
538 points by the-enemy on June 28, 2019 | hide | past | favorite | 192 comments

A flying drone is a really solid idea for a Titan lander for a couple reasons:

* The surface atmosphere density is higher than Earth's (1.5 atm)

* Gravitational force is much lower (0.15g)

* We don't know a lot about the surface composition or topography, so wheels and motors represent a challenge

* Visibility may be poor, making visual navigation tricky (though that's also a problem for a flying vehicle I suppose)

I've heard people ask about "why a nuclear power source?" Saturn is 10x as far from the sun as Earth, so sunlight is about 1/100th as bright. In addition, Titan's atmosphere blocks most of that. There really isn't any other realistic option.

I hope it works and they take videos.

In addition to lack of solar energy, I wonder if nuclear power source is necessary to keep batteries or other electronics warm enough to function properly.

Conversely, on Titan, we won't need to worry about heat sinks as everything is kept at ~94K in a bath of liquid and frozen methane. Perhaps in a few hundred years AWS's most popular region for intensive compute will be under Titan's methane sea. High spin up cost, but cheap super-conduction environment once you're up.

Interestingly they actually exploit these cold temperatures to keep things cool. The Dragonfly Gamma-Ray and Neutron Spectrometer(DraGNS)'s gamma ray detector is mounted outside.[0] In most other probes the detector would need to kept cold with a cryocooler. [0]https://www.jhuapl.edu/techdigest/TD/td3403/34_03-Lorenz.pdf

Hah, I was always intrigued by the idea of placing solar cells on the bright side of Mercury and servers on the dark side. I wonder what other good options might exist in the solar system.

Mercury's whisper thin atmosphere won't be much use for cooling anything, though possibly the surface would be. However, the real problem is that Mercury isn't actually tidally locked anyway.

In certain regions on Mercury the temperature stays within 1 degree of room temperature less than a meter underground. http://einstein-schrodinger.com/Mercury_temperature.pdf It’s actually relatively habitable. http://einstein-schrodinger.com/mercury_colony.html

> In fact, if we delay until the distant future, or even 50 years or so, such an effort probably will become impossible. This is because us humans will consume the Earth's non-renewable energy and mineral resources almost completely within the next 50-100 years, severely reducing our discretionary income for costly activities such as space travel.

I wonder when that was written...

Likely around 2013 by the Wayback Machine.

Makes me think of the Gell-Mann amnesia effect.

You could have the facility move constantly to keep the facility straddled across the sunlight line. At the equator, this would require constantly moving at about 7 mph, though you could reduce the speed necessary by moving to higher latitudes.

Appears in 2312 by Kim Stanley Robinson.

They move the whole city around the planet at 7mph!! 10/10 would recommend

Sounds like Absolution Gap and/or a less annoying version of the Mortal Engines movie (please tell me the book was better than this).

Also features in Charlie Stross, Saturn's Children.

Or another scifi novel, West of January by Dave Duncan.

Also appears in Asimov's classic "I, Robot" collection, as a Powell and Donovan story called "Runaround"[1].

[1]: https://en.wikipedia.org/wiki/Runaround_(story)

To add to the vein of sci-fi novels using this idea: Inverted World by Christopher Priest. Well, similar concept but weirdified in the 1970’s fashion.

Yeah but if you break down...

Like in the scifi books?

Reminds me of the book Absolution Gap

Mercury doesn't keep the same side to the sun all the time. So you'd need to either bury everything deep enough (obviously not possible for solar cells), or keep them such that they're always on the terminator. The latter has been explored in Kim Stanley Robinson's work, 2312.


The poles of the moon. Have 3 "legs", and the alternate being the hot and cold areas.

Yes, you need equipment that can swap being hot and cold, but it's a lot easier to get to :)


I find it kind of funny that you think AWS will still be around in a hundred years.

This paper company was founded 771 AD: https://www.shinise.ne.jp/j_kyoto/voices/vol/48/48-d.html

It's not even the longest-lived company in the world. This construction company was founded in 578 AD and continuously operated until 2006 when it was bought by a larger company: https://en.wikipedia.org/wiki/Kong%C5%8D_Gumi

100 years ago was only 1919 -- here are some random companies from 1919 that I found on Wikipedia (ignoring for a moment that this is plainly surviorship bias):








Companies surviving for 100 years isn't quite routine but it's certainly not so rare that its surprising when one does. I don't think it's at all inconceivable that Amazon could stay open for a hundred years. It's made it past the first 10 years, the turbulent start when most companies are culled. I'd wager that the biggest threat to Amazon surviving to 100 is being broken up a la Bell/Standard Oil.

The Avedis Zildjian Company, now an American-based cymbal manufacturer, was founded in Constantinople in 1623. Hell, even Nintendo's 123.


A company lasts just 11 years on average on the S&P 500 now. Companies are surviving for shorter time periods now then they used to.

First off, what is your source for that average? This report (https://www.innosight.com/insight/creative-destruction/) has a much higher average, and forecasts a fall to 12 years by 2027.

Second, that's average time in the S&P 500 index. As noted and n the report, there are many reasons besides going under that companies drop off the index. That number doesn't really say much about longevity of the company.

Like with pre-modern human lifespans, there's a VERY long tail on that number.

For ones maybe more familiar to an American audience and/or to techies:

Bayer (1860s Germany), Johnson & Johnson (1886), 3M (1902), the Coca-Cola Company (1892), IBM (1911), HP (1939), Mitsubishi (1870), Wells Fargo (1852).

The italian bank Monte dei Paschi di Siena was founded in 1624, they even use some of the centuries old building as offices...it's not doing very well but it's still there

The oldest preserved share of any company is from 1288. It's since been merged, but it's still around.


Even after being broken up, AWS would still exist - it just wouldn’t be part of the amazon conglomerate

AWS is different from Amazon though. AWS is a cutting edge technology in a fast moving industry that is likely to be made obsolete in the next 20 to 30 years.

Heck, IBM is 100+ lol

That's a good point - the "waste" heat from an RTG (which is only about 5% efficient) is very useful in those extreme cold temperatures.

NASA makes a smaller RTGs for heating tasks, they can scale smaller if they don’t need to generate electricity.

Super fast compute, but awful ping…

To put it into perspective:


According to this (at the time of reading) a one way trip at the speed of light is ~75 minutes, so you will have approximately two and a half hours of ping.


Still, it raises an interesting question: how would a hypothetical Earth-Titan network protocol work?

That protocol exists, it is called Delay-Tolerant-Networking.


Can't do much about the time it takes light to get here, so I guess the answer is we'd have to learn to love 75 minute ping :)

Alcubierre warp drive powered Sneakernet?

If you can't be with the one you ping, ping the one you're with.

The InterPlanetary File System is a thing, it just isn't interplanetary yet: https://en.wikipedia.org/wiki/InterPlanetary_File_System

Batch instead of stream I'd reckon.

Perfect for mining bitcoin

Not really; if you find a block it will mostly likely have been beaten by someone else's block by the time yours reaches most nodes...unless there is a Saturn based side chain or similar.

This will sound crazy, and I'm not suggesting the consumer would deal with it directly, but I think we'll need coins for each planetary body and another one for the solar system that has a much longer block time. More scales would be useful, but these are the minimum. Repeat for each star, with MilkyWayCoin having an absurd block time.

It depends if the "most nodes" are on Mercury or on Earth.

Might be suitable for quantum computing ... Re. thin atmosphere and low gravity, humans could probable be able to fly wearing wings. So if we put a base there it would not be boring.

Never thought about this before, in theory does this bring super conductors closer to reality?

Why do you think they launched a deep space reviving network at re:invent last year?

Well we don't want to disturb the environment too much

The data rate from the surface of titan is abysmal. Even with a relay, we won't get much video, but man, I hope we get some.

From a scientific standpoint, there's really no value in downlinking video as opposed to still images. It costs several multiples worth of scarce downlink bandwidth, for a tiny gain in what there is to see of the same rocks at slightly different angles. Same reason we didn't have New Horizons at Pluto or the various Mars rovers do any video.

There might be some scientific value for taking video. One measurement where video might be valuable is measuring the saltation threshold, or the wind speed at which grains begin to move, of the surface using rotor downwash. These measurements are important to understand the dune pattern on Titan. This could be pretty weird as the dust on titan is believe to be made of something similiar to moth balls, which could stick to each other like packing peanuts due to frictional electrostatic charging.

[0]https://www.jhuapl.edu/techdigest/TD/td3403/34_03-Lorenz.pdf [1]https://www.news.gatech.edu/2017/03/27/electric-sands-titan

Why is bandwidth so scare still? Satellites in geosynchronous orbit on earth can do terabit/sec of total capacity now.

Obviously latency is going to be extremely high, but I can't really understand why data rates are still so low?

Inverse square law. For the same transmit power, your received signal strength diminishes with the square of the distance

That received signal strength is what determines channel capacity (C) which is the upper limit on the bit rate you can get.

see Friis and Shannon's channel capacity

[0] https://en.wikipedia.org/wiki/Friis_transmission_equation

[1] https://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theore...

Yes, I get that. But it seems that performance has barely improved since the 1970s despite the massive gains in telecommunication efficiencies since then. Or is the SNR so poor that even 1970s era technology was able to be close to the limit?

These are physical restrictions, not technological.

What about the laser technology NASA is developing? That should be a lot faster than current radio based technology?

Titan has smog in the visible spectrum. Details matter! The technology is also not that mature, yet.

Focusing a laser at that range requires a rather large diameter heavy set of optical components.

You will need a blinding-strong laser.

Because the signals have to travel so much farther and are so much weaker when they arrive. It's amazing that any data at all can be extracted from a radio signal that travels a billion miles.

Spacecraft transmit power and antenna size is limited. This means the amount of power that arrives at earth is rather low because microwaves spread out quite a bit with distance. The other issue is that NASA only has so many big radio dishes in the deep space network[0] to gather this small amount of power and extract a signal. Technology has improved, but in order to get much higher bandwidth we'd need bigger dishes. We also need at least three around the globe to get continuous coverage. Although perhaps by the time this mission lands we could have multi-kilometer aperture receivers on the ground or in space. Laser communication could allow for much higher bandwidth, because lasers have a shorter wavelength they don't spread out as much with distance. However, laser space communication is in its infancy and would not work well on Titan due to the smog.


Maybe workaround transmission power by reflecting and modulating a signal over an existing power source. Like a very big mirror with an LCD pixel in front of it.

"one over r-squared"

Latency is high, but the power you have to pump through an antenna / laser to get enough watts on the receiver goes up really fast with distance.

Here's a summary that touches on it if you'd like to learn more: http://www.qrg.northwestern.edu/projects/vss/docs/Communicat...

And here's a detailed derivation for voyager. https://space.stackexchange.com/questions/24338/how-to-calcu...

I don’t think you realize just how far away the outer solar system is.

Low transmit power. Long distance. Very low SNR at receiver.

Don't get your hopes down! It's still very possible that we'll get some good, if not real-time, video out of this!

Ah, we likely will not get real time video. Maybe APL has some tricks I'm not privy to. Source: I asked a DSN coms engineer.

There will be at least an hour delay. Saturn is pretty far

10 seconds of video from Titan would change the world. It's shame we don't have this from Mars already. So it would take a few weeks to transmit - we got time.

Now figuring out which 10 seconds to select and send to earth... that'll be interesting. An on-board cache of x GB data storage, with key frames taken every 30 minutes, would probably be able to select some pretty compelling 10 second segments.

What about the world would be different after getting a 10 second video from Titan?

It would be inspiring for me at least.(Assuming something was moving)

Send them all, just pick a likely-nice one for sending while the eyes of the world are on Mission Control.

Caching everything then sending it at leisure is working nicely for New Horizons.

No 4K flyovers for Instagram?

I mean sure, eventually, over many down link cycles. But not real time.

Space travel just makes it utterly clear there is on such thing as real time. Computing is constantly running up against the speed of light.

It's not about latency, it's about power required to transmit. From far away, you need to push lots of power through to get a readable signal on the receiver side. It's kinda-sorta like seeing a flashlight.

In a sense tho, at-the-speed-of-light is real time, as it's the maximum speed of anything.

If, as clock A nears the speed of light it appears that stationary clock B is slowing down, doesn't that mean that at the speed of light is no time? Does a photon in a vacuum arrive instantly at its destination? If a photon looks at another photon, does the other photon appear not to be moving at all, or... Ouch my brain.

> If, as clock A nears the speed of light it appears that stationary clock B is slowing down, doesn't that mean that at the speed of light is no time?

If clock A could reach the speed of light (which it can't), then, yes, clock B would appear to be 'frozen in time'.

> Does a photon in a vacuum arrive instantly at its destination?

From the perspective of any possible observer, no, it always appears to be traveling at the speed of light. If an observer could travel at the speed of light (which it can't), then, yes, it would appear as if it arrived instantly in the sense that clocks at both its source and destination would appear to be not running at all.

> If a photon looks at another photon, does the other photon appear not to be moving at all, or... Ouch my brain.

Yeah, this is tricky. Photons can't look or see – what could that mean as looking/seeing involves detecting photons (or, in the sense that something like echolocation is 'seeing', detecting a pattern of matter, e.g. sound)? In a sense, not moving at all or both moving at the same maximum speed don't seem to be much different, from the 'perspective' of a photon.

Somewhat related, this video describes how, if one could travel on a vehicle that could accelerate at a constant rate continuously for decades, one would eventually see the cosmic microwave background radiation as a rainbow ring because traveling closer and closer to the speed of light would shift the apparent frequency of the radiation first into the visible spectrum (and then beyond it).

My comment was mostly tongue in cheek, I know photons don't have eyes. :)

Not completely related, but you reminded me of something interesting I remember hearing about neutrinos. Apparently (HN physicists please correct me if I'm wrong), neutrinos have an extraordinarily tiny objective lifetime, and the only reason we can detect them is that, because they travel so close to the speed of light, they experience almost no passage of time in while in flight.

I kind of wish it had an airship counterpart. Inflating a dirigible there would take advantage of the same atmosphere + gravity benefits with the added bonus of not needing constant power to move around.

Good point: I seriously wonder if they considered a dirigible design. Buoyancy + directional propulsion does seem simpler in my space-novice opinion compared to a quadcopter. A blimp would be slower than a quadcopter, but nobody's going to be piloting the thing in real time, so that shouldn't matter.

Yes, that was a mission proposal years ago, a blimp and quads. It was not selected then or rehashed this time. In addition, a blimp only concept has been floated (ha!) as well.

Blimp only wouldn't be able to take ground samples easily

How does one test on earth, a drone for a different atmospheric and gravitational environment? Some great drone simulation techniques are going to come out of this project.

No problem. Large atmospheric chamber or controlled wind tunnel. Pump the pressure up or down, change the gas mixtures, whatever. Gravity, partially support the drone's weight. NASA is good at this stuff.

Yes that's how they tested the Mars drone.


Will this be the first-ever instance of nuclear-powered flight?


>> The Pentagon is aware of a Russian test of a nuclear-powered cruise missile but the system is still under development and had crashed in the Arctic in 2017.[17][18][19] A RAND Corporation researcher specializing in Russia said "My guess is they're not bluffing, that they've flight-tested this thing. But that's incredible."



I hadn't heard of the 9M730. That page links to one for the US Air Force's Supersonic Low Altitude Missile (SLAM) or "flying crowbar" of the 50s and 60s, which makes for fascinating reading: https://en.wikipedia.org/wiki/Supersonic_Low_Altitude_Missil...

This case is different though, using the fission reaction to generate electricity which in turn powers the electric motors among other things.

The nuclear powered missiles use the fission reaction to heat incoming air similar to how a jet engine works.

No fission reaction, just radioactive decay in Dragonfly's case. It will use an RTG (radioisotope thermoelectric generator) not unlike Curiosity and most missions to the outer planets to date.

Just a note - radioactive decay is is fission, since it involves a nucleus splitting apart.

No, not quite. One of the types of radioactive decay is spontaneous fission, but it's not relevant in the context of RTGs. Alpha decay (the emission of a 4He nucleus) might in principle be called "fission" but in practice is not. Beta decay involves no splitting whatsoever.

RTGs are heavy; I suppose this means that it'll park itself for a long time to charge its batteries and then do a quick flight and repeat. Which sounds like it could work pretty well for this use case.

On the other hand, a hot-air balloon kept aloft by excess heat from radioactive metal might be a more attractive option if we were selecting proposals based on awesomeness.

Does that mean a nuclear powered cruise missile could stay airborne until mechanical failure? That would make future warfare... interesting.

It isn't all that much of a game changer. Mid-air refueling means that bombers can stay airborne a long time. Four or five bombers rotating back and forth can maintain one "on station" continuously. So the capability is already there. This tech would just make it more scifi.

Why bother? Rocket fuel is cheaper than nuclear fuel and rocket missiles can already hit anywhere.

Because a nuclear-powered missile can in principle fly in circles at low altitude off your enemy's shores for months at a time without landing or refueling, ready to be called down at any time with no detectable warning.

Well, if I am your enemy, I sure as hell won't let your missile cruise around my shore for a month

The difference between rocket fuel as a power source and nuclear radioactive decay as a power source is like comparing C4 explosive and a log fire in your fireplace. Once it great for providing a huge, fast release of energy, the other is great for providing a slow, steady release of energy.

Cheaper, easier to mass produce, doesn't need an unusually special launcher, hard to distinguish from air to air and other defensive missiles, easier to disguise the number of warheads waiting in readiness, can take an indirect/stealthy course, hard to shoot down, can include smart tracking for moving targets like carrier groups.

Maybe so it can double as a shitty nuclear bomb. I'm gonna crash my small nuclear reactor into you.

NASA has been using nuclear powered probes for 50 years. It is called a redioisotope thermoelectric generator (RTG).


Unfortunately, there is a shortage of plutonium-238 to run these RTGs (see above story). I guess that will get resolved somehow.

The current Mars Curiosity rover is powered by an RTG. Since this is the first flying (post-landing of course) probe I suppose it will be the first nuclear powered flight of a planetary probe.

DOE has restarted Pu238 production. They're only making about a pound a year but they're still scaling up

America and Russia have both put proper fission reactors into space too.

Probably a dumb question, but how does the nuclear source work? Nuclear powerplants work by heating steam to turn a turbine. This drone won't have heavy water reservoirs so how does it convert the fission heat into electricity? Stirling engine?

Most nuclear power sources for space stuff works by Peltier effect. See Radioisotope thermoelectric generator.

radio-isotope decay -> heat -> Peltier stack -> electricity.

Advantages: no moving parts, no vibration, infinitesimal mass change, exceedingly reliable. 'Small'

Disadvantage: Efficiency kinda crummy at ~5%. Slowly loses output as fuel decays and the Peltier stack degrades.

Probably an RTG [1], it's what NASA normally uses. It's thermoelectric [2]: Heat (in this case from radioactive decay) is converted directly into electricity without moving parts.

[1] https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_ge...

[2] https://en.wikipedia.org/wiki/Thermoelectric_effect#Seebeck_...

Just like nuclear sources work on sattelites. You produce heat with fission or nuclear degradation and then thermoelectric conversion.

Why arent we just mass launching probes to all the planets?

Serious question: Why is it not OK to have a standard sensor array on every planet in the solar system?

> Why arent we just mass launching probes to all the planets?

Because we don't live in a fictional sci-fi universe where launching things into space doesn't cost a ridiculous amount of money, time and effort, and can't only be done at certain times from certain locations in order to get the orbits right, or where years of effort and millions of dollars (or whatever currency) don't also go into building the things to be launched into space. The world has better things to spend its money on.

>Why is it not OK to have a standard sensor array on every planet in the solar system?

What is a "standard sensor array?" We've already sent a lot of probes to a lot of places[0] around the solar system. But read the rest of this thread - it's a lot more complicated than it seems. Also, remember how hostile and difficult the solar system can be. Jovian planets don't even have a solid surface to be "on," for instance, and Venus has a pressure of 90 atmospheres and it rains sulfuric acid.


To the second question: since each mission is expensive and time-consuming, scientists reasonably want the best sensors for each mission.

That's both the tech upgrade during the n-year coast phase, and the investigation upgrade as they work out new things to investigate.

It's not as straightforward as spamming the system with cameras. That's bound to happen more, after the MarCO cubesats had success flying along with Insight.

What about hydrogen fuel cells? Isn't the whole place basically nothing but fuel?

it's all fuel, but there's no oxidizer

Those work by combining H with O. Not much available oxygen there.

is there no wind on Titan? What if there's a windstorm and it crashes the drone? At least a vehicle could resist crashing, unlike a drone.

> Scientists suspect that Titan might even have water—real, actual H2O—lurking beneath its surface.

Not just a little, but a lot of water:

> The density of Titan is consistent with a body that is about 60% rock and 40% water.

> ...

> Pre-Cassini models of impact trajectories and angles suggest that where the impactor strikes the water ice crust, a small amount of ejecta remains as liquid water within the crater. It may persist as liquid for centuries or longer, sufficient for "the synthesis of simple precursor molecules to the origin of life".[107]


> The density of Titan is consistent with a body that is about 60% rock and 40% water.

That's extremely misleading.

First, rocks have different densities. Sandstone weighs 2g/cc, basalt weighs 3g/cc, so a density "consistent with" 50% basalt, 50% water would be equally consistent with 100% sandstone, not to mention the possibilities of rocks with drastically different densities such as pumice or iron.

Secondly, we are pretty certain Titan has large quantities of liquid methane and/or ethane (check the same Wikipedia link) which certainly account for some of the difference in density between Titan and other rocky bodies.

So yes, there is water on Titan, but it's about as likely to be 40% water as it is to be 40% cheese or 40% iPhones, even if its density suggests a makeup consistent with that.

> That's extremely misleading.

You're right - I should have said: "potentially a lot of water."

Sandstone (silicon oxides) seems unlikely given the reducing nature of the atmosphere. I'm no expert, but when liquid hydrocarbons rain down, there's not a lot of free oxygen on the surface at least. Ditto for basalt, which is about 40-50% silicon oxide. Still there could have been some process by which the interior sequestered most of the planet's oxygen, leaving what remained on the surface as water.

In contrast, liquid hydrocarbons seem plausible given the stuff rains down from the atmosphere and its density (methane ~0.5 g/mL, -162 C).

Titan's orbit provides some evidence consistent with a body that's more dense at the surface than at the core. One explanation is large amounts of subsurface liquid, but there are others:


There's been some discussion about the apparent massive block of ice in Titan's surface, so the idea that Titan's putative subsurface ocean could contain water isn't too wild a speculation:


A subsurface ocean composed of water and liquid hydrocarbons would be consistent with everything I've been able to find so far.

Thanks, I seemed to remember reading about H2O on Titan. When the article didn't mention it, I thought I was confused. Didn't bother to look it up. Your comment furthered my understanding.

I think this type of projects would be a great bipartisan way to unite the country, as happened during the space race in the middle of the 20th century.

It might also revive some interest in STEM.

Dragonfly is a super exciting mission. Between it and the other New Frontiers finalist, CAESAR, it makes sense that Dragonfly would win because the ESA just announced their own comet exploration mission (the Comet Interceptor, which is 3 spacecraft that will loiter together at L2 until an interesting comet or Oumuamua-like interstellar object wanders into the inner solar system).

Anyway, Dragonfly: RTG-powered quadcopter to fly around Titan's low gravity and dense atmosphere. Over its 2.5-year primary mission, Dragonfly should cover ~180 kilometers of territory.

Self-promotion: If you're into space exploration, check out our weekly space industry newsletter called The Orbital Index (https://orbitalindex.com). We're going to cover this in depth in next week's issue.

That's a huge range!

I love this mission. From a science point of view it’s probably good to send similar and well tested rovers to Mars. But to me it gets boring.

I think NASA used to get a lot of fascination from doing the seemingly impossible like flying to the moon. So I think a mission like this will be fascinating for a lot of people. Also it may spawn off a lot of technology. I hope for a submarine mission to Europa.

I think a flying mission is actually superior to a rover as it can cover far more ground and reach some sites that wouldn't be feasible for a rover. And Titan is uniquely suited to using flight to explore as its gravity is a factor 7.25 lower and its atmosphere a factor of 4.4x denser. That means it's about 30 times easier to hover and covering the same distance is at least 7 times as efficient as on Earth, besides having lower terminal velocity.

Even this relatively "inefficient" quadcopter (8 rotor) design could cover dozens of miles (~60km, more than any Mars rover has ever done in its entire mission) in a single hop (which could be recharged by the MMRTG in a single week-long night), although prudence suggests shorter hops at first. That means in principle over its ~10 year lifespan (assuming it can last as long as Cassini did...) it could nearly circumnavigate the entire planet (diameter of ~5000km, day period of about 16 Earth days) while visiting dozens of sites. Granted, range will likely be much more modest as the mission operators will be focusing on not losing this valuable asset, but it shows just how powerful the ability to fly could be. It can visit more sites than all the surface robotic missions to Mars combined. In that sense, it's a fantastic scientific value. And I think the public will absolutely love it.

Information from the Dragonfly proposal document: http://dragonfly.jhuapl.edu/News-and-Resources/docs/34_03-Lo...

> over its ~10 year lifespan (assuming it can last as long as Cassini did...)

Cassini wasnt exposed to solvents, rocks and didn't have moving parts (at least not to keep it aloft). Have they made a public statement about lifespan?

Yes, the planned mission time is 2.7 years. MMRTG should provide sufficient power for at least 8 years.

I would guess you can't take much instrumentation on a drone so a rover has advantages there. Anyway, I am excited about this.

Same order of magnitude, actually. Dragonfly is about half the mass of MSL, and because it's so easy to hover, it can have a pretty decent scientific payload. A rover with an arm can more easily approach specific rocks and sample them, though. But Titan is a very mysterious world that we can't get a super good look at from orbit (and which we've barely even glimpsed on the surface), so being able to fly around to many sites is going to be very helpful. Titan has some really interesting and varied geography, too, so the pictures are going to be really cool.

Damn! That's a BIG drone. Should have read closer but now I see 450kg. MSL is like a small car.

This is why theres a helicopter going to Mars.

Indeed... although on Mars it's about 15 times harder to hover than Earth due to the 50x lower atmospheric density.

Isn't there wind on Titan?

It's interesting that there is no existing (or planned) launch vehicle that could perform a direct injection for this mission. Getting to Saturn is really, really hard, and without multiple gravity assists from the inner solar system it would be simply impossible.

Too bad it results in an 11 year transit time though! Flying direct would save almost 8 years of that...

I don't think that's accurate, if you're willing to allow (perhaps multiple) kick stages. A naive Hohmann calculation will be misleading as you can do a massive Oberth burn deep in Earth's gravity well before leaving, and entry will be done aerodynamically (not propulsively).

Even spaceX's starship/BFR with LEO refuel wouldn't work?

The delta-v required for a trip to Titan, according to this[1], is 28.43 km/s. Optimistically, a fully re-fuelled startship in LEO has ~10km/s of delta-v to spend, afaik.


Starship can do better than that if stripped down to expendable use. About 13km/s: https://twitter.com/elonmusk/status/1111798912141017089

Also, you're reading that delta-v map completely wrong. The red arrows mean you can aerobrake. So it only takes about 4.1km/s to reach Saturn if you start out at a highly elliptical (near escape) Earth orbit and do a large departure burn at perigee. (See here: https://en.wikipedia.org/wiki/Delta-v_budget#Interplanetary ...the 7.3km/s if the burn is done starting in LEO, minus the 3.2km/s benefit you'd get if starting near c3=0. Or you add up the numbers on your delta-v map that can't be done using aerobraking, and you get the same 4.1km/s delta-v if starting from Earth escape.)

...so a fueled up Starship could send a payload direct to Titan and still have enough propellant to propulsively brake back to Earth orbit immediately after sending the Titan payload on its way.

(But that's just one option... Lots of other vehicles could do it if you used refueling or some high performance kick stages or in orbit rendezvous.)

So it would work! Thanks for the analysis.

Maybe answering my own question with some further thought. I guess even if it could get there, it likely couldnt return which would be a big waste of a reusable starship.

Why do you think it would be unable to return? I'm curious.

Naively, a round trip requires twice the delta-v, which means you need to launch with a lot more than twice the fuel.

Maybe they could produce more fuel and oxidizer in situ, and maybe Earth is a more attractive target for aerocapture, and maybe gravity assists line up better one way or the other, but it's not a bad starting point to assume a round trip is far more expensive than a one-way trip.

I'm not sure on what basis he thinks Starship might be able to get there in the first place.

Yeah that was my thinking. And I didn't have a basis for thinking it could get there in the first place which is why I asked the initial question. I didn't realize just how high the delta v requirements were for Saturn.

Yeah, I didn't mean to accuse you of making assumptions; I just wanted to call out one of the obvious well, actually replies that my own comment might have received.

It is an interesting question for sure, especially given that one of the stated goals for Starship (IIRC) is to enable exploration of the outer planets.

Sorry for the late reply. Titan has lakes of liquid methane rather than water. Raptor is a methalox engine. I think refueling on the planet would be quite possible.

There is no doubt in my mind that with the right equipment on the surface of Titan you can refine methane out of the lakes, electrolyze oxygen from the water ice of the crust, and fuel a Starship.

Can you fit that equipment in a single Starship, by mass and volume? Is that what we're talking about here? No idea.

> Getting to Saturn is really, really hard

Why is that?

Just the speeds required. This mission will effectively have a speed of about 17km/s faster than the speeds just to get to low Earth orbit after its final gravity assist.


Gravity is a b..ch :-)

This is great news. When Huygens landed on Titan, the images sparked my interest in physics and planetary science, and eventually I went on to do research in solar physics.

What’s Titan look like this time of year?


Exciting to see reality (almost) following fiction. Gattaca is an excellent film, if you haven’t seen it.

Mad props to the scientists and engineers making something like this possible. In an alternate life I would choose to be an astrophysicist or rocket engineer. Hopefully I will be more intelligent in the next life.

Associated read: "Titan" by Stephen Baxter. Hard SF describing a manned mission to Titan using present-day level tech; great attention to detail, but be warned that the overall tone is rather depressing.

Myself, I'm absolutely fascinated by the confirmed hydrocarbon lakes and rivers on Titan and can't wait to see actual optical images from up close (so far we only got synthetic-aperture radar images [0]).

[0] https://en.wikipedia.org/wiki/Titan_(moon)#Lakes

I can't believe it's been that long since Huygens was sent to Titan. I remember listening to some radio show (NPR?) that was broadcasting the touchdown live.

Also, it's interesting that since they can't study Titan very well visually (you can't point a telescope at it and map the surface like you can with Mars) they're planning on sending a rover that can cover far more distance since they have less idea what will be "interesting" beforehand.

I worked on prototypes of the experiments in the Surface Science Package at uni in 1991 - boy do I feel old!

Even then we were speculating on flying or floating probes for future missions there. At the time it was assumed that the surface could well be entirely liquid.

I'm interested to see how this mission is couched from a PR standpoint (specifically the long long transit time). Emily Lakdawalla from the planetary society had a good tweet related to this: https://twitter.com/elakdawalla/status/1144492247032799238?s...

I also found a really good write-up of the mission here: http://www.4erevolution.com/en/dragonfly-un-drone-a-propulsi...

It is nice that multiple public sector agencies worldwide are doing space travel now, with the private sector close behind.

Relying solely on NASA and the political funding machinations of the White House and Congress would put our understanding of the planets very far behind.

I'm confused by your comment. this is absolutely a NASA mission, subject to all the whims of congress that any other is.

APL has long bid on missions and instrument proposals just like other institutions.

Its just a statement of fact.

NASA likely wouldnt even have revisited this moon without the European probe taking pictures under the atmosphere

It is nice that multiple public sector agencies worldwide are doing space travel now

Ah, I see. I agree, worldwide collaboration and competition is very healthy for a space program.

>To protect the hazy moon, engineers deliberately shoved Cassini into Saturn, a gaseous planet incapable of hosting life.

Can we be 100% sure there isn't life.

We can be sure that Earthling life wouldn't survive in Saturn, thus posing no threat to hypothetical Saturnian biology.

Almost all Earth life sure, but I wouldn't bet on absolutely none being able to survive. NASA can't even completely sterilize their vehicles and payloads already.

The spacecraft vaporized in Saturn's atmosphere

They are planning to send it up in 2026? What are they going to be doing for 6+ years?

They just announced it today. They don't have a probe yet. They have to design and build and test all of the equipment and systems that are going to go into space. I think it's pretty reasonable for this to take 6 years.

NASA is really good at planning future missions. Implementing them? I've heard hundreds of fantastical half-baked ideas and very few of them materialize over the course of my 46 years on earth.

Eh, almost every NASA robotic mission that has gotten this far in the design and selection process has also flown. They're way past the "fantastical half-baked idea" stage. The financial reality is that NASA can only finance one or two billion-dollar missions per decade, and the competition is rather fierce. To be selected as the New Frontiers class mission of the late 2020s is a big deal, and you can be sure that at this point the proposing team has made a very solid case for their mission.

Yup. The robotic program has a very good track record of successes, even for crazy stuff like the Mars Science Laboratory’s sky crane descent stage: https://m.youtube.com/watch?v=Ki_Af_o9Q9s

It’s the human spaceflight program that has had the, um, difficulties. There are signs of hope, though.

Their robotic programs are generally great successes though - Mars rovers, Saturn, Pluto for the most recent achievements. Incredible stuff, and unmatched.

Probably because the senate keeps their corrupt hands off of these types of missions.

Venus and Titan have in common that probes landing there tend to only operate a few minutes before failing due to the extreme conditions.

A helicopter sounds great, but perhaps it would make sense to try to simply make a probe that can stay alive there long enough to do anything other than send a couple pictures back.

> Venus and Titan have in common that probes landing there tend to only operate a few minutes before failing due to the extreme conditions.

Venus, definitely. Titan though? Huygens is the only probe that's ever touched down there, and it's operational life was tied to its battery life and the fact that Cassini wouldn't be around very long to listen to it. Cassini was on a flyby trajectory, not an orbit around Titan, so as soon as the orbiter went over the horizon, that was it. Outfitting Huygens with enough power to stay on for future flybys would require MUCH more power, a job for which only an RTG would be appropriate since solar is out of the question that far out/under that atmosphere, and batteries just flat out don't last that long.

Nothing about the moon itself prevented a long operational life.

This is not true. The only reason the previous probe (Huygens) only lasted a few hours is because it was battery powered (and the battery wasn't particularly large). This probe will carry a power source powered by the radioactive decay of Plutonium 238 (virtually all the radiation being alpha particles, which are easily blocked by the casing of the power supply and thus will not hurt the electronics or ground crew) that can provide 50-100 Watts of power for years or even decades.

As I mentioned elsewhere in this thread, before Huygens we expected that the surface might well be entirely liquid, giving us at best only a few minutes to run the experiments and return the data before it sank. There was no point carrying too much battery capacity in that case.

No. Huygens was designed to float and last hours. The battery capacity is why it lasted so short.

That's what this is. It's much easier to heat something in the cold of Titan than to cool something in the heat of Venus.

I'll be 43 when this craft arrives there. Damn.

I’ll be 43 in March. Damn.

What. How are they going to detect life on titan? They can't even detect life on mars. I mean to say, even when we know the kind of life we are looking for we get confused about how to confirm or deny its existence. So they want to design a small flying drone that works in extremely hostile conditions, that also has the kinds of sophisticated instruments needed to look for life? And not just life, life of potentially a completely unknown form, given the widely different surface conditions. This just seems like a weird mission. Finish up the Viking labelled release experiments on mars first, then go take a look in the mid Venusian atmosphere. Then take a gander at europa.... Weird mission

> Finish up the Viking labelled release experiments on mars first, then go take a look in the mid Venusian atmosphere. Then take a gander at europa

This is exactly why I like HN. Here, you have the true experts contributing valuable science with their credentials laid bare, as opposed to the pencil pushers at NASA who probably only approved this mission because it sounded cool.

I think you need to relax the idea of 'detecting life' towards 'detecting evidence of life', i.e. evidence of populations of locally-entropy-defeating systems that reproduce.

Once you relax the requirement that 'answers' must be 'yes or 'no' to 'more likely' or 'less likely', it should be clearer how one would go about searching for life. For one, is there chemical activity one wouldn't otherwise expect if there was no life?

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