Titan Colony

[Eric Hedman]

I found this article that had been originally published in Scientific American in 2016 about why Titan is the best spot in the solar system for an off world colony:

https://getpocket.com/explore/item/let-s-colonize-titan?utm_source=pocket-newtab

[Shevek23]

I like Titan a lot, for a bunch of reasons.

There are three big drawbacks:

1) Saturn is a hell of a long way away. If we can't make superadvanced ships that can get there in a couple months--and for transit times like that we are probably looking at torch ships, or anyway something that can maintain a pretty serious thrust, a tenth of a G or so, for the entire duration, so that's basically a torch ship lite--then crews going there would be exposed to cosmic rays with essentially zero protection for years.

Conceivably we could make Battlestar Galactica. That is, make a ship that has CR absorbing walls some 10 tonnes per square meter in mass. We might get that down to 6 or maybe 5 tonnes, but that would be the red line limit I think. Such a vessel would have really stupendous mass, and it gets much worse per crew member the smaller we make it. Basically to be cost effective we would be talking making a full on multiple thousand person space habitat, and then putting engines and fuel tanks on it. We can write stories about this, without having to imagine they invented any technology we don't have now. Before it is economically possible to actually do it though, I would think we would have more advanced tech.

Another advanced tech would be to put the crew into hibernation. If the hibernation process also by some amazing miracle rendered people less susceptible to CR damage, we could be in luck then. But it hardly seems reasonable to anticipate that! I'd expect the reverse, if you have people in torpor bordering on a medical coma, their metabolism somehow slowed down, I'd think any mechanisms the body has to repair ionizing radiation damage as many theorize we do would be weakened and slowed too, and a given rate of dosage will therefore be multiplied in its damaging effect. So the main benefit of going into suspended animation would be to be able to confine people to very small little boxes, coffins in effect, and that gets the volume that needs to be shielded from CRs down. But a decent sized crew is going to still require a ship that is mostly CR shielding, plus of course anything anyone actually needs at Titan.

Without any of these rather science fictional, even at this late date, options, the first and last being entirely speculative SF science albeit vaguely plausible, Saturn and therefore Titan are just plain out of reach.

(I also think if you do the math for Starship delta V to 10 AU on a Hohmann orbit, aside from the trip taking years, the mass ratio is still forbidding. If we invented a Marvel comics super-serum tomorrow that renders people immune to cosmic ray damage, and picked a crew who are prepared to spend several years coasting out to Saturn, we'd still need to come up with a plan for the dang rocket to launch them!)

2) Colonizing Titan has many advantages, but a big drawback is the low surface gravity. Titan is bigger than Luna but its surface gravity is lower, at 1/7 G or so. I think the chances are slim to none that human beings can be conceived, gestated, birthed, and raised from infancy to adulthood in such conditions. I have notions of gigantic centrifuges (actually, train car habitats running on banked tracks) and my personal guess is, people can go back and forth between adequately high G and low G without ruining their health too much. That's just a guess though, we don't know. It is conceivably possible that Lunar G, and even Titan surface G, can serve. That would be nice to know. But it hardly seems a smart bet!

3) Power sources? In a Venus cloud colony, there is lots of sunlight for solar power half the time. On the Moon or Mars, the sun is there half the time, minus major darkening during Martian dust storms, and on Mars solar intensity is half that on Earth.

Given power, for heat and other purposes, I would face trying to live in a 100 K environment. It is a matter of insulation--and turning the heater on.

But where will this wattage come from on Titan? At Saturn the solar intensity is down to 1 percent that at 1 AU.

Two possibilities--nuclear power, and wind power.

Nukes on the Moon or Mars are first of all closer to Earth for replacement fissionable "fuel" when a given installation is too depleted to keep running. That would be expensive which is why I figure solar power is the way to go really. The only way to go on Venus IMHO though some applications might benefit from heavy nuclear power sources (I am talking cloud colonies floating at 55 km above the datum, not attempting to land on the surface!) 10 AU out is a long way to have FedEx ship you new fuel units though!

So on the Moon, or Mars, it is not inconceivable extensive exploration will find fissionable materials deposits for a domestic nuclear fission processing industry.

I put the chances of that as slim to none on Titan though! Titan is largely made of ice, and other materials that are volatile at Earth temperatures. There are probably all sorts of fissionables and other heavy metals, but they will have sunk down to the core of the moon. What can be dug up near the surface will not include much in the way of uranium or thorium! That's my guess.

Now one thing I like about Titan a lot is that it will be relatively easy to make spacecraft that take off from its surface, climb up until the atmosphere is thinner, then blast off on to low Titan orbit--and from there, Titan is spang in the middle of Saturn's larger system of moons. It should be easy to go over to other moons and while most of them are iceballs too, they mostly won't be so differentiated, also they will be peppered with meteor collisions, which for impactors that are themselves orbiting Saturn and falling onto quite small bodies, will have rather low energy and so most of their material might be found scattered in a rather small area. Titan colony might be able to profitably mine the other moons for heavier metals and so forth.

But that's a long shot.

Meanwhile, there might be wind power. The winds are not strong, usually anyway, near the surface, but as one climbs up, the atmosphere is circulating. At a moderate altitude, the air might still be thick enough to bear a hydrogen aerostat or even a kite aerodynamically lifted, and tethered to the ground, and support a wind turbine power generator.

This could be what makes routine human life on Titan possible, assuming the low gravity is not a fatal barrier. Given power, we can make good insulating and air-containing materials, and with enough layers and enough power flowing in reliably, keep these habitats warm, and power lights to grow plants, and so forth. Given that, and rocket ships of some kind to go to other moons on expeditions to fetch back any heavier elements required, in situ light element resources would seem pretty adequate.

The third issue is then the most negotiable. Saturn's sheer distance, and Titan's low gravity, cannot be wished away so easily. I like Titan, but I don' think it is the realistic place to set our eyes on today.

[Oli]

From the article:

On the surface, vast quantities of hydrocarbons in solid and liquid form lie ready to be used for energy. Although the atmosphere lacks oxygen, water ice just below the surface could be used to provide oxygen for breathing and to combust hydrocarbons as fuel.

*facepalm*

[TripleSeven]

I found this article that had been originally published in Scientific American in 2016 about why Titan is the best spot in the solar system for an off world colony:

https://getpocket.com/explore/item/let-s-colonize-titan?utm_source=pocket-newtab

if we can get there the moons of Jupiter and Saturn are probably the key places for human settlement...sadly we are at least a century away at current progress

[qraal]

I like Titan a lot, for a bunch of reasons.

There are three big drawbacks:

1) Saturn is a hell of a long way away. If we can't make superadvanced ships that can get there in a couple months--and for transit times like that we are probably looking at torch ships, or anyway something that can maintain a pretty serious thrust, a tenth of a G or so, for the entire duration, so that's basically a torch ship lite--then crews going there would be exposed to cosmic rays with essentially zero protection for years.

A SpaceX Starship can do the mission in 2 years flight-time, assuming a refuel in the Earth-Moon Lagrange Point 2, with aerobraking at destination. Re-entry is at ~14 km/s, which might be brutal. I'm not sure of the braking profile details.

Another advanced tech would be to put the crew into hibernation. If the hibernation process also by some amazing miracle rendered people less susceptible to CR damage, we could be in luck then.

From what I've read, the radiation susceptibility is lower, as the damage has less chance to multiply (i.e. cancers/mutations). But we don't have a huge biomedical data set to claim the damage is insuperable. Contra news-mongering work giving massive prompt doses to mice, which is not the same as lower doses over time to humans.

Without any of these rather science fictional, even at this late date, options, the first and last being entirely speculative SF science albeit vaguely plausible, Saturn and therefore Titan are just plain out of reach.

Hasn't been tried so we really don't know.

(I also think if you do the math for Starship delta V to 10 AU on a Hohmann orbit, aside from the trip taking years, the mass ratio is still forbidding.

It's not, if ISRU is available at the other end. But that's true for Mars too.

2) Colonizing Titan has many advantages, but a big drawback is the low surface gravity. Titan is bigger than Luna but its surface gravity is lower, at 1/7 G or so. I think the chances are slim to none that human beings can be conceived, gestated, birthed, and raised from infancy to adulthood in such conditions. I have notions of gigantic centrifuges (actually, train car habitats running on banked tracks) and my personal guess is, people can go back and forth between adequately high G and low G without ruining their health too much. That's just a guess though, we don't know.

Agreed with your last point.

3) Power sources? [..]

Meanwhile, there might be wind power. The winds are not strong, usually anyway, near the surface, but as one climbs up, the atmosphere is circulating. At a moderate altitude, the air might still be thick enough to bear a hydrogen aerostat or even a kite aerodynamically lifted, and tethered to the ground, and support a wind turbine power generator.

That's a fascinating option. The super rotation in the higher atmosphere could be a better power source than here on Earth - here, they're still working on achieving it. Once it's proven on Earth, then extrapolating to Titan will be reasonable.

Titan is a LONG way, but it's not quite as impossible as a first glance would conclude.

[Shevek23]

...

A SpaceX Starship can do the mission in 2 years flight-time, assuming a refuel in the Earth-Moon Lagrange Point 2, with aerobraking at destination. Re-entry is at ~14 km/s, which might be brutal. I'm not sure of the braking profile details.

Can you give me the orbital elements on that?

I have in fact been working on it and it seems to check out, but I haven't got the delta-V at Earth launch down below 17,000 m/sec yet. To be sure with buddy tankers, possibly disposed of, it might work out--I don't see how staging out of L2 is our friend though, Oberth effect, burning nearly skimming Earth's atmosphere, is a better friend.

Now regarding the atmospheric entry at Titan--a Hohmann orbit to Saturn takes six years, but when you get to Titan the encounter speed is well under 6 km/sec.

Barreling in at 14 km/sec is problematic! I don't think you've considered the big problem there. Let me explain:

I've seen Musk tweet out "13 km/sec" as a goal for SS, not going as high as 14 though. The faster SS can survive an entry the better, but it will have a realistic upper limit. But this is not the big problem (nor am I talking about the speed of encounter of Earth on a reciprocal return to Earth 2 year trajectory, that's likely to be another show stopper though).

No, I mean this--aerobraking at a small body like Titan at high speed relative to its own orbital speed involves having to force the ship down, because the initial grazing speed is way above escape velocity--at escape velocity you need to aerodynamically provide down force double the gravity field, at some multiple of escape velocity it rises as the square of the ratio, and the higher the speed is relative to orbital, the longer you have to angle the entry angle of attack to force the ship down and not go skipping off.

Now Titan of course has a low gravity, and furthermore the air is so thick that the altitude where air is the right thickness for initial braking is way up there on a small radius, so gravity there is lower and radius of the circle (well, spiral) as you brake is higher, which helps. Have you done the math on how high the acceleration is to stay in the circle? I eventually did--I didn't look into the partial relief we might get from coming in some hundreds of KM above the surface, but just taking the basic parameters of Titan as inputs, I figured that arriving at 14 KM/sec, we need to hold the ship down with 75 m/sec^2, that's 7.5 G!

This is a showstopper several ways--to begin with neither ship nor cargo nor crew are likely to be able to bear that stress; equally importantly, thermal flux is the multiple of force times speed, and here both speed and force are way above design standards--the ship will in fact melt!

We have to come in gentler than that!

...

({me}I also think if you do the math for Starship delta V to 10 AU on a Hohmann orbit, aside from the trip taking years, the mass ratio is still forbidding.

It's not, if ISRU is available at the other end. But that's true for Mars too.

Strangely enough, I do recall that SS takes advantage of aerobraking when possible, though you can't assume that it can land on just any planet with an atmosphere at whatever crazy speed one likes! There are some limits, but of course I was talking about using aerobraking and after that on Titan, ISRU is partially a matter of putting a hose on a convenient methane pond. It's more than that, we have to filter and check the methane--but by golly we don't have to synthesize it! ISRU is mainly a matter of separating oxygen out of ice.

But this is available to us if and only if we can 1) send the ship on a suitably energetic initial trajectory and 2) said ship survives the entry attempt! It is these limits, one burn and one landing, i am looking at, not being silly and imagining SS needs to carry its return propellant.

...

3) Power sources? [..]
{me}
Meanwhile, there might be wind power. The winds are not strong, usually anyway, near the surface, but as one climbs up, the atmosphere is circulating. At a moderate altitude, the air might still be thick enough to bear a hydrogen aerostat or even a kite aerodynamically lifted, and tethered to the ground, and support a wind turbine power generator.

That's a fascinating option. The super rotation in the higher atmosphere could be a better power source than here on Earth - here, they're still working on achieving it. Once it's proven on Earth, then extrapolating to Titan will be reasonable.

Titan is a LONG way, but it's not quite as impossible as a first glance would conclude.

I think your 2 year trajectory cannot work, mainly because of the severe G stress and hence heating during entry at Titan.

As for air borne high atmosphere wind turbines I can hardly take credit for that basic idea--but I have never seen a version where the turbines are borne on an aerodynamic structure, aka "kite"!

Balloons work real well on Titan, due to the dense atmosphere and very low temperature.

[qraal]

...

A SpaceX Starship can do the mission in 2 years flight-time, assuming a refuel in the Earth-Moon Lagrange Point 2, with aerobraking at destination. Re-entry is at ~14 km/s, which might be brutal. I'm not sure of the braking profile details.

Can you give me the orbital elements on that?

I have in fact been working on it and it seems to check out, but I haven't got the delta-V at Earth launch down below 17,000 m/sec yet. To be sure with buddy tankers, possibly disposed of, it might work out--I don't see how staging out of L2 is our friend though, Oberth effect, burning nearly skimming Earth's atmosphere, is a better friend.

I forgot to clarify it's launch from EML-2 into an Oberth burn very close to Earth :-)

[edzieba]

No, I mean this--aerobraking at a small body like Titan at high speed relative to its own orbital speed involves having to force the ship down, because the initial grazing speed is way above escape velocity--at escape velocity you need to aerodynamically provide down force double the gravity field, at some multiple of escape velocity it rises as the square of the ratio, and the higher the speed is relative to orbital, the longer you have to angle the entry angle of attack to force the ship down and not go skipping off.

An alternative would be to aerobrake around Saturn instead. That comes with some issues of its own (chiefly radiation) but allows for a longer braking trajectory through lower density atmosphere.

As for air borne high atmosphere wind turbines I can hardly take credit for that basic idea--but I have never seen a version where the turbines are borne on an aerodynamic structure, aka "kite"!

There are several kite-lifted turbines currently undergoing testing, including baloon-aerofoil hybrids and ones that utilise autorotation of the turbine blades themselves to provide aerodynamic lift rather than a fabric canopy.

[Pete]

From the article:

On the surface, vast quantities of hydrocarbons in solid and liquid form lie ready to be used for energy. Although the atmosphere lacks oxygen, water ice just below the surface could be used to provide oxygen for breathing and to combust hydrocarbons as fuel.

*facepalm*

WHY the facepalm?
"Mining" Oxygen from water deposits will need to be done in any case, for life support.
Canned oxygen, plus a nice scoopful of lakejuice (mostly Ethane) will serve just *fine* as a power source for vehicles, localized heating, power fuel cells, etc.

No-one is suggesting using the combustion of this oxygen as PRIMARY energy source, of course. That would be stupid, as extracting it from the water (and getting the water out in the first place) will require a lot more energy.

[edzieba]

From the article:

On the surface, vast quantities of hydrocarbons in solid and liquid form lie ready to be used for energy. Although the atmosphere lacks oxygen, water ice just below the surface could be used to provide oxygen for breathing and to combust hydrocarbons as fuel.

*facepalm*

WHY the facepalm?
"Mining" Oxygen from water deposits will need to be done in any case, for life support.
Canned oxygen, plus a nice scoopful of lakejuice (mostly Ethane) will serve just *fine* as a power source for vehicles, localized heating, power fuel cells, etc.

No-one is suggesting using the combustion of this oxygen as PRIMARY energy source, of course. That would be stupid, as extracting it from the water (and getting the water out in the first place) will require a lot more energy.

You need to crack that water to get that Oxygen (electrolysis). If you then go and use that O2 to burn with a hydrocarbon to generate that energy, you've make a net energy loss.

[Shevek23]

...

WHY the facepalm?
"Mining" Oxygen from water deposits will need to be done in any case, for life support.
Canned oxygen, plus a nice scoopful of lakejuice (mostly Ethane) will serve just *fine* as a power source for vehicles, localized heating, power fuel cells, etc.

No-one is suggesting using the combustion of this oxygen as PRIMARY energy source, of course. That would be stupid, as extracting it from the water (and getting the water out in the first place) will require a lot more energy.

You clearly understand the basic physics involved. The oxygen is not free oxygen, so our power supply has to be something else.

I can't speak for the person writing the facepalm, but I do fear you are underestimating how stupid popular science writers can sometimes be.

I have a whole rant against those people who talk about cloud colonies at Venus without doing the math and realizing it makes a huge difference there whether we use hydrogen or air for lift gas, and air or even pure nitrogen is quite inferior--but the main point here is the artists who then draw pretty pictures of cities in bubbles with skyscrapers nearly touching the top of the bubble. Even if they were using hydrogen and not air for the lift, it cannot be like that! The volumes required would dwarf suitable structures. These artists did not do the math. And of course that is supposed to be air, not hydrogen, and air has 1/3 the lift in Venus's carbon dioxide atmosphere.

So here, I do think the person gushing about energy lying around for the taking was mindlessly assuming hydrocarbon=FUEL! without stopping and thinking that combustion requires free oxidant of some kind, and what are fuels here on Earth are not, on a planet with no free oxygen in the atmosphere.

If there were oxygen lakes, it would be another story--but then, how could there be the hydrocarbons? They'd burn at some point and either the free oxygen source is overwhelmed and it is all consumed, or the hydrocarbon source is.

And of course it takes a power flow of some kind to generate chemical potential. On Earth our atmospheric oxygen is put out by photosynthesizing life. If in fact we observed a mix of substances on Titan whereby chemical energy could be released by combining them, we would have very very strong reason to suppose there might well be life there. Now life is not magic, in fact it is not uncommon for lifeless systems to produce lowered local entropy and accumulate "order"--sand dunes for instance acquire elements of structure just from wind blown phenomena. Life is part of a larger class of "reversed entropy" phenomena that result when there is a flow of useful power.

Titan has scanty sources of useful power. Sunlight is practically close to nothing there, and I don't think it gets an enormous amount of tidal flexing. Because of its cryogenic conditions, we can imagine quite useful processes going on on very scanty power; we might find a weird alien kind of life there after all.

But lakes of methane, lying in proximity to lakes of oxygen?

No way!

I am not so much facepalming as pounding my head vigorously on the desk as blood spurts out. I do think some "science journalists" are really that dumb, or unthoughtful.

[Shevek23]

...
An alternative would be to aerobrake around Saturn instead. That comes with some issues of its own (chiefly radiation) but allows for a longer braking trajectory through lower density atmosphere.

I'd have to do the math, but I suspect this is a no-go, quite aside from the serious radiation issues, because diving that deep into Saturn's well would involve really tremendous braking speeds.

Maybe it works out if we are really careful to stay up high enough to be braking in very very thin "air," mostly hydrogen of course. We don't have to brake off all the speed as with planetary entry, just skim off enough that we then orbit back up to Titan. Such a scheme, if the math works out and we can handle the radiation, would address the issue of timing to best approach Titan too. We don't need to reduce the Titan encounter down to minimum either, just bring it into range of what we can handle with assurance.

For instance when I did the math on the Hohmann transfer, the encounter speed was down around 5000 m/sec or so, and while that is also well above Titan orbital speed it would be low enough to be about 3/4 G downward centripetal force needed, and some fraction of that is Titan's own gravity of course. SS routinely has to generate upward lift countering Earth's gravity anyway, so if we are in the ballpark of 1-2 G's we are OK.

Looping up from Saturn at minimum energy, the transfer orbit would be very elliptical so it would be going slow at Titan orbital radius, so most of Titan's orbital speed would be the encounter speed. To go faster, meaning we braked off less Saturn encounter speed down at the big planet, involves apapsis (apochrone?) higher than Titan so we'd be zooming past with some radial speed, but a certain amount of that is OK.

It might work out, but just remember if we come in with enough energy to be going 14 km at Titan if go there directly, we must be going a lot faster skimming Saturn!

[edzieba]

...
An alternative would be to aerobrake around Saturn instead. That comes with some issues of its own (chiefly radiation) but allows for a longer braking trajectory through lower density atmosphere.

I'd have to do the math, but I suspect this is a no-go, quite aside from the serious radiation issues, because diving that deep into Saturn's well would involve really tremendous braking speeds.

The goal is to stay as high in the upper atmosphere as possible (using negative lift), and use the prodigious dimensions of Saturn to spend a long dwell time in that upper atmosphere to bleed energy slowly. Potentially even dip in and out during a pass to bleed heat if you have a radiatively cooled heatshield. Even from 14km/s you have many tens of minutes of travel-time skimming through Saturn's upper atmosphere with which to brake.

[rakaydos]

...
An alternative would be to aerobrake around Saturn instead. That comes with some issues of its own (chiefly radiation) but allows for a longer braking trajectory through lower density atmosphere.

I'd have to do the math, but I suspect this is a no-go, quite aside from the serious radiation issues, because diving that deep into Saturn's well would involve really tremendous braking speeds.

The goal is to stay as high in the upper atmosphere as possible (using negative lift), and use the prodigious dimensions of Saturn to spend a long dwell time in that upper atmosphere to bleed energy slowly. Potentially even dip in and out during a pass to bleed heat if you have a radiatively cooled heatshield. Even from 14km/s you have many tens of minutes of travel-time skimming through Saturn's upper atmosphere with which to brake.

There's also an 850m/s margin between Saturn escape and minimum titan transfer.

[Shevek23]

Braking is governed by magnitude of force achieved times relative speed equaling heat flux; details of the radiated spectrum and thermochemistry of direct contact with the TPS also matter somewhat, moreso with the old ablative concept (which however had the virtue of being able to trade off more intense heating for shorter duration). Just looking at the basic metric of wattage of heat, the faster we are skimming an atmosphere, the gentler the force must be to stay below red-lining the capacity of the TPS.

At some point I might be able to tackle the math and see for myself what Saturn atmosphere skimming speed would be, at various approach speeds (which probably make little difference in such a deep dive into such a deep well). If the product of speed times force, which will force the attainable maximum accelerations downward, works out, then yes this is an option, but as you all noted, radiation in proximity to Saturn remains a severe consideration.

To be sure, if SS has suitable protection against extremes of solar particle radiation, I don't think Saturn's belt particles at their worst will exceed that! I believe those captured belt particles will be lower in energy than solar ones, albeit perhaps far more numerous, and with charged particles, a finite layer stops all of them, so intensity doesn't matter if the thickness is enough to stop the solar stuff. Whereas thickness that just slows but not stops the solar stuff is worse than no protection at all, or little better; charged particles do most of their damage with the last electron volts of their kinetic energy. The question then is how many of Saturn's belt particles are higher energy than feasible shielding designed to stop solar events can stop dead.

Meanwhile even two years transit times seems like an awful long time for crews to be exposed to cosmic ray cumulative damage. How serious that is is highly controversial, but few people are so gung ho as to pretend 2 years exposure is no problem. (Some hold to that of course). I'm open minded in the sense I admit we don't know one way or the other, but to me that means we have to assume the worst for now, and hope experience and experiments prove otherwise.

One of my very favorite things about Titan is that the atmosphere is plenty protection against the worst radiation hazards we can imagine. We have reason to think CRs can get worse with variations in Solar magnetic field, and that Earth's field will weaken cyclicly, and this is already happening. But people on Titan are pretty snug under a lot more shielding than Earth's atmosphere even offers. Their CR dose should be well below the levels we are used to on Earth--perhaps not a lot better as more medium-energy particles that reach the surface of Earth but then blast right through us doing less damage (still a lot but less than if they were stopped) are slowed just enough to stop in our bodies, but I think clearly the particles that are doing that on Earth would be stopped dead, along with lots of intermediate ones, and the number of particles arriving at the surface in the right energy range to do worst damage are going to be lower on Titan's surface than here on Earth.

And lower energy stuff would be stopped dead with a lot less atmosphere than either Titan or Earth have, though I think Mars's is so thin as to be practically worthless in this respect. All the Solar output (but for a tiny portion) and all the orbital stuff, which is particles energized by primary input spalled into space and accumulated in the field, will be no problem at all.

I think people will have to leave Titan and go roaming around the moons to find heavy metals, scrounged from impacts of small bodies on the bigger moons, but they'll be able to scoot around pretty fast and delta-V is low, if the ships they do this in can aerobrake (at very modest velocities!) at Titan.

[Shevek23]

Another tricky thing, that SS as designed cannot handle--on the surface, SL Raptor engines are no good, due to the high pressure. But I think the problem contains its own solution--SX can install extra engines, that are essentially turbofans, to use the very high atmospheric density for very energy efficient thrust. The low gravity means quite modest thrust is needed; the high density air that extends very far upward dropping in density slowly means we need to avoid high speeds until we are quite high up--it all points to essentially jet engines. Jet engines have low thrust/weight ratio, but thrust requirements are modest.

I don't think we can make them "air breathing," that is carry oxygen but not fuel, because while the lower atmosphere is laced with hydrocarbon smog, it is patchy and variable in concentration. It isn't gas mixed evenly, it is colloid droplets suspended haphazardly, which is why it is clouds. At low altitude we can probably rely on a fluctuating amount of free methane and other hydrocarbon fuel, but even there I think we need to inject some carried fuel, along with the oxygen.

But given that we do have to carry most of the fuel and all the LOX, airbreathing turbines, or maybe even turboprops, can take us up pretty high and then we can switch to high thrust from the SL Raptors, and eventually the V-Raptors. Generally speaking with rockets, we have to trade off mass flow against Isp for a given power output, but with ingestion of Titan's mostly nitrogen atmosphere and combustion as in a jet engine, the heat generated by X amount of meth-lox propellant heats "free" nitrogen resulting in higher thrust by far for a given wattage of heat, so the turbine engines would sip propellant, even factoring in that something close to 4 times the mass versus an oxygen atmosphere methane burner would require has to be fed in. Again we need quite low thrust because the dead weight of the ship is quite low in 1/7 G whereas we don't want high airspeed until the air thins down quite a lot, we can climb leisurely at below sonic speed (which is much lower than on Earth,  below 140 m/sec I guess so climb speed is like 120 m/sec if that, around 240 knots, so basically WWII era bomber/transport plane speeds) until the air is down to half Earth SL density.

In fact, were it not for the requirement such a ship might have to land on Earth someday, we could omit the SL Raptors and have just V-Raptors, which will fire well enough with pressures modestly below Earth SL; they work in Earth's atmosphere anywhere above 3.5 km altitude, so around 1/2 Earth surface density. We'd therefore want to ascend a scale height to get the density down there, on airpushing engines of some kind working over that range--again, props can do it, though I think a turbofan is probably better. A Titan scale height is going to be 7 times Terran as far as gravity is concerned, but lowered by lower temperature, so overall I think about triple Terran, say 30-40 km to get to rocket firing altitude at 240 knots or so. at 8 seconds per km, we need to power the turbines about 5 minutes.

Landing is the same thing in reverse; we aerobrake and skydive at a very low terminal velocity down to a kilometer or less above the surface, and fire up the turbines or turboprops to come down gently, no engine blast from Raptors either possible or required.

I'm thinking an SS modified for Titan service but ultimately someday returning to Earth requires two turbofans, kept inboard usually, installed under hatches in the upper "leeward" light or no TPS, as high up as we can manage, which extend outward on short booms. We need something in excess of 2.1 MN thrust all up, say 2.5 or so--sustaining airspeed against drag below sonic speed will not be tremendous, so mainly we are looking at lifting just under 1500 tonnes mass dead weight in low Titan gravity for launch. Landing is much easier of course. Either way the high-mounted jets will be intaking quite dense and cold nitrogen near the surface, with variable amounts of hydrocarbons but those are at best supplementary.  The tricky bit is delivering consistent thrust over a great range of density of air intake.

The idea some pep[le have SS can operate as an airplane "gliding" to land on Earth seems silly in the extreme to me, but taking off from Titan it might work actually. Very modest thermal power can provide great thrust in thick low level atmo, then as the "air" thins it can angle over and body surf on dropping density. I'm not sure this is possible, though the claim that the "skydiver" descent at allegedly 66 m/sec in our atmosphere happens at that speed suggests it ought to be sort of possible. Lift to drag ratio of elongated bodies at an angle of attack is pretty poor, and it basically works as the pitching moment to flip the body to go crosswise to the slipstream, which is stable but of course most draggy, is countered by tail fins that provide lift double the pitching force at that end, so it is a question of how strong the pitching moment is and whether the hull can handle the bending moment of two forces lifting essentially on each end, as well as whether lift/drag ratio goes below 1. But all we really have to do is get the SS up to where the SL Raptors are effective, around Earth SL pressure, which is a scale height or so up, then those engines provide several times the weight of a full SS on Titan, and soon after that the V-Raptors will work too, indeed we can shut down the SL Raptors shortly after that and use the higher Isp of the V Raptors alone.

So that is the mission envelope of nitrogen-ingesting turbojet type engines. At low altitude the incredibly dense atmosphere means we need a lot of propellant to heat it much, but thrust will be quite high on modest power, as we rise we need more heat input, but even at V Raptor firing altitude jet engines should be quite effective still. SS could be going supersonic then, but I suspect it is best to stay subsonic until the jets can be retracted.

[Shevek23]

Re aerobraking at Saturn:

Escape velocity from Saturn is 35.5 km/sec. Starship is designed to handle entering Earth's atmosphere at around 8 km sec or a little more, and pull maybe 2-3 G. We have to bear in mind the forces lifting or holding down the ship, in line with the radius to the center, and those braking the ship more or less perpendicular to the radius, add up as vectors, at right angles to each other so it is Pythagorean addition to be sure. But it means that if SS is undergoing net acceleration of 3 G in aerobraking at Earth, the actual braking is lower than 3 G, because the lift force has to be added into the total.

So, say we have empirically a thermal upper limit of 190tonnes*8000m/sec*30m/sec^2, and we can brake up to this limit, and to brake any harder would overheat the TPS and damage or destroy the ship. So when Musk tweeted he wanted SS to be able to handle speeds up to 13 km/sec that means 24/13 or a bit under 2 G total is all the braking force that can be tolerated at that speed. A lighter SS can brake at a higher G, a heavier one is more limited.

So now we come in to Saturn at say a bit over Hohmann approach speeds, at 6000. Escape speed and approach speeds add Pythagorean too, meaning we will skim the appropriate altitude in Saturn's upper atmosphere at 36 km/sec pretty exactly. At that speed, we are going 4.5 times faster than SS entering Earth's atmosphere from LEO, and therefore must limit G to 6/9 of a G, or around 6.5 m/sec^2.

We must however exert a Saturn G downward to stay in a circular path at the right altitude for that force to prevail! In fact we need to sink downward as we slow, but it becomes easier to do that as we slow.

Saturn G is about 1.065 Earth's, so we need to have total acceleration well over 11 m/sec^2, but we are limited to something little over half that! Or another way to put it--if you can show SS can handle braking at 5 or 6 G in Earth's atmosphere, then we might be in business trying to brake off speed we don't want this way.

But I don't think SS as currently designed can handle that at all. If it had ablative TPS, it might be able to handle it, and perhaps we can get SpaceX to put a layer of ablative on over the ship for this mission though it might cost a significant mass.

Now for your 2 year trajectory I have lost the numbers I had noted down, but clearly it would be trying to stay in the right atmosphere layer at an even higher speed, and the magnitude of the G force needed to hold it down is even greater, whereas the allowable maximum total G force is less due to the higher speed.

I think if we want SS to get to Saturn in 2 years or less, we need an alternate sort of drive. Something like the MSNW fusion pulse drive concept about half a decade ago. But I have not heard much of that project the past 5-6 years since...I fear it was sacrificed to the SLS God.

Well there are others offering to deliver low thrust but high Isp for long periods of time. The MSNW lithium kinetic-fusion pulse drive was pretty neat in a lot of ways though. One being that this drive was of a size that be stowed on a Starship.

[M.E.T.]

Construct a DE-STAR orbital laser array on each end and you can have fast laser propelled travel between Earth and Titan on an ongoing basis.

If Starship works as planned and drops cost/kg to orbit dramatically, we can build a DESTAR above Earth within a couple of decades.

Constructing one at the Saturn end will take a bit longer, but the first DESTAR can help with everything from propulsion to beaming power to the Titan colony and even astro/geo-engineering if needed.

Once the second DESTAR is up and running at the opposite end, everything becomes much easier.

[Shevek23]

Construct a DE-STAR orbital laser array on each end and you can have fast laser propelled travel between Earth and Titan on an ongoing basis.

If Starship works as planned and drops cost/kg to orbit dramatically, we can build a DESTAR above Earth within a couple of decades.

Constructing one at the Saturn end will take a bit longer, but the first DESTAR can help with everything from propulsion to beaming power to the Titan colony and even astro/geo-engineering if needed.

Once the second DESTAR is up and running at the opposite end, everything becomes much easier.

Have you got a link describing how that particular system works?

[Shevek23]

Meanwhile I might be underestimating the usefulness of SL Raptors on Titan. The pressure is not tremendously higher than Earth's, 1.45 as great versus Earth sea level.

My RPA software lets me write in higher ambient pressure than Earth sea level but it does not seem to do anything with it, it still does altitude performance starting at one bar and going down. I can sort of simulate what might happen by lowering engine combustion chamber pressure to a bit over 2/3, to 207 bars versus 300, that should give the same ratio of pressures, and when I do that no flow separation emerges; SL Isp drops from 330 to 318, that is no big deal.

I don't know if it is valid though; the pressure is as given but with the much lower temperature the density will be over 4 times that of Earth air.

That's why I think blasting up on full SL thrust might not be advisable; between the much lower sonic speed and the much denser air, we might waste a lot of propellant and even fact structural issues pressing too hard. With nearly 600 tonnes of thrust available and only 200 or so weight, it should be possible to fire all three engines and rise quite briskly, but then we'd want to throttle back to one engine to just sustain speed below sonic speed. The jets I imagined might be rather problematic, but it seems wasteful to me to cruise below sonic speed until we reach altitudes where the whole 6 engine set can be used, which will be when pressure is down below 70 percent or so of Earth SL, or half Titan surface pressure, some 15-20 km up. At say 150 m/sec. it does not take too long to get there, but we might burn up a lot of methlox inefficiently in the interim.

Also, if we can manage auxiliary engines that react on the air somehow, we could avoid blasting the ground with high temperature Raptor exhaust.

Now landing is really easy; I suppose terminal falling speed with the sorts of mass loadings we can expect would be pretty low, say 10-30 m/sec; it would require remarkably little to arrest that.

[M.E.T.]

Construct a DE-STAR orbital laser array on each end and you can have fast laser propelled travel between Earth and Titan on an ongoing basis.

If Starship works as planned and drops cost/kg to orbit dramatically, we can build a DESTAR above Earth within a couple of decades.

Constructing one at the Saturn end will take a bit longer, but the first DESTAR can help with everything from propulsion to beaming power to the Titan colony and even astro/geo-engineering if needed.

Once the second DESTAR is up and running at the opposite end, everything becomes much easier.

Have you got a link describing how that particular system works?

The whole interview is worthwhile to understand the system. The propulsion specific implications start at around the 9 minute mark.

[gideonlow]

Might it be possible to aero-capture at Titan into Saturn orbit, and then come back around to Titan on an elliptical orbit for additional braking, capture, and finally entry (once or multiple times)?  This seems like one possible way to break-up the total velocity reduction into multiple parts with commensurately reduced heating each time.  Presumably there would be some trade-off between the added time to complete the multi-step process and the potential improvement in interplanetary cruise time/speed.

[Paulus]

Would it be possible to use Saturn's Rings for braking?
Especially I am thinking about the E Ring which consists of very small particles.

[bad_astra]

From the article:

On the surface, vast quantities of hydrocarbons in solid and liquid form lie ready to be used for energy. Although the atmosphere lacks oxygen, water ice just below the surface could be used to provide oxygen for breathing and to combust hydrocarbons as fuel.

*facepalm*

WHY the facepalm?
"Mining" Oxygen from water deposits will need to be done in any case, for life support.
Canned oxygen, plus a nice scoopful of lakejuice (mostly Ethane) will serve just *fine* as a power source for vehicles, localized heating, power fuel cells, etc.

No-one is suggesting using the combustion of this oxygen as PRIMARY energy source, of course. That would be stupid, as extracting it from the water (and getting the water out in the first place) will require a lot more energy.

You need to crack that water to get that Oxygen (electrolysis). If you then go and use that O2 to burn with a hydrocarbon to generate that energy, you've make a net energy loss.

You have ethane in abundance on Titan. With some robotic factory nursuries stocked with candidatus argoarchaeum cultures to help start cracking ethane in water slurry, and then a second stage production for o2 from algae factories. It would take time, but if you're not in a huge hurry you could have a good supply of o2 ready by the time people arrived.

[edzieba]

With the amount of solar concentration needed to sustain your algea at 3.7% the normal solar irradiance (plus heating to keep them alive), that's effectively just solar powered cracking with extra steps.

[bad_astra]

Not really. If you have to concentrate solar to these farms for heat and light, it could be done. But it doesn't have to be done.

I would not assume solar is the way to go on titan, in any case. But if there were some reason to begin farming microorganisms on Titan it would be best to have compact fission reactors. Long term, and I believe discussing something like Titan settlements it is safe to put in on the table, a fusion power setup on the lines of something like Helion's system is far more likely.

[MichaelBlackbourn]

Would the methane lakes have tides on Titan? Can we use tidal power?

[Paul451]

Would the methane lakes have tides on Titan? Can we use tidal power?

Titan is tidally locked. So no moving tides to exploit.

(Except solar tides, but at Saturn they'd be trivially small. Tidal force falls with the cube of distance.)

[rakaydos]

Would the methane lakes have tides on Titan? Can we use tidal power?

Titan is tidally locked. So no moving tides to exploit.

(Except solar tides, but at Saturn they'd be trivially small. Tidal force falls with the cube of distance.)

Would Tital got Jovian tides  when the planets aligned? Would jovian tides be larger or smaller than solar tides at that distance?

[Paul451]

Would the methane lakes have tides on Titan? Can we use tidal power?

Titan is tidally locked. So no moving tides to exploit.
(Except solar tides, but at Saturn they'd be trivially small. Tidal force falls with the cube of distance.)

Would Tital got Jovian tides  when the planets aligned? Would jovian tides be larger or smaller than solar tides at that distance?

Saturn is further from Jupiter than Earth is. So the tidal force on Titan from Jupiter is smaller than the tidal force on Earth from Jupiter. Which is to say, unnoticeable.

The tidal force of Mimas on Titan would be higher (which is to say, unnoticeable.)


There might be a geothermal effect that could be exploited for power. If water on Titan is like rock in Earth's crust, and Titan shows geology, then there might be hot-spots of underground liquid water that can be exploited by an ammonia loop (for example).

That said, I'm not seeing the benefits in colonising Titan (at least by baseline humans. Post-singularity, ask me again.) Even temporary scientific bases seem unlikely (compared to teleop'ing robots from a nearby orbital facility.)

[sebk]

We must however exert a Saturn G downward to stay in a circular path at the right altitude for that force to prevail! In fact we need to sink downward as we slow, but it becomes easier to do that as we slow.

Saturn G is about 1.065 Earth's, so we need to have total acceleration well over 11 m/sec^2, but we are limited to something little over half that! Or another way to put it--if you can show SS can handle braking at 5 or 6 G in Earth's atmosphere, then we might be in business trying to brake off speed we don't want this way.

Actually we don't need to go perfectly circular. Hyperbolas and ellipses are pretty close to a circle near periapsis and Saturn is big. On Earth aerobrake you'd generate zero to slight positive lift for sth like 1.5g breaking. To capture from 13km/s to GTO like elliptic orbit (~10km/s) we need to shed 3km/s. Saturn is ~11 times bigger, the speed is about 3x bigger, thermal limit for g/load is 3x smaller (for about 0.5g), and you need to shed the same speed (~3km/s).

Why just 3km/s? This is Oberth effect in deep deep well of Saturn. 14km/s overspeed in free space is just 3km/s above escape near Saturn surface.

With 3km/s to lose things match. Saturn curvature seems low enough to allow the capture. The curvature of Saturn to allow capture would have to be 9x smaller that Earth's, but it's 11x smaller so even better. But this is not all, the atmospheric corridor width must be scaled too. But hydrogen-helium atmosphere in Saturn's "surface" gravity which pretty much like Earth means 10x higher scale height, so also matches well with scaling the curvature (the corridor width is 10x the Earth's one).

Saturn looks like a perfect match for the Earth for aerocapture purposes

[JulesVerneATV]

Saturn's moon Titan just broke one of chemistry’s oldest rules
https://www.sciencedaily.com/releases/2025/10/251016223031.htm

NASA's nuclear drone that will explore Titan's methane lakes passes extreme tests
https://www.earth.com/news/nasas-nuclear-dragonfly-drone-that-will-explore-titans-methane-lakes-passes-extreme-tests/

Tethered Ring Space Launchers