Overview
After humanity has colonized and begun terraforming
Mars, the next likely destination would be Saturn's moon Titan. One of the drawbacks of Mars is that it lacks nitrogen which is needed to grow food and also to create a breathable atmosphere. Enormous aerostat or NIFT spacecraft could harvest nitrogen and other resources from Titan's atmosphere and then transport these resources to a nuclear propulsion spacecraft. Given that Titan's gravity is only one-sixth as strong as that of the Earth's, we could use Titan's indigenous resources to construct a space elevator where nuclear propulsion spacecraft could be launched from. These spacecraft would carry their payload to Mars and, after arriving, all of that nitrogen could be deposited into Mars' atmosphere. It would also be very useful to send nitrogen to the Moon and to settlements along the asteroids in the inner-asteroid belt where nitrogen could be used for growing food. And after settling Titan, humans would likely go on to harvest helium-3 (which could be used to power nuclear fusion spacecraft) from Saturn and the other gas giants in the solar system which will be used to power nuclear powered spacecraft to the Kuiper belt, the Oort cloud, and perhaps even to the stars..
Harvesting resources from Titan and the Jovian systems
Around the 22\(^{nd}\) century, there would be a high demand for nitrogen on Mars to support the greenhouses which sustain millions of martian humans and also to support the terraforming project which involves releasing copious amounts of nitrogen into the atmosphere. And around this time, it is very likely that humans will have developed sustainable nuclear fusion to power the Earth and spacecraft. The next destination after the Moon, the inner-asteroid belt and Mars (discussed in previous lessons) is Titan—one of Saturn's moons. Saturn contains scores of moons but Titan is the most massive one by far with a mass which dwarfs that of all of Saturn's other moons combined. There are a few other reasons why Titan would be humanities next destination and not Jupiter which also contains enormous amounts of nitrogen. Jupiter is so massive that by time a nuclear propulsion spacecraft arrived at this planet it would need to be going about \(29.5km/s\) to achieve a stable orbit around Jupiter in order to harvest and collect nitrogen from its nitrogen-rich atmosphere. But entering into a stable orbit around Titan and subsequently landing on one of its continents would be much easier. Titan is the most congenial extra-terrestrial world for human settlement besides Mars since it contains all of the fundamental ingredients necessary to support life including nitrogen, oxygen, methane, and carbon dioxide. This is why Titan would be the next world in the solar system that we humans settled.
Although Titan is much smaller than the Earth, its atmosphere is more massive. Titan's atmosphere is so enormous that its atmospheric pressure on its surface would be more than 50% greater than that of Earth's at sea level. For this reason, humans living on Titan's surface would not need to wear heavy and cumbersome pressurized space suits. But since Titan is very cold, they would need to wear specialized suits to keep them warm. Also, since there are only trace amounts of oxygen in Titan's atmosphere, they would need to wear tanks of liquid oxygen. But since Titan's gravity is just a mere one-sixth that of the Earth's, these liquid oxygen tanks would weigh hardly anything. Furthermore, with the combination of Titan's thick and dense atmosphere and super lower gravity, humans could strap on a pair of wings and fly (like in the lunar hotels discussed in the article, Colonizing the Moon) as illustrated in the artist depiction below. With all of the essential ingredients necessary to support life already there, Titan could support a biodome of plants and livestock enclosed inside of a hemispherical dome. Titan's gravity is likely far too weak for humans to adjust to, but this issue could be circumvented by constructing an artificial rotating habitat which emulated Earth's gravity. This is where humans on Titan would live. Furthermore, by using Titan's indigenous resources, a space elevator could be built on this world and used to propel NIFT spacecraft to other places in the Saturnian system such as Saturn's other moons besides Titan, or to one of the icy bodies comprising Saturn's rings, or to Saturn's atmosphere. These spacecraft could scoop methane from Titan's atmosphere and use it as a propellant to navigate Titan. Such a spacecraft could either extract nitrogen directly from Titan's atmosphere or it could intercept a aerostat in orbit around Titan. (A aerostat is a large blimp-like vessel.) It would contain stockpiles of nitrogen and methane which could be loaded onto the NIFT before it takes off. In either case, after the NIFT spacecraft has had collected a payload of nitrogen, it could make a rendezvous with a nuclear propulsion spacecraft on board the space elevator. Fleets of such spacecraft could set sail towards the inner-solar system and transport nitrogen to humans living on Mars, the Moon, or along the asteroids in the inner-asteroid belt.
"With an average temperature of -180 C all water here is frozen hard as rock. In fact, the surface landscape of Titan is indeed mostly made of frozen water ice. But Titan's atmosphere is rich in hydrocarbons such as methane and ethane, and the low temperature is perfect for these elements to occur naturally in three states; frozen, liquid and gas. So, just as on Earth where we have a water cycle (ice melts, becomes water, water evaporates into clouds, turning into liquid and becomes rain and so forth), Titan has a methane cycle. Methane evaporates and rises to form clouds, eventually turning into rain, falling over the surface. And this is the most amazing part; the rain in some places is enough to fill entire lakes. Lakes of methane!
Titan is the only place in the Solar System, other than Earth, known to have large bodies of liquid on its surface. And they are really there, huge lakes, with shorelines, islands and small archipelagos. This scene takes place over a lake know as Ligeia Mare, the second largest on Titan, about 500 kilometers in diameter, located in the north polar region of the moon.
The second fantastic feature I wanted to illustrate is the combination of Titan's very dense atmosphere and its relatively low gravity. As a human on Titan you would weigh about 14% of what you do on Earth, and in the dense atmosphere it would be enough to strap wings on your arms to make you able to fly like a bird. On Titan you could fly like a bird, over lakes of methane! (If you wore some really warm clothes of course.)" Image and image description credit: WANDERERS - a short film by EriK Wernquist
After settling and industrializing Titan, humans would expand their industrial activities and interplanetary commerce to include the atmospheres of Saturn and Jupiter which, along with Uranus and Neptune, contain more \(H_3\) than anywhere else in the solar system. This is why the engineer Robert Zubrin declared that the Jovian planets are a prelude to interstellar travel to distant solar systems. These gas giants contain all of the \(H_3\) necessary to power \(D\)-\(H_3\) nuclear propulsion spacecraft to the stars.
When peered at from an Earth-based telescope or distant space probe, Saturn's rings look solid. But when viewed very close up one can see that these rings are in fact comprised of trillions of little ice worlds. Any humans that are on these worlds could build bases and infrastructure underneath the ice and facilitate water extraction processes. This water could be exported to Titan and used to help sustain the biosphere established on that world including humans and, also, all of the plants and livestock living inside of biodomes. The raw ingredients on Titan and Saturn's rings would provide all the sustenance necessary to support a long-term human presence in the Saturnian system as these human explorers harvest nitrogen and \(H_3\) from Titan's and Saturn's atmospheres and send these resources to outposts established in the inner solar system.
This article is licensed under a CC BY-NC-SA 4.0 license.
References
1. Zubrin, Robert. Entering Space: Creating a Spacefaring Civilization. New York: Jeremy P. Tarcher/Putnam, 1999. Print.
2. Fraser Cain. "What About a Mission to Titan? It's Time to Explore Saturn's Largest Moon". Online video clip. YouTube. YouTube, 25 March 2017. Web. 21 October 2017.
3. Wernquist, Erik. Ligeia Mare. Wanderers. Web. 21 October 2017.