The 5 places man could live in the solar system

SpaceNut · 2016-06-26 22:40:35

World going to hell? Here are the Solar System’s five most livable places

We have discussed each and every one of these places and here is the round up.

MARS

The good: Mars is the obvious choice. It is close enough for humans to travel to with existing propulsion technologies within about six to nine months. The planet also has soil, surface ice at the poles, and liquid water below ground at lower latitudes. There is enough sunshine to provide solar power. The thin Martian atmosphere provides a modicum of protection from cosmic and solar radiation. All of the above factors suggest that humans could build a somewhat sustainable colony over time on Mars, although it would largely be an indoors existence.
The bad: There is so little atmosphere that it might as well not exist. About 19km above the Earth, pilots reach the Armstrong limit, where water boils at the temperature of the human body, and the atmosphere is about 6 percent that of Earth's surface. The Martian atmosphere is about one-tenth the value of the Armstrong limit. An exposed human on the surface would die within a few dozen seconds. The recent discovery that solar wind has stripped the Martian atmosphere away over billions of years has also dealt a blow to hopes that the world might be terraformed by releasing carbon dioxide trapped in Martian rocks.

MOON

The good: Proximity. Humans can get to the Moon within a few days, making travel and resupply by far the easiest of any off-world location. Scientists also believe that ample amounts of water ice exist at the lunar poles, providing a hefty source of drinking water, radiation shielding, and rocket propellant. The moon's surface contains valuable minerals, such as silicon, which could be used to make solar cells, and Helium-3, which might be a good source of energy. It is also plausible that large lava tubes exist just beneath the Moon's surface, which could be large enough for human cities.
The bad: The Moon has no atmosphere, of course, making surface activities hazardous and leaving astronauts vulnerable to radiation. The Apollo astronauts, too, found the Moon's dusty surface was difficult to contend with when they brought the dust back into their spacecraft. Finally, if Earth well and truly does go to rot, would the Moon perhaps be just a little too close?

VENUS

The good: An atmosphere! We're not talking about the surface of the planet, where the crushing atmospheric pressure is equivalent to about 900 meters below the surface of Earth's oceans, and the temperature is a boiling 462 degrees Celsius, on average. We’re talking about 50km above the surface, where the atmospheric pressure is equivalent to that on Earth and temperatures range from 0 degrees to 50 degrees Celsius. Moreover, the remaining Venusian atmosphere provides radiation shielding. A human might sun oneself on an open-air deck wearing only a breathing mask. NASA has already done some preliminary work studying a floating airship concept with its Project HAVOC.
The bad: When it rains, it rains sulfuric acid. This would damage solar panels and the airships themselves, not to mention any humans caught unawares out in it. The other problem is resupply of water or metals. Reaching Venus’s atmosphere would be more difficult than getting to the Moon or even Mars, and launching from the airships would require rockets nearly as powerful as those needed to take off from Earth.

TITAN

The good: Energy, and lots of it. The great lakes of Saturn's moon Titan are filled mostly with pure methane, providing a near limitless supply of power for human activities. The surface pressure is about 1.4 times that of Earth, too, which means it is one of the few places in the Solar System where humans wouldn't need a pressure suit (aside from an air mask) to walk outside. The nitrogen, methane, and ammonia in Titan's atmosphere could be used as fertilizer to cultivate crops in greenhouses, and there may also be subsurface water. The thick atmosphere would provide good radiation shielding.
The bad: Temperature and distance. The surface of Titan is about -180 degrees Celsius (so no pressure suit, but LOTS of layers of warm clothing). And since this moon orbits Saturn, it is the farthest of any of these options, requiring the better part of a decade for humans to reach with current propulsion systems

CALLISTO

The good: Callisto is not as famous as some of the Jovian moons, such as Europa, but it probably would be the best one to live on. Comparable in size to Mercury, it is the most distant from Jupiter of the planet's four large moons, which means it receives less radiation from the gas giant. Spacecraft have observed bright patches of ice on the moon's rocky surface, and deeper inside the planet there’s probably a salty ocean that is 50 to 200km deep. With its Human Outer Planets Exploration study, NASA has looked at sending humans to Callisto eventually, due to its geological stability and the potential to turn its surface ice into rocket propellants.
The bad: It's not as far as Titan, but Callisto is still several years of travel from Earth. The moon has only a tenuous atmosphere, so it would not be unlike living on the surface of Earth's own Moon. And while the radiation levels are lower than Jupiter's other moons, they are still higher than Titan and some of the other alternatives. Solar panels would be of limited use for colonists as Callisto receives only about 1/25th of the solar energy that Earth's Moon does

RobertDyck · 2016-06-26 23:19:56

When I was a child, I read a science fiction novel by Robert A. Heinlein: "Farmer in the Sky". Written 1950. It talks about a homestead on Ganymede. I keep thinking Ganymede is suitable. It's the largest moon in our solar system. Larger than Mercury, although not as large as Mars. Surface gravity 1/7 Earth; Callisto is only 1/8 Earth. When I read about Ganymede in the high school library, I expected greater surface gravity. However, gravity was measured by the Galileo orbiter. It has lower density than other planets or Earth's Moon. Lower mass means lower surface gravity.

Ganymede has a magnetic field.
Astro Bob, 13 March 2016: Lucky Friday The 13th For Auroras? / Ganymede Auroras Hint At Hidden Ocean
The following image is aurora of Ganymede, taken in UV by Hubble Space Telescope, superimposed over image of Ganymede taken by Galileo...
Ganymede-auroras-tight-NASA_ESA.png?resize=400%2C382

Ganymede has to deal with radiation belts around Jupiter, but it has a magnetosphere to protect it. Is it enough? We don't know.

Ganymede has a stony surface, with hundreds of kilometres of ice beneath. Probably dirty ice. Analysis of the aurora indicates there's a liquid water layer deep down. First estimate is 100km deep, which is roughly 10 times the depth of Earth's ocean. They estimate a salt water ocean, to be able to produce a strong enough magnetic field to produce aurora like that. And they estimate the ocean is 150km beneath the surface.

RobS · 2016-06-26 23:33:13

I would quibble with the methane of Titan being an endless reservoir of energy because you need oxygen to burn the methane, and Titan has no free oxygen. We could always crack water to get oxygen, but then we have hydrogen, too. It is possibly Titan has geothermal and wind power, though.

I'm not sure how easy it is to deal with the extreme cold, either. People don't go outside at all at the South Pole in the winter, except for very short times, and Titan is a lot colder.

Terraformer · 2016-06-27 05:06:24

Well, I'm glad they didn't mention by would-be adoptive homeworld of Ceres, because I don't want competition, though I think it would be in the top 5. Abundant water ice, no radiation belts, close enough that you can still use solar power, they've discovered ammonia there so you can fertilise crops, the gravity is low enough that a space elevator isn't particularly difficult to engineer... the gravity is low, but you can construct rotating habitats for that. I'd put Ceres in 2nd or 3rd place, with Mars in top position (well, after Earth, obviously).

Tom Kalbfus · 2016-06-27 08:53:44

RobertDyck wrote:

When I was a child, I read a science fiction novel by Robert A. Heinlein: "Farmer in the Sky". Written 1950. It talks about a homestead on Ganymede. I keep thinking Ganymede is suitable. It's the largest moon in our solar system. Larger than Mercury, although not as large as Mars. Surface gravity 1/7 Earth; Callisto is only 1/8 Earth. When I read about Ganymede in the high school library, I expected greater surface gravity. However, gravity was measured by the Galileo orbiter. It has lower density than other planets or Earth's Moon. Lower mass means lower surface gravity.
Ganymede has a magnetic field.
Astro Bob, 13 March 2016: Lucky Friday The 13th For Auroras? / Ganymede Auroras Hint At Hidden Ocean
The following image is aurora of Ganymede, taken in UV by Hubble Space Telescope, superimposed over image of Ganymede taken by Galileo...
http://i2.wp.com/astrobob.areavoices.co … =400%2C382
Ganymede has to deal with radiation belts around Jupiter, but it has a magnetosphere to protect it. Is it enough? We don't know.
Ganymede has a stony surface, with hundreds of kilometres of ice beneath. Probably dirty ice. Analysis of the aurora indicates there's a liquid water layer deep down. First estimate is 100km deep, which is roughly 10 times the depth of Earth's ocean. They estimate a salt water ocean, to be able to produce a strong enough magnetic field to produce aurora like that. And they estimate the ocean is 150km beneath the surface.

Water ice makes a great radiation shield as well, and we could probably melt tunnels beneath Ganymede's surface, and the "dirt" in the ice probably contains a lot of useful materials we can build stuff out of. Solar panels would still be of some use, the first settlers on Ganymede will have lots of real estate to lay those solar panels down on, we would need to make or bring 25 times as many solar panels as we would on Earth, but at those cold temperatures, the solar panels would convert the sunlight they do receive to electricity with maximum efficiency. One could also manufacture mirrors locally, you could use mirrors to concentrate sunlight onto solar cells. You could also concentrate sunlight on habitable domes. Water ice is nice and transparent, would make a nice radiation shield but would also let through sunlight, have some insulating glass or plastic underneath to keep the warm temperatures produced by the sunlight within the dome.

Lets for example assume a dome is 100 meters wide, about the size of two football fields, how many mirrors would we need to light it up? An array 500 meters wide would do the trick. Ganymede rotates once every 7.15 days, not as bad as the Moon so we might need twice the collection area as that, a 700 meter wide array would collect twice as much solar energy as a 500 meter wide array. I figure lets do a whole kilometer to take care of any inefficiencies related to converting solar energy into electricity., that would bring in 4 times as much energy as needed to keep the dome warm and illuminated. So what do you think? can we bring a square kilometer of solar cells to Ganymede, or how about just an array 250 meters by 250 meters surrounded by mirrors to concentrate sunlight on them, and maybe a small 100 meter dome in the center to receive natural sunlight when its available, use electricity to produce that sunlight artificially when its not. I think the obvious way to store energy would be with hydrogen fuel cells. Use the excess electricity to crack water ice into its components, and then run fuel cells on them to power the settlement in the dark.

Last edited by Tom Kalbfus (2016-06-27 08:54:34)

Tom Kalbfus · 2016-06-27 09:08:42

RobS wrote:

I would quibble with the methane of Titan being an endless reservoir of energy because you need oxygen to burn the methane, and Titan has no free oxygen. We could always crack water to get oxygen, but then we have hydrogen, too. It is possibly Titan has geothermal and wind power, though.
I'm not sure how easy it is to deal with the extreme cold, either. People don't go outside at all at the South Pole in the winter, except for very short times, and Titan is a lot colder.

We may need nuclear fusion to get there, so we use it to heat the place once there as well. I think a fission rocket might work as well, but we'd have to bring our own nuclear fuel. We could use liquid oxygen to power our vehicles and other portable devices on Titan. Liquid oxygen wouldn't need much insulation, or it could simply be held under pressure to be kept from boiling off at normal outside temperatures.

The average temperature on Titan is 93.7 K (−179.5 °C)
The boiling point of liquid oxygen is at 90.19 K (−182.96 °C; −297.33 °F) at 101.325 kPa (760 mmHg).
But the surface pressure of Titan's atmosphere is at 146.7 kPa (1.45 atm).
I think liquid oxygen could exist on Titan's surface in an open container! We could fill the gas tanks of our Titan vehicles with liquid oxygen the same way we fill our cars with gasoline!
Liquid methane has a boiling point of 111.66 K and a freezing point at 90.7 K
Titan's gravity is at 1.352 m/s2 (0.14 g) (0.85 Moons), so if we had a bi-propellant fuel, it would still weigh less than on Earth. The dangerous nuclear reactor would stay on one place and manufacture fuel to be distributed throughout the colony and to fuel vehicles and space suits no doubt. I think those would need to be actively heated, not just insulated!

Tom Kalbfus · 2016-06-27 09:27:46

Terraformer wrote:

Well, I'm glad they didn't mention by would-be adoptive homeworld of Ceres, because I don't want competition, though I think it would be in the top 5. Abundant water ice, no radiation belts, close enough that you can still use solar power, they've discovered ammonia there so you can fertilise crops, the gravity is low enough that a space elevator isn't particularly difficult to engineer... the gravity is low, but you can construct rotating habitats for that. I'd put Ceres in 2nd or 3rd place, with Mars in top position (well, after Earth, obviously).

Well Ceres is a dwarf planet 945 kilometers (587 miles) in diameter. What if we built a ring around its equator? Lets make the ring 100 meters wide, and if we rotate it at 2152.589632280152 meters per second or 22.986306145880191858179839941061 minutes for a rotation, we'd have 1 gravity on its inner surface. Normally it would be quite challenging to build a Stamford Torus that big, but we have Ceres to anchor the ring against. We just build a track, anchor it firmly to the crust. This would be equal to 4813.886901 miles per hour! Ceres at its worst is 2.9773 AU from the Sun which means we need almost 9 times the collecting area for Solar energy, we should double that and make it 20 because Ceres rotates once every 9 hours. We would power he settlement with Fuel cells in the dark and rely on Solar energy to make the fuel and power the settlement during the short 4.5 hour day. The living space would be 100 meters times 2968.8050576423546103471979971991 kilometers, that would be 296880505.76423546103471979971991 square meters, that would be 73,360.48 US acres of real estate We could house 4 times as many if we distribute one quarter acre per person, that would be 293,440 people!
acres

SpaceNut · 2016-06-27 17:20:54

Yes we could go to the moon if we should chose to do so. The next is a tossup as to what we are ready to do on the short timeline not being multiple decades as Mars is about the same as Venus if we do not land and the only benifit for mars is its moons to explore that makes it edge ahead of venus for the number 2 spot if we can not land.
Titan and calisto are just not in the realm of probable and if anything we shoud focus next on the asteriod belt as there happens to be lots of useable materials and science to explore at each of the pieces of rock.

GW Johnson · 2016-06-27 17:46:16

Longer-term, the asteroids hold more promise than any of the planets or their moons. There's more possible stuff there to use, and a smaller gravity well out which to extract it, than any other location in the entire solar system. So, the old sci-fi tales about asteroid miners will probably end up being true. Gonna take us a while yet to make it true, though.

GW

Tom Kalbfus · 2016-06-27 21:55:09

SpaceNut wrote:

Yes we could go to the moon if we should chose to do so. The next is a tossup as to what we are ready to do on the short timeline not being multiple decades as Mars is about the same as Venus if we do not land and the only benifit for mars is its moons to explore that makes it edge ahead of venus for the number 2 spot if we can not land.
Titan and calisto are just not in the realm of probable and if anything we shoud focus next on the asteriod belt as there happens to be lots of useable materials and science to explore at each of the pieces of rock.

Actually Jupiter's moon system has more mass than the entire asteroid belt. (excluding Jupiter)
There are 67 known moons of Jupiter, most of them are the size of asteroids, of particular interest are Callisto 4820.6 km diameter, Leda 16 km diameter, Himalia 170 km diameter, Lysithea 36 km diameter, Elara 86 km diameter, Anake 28 km diameter, Carme 46 km diameter, Pasiphae 60 km diameter, and Sinope 38 km diameter.
These outer moons are outside Jupiter's radiation belts, and they are quite close together compared to the asteroid belt, and remain so. It would be possible to have commerce between them, and even the small ones are quite massive compared to many of the asteroids.

RobertDyck · 2016-06-28 05:24:08

I've heard the argument that Callisto is outside Jupiter's radiation belts, while Ganymede is not. But that isn't true.

As you can see above, Callisto is inside the Magnetodisk. Outside the direct current sheet, but is that significant? This looks like radiation is a matter of degree, not present/absent. And Ganymede has a magnetosphere, so how much reaches the surface? That's the only thing that matters.

Tom Kalbfus · 2016-06-28 08:40:52

Another place that is relatively radiation free is right above Jupiter's atmosphere, the trace gases above the atmosphere sweeps the orbital space in that region free of charged particles, since they can't build up to lethal concentrations, much as our low orbital space where the ISS orbits is also relatively free of radiation. Humans could settle that region, with the requirement that they expend propellants every now and then to stay in orbit and not fall into Jupiter's atmosphere. A typical orbit in this low region takes about 3 hours. The hard part about settling this region would be getting humans through the intense radiation bands. Fortunately Jupiter provides a lot of rocks which could be used as shielding on the way down. If you can put enough water ice between yourself and the radiation, then you could be protected. Once inside you get out, and use the fringes of the atmosphere to slow down into a nearly circular orbit, the massive rock-ice shield you used to get here becomes a meteorite burning up in Jupiter's atmosphere. Once in that low orbit region, Jupiter's magnetic field protects you from the most powerful solar storms the Sun can throw at you.

Antius · 2016-06-28 11:21:41

GW Johnson wrote:

Longer-term, the asteroids hold more promise than any of the planets or their moons. There's more possible stuff there to use, and a smaller gravity well out which to extract it, than any other location in the entire solar system. So, the old sci-fi tales about asteroid miners will probably end up being true. Gonna take us a while yet to make it true, though.
GW

I tend to agree. Stony asteroids greater than 2km in diameter are good candidates for shell world colonisation. It would be easier to arrange artificial gravity under microgravity conditions than to attempt to build the massive bearings needed for a roulette wheel type colony on a world like the moon. Just hang buildings from cables inside the shell and rotate them.

In many ways, Titan is the least habitable of the bunch. Whilst having an atmosphere is superficially useful, but heat fluxes would make any EVA very difficult. And you aren't just dealing with heat flux into a cold dense gas, but boiling heat fluxes if it starts raining liquid methane.

Calisto is only slightly more habitable than Ganymede. Solar power is almost useless so far from the sun. It would make sense for any society to pursue a subsurface existence, using fusion power for energy and growing food in compact artificially lit vertical farms. In which case the radiation issue is far less important.

Antius · 2016-06-28 11:34:44

Tom Kalbfus wrote:

Another place that is relatively radiation free is right above Jupiter's atmosphere, the trace gases above the atmosphere sweeps the orbital space in that region free of charged particles, since they can't build up to lethal concentrations, much as our low orbital space where the ISS orbits is also relatively free of radiation. Humans could settle that region, with the requirement that they expend propellants every now and then to stay in orbit and not fall into Jupiter's atmosphere. A typical orbit in this low region takes about 3 hours. The hard part about settling this region would be getting humans through the intense radiation bands. Fortunately Jupiter provides a lot of rocks which could be used as shielding on the way down. If you can put enough water ice between yourself and the radiation, then you could be protected. Once inside you get out, and use the fringes of the atmosphere to slow down into a nearly circular orbit, the massive rock-ice shield you used to get here becomes a meteorite burning up in Jupiter's atmosphere. Once in that low orbit region, Jupiter's magnetic field protects you from the most powerful solar storms the Sun can throw at you.

Jupiter's atmosphere would be an awful place to live. The gravity would be over 2.5 times Earth surface. The lift provided by a hot hydrogen balloon would be poor, even at large temperature differences. The delta-v needed to get out again is prohibitive. Quite literally a death trap. Why would you go there is the first place?

As for traversing the radiation belts, magnetic fields provide a better mass-ratio than solid ice. Ultimately, magnetic shielding both static and on spacecraft, may make the inner moons of the Jovian system reachable by human beings. Iron solenoids on Amalthea and Io, could shield selected portions of their surface and colonies could be built under their protective umbrellas. It doesn't matter if the electromagnets weigh thousands of tonnes as they won't have to move. In truth, these worlds are so deep in Jupiter's gravity well that they will always be at a strong disadvantage to worlds further out. People make money through commerce and a deep gravity well is a barrier to trade.

Last edited by Antius (2016-06-28 11:35:46)

Tom Kalbfus · 2016-06-28 12:20:29

Antius wrote:

Tom Kalbfus wrote:
Another place that is relatively radiation free is right above Jupiter's atmosphere, the trace gases above the atmosphere sweeps the orbital space in that region free of charged particles, since they can't build up to lethal concentrations, much as our low orbital space where the ISS orbits is also relatively free of radiation. Humans could settle that region, with the requirement that they expend propellants every now and then to stay in orbit and not fall into Jupiter's atmosphere. A typical orbit in this low region takes about 3 hours. The hard part about settling this region would be getting humans through the intense radiation bands. Fortunately Jupiter provides a lot of rocks which could be used as shielding on the way down. If you can put enough water ice between yourself and the radiation, then you could be protected. Once inside you get out, and use the fringes of the atmosphere to slow down into a nearly circular orbit, the massive rock-ice shield you used to get here becomes a meteorite burning up in Jupiter's atmosphere. Once in that low orbit region, Jupiter's magnetic field protects you from the most powerful solar storms the Sun can throw at you.
Jupiter's atmosphere would be an awful place to live.

Did I say in Jupiter's atmosphere?

This is a diagram of Earth's atmosphere layers, technically the area where are low earth orbiting satellites orbit is called the Thermosphere, Jupiter has one too.

Just above the stratosphere in this diagram is Jupiter's thermosphere, now this thermosphere is not thick enough to stop objects from orbiting it, over the long haul, objects at this altitude will slowly decay in its orbit, and like skylab will plummet down into the atmosphere, but that can be years. What the thermosphere does do is prevent radiation bands from building up here, because it takes a long time for Jupiter's magnetic field to collect these charged particles at this distance from the sun, the hydrogen atoms in this near vacuum are thick enough to prevent such radiation build up, so it is safe for astronauts in their space suits here! As you can see in the diagram of Jupiter's atmosphere, it does have a habitable region, if humans can tolerate air pressures of around 7 bars, and I think they can.

The gravity would be over 2.5 times Earth surface.

Astronauts and fighter pilots have endured greater G-loads, and the military is working on exoskeletons, and it already has counter-pressure suits for its fighter pilots. So a human to survive in Jupiter's lower atmosphere would need these things, and also would need to breath a mixture of helium, nitrogen and oxygen, which deep divers do all the time. The temperature as you can see at the water cloud region isn't too bad. If you could just deal with the gravity, the rest isn't that much of an obstacle. Also in Low Jupiter orbit, you wouldn't feel those 2.5-Gs, you would feel weightless just like you do in low Earth orbit, except in the case of Jupiter, it would take 3 hours to complete each orbit instead of 90 minutes. Building structures in Low Jupiter orbit would be the same as in low Earth orbit, you need to hold in air, no need to worry about the radiation, as the magnetic field around Jupiter and the Thermosphere takes care of that.

The lift provided by a hot hydrogen balloon would be poor, even at large temperature differences.

It is basically a hot air balloon, you just need an energy source to keep the "air" meaning hydrogen, hot relative to the surrounding "air". If hydrogen leaks out, you just pump it back in and heat it.
Hot%20Air%20Balloons%20(2).jpg
You need something like this, the heat source instead of a flame would likely be a nuclear reactor

The delta-v needed to get out again is prohibitive. Quite literally a death trap. Why would you go there is the first place?

It would be a good place to set up a penal colony. Jupiter would make an excellent prison planet, no one is going to escape from it, but they could be kept alive there. From Low Jupiter Orbit its easier, you still need radiation protection to survive on the journey out however.

As for traversing the radiation belts, magnetic fields provide a better mass-ratio than solid ice. Ultimately, magnetic shielding both static and on spacecraft, may make the inner moons of the Jovian system reachable by human beings. Iron solenoids on Amalthea and Io, could shield selected portions of their surface and colonies could be built under their protective umbrellas. It doesn't matter if the electromagnets weigh thousands of tonnes as they won't have to move. In truth, these worlds are so deep in Jupiter's gravity well that they will always be at a strong disadvantage to worlds further out. People make money through commerce and a deep gravity well is a barrier to trade.

One can use a system of tethers to lower oneself towards Jupiter and to also climb out of its gravity well. Lots of materials in the Jupiter system to build things out of too, and they are in relatively close proximity to each other, while the asteroid belt is more spread out and diffuse.

GW Johnson · 2016-06-28 15:55:21

Just what are you going to make these "tethers" from, and just exactly how?

GW

Tom Kalbfus · 2016-06-28 17:05:54

GW Johnson wrote:

Just what are you going to make these "tethers" from, and just exactly how?
GW

Well for one thing, Jupiter has rings, they are not as showy as those of Saturn's, but they are there, and in sufficient amounts to make tethers out of, and there are plenty of moons, 68 of them in fact, and there are most likely more! The small moons are easier to mine because of the low gravity.

GW Johnson · 2016-06-28 18:59:05

Tom:

How are you going to turn ices and rocky minerals into engineering materials that have tensile stress capability with some degree of resilience? THAT is the question I asked, which you DID NOT answer.

Whether it comes from moons, rings, asteroids, or passing spaceship exhausts doesn't matter a tinker's damn. What matters is how to make useful materials out of stuff like that. Your replies indicate you have zero clue how such might be done. So join the club, no one else knows how to do that, either. It is a technology that does not yet exist. It is science fiction.

It will remain science fiction until someone actually figures out how to do it. I'm not holding my breath waiting, either!

GW

Last edited by GW Johnson (2016-06-28 18:59:32)

Tom Kalbfus · 2016-06-28 20:30:48

Usually most materials are manufactured by chemical synthesis, just ask an appropriate engineer how its done, I am not one. the strongest material is carbon, and I'm pretty sure Jupiter's ring materials has carbon in it.

RobertDyck · 2016-06-29 04:43:25

Sound like your talking something from Star Wars. Lando Calrissian's gas mine.
history-1_b45d9282.jpeg?region=0%2C0%2C800%2C340

Tom Kalbfus · 2016-06-29 06:51:14

Jupiter has Helium-3, it is probably the largest source of it besides the sun. Jupiter also rotates quite fast. It has an almost 10 hour day, and the orbital period for a low orbit is only three hours! At higher altitude it is 10 hours.
At Jupiter's radius (71,492 km) its 2.9641440306301296 hours for 1 orbit. At 160,000 km in radius, the orbit period is 9.924145125788737 hours. Jupiter rotates once every 9.925 hours, so the 160,000 km level is Jupiter's synchronous orbit. If one were to build a standard space elevator for Jupiter, one would start from there. But considering that there are two known moons orbiting within that distance the logical place to build a space elevator from would be from its innermost Moon Metis. Metis has an orbital period of 7 hours and 4.5 minutes, about 3 hours shorter than Jupiter's rotation which is 9.925 hours The end of the space elevator would be hanging in the atmosphere. Jupiter spins at its equator at 45,259 km/hour The end of the elevator within the atmosphere would be moving at 64,171 km/hour, the difference between the two velocities is 18,912 km/hour or 5.25 km/sec. At the end of the tether, you'd weigh only 2.075 times your Earth weight because of that rotation. To use the tether, a rocketship would first have to accelerate to 5.25 km/sec and then leap out of the atmosphere and catch onto the end of this tether, then it would climb the tether up to Jupiter's Moon Metis, and then continue up another tether extending from Metis's far side and use centrifugal force to fling to a higher orbit around Jupiter.

Last edited by Tom Kalbfus (2016-06-29 06:56:25)

GW Johnson · 2016-06-29 09:09:27

I like the idea of an O'Neill habitat. I do not think we are yet quite ready to build one. I certainly do not like the numbers O'Neill used in his calculations. Here's why:

When I look in data references like Mil Handbook 5, I simply do not find properties for “1920’s steels” as high as O’Neill used in his calculations. The structural steels really haven’t changed much in over a century, anyway, other than some really tough new alloys for high-temperature service in jet engines.

For low-carbon steels like an AISI 1025, you have ultimate tensile strength near 80 to 100 kilo-psi (ksi), and yield near 36 ksi. These have quite a lot of strain at failure, so the stress-strain curve integral (“resilience”) is high. They will deform quite a ways before they break, absorbing quite a bit of energy. They usually do not heat treat very well, if at all. About 700-800 F is the max temperature exposure allowable, and strengths are rather low (around factor 5 to 10 reduction) when that hot. Density is 0.283 lb/cu.in (pci), compare that to water at .0361 pci. Strength/weight is measured by ultimate tensile strength divided by density: 80 to 100 kilo-psi/pci = 283 to 353 kilo-inches.

High carbon steels like a tool steel can have ultimate strengths near 200 ksi, with a yield well over 80 ksi, but they have very low strain at failure, which is inherently a low resilience. These give little warning and just suddenly shatter-crack in a brittle fashion, like a piece of glass. These are the heat-treatable alloys. Not heat-treated, their properties look like the low carbon steels. (You get the high strengths by heat treat.) You pay for such strength with loss of resilience. These are also limited to around 700-800 F exposure, or you lose your heat treat and your strength. Density 0.280 pci is typical. Strength/weight is near 700 kilo-inches.

The 300-series stainless steels are usually around 90 ksi ultimate, 30 ksi yield. They are not heat treatable, but they are cold-workable to higher strengths. Usually they are produced in the annealed (not cold-worked) condition. Resilience is quite good in the annealed condition, far lower when cold-worked stronger. Temperature exposures allowable are generally up to 1200 F with crudely half he annealed strength, knowing it will be fully annealed after even a modest temperature exposure. Some alloys (310 and 316) can go even hotter (near 1600-1800 F) without severe corrosion and scaling. Density near .289-.290 pci is typical. Strength/weight ~ 310 kilo-inches. The advantage here is higher temperature exposure for about the same strength to weight at room temperature as the low carbon steels. Strength to weight hot is better than any carbon steel hot.

The titaniums are no better in strength than the high carbon steels, and cannot be worked-to-shape the way most steels can. Titanium has very poor resilience. It goes no hotter than carbon steel does. Its only advantage is about half the density of the steels. Density from 0.161 to 0.175 pci is typical. Strength/weight is its sole advantage at ~ 1170 kilo-inches. The two beta-phase titanium alloys that actually can be worked-to-shape unfortunately age at room temperature over time, which means their crystalline structure gets coarse, they lose all their strength, and they spontaneously crack. The alpha-phase alloys cannot be worked-to-shape, you have to “carve” your parts out of solid blocks.

Plain pure aluminum is really soft and crummy: around 13 ksi tensile strength at best. You have to alloy it properly with copper to create the alloy “duralumin”, in order to get useful properties. Some of these are heat treatable, some are not. Aircraft-type heat-treated alloys might have as much as 60-68 ksi tensile strength. They’re all irreversibly “soft butter” at about 300 F, and a white-hot molten puddle at 900 F. Density from .098 to .100 pci is typical. Strength/weight 680 kilo-inches explains its widespread use in aircraft structures that do not get hot: just like high-carbon steel, but much lighter. You cannot use it where things get hot, like engine mounts, or for skins flying at or above just about Mach 2 through cold stratospheric air (air friction boundary layer recovery temperatures near 200-240 F).

Your working stress has to be well below the theoretical material strength because you need factors of safety to cover the things you do not know, or the risks you cannot quantify. These factors are entirely experience-based. Take for example a high-carbon steel at 200 ksi ultimate with about a heat-treated yield of 100 ksi. Use my industrial equipment design preferences. Factor 4 below ultimate is 50 ksi. Factor 2.5 below yield is 40 ksi. The lesser is 40 ksi, and that’s my design stress level, not O’Neill’s 100+ ksi.

And, I would only go that high if there were no cyclic loads (a fatigue risk), and no heat exposures (direct strength reduction plus a creep failure risk). Both of those limit and reduce the working stress allowable in your design, sometimes rather sharply.

For example, I might allow a working hoop stress in a 304 stainless steel pipe to be 12 ksi at room temperature. That’s yield-limited with my industrial factors from 75 ksi ultimate and 30 ksi yield. Hot (1200 F), it is creep-limited to about 10 ksi. But, hot (1200 F), it is yield-limited to only 6 ksi, because of the strength reductions with temperature (44% ultimate, 50% yield; yeah, they’re different!). Thus I would size wall thickness for hot service based on hoop stress not to exceed 6 ksi, and with no other loads applied.

I would use different knockdown factors for an aircraft flight structure. Generally I use factor 1.1 below yield, except where reduced for fatigue life limitations, or also reduced by hot creep failure in a hot-structure situation. But, either way, you cannot just use the theoretical strength the way O’Neill did.

Most physics majors do not understand such nuanced issues in design, because that kind of thing was not in their education. The mechanical engineers are actually trained to do this by their education. Those who do it for a living have years of real experience doing this. Old guys like me did it for decades with nothing but a pencil and paper and a slide rule or pocket calculator, which means we know the complicated nitty-gritty of it very, very intimately.

We old guys would never trust somebody else’s computer code solely for these answers, either. There are too many garbage-in/garbage-out problems with computers, especially if the person setting up the inputs doesn’t know how to do it by hand for himself. Ignorance really is quite dangerous in design.

GW

ps - resilience in a space habitat structure really is important. You wouldn't want the entire structure to shatter and explode like a bomb under its internal pressure, just because it got hit by one little paint flake, would you?

pps -- oops, wrong thread, but that's OK.

Last edited by GW Johnson (2016-06-29 09:28:12)

Tom Kalbfus · 2016-06-29 09:26:16

Fair enough, but you probably meant for this post to go to the O'Neill thread. But we can build O'Neill colonies in orbit around Jupiter as well. Not sure what the radiation environment is around Metis, but it is embedded in a ring, that might help. s for mining Jupiter, it would require carbon nanotube space elevators, and would use the moons orbital energies to lift these gases out of Jupiter's gravitational well. That is we would slowly draw the moons closer to Jupiter in exchange for lifting gases up. Helium-3 is on gas, there is also plain old hydrogen, which we could send to Venus to make an ocean with, and supply floating habitats in Venus' atmosphere with water. Place a hydrogen gas bag around a breathable envelope of air, feed the hydrogen through fuel cells and combine with excess oxygen to make water. The water is used to grow plants which make oxygen, human colonists consume the plants for food, drink, bath and wash in the water, and use some water for flushing their toilets, and the waste water is dumped into Venus' atmosphere and Venus does the rest. Over time this dilutes Venus' acid clouds, Venus gets even hotter down below, making it easier to free oxygen for carbon-dioxide, and so we slowly build up the water content of Venus.

GW Johnson · 2016-06-29 10:05:57

Just parking space habs in places like L-5 is probably how this gets started. Much safer than risking Jupiter radiation and gravity well problems, or the lethality of Venus's surface.

GW

Tom Kalbfus · 2016-06-29 10:50:16

Yeah, probably. I was thinking of the longer term, and the Juno probe is coming up, so Jupiter is on the mind of many people at this moment. One idea is to build a hab around an orbital tether, or a space elevator. Build enough space elevators and connect them with a planetary ring at geosynchronous orbit. Which is at 35,786 km. At this distance, you could wrap an extended Model 1 Space colony along this orbit, lets use a radius of 100 meters in this example. If it rotates 3 times per minute, it will produce 1-G of spin gravity. The circumference of this orbit is 224,850 km so we bend this cylinder into a circle and make it 224,850 km long and rotate it inside out through the ring it forms. Now at 35,786 km radius, this bending is barely noticeable. The surface of the rotating cylinder would have to stretch and compress with every rotation, but the amount of stretching and compression needed to make this happen is very small, and the momentum of the rotation would be greater than the energy needed to compress and stretch these surfaces every 20 seconds. I use the radius of 100 meters because this minimizes the differences in orbit radii, keeping it to 200 meters. So the surface furthest away from Earth is at 35,786,100 meters, and the surface closest is at 35,785,900 meters and the difference between these two radii and circumferences is 1.0000055887933515714289706280965, this is the number you get if you divide the larger radius by the smaller. this is a 0.00055887933515714289706280965% difference, I think even steel can stretch this much, but if your really concerned about it, we can segment it and include rubber expansion joints.

The amount of real estate this represents is 141,277,421,632 square meters,
or 34,910,271.52 US acres.

The inside of this hollow cylinder would seem fairly straight, one football field above ones head would be the center of the axis of rotation, look in either direction along the cylinder and it will seem to "diminish to infinity", the slight curvature of this orbit would not be apparent.

Now where would the space elevators go? You can have a counter-rotating segment which slides past the rotating cylinder surface, and use a plasma window to cover the gap to prevent too much air from leaking out into space, this air can always be replaced anyway by more air brought up from Earth.

Last edited by Tom Kalbfus (2016-06-29 10:58:58)

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