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I'm initiating this thread in response to a suggestion by moderator thanson43206. A repository point for all suggestions regarding missions, research proposals, and wild comments involving Callisto.
Last edited by Oldfart1939 (2024-03-18 22:34:20)
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This post is reserved for an index to posts that may be contributed by NewMars members over time.
Best wishes for success with this interesting and timely new topic!
The researchers, project managers and supporting staff members who will be carrying out a mission to Callisto are alive on Earth today.
If we have a reader not yet a member, who would like to help OF1939 develop this topic, please see the Recruiting topic for procedure.
This topic has the potential to become a rallying point for all (or at least some) of the folks who will become involved in this mission.
Some will be making a lifetime commitment, but most will be pitching in on short but vital tasks that need to be defined and then completed.
To start with, there is need for an outreach campaign using free media, such as email or the newer services such as Facebook.
If someone ** does ** apply for membership to assist with development of this topic, please plan to participate for some time.
(th)
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I think there is a misconception that Callisto is a low radiation environment. It does receive far less charged particle radiation from Jupiter magnetosphere. But so far as I know, it is still subject to the radiation background of cosmic rays. It also has no atmosphere. So radiation doserates would presumably exceed those on Mars surface. Does anyone have any information that can give a more complete picture on Callisto surface radiation?
Aside from that, its surface is rich in volatiles but also contains substantial non-ice components which can be used to build infrastructure. Living here would require that colonists are able to produce food efficiently without sunlight. Jupiter is over 5AU from the sun. But this also begins to look like a prerequisite for Mars colonisation. For small exploratory missions, astronauts can bring food with them. The only question is the increased food mass due to the longer flight time to a more distant body.
One additional question is the amount of dV required to match velocity with Callisto. How would this effect mission propellant requirements? Callisto is further out than the other galileans. But the velocity a ship would pick up from entering Jupiter's gravity well will still be substantial. And Callisto has no atmosphere to use for aerobraking.
Last edited by Calliban (2024-03-20 04:14:29)
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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For Calliban re #3
Thank you for the hint for someone to follow up in navigation planning ....
GW Johnson is away at a conference right now, so we'll have to wait for his return, but I'm hoping he might be willing to consider the interesting question you posed, of how best to plan a flight from Earth to Callisto, so that residual velocity at encounter is minimal.
This dedicated topic has plenty of room for addition of facts about the Moon, and for detailed plans for an expedition there.
A human base seems on the ambitious side to me, but we may well have members willing to tackle the challenge.
A probe to visit Callisto is likely, depending upon funding. Ground truth would be helpful.
(th)
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I found this for it:
https://en.wikipedia.org/wiki/Callisto_(moon)
Quote:
About 0.01 rem
The radiation level at Callisto's surface is about 0.01 rem (0.1 mSv) per day, which is just over ten times higher than Earth's average background radiation, but less than in Low Earth Orbit or on Mars1. Callisto sees lower radiation levels and less influence from the Jovian magnetosphere than Ganymede and Europa because of its remote location, orbiting beyond Jupiter's main radiation belts
https://www.universetoday.com/57581/cal … 0-300%20km.
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Evidence of this ocean include Jupiter’s magnetic field, which shows no signs of penetrating Callisto’s surface. This suggests a layer of highly conductive fluid that is at least 10 km in depth. However, if this water contains ammonia, which is more likely, than it could be up to 250-300 km.
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Composition and Surface Features:
The average density of Callisto, at 1.83 g/cm3, suggests a composition of approximately equal parts of rocky material and water ice, with some additional volatile ices such as ammonia. Ice is believed to constitute 49-55% of the moon, with the rock component likely made up of chondrites, silicates and iron oxide.Callisto’s surface composition is thought to be similar to its composition as a whole, with water ice constituting 25-50% of its overall mass. High-resolution, near-infrared and UV spectra imaging have revealed the presence of various non-ice materials, such as magnesium and iron-bearing hydrated silicates, carbon dioxide, sulfur dioxide, and possibly ammonia and various organic compounds.
Quote:
Beneath the surface is an icy lithosphere that is between 80-150 m thick. A salty ocean 50–200 km deep is believed to exist beneath this, thanks to the presence of radioactive elements and the possible existence of ammonia. Evidence of this ocean include Jupiter’s magnetic field, which shows no signs of penetrating Callisto’s surface. This suggests a layer of highly conductive fluid that is at least 10 km in depth. However, if this water contains ammonia, which is more likely, than it could be up to 250-300 km.
Beneath this hypothetical ocean, Callisto’s interior appears to be composed of compressed rocks and ices, with the amount of rock increasing with depth. This means, in effect, that Callisto is only partially differentiated, with a small silicate core no larger than 600 km (and a density of 3.1-3.6 g/cm³) surrounded by a mix of ice and rock.
https://en.wikipedia.org/wiki/Magnetosphere_of_Jupiter
Quote:
Jupiter's magnetic field is enormous, with a volume one million times that of Earth’s magnetosphere1. Its equatorial field strength is about 417.0 μT (4.170 G), which corresponds to a dipole magnetic moment of about 2.83 × 10 20 T · m 32. This makes Jupiter's magnetic field about 20 times stronger than Earth's, and its magnetic moment ~20,000 times larger2. Jupiter's magnetic field extends up to nearly 2 million miles from the planet and its influence likely reaches beyond the orbit of Saturn3.
So then, the globe or comet tail of the magnetic field is enormous. Although we consider solar as feeble at Jupiter, consider the enormous volume of the magnetic field. If you had concentrating mirror in selected rings, then the amount of sunlight that could be intercepted would be enormous. A sort of inverse Dyson Swarm.
While it is true that Jupiter has wicked magnetic radiation belts, so does the Earth, but then it seems the Callisto has a more merciful place in the field. It may be that there are better orbits than Callisto for radiation.
So, now Callisto being made, at least on the surface of materials for mirrors and seas, then it seems to me that that can be a path to take with the Jupiter system, at least with Callisto.
I have the sunlight level at 3.7% that of Earth, but then consider if a world is not occulting your solar collector in orbit, sunlight is constant, unlike the surface of the Earth, so multiply that by 3.7 by 2 = 7.4% as the equivalent that you would get on the surface of the Earth. Of course clouds and atmosphere also block additional light on the surface of the Earth.
But then consider how large the orbits of Jupiter could be, the sphere for that. Some of that would have magnetic protection and you could propel in the magnetic field as well.
So, not a small reward, if you can do it.
Done
Last edited by Void (2024-03-20 21:50:53)
Done.
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I recall reading that both Callisto and Ganymede have very tenuous atmospheres of Carbon Dioxide, the density correlated to the very low gravitational constants. I can't recall the source of this information--possibly in Robert Zubrin's book "Entering Space."
I envision Callisto as strictly a research station and possibly a safe haven from longer deep space missions to the Saturn system. Allow a crew to have some new social activities and not be worried about the systems on the space vessel
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The maximum background radiation dose rates in certain parts of Ramsar, Iran can be over 7X higher than the surface of Callisto, but there doesn't appear to be any increase in cancer rates when compared to other cities in Iran with far lower background radiation levels. The same phenomenon was notice in other cities with high background radiation levels, but Ramsar is the extreme outlier. That city has very high background radiation, more than what is allowed for workers who operate nuclear power plants, but no marked increase in cancers. This seems to suggest that the Linear No-Threshold principle may not be very scientific, even if the reasoning behind it is sound. This should not be taken to mean that there is no risk, or that we can throw any old group of humans on Callisto and except the same results, and the mean dose on Callisto will be about 4X the mean dose in Ramsar, albeit far less than the maximum annual doses received in Ramsar. If you have a nuclear energy source, then you have a way to live there. The most deleterious effect from living there will likely be the very low gravity, relative to Earth.
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The surface appears to consist of a mixture of silicates and ice. It should be possible to use a low temperature heat source to melt tunnels through the ice. An aqueous homogenous reactor perhaps? Operating temperature would not need to exceed the boiling point of water. The liberated material will be a mixture of water and silicates, which should seperate out by gravity. After applying insulation panels to the walls, the tunnels could be pressurised and heated.
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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The natural average Earthly background is about equal to the US average background of about 300-330 milli-REM. Sorry, I do not know how to convert that. It's 0.3 to 0.33 REM/year, which is not a very large number. (Supposedly, about a third of that background traces to coal burned in power plants. Coal is slightly radioactive, as is frack water backflow.) It is very important to note that natural background varies strongly with location. In the mountains where ore-bearing rocks are near the surface, and there is significant radon gas coming from underground, it is supposedly as much as 10 times higher (3-3.3 REM/year). REM is "Roentgen Equivalent Man", meaning radiation intensity multiplied by a human vulnerability factor.
For comparison, the space radiation environment outside the Earth's Van Allen belts is mostly a drizzle of cosmic rays plus some solar wind, peaking at 60 REM/year at solar minimum, and only about 24 REM/year at solar maximum. These were predicated on an expected 3% increase in the rates of cancer late in life. Apparently, the solar wind slows the cosmic rays down a lot, and the solar wind is stronger during solar max. That's a pretty good estimate for Venus/Earth/Mars space. Not so sure about Jupiter and beyond. Even with the heliopause way beyond Pluto.
Before they were recently changed (lowered slightly), the astronaut exposure criteria were no more than 50 REM accumulated in any one year, no more than 25 REM accumulated in any one month, and a career exposure limit that varied with age and gender, but which usually falls in the 300-400 accumulated REM ballpark. 50 REM accumulated over only an hour or two is fatal to 50% of those exposed, and 100 REM in an hour or two is fatal to 100% of those so exposed. Time makes an enormous difference.
Those larger doses are well known since not long after Nagasaki and Hiroshima. I saw them documented in AEC's report "Effects of Nuclear Weapons, 1957". It's the lower doses around 1-10 REM/year and less, that are not well known from any data, which is where the linear-with-dose-rate scaling is used. The assumptions underlying that dose rate scaling, are still only assumptions. There is no recognized data.
The fallout from a nuclear surface burst close by can be as high as 5000 REM/hour, based on the explosions in Japan, and after the warhead tests in the Nevada desert! It can be lower, even a lot lower. But you cannot count on it being lower, because sometimes it's just high! Air bursts at significant altitude are a lot lower in fallout radiation intensity. (500-5000 m is not significant altitude!) Lots lower if the fireball does not come close to touching the surface. Most of the fallout is surface dust brought up through the incredibly-radioactive fireball materials by the columnar suction that creates the mushroom cloud.
The lethal space radiation threat is NOT cosmic rays! Never was, never will be! There are many who tell you it is, but they are lying to you! It is instead radiation released in a burst by explosions on the sun. In a word, solar flare events, which occur erratically, and are very, very directional. These are quite comparable to nearby nuclear weapon explosions. Incredibly intense radiation intensity rates, and over in a few hours.
The only other thing to understand is that not all radiation is the same. Cosmic rays are mostly hydrogen nuclei moving at near lightspeed. These are very difficult to shield. Solar flare particles are mostly hydrogen and helium nuclei, moving very much slower at solar wind speeds. Those are much, much easier to shield against, which is what the 25 g/cm^2 figure of merit for shielding is all about. Van Allen belt radiation is mostly solar flare and wind particles caught in Earth's magnetic field, but still moving in circles about the field lines at something like solar wind speeds. Intensity resembles solar flare events and nearby nuclear explosions.
GW
Last edited by GW Johnson (2024-04-15 15:41:37)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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I will point out to our members that Robert Zubrin's book, "Entering Space" details out the radiation environment on Callisto and other Jovian moons. I would be interested in the views of others here about his assessment. The background cosmic rays are not an immediate threat to life and becomes problematic after a half human lifetime of exposure. IMHO, Callisto would be an admirable site for a large astronomical observatory and radio observatory. The human population there could maintain the systems more readily than we can "fix" Hubble and the JWST.
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Interesting idea. I take it Callisto is outside Jupiter's radiation belts.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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GW-
That is for the most part correct; there is one period during the orbit around Jupiter where there's a radiation "plume" which greatly increases the effects with concurrent radiation. I may be in error writing this in it's details, as I've loaned my copy of Entering Space to a friend and can't check this. I will check these details and update as needed.
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I was interested in Ganymede years ago because the book "Farmer in the Sky" by Robert A. Heinlein talked about homesteading there. I posted the idea of a system of orbital mirrors to increase illumination and heat. Enough mirrors to triple cross sectional area. That was before we discovered Jupiter's radiation belts. Ganymede is the largest moon in our solar system. But the Galileo probe measured it's flight path as it passed Jovian moons measuring gravity by how much it deflected the probe's flight path. Ganymede must have low density to deflect the probe's flight path that little. Then calculating surface gravity, Ganymede has 1/7th of a G, Calisto has 1/8th. I tried to devise atmosphere that would be breathable on Ganymede, and would work on Calisto too. A mixture of oxygen and sulphur hexafluoride. The idea is a heavy gas to produce sufficient pressure in light gravity. That gas is clear, colourless, odorless, and non-toxic, so as benign as nitrogen on Earth. It's also a super greenhouse gas so would help trap heat in. Air currents would have to mix the gasses so they don't stratify; you need oxygen at the surface where you breathe, not just the top of the atmosphere. So it may have to be windy. A thick atmosphere would block what radiation does reach Callisto. Density indicates the moon must be covered with dirty ice. So there should be plenty of ice available.
My mirror system would result in twilight illumination 24/7 at moderate latitudes. Lower latitudes (<30°) would have illumination most of the day, but there would be brief darkness in the middle of the night. Equator would have the greatest period of darkness. It's tide-locked so it's rotational period is equal to it's orbital period: 16.6890184 days. Assume the area of darkness on the night side is 1/3 the moon's diameter because mirrors extend to 3 times the moon's diameter. That means at the equator it has 5.563 days of darkness and twice that time of light.
Jupiter's semi-major axis is 5.2038 AU so light of a Jovian moon is 3.6828% that of Earth. A mirror system that extends to 3 times the moon's diameter would increase illumination 9 times. That makes it 33.2354% Earth. Adjust for periods of light vs dark, and direct illustration vs only mirrors. Surface would be a little dimmer than Mars.
Of course if you surrounded the moon with mirrors like that, a surface telescope wouldn't work.
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GW-
Upon checking, I found a reference stating that the surface radiation on Callisto is 0.01 rem per day without any protective measures.
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0.01 REM/day*365 days/year = 3.65 REM accumulated (slowly) in one year, compared to the old safety limit of 50 REM in one year. OK.
0.01 REM/day*30 days/month = 0.3 REM accumulated slowly in 1 month. Compare to the old safety limit of 25 REM in one month. OK.
0.01 REM/day*365 day/yr*10 years = 36.5 REM accumulated over a career 10 years long. Compare that to the old career safety limit of something in neighborhood of 300-400 REM accumulated over the entire career, which varied with age and gender. Looks OK to me.
I know they recently lowered the limits, but only a little bit.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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It all depends on how much risk we are willing to take. To put the consequences of radiation dose into perspective: A 100REM (1Sv) dose will reduce an adult humans life expectancy by about 18 months and will add a 5% additional risk of dying from cancer. Those are the risks all else being equal. Assuming the astronauts live healthier than average lives and don't smoke, it is likely that the consequences of a 1Sv dose will not result in a measurable increase in cancer mortality relative to a random sample of Earth based humans. That is because humans are subject to a lot of toxins, radiation being but one. Air pollution, tobacco smoke, unhealthy foods and alcohol, all place carcinogenic loads on the human body. If astronauts on deep space assignments are exposed to less of these, then the effects couod easily counterbalance even a large lifetime radiation dose.
Something else to consider though is that cosmic rays contain heavy nuclei of atoms travelling at a large fraction of C. If one of those passes through a nerve or other sensitive tissue, it could do enough local damage to impair the function of the tissue. This is one way that cosmic radiation is different to background radiation here on Earth. Fortunately, heavy nuclei are a relatively small component of cosmic ray flux. Still I wonder what the effects would be if someone were hit by an OMG particle. There are single cosmic ray particles with as much energy as air rifle pellets. Now thats gotta hurt!
Last edited by Calliban (2024-04-17 16:11:50)
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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Overall, the risk is similar to being an airline pilot who flies routinely around 36,000 feet approximately 300 days per year. The daily exposure would be far less on Callisto, as a regolith covered habitat needed for thermal protection, in addition to radiation, would be where most activity would take place. Figure maybe only 4-6 hours per day outside the habitat would reduce the radiation exposure by 75%.
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The main challenges of living on a body that far from the sun are growing food and keeping warm. Ice is a mediocre insulator, roughly equivelant to rock, with thermal conductivity 1-3W/m.K. So a thick layer of ice will be useful in minimising heat loss from habitats. That will double as a radiation shield.
Growing food is much more challenging. Recent experiments have proven very succesful at growing simple plants, algae and fungi in acetate solution. This could eventually allow the efficient conversion of electrical energy into food based energy. If this succeeds, we won't need sunlight to produce food. A fission or fusion reactor can provide the required energy. With technology like that, we really could colonise almost anywhere.
Over a very long period on Ganymede and Callisto, we could use solar mirrors, greenhouse inducing aerosols and fusion reactors to warm up the surfaces of these moons. This will result in the development of thin water vapour atmospheres as water ice sublimes. UV radiation from the sun will gradually break this down into H2 and O2, with the former escaping into space. The moons will gradually accumulate O2 dominated atmospheres. It may take tens of thousands of years to build an atmosphere that humans can breath. But we are in this game for the long term. Once a thin atmosphere is created, we could bombard it with ice packages from Jupiter's other moons. This would hypersaturate the upper atmosphere with water vapour, speeding the process up.
Last edited by Calliban (2024-04-18 08:24:52)
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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