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Jovian System has better colony sites than moon&mars

  1. Jan 21, 2004 #1

    marcus

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    The Jovian system is a superior target for self-sustaining colonization.

    Quite a bunch of PF people (Nereid, all the mentors in earshot, and plenty of others) know the facts.

    It is a beautiful and interesting system consisting of a variety of different moon-size objects within comparatively easy reach of each other. Trips between Jovian moons take only a few days.

    One key fact is the availability of reaction mass for propulsion.
    Europa has a thick ice shell covering its liquid water oceanic layer. Missions to the Jovian system might be equipped to take on reaction mass (water or liquid hydrogen) at Europa.

    Europa ice is estimated to be many kilometers thick.
    A colony with abundant nuclear electric generating capacity
    could hollow out habitats in the ice, far enough below the surface
    to be structurally secure.

    Other moons such as Ganymede and Callisto look interesting too, and appear to have water ice.

    Presumably the ice on Europa is rocky---has minerals mixed in with it.
    It should not be too difficult to design a chemical plant to extract the raw materials for civilization.

    Personally I would not want to go anywhere as dry and barren as mars and the moon----though mars has some lovely desert landforms, shaped in part by wind.

    Natural beauty is important and the spectacular thing Europa has is a sky with the planet Jupiter in it. Jupiter diameter is 143 thousand km and the distance from Europa is 671 thousand km.

    This means the angular width of jupiter is about 12 degrees.
    Compare this with the full moon seen from Earth which is 1/2 degree wide. We are talking about a gorgeous planet 20 times wider than the full moon is in our sky. 400 times bigger in angular area, than the full moon. With more colors and cloudforms to make it interesting.
    This is a very romantic sight.

    Humans living in the ice-caves of Europa would probably go to the surface for their honeymoons. They might even reproduce prolifically because watching Jupiter and the other Jovian moons is so romantic.

    Films made at Europa might have a good boxoffice on Earth.

    The Jovian system would be a fun place to inhabit for many reasons, including the fact that the trip from one "planet" to the next takes only a couple of days. Each Jovian moon goes around the primary in a few days or a week. So transfer orbits have similar periods.

    In the Solar system trips between planets take on the order of years,
    whereas in the Jovian system trips take on the order of days. Plus reaction mass for propulsion is available in a not-very-deep gravity well. Energetically, water at Europa's surface is a lot more accessible than water at the Earth's surface. So as a supplier of propellant it is a good bargain to switch over from Earth to Europa.

    I do not like the "moon-mars" initiative which seems to me a bad investment and destructive of human aspirations.
     
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  3. Jan 21, 2004 #2

    enigma

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    Some problems though are:

    the multiple month long trip there or back,
    the low levels of sunlight for producing food,
    the large amount of radiation trapped in Jupiter's Van Allen belts. [are they called that there?]
    Any ship designed to get people home from Jupiter would need to be HUGE. It's an enormous gravity well... [itex]\mu_{Jupiter}[/itex] = 1.26e8 vs [itex]\mu_{Earth}[/itex] = 3.986e5
    Etc.

    EDIT: fixed numbers... *&^#% website giving G with meters instead of km
     
    Last edited: Jan 21, 2004
  4. Jan 21, 2004 #3

    enigma

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    I just ran numbers. If you go in, you ain't coming back out.

    It takes a delta V of 19.5km/sec to escape from Jupiter's gravity at Europa's distance.

    Compare with ~11.2km/sec to escape from Earth.

    Using a rocket with hydrogen and oxygen as fuel and oxidizer electrolyzed from Europa's water, you'd need 80 times the mass of the rocket in propellants, regardless of size.

    Ain't gonna happen.

    EDIT: fixed numbers
     
    Last edited: Jan 21, 2004
  5. Jan 21, 2004 #4

    marcus

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    I believe your number is off by around a factor of three here. Not that it matters awfully.

    Rough backofenvelope Europa's orbital speed is around 13.7 km/s
    so escape from Europas distance out is around 19.4 km/s
    The delta V is the difference-----19.4 minus 13.7

    this is only 5.7 km/sec

    this delta V is a factor of 3 different from the figure you quoted of 19.5
     
  6. Jan 21, 2004 #5

    enigma

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    Ach. Of course you're right.

    You'd still need a bunch of delta V to do the orbital transfer to Earth's orbit around the Sun, which isn't a small number, though.
     
  7. Jan 21, 2004 #6

    marcus

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    What you say does not sound reasonable in light of, for example, NASAs own studies of the feasibility of manned missions to Jovian moons.
    These were done in a fair amount of detail and involved
    optimizing so as to make considerable use of Jupiter's own gravity
    and the gravity of other moons.

    I do not recall any figure like the one you offer, of a delta V for escape from Jupiter gravity at Europa distance of 19.5 km/s
    or a fuel payload ratio of 80. These figures seem out of line.

    Also your conclusion "aint gonna happen" seems out of line compared with NASA's fairly detailed mission proposal.

    Maybe not gonna happen in the future we envision now, with a misdirected program. But the future changes.

    One more thing, as regards the flat statement of impossibility.
    At one time NASA had a nuclear rocket development program that was based not on explosion but on using a reactor to heat propellant.
    For example the reactor may heat hydrogen, or water, to use as reaciton mass. I do not consider it totally certain that NASA will never re-embark on nuclear rocket development. So your calculation with chemical booster might not apply. Another case where I question
    your flat statement of impossibility.
     
  8. Jan 21, 2004 #7

    enigma

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    You were right, I flubbed up. It isn't the delta V, merely the escape velocity. That comes from the Vis-Viva equation. The fuel ratio comes from the ideal rocket equation.

    It's possible to work out nuclear thermal rockets, but that improves your Isp by a factor of 3 or so. Half the mass of the ship in fuel to leave Jupiter's gravity. You still do need huge amounts of fuel to get back home, both to decelerate on a transfer ellipse, and then to decelerate again once you get to Earth. I'm not sure if it's possible to do a reverse gravity assist, or how much velocity you could bleed off from there.

    Nuclear thermal rockets are a long way from operational status, unfortunately.

    Impossibility may be a bit harsh. Anything is possible. I'll tone my statements down to: highly unlikely anytime in the near term.

    To be fair, I would love to have our current resources going into exploration missions to the Jovian moons, but bases there? well... they're just too far away from us, IMO.
     
  9. Jan 21, 2004 #8
    Would tidal effects of jupiter and the other moons on europa be a major concern for habitats built into the ice?

    edit: Not trying to be negative, just curious. It is an exciting idea. I would love to have a 12 degree Jupiter in my sky.
     
    Last edited: Jan 21, 2004
  10. Jan 21, 2004 #9

    marcus

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    Mission design people have gotten quite clever about using gravity assist and indeed a "reverse" assist is quite practical on homeward leg

    you are welcome to put nuclear thermal propulsion out of mind and imagine only H2 and O2 chemical

    for anyone who wants to try some back of envelope trials
    here is Hohmann transfer ellipse stuff.

    orbital speeds of earth and jupiter are about 30 and 13 km/s
    as y'probly know
    to get to jupiter (without any gravity assist shenanigans) takes a delta V kick of about 8.5 at earth
    and another (to catch up with jupiter) delta V of about 5.5

    that is the ellipse starts at about 38.5 peri and
    gets out to jupiter at about 7.5 ap (so it needs 5.5 added to catch up)

    but the catching up can be done with the help of the gravity and the orbital speed of the moons

    have to go, back later
     
  11. Jan 22, 2004 #10

    marcus

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    well Im back. dont know if this thread will go anywhere though

    everybody understand Hohmann transfer ellipse?
    delta V at earth of 8.5 km/s
    added to earths orbital 30 km/s
    puts you on an ellipse with aphelion at jupiter
    at which point the jupiter system is coming at you
    at 5.5 km/s

    and Callisto for example has an orbital speed of 8.2 km/s and escape from the jupiter system from Callisto's distance takes delta V of 3.4 km/s. Mission design people PLAY with the possibilities like teenagers play with weaving in and out of traffic on the freeway.

    You are coming into the jupiter system at 5.5 km and there is a lot that you can do by way of "reverse gravity assist" as enigma called it. Some people are good at this and I am often amazed by their ingenuity.

    Anyway I doubt you need to supply the whole arrival delta V of 5.5 from your own engine. I think you get a lot of that out of the Jovian system. And I think it is reversible. Going or coming the cost is going to be on the order of 8.5 plus a fraction of the 5.5, on the order of 10 km/s.

    the problems are extremely tough. The trip is 2.7 years on the transfer ellipse (one half of it). That is already a grave if not horrendous problem right there.

    But the delta V is not all that bad.
     
  12. Jan 22, 2004 #11

    marcus

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    Jimmy! I didnt see that someone else had dropped in.
    I bet you are right, as regards Europa. the surface looks like it breaks now and then, probably from tidal action, and liquid water comes to surface and freezes. But I dont know!!!
    Maybe there is someone here at PF who knows what has been learned about Jovian moons.

    As for the 12 degree Jupiter (or however many degree, I was making a quick estimate) I would love that too. It is a beautiful orb for sure.

    I wonder if there is any practical way to harness natural temperature differences to generate power. Assume there is plenty of nuclear power but nice to be able to supplement or gradually replace that
     
  13. Jan 22, 2004 #12
    Thanks for your reply Marcus. I remembered reading that the ice on Europa would crack letting water well up onto the surface. I thought it might be because of tidal forces. Wasn't sure though.

    What temperature differences did you have in mind?

    And in the spirit of this thread:

    [​IMG]
    [​IMG]

    Images captured from Celestia

    How do you embed an image in a post? I thought the img tag would do it but it just displays the url.
     
  14. Jan 22, 2004 #13

    marcus

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    Wow
     
  15. Jan 22, 2004 #14

    marcus

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    Its late and I dont know the answers anyway.

    I am going to have to read something about the main Jovian moons.

    regards to you,

    great pictures
     
  16. Jan 22, 2004 #15
    That's quite alright. I should get off my lazy backside and research this myself as well. This is a great thread and I hope it spawns lots of discussion. I enjoyed your ideas about colonizing the Jupiter system. The posts about Hohmann transfer ellipses was especially interesting to me. Anyway, I need to climb into bed myself.

    As far as the pictures, thanks. I don't really really deserve any credit. Celestia did all the work.
     
    Last edited: Jan 22, 2004
  17. Jan 22, 2004 #16

    enigma

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    Alright

    If your Hohmann numbers are correct (I have no reason to doubt they are), I got ~8.6 times the mass of the craft in propellants. If you then add in the numbers for leaving Europa, say 5km/sec, you're up to 29 times the mass of the craft. From Callisto, using your number of 3.4km/sec, it's ~20 times the mass of the craft.

    That's a lot of fuel, but if the need is there, you just design around the need. You can plug in extra gravity assists, increasing the time. You can switch to an ion drive, but you couldn't harvest the fuel in-situ. You can go multi-stage, but that would increase system complexity, and be especially risky after a 2-3 yr minimum stationed in space without operating (on the trip there, plus mission time). It's possible (someone would have to run the numbers) that at the relative distances to the sun of the Earth and Jupiter that a bi-elliptic transfer may save fuel. It would add much time to the trip, unfortunately. Not a good alternative for manned return missions.

    One really big problem I can see is you'd have to design cryogenics systems for the propellants that are built to operate for 6 years without a failure. That's a huge engineering feat. Add that to the potential for outgassing, as well as course correction and Earth re-entry delta V...

    Humans in space are messy.
     
  18. Jan 22, 2004 #17

    marcus

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    Oh yes, that is the main point, is it not?

    I've always favored robotic space exploration over manned.
    Machines do better in space and the robot probes have consistently
    produced far more interesting information at less cost.

    My point is that IF a decision is made at the policy level to
    promote manned space ventures with extended stays (which might in itself be a wrong decision) then there are better ways to spend the money and lives----worthier manned space ventures, I mean.

    I wont bother to reply to your points which seem to be general arguments against putting people into space (with all the extra equipement and fuel that entails). Because the premise is that we do that. Assuming we are to have extended stays on the Lunar/Martian surface or on some other body instead, lets compare relative merits
     
  19. Jan 22, 2004 #18

    russ_watters

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    You have any info on that? It seems pretty far fetched. I'd be awfully surprised if the study went beyond the "gee, wouldn't it be cool if..." level.

    The biggest hurdle I see is the size of the rocket due to the length of the trip. "Enourmous" doesn't even begin to describe it. Getting to the moon took only a few days and as such, life support wasn't that big of an issue. Getting to mars (just getting there, not doing anything or coming back) takes a good 6 months and the minimum total duration of the trip is about 2.5 years. Just getting to Jupiter would take more like 5 years. A ship with provisions for supporting a crew for that length of time would be huge - something to make Clarke's "Discovery" look like a dingy.

    I'm thinking $100 billion for a trip back to the Moon (Apollo style - no base), $1 trillion for Mars, and $10 trillion for Jupiter. Awful, awful ideas.

    I base this all on a key assumption: existing or near-future technology. Barring a quantum leap in propulsion technology (even scaling up ion propulsion would require at least a 10 order of magnitude improvement), we'd have to haul/make hydrogen and oxygen.
     
    Last edited: Jan 22, 2004
  20. Jan 22, 2004 #19

    marcus

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    You are saying using jupiter and its moons gravity is far fetched but this has already been done. Several probes have been there and taken pictures. When they go in, the paths is optimized to take advantage the system's own gravities, those of the moons as well as the primary. Gravity assists are demonstrated technology and have been used with some finesse on a number of missions.

    You are wrong about the 5 years. At least according to my CRC handbook which gives Hohmann ellipse data. Half the period of the transfer ellipse Earth-to-Jupiter is about 2 and 3/4 years.

    It is not 5. There is a significant difference.

    this information is available to anyone who has the standard handbook of physics and chemistry. Probably also on the web.

    As for the manned-mission studies done by NASA, I went down to the Engineering Library at the nearest educational institution. There is shelf after shelf of thick NASA books working out feasibility and grubby details of various missions that were considered when Manned Space was fashionable. IF they actually do revive Manned Space to a real significant extent then a lot of that that grubby detailed stuff becomes relevant again

    It sure as hell was not limited to the "gee wouldnt it be cool" level. They were doing serious homework (in the years after Apollo). And that homework is sitting down at the library waiting for someone to blow the dust off.
     
  21. Jan 22, 2004 #20

    russ_watters

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    Sorry, I could have pared down the quote a little better - I was referring to the study.
    Fair enough. I pulled that out of the air. 2 3/4 years one way is still quite significant.

    And I am still dubious about what these studies found. When manned spaceflight was "fashionable," they'd no doubt be willing to spend a hundred grand studying everything that popped into a mission planner's head, but I don't think that means they ever considered it a reasonable possibility. It might just mean they wanted to know.

    I'm looking for this type of info. So far, I found some on MARS. It includes an estimate of $1 trillion for a single mission. THIS one says the cost of Bush I's Mars mission would have been $400 billion. That seems overly optomistic since it also says the original Apollo program cost $150-$175 billion in today's dollars (anyone think any government program ever meets its budget?). THIS one has some specific info on the early space program's costs.
     
    Last edited: Jan 22, 2004
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