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B Interplanetary travel, Arctic sea ice

  1. Mar 12, 2018 #1
    I'm a software developer, no formal astro-physics education, but would like to pose some questions/hypotheticals regarding interplanetary travel, and/or dynamic positioning of Earth orbiting objects using extraterrestrial fuel sources.

    1. Asteroid-based hitch-hiking to other planets.

    Hypothetically, could an Earth-launched spacecraft a) attach to a small asteroid (to be identified in advance), b) use its own rocket fuel to alter the orbit of the asteroid such that it would be drawn into a steeper solar orbit, resulting in a slingshot trajectory which would carry it past a target planet, where it would disconnect from the asteroid, and go into orbit over the target planet? In theory, converting the potential energy of the asteroid's current stable solar orbit, into a free-ride to a distant planet using less on-board propellant than it would otherwise use going direct?

    2. Restoring multi-year sea-ice in the Arctic.

    At the moment (March, 2018) the Arctic ice-cap has (over four decades or so) lost roughly 80% of the multi-year sea-ice, which determines the annual minimum albedo of the polar cryosphere. During periods when little or no multi-year ice is restored (such as we're in now), this locks in an increase in the amount of solar energy which is absorbed by Arctic seas & winds-aloft (rather than being reflected back into space), which in-turn raises water temperatures -- causing primordially sequestered shallow sea-bed methane-hydrates to melt, which in-turn may accelerate summer snow-melt on the Greenland ice-sheet, and cause anaerobic methane generation on Arctic land-masses due to warming of perma-frost.

    Since methane is a very potent greenhouse gas (greater than CO2) this could (theoretically) lead to a feed-back loop, resulting in a catastrophic release of methane into our atmosphere. Question:

    Is there a plausible way to deploy what amounts to an orbiting 'solar-shade', permanently positioned to cast a shadow over the Arctic, thereby enabling the restoration of some of the multi-year sea-ice which has been lost?

    Assuming such a structure could even be assembled, I believe it would require daily re-positioning, hence a design which would benefit from either the use of solar-wind, or some other extraterrestrial fuel source.

    It seems to me, while we cannot be certain current warming trends will continue, and/or that primordial methane-hydrates will actually make it into the atmosphere, climate scientists estimate the potential amount of sequestered methane release at 1000-5000 gigatons in the Arctic alone, compared to an accumulated total of 400-500 gigatons of carbon emissions over the last 200-300 years from anthropogenic sources.

    Given the remarkable advances in recoverable booster-rocket technology we're witnessing from SpaceX and others, I would argue that in terms of our priorities for applying those new technologies: containing a potentially existential threat to our biosphere here on Earth, should take precedence over landing humans on Mars. At a minimum, I would hope the scientific community in general (and the United States in particular) should act immediately to quantify the threat posed by Arctic methane releases which are already under way.

    Hoping this forum is an appropriate one for these subjects.
     
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  3. Mar 12, 2018 #2

    Bandersnatch

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    Hi, and welcome to PF!
    You don't actually gain anything from doing that. You don't gain any energy from riding an asteroid and then detaching from it, while you do need to expand (a lot!) of energy to change its orbit. You're better off riding your rocket alone.

    There are some ideas like that thrown around. Google for the key word 'Geoengineering' - just read what legitimate (i.e. academic-related) sites tell you, as e.g. the second hit I get from Google is a crackpot site.
    Start e.g. here:
    http://www.geoengineering.ox.ac.uk/what-is-geoengineering/what-is-geoengineering/

    edit: grammar
     
    Last edited: Mar 21, 2018
  4. Mar 12, 2018 #3

    phinds

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    Your title and your post are not about the same thing
     
  5. Mar 12, 2018 #4

    Bandersnatch

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    It was moved from another thread. Blame the mentors.
     
  6. Mar 12, 2018 #5

    phinds

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    OK. BAD mentors !
     
  7. Mar 12, 2018 #6

    mfb

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    I adjusted the title.
    There are no orbits where things would constantly be above the Arctic as seen from the Sun.
    Earth is huge. The largest solar sail (could double as sunshade) ever deployed was a square of just 14m x 14m. You need 5000 of them to cover a single square kilometer, and 6 billion to cover 1% of the surface of Earth as seen from the Sun (ignoring orbits here).
     
  8. Mar 12, 2018 #7

    phinds

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    See, there you go again, bringing facts into the discussion. Spoilsport :smile:
     
  9. Mar 13, 2018 #8
    Thanks for the prompt reply. (I figured it was a longshot.) I do believe the scientific community needs to take the situation in the Arctic seriously, at least by carefully monitoring how much primordial methane is entering the water-column. Last I checked, it appears to be remaining there (dissolved perhaps). However, what happens if it reaches a saturation point? (If you search on 'Peter Waddhams methane arctic' on YouTube, you'll find authoritative discussions on the status of this one.

    Perhaps an interesting segue for this topic: Could a fleet of trawlers extract the methane from the Arctic sea-water, and either use it directly, or find a way to convert it into hydrogen? There's a startup company here in the Pacific Northwest: www.inentec.com which is pioneering the use of 'plasma-gasification' to convert garbage/refuse into hydrogen (with CO as byproduct). Of course burning the methane itself is an option, but you still need to find a way to re-sequester the CO2. One way or another, most of the commentary I've seen on this subject suggests that large releases of primordially sequestered methane into the atmosphere could have grave consequences.

    Thanks again for considering these ideas. The underlying problems need to be addressed by people who fully understand the science.
     
  10. Mar 13, 2018 #9

    stefan r

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    Yes, large fleet of trawlers could do severe damage to the ocean. Yes, you can actually extract most things from sea water. People have published plans to extract gold and uranium. It is highly unlikely that you would extract enough energy from the methane to power your trawlers. Building the system would also require large energy expenditures.

    Fracking is a major source of methane. Fracking is also a major source of methane emission. Off shore operations are much more complicated. It is very likely that the fraction of lost methane would be higher. Fracking close to the surface would be especially prone to leakage. The clatharates that are close to the surface are the most likely to be destabilized by warm ocean currents.

    Bio-gas plants can produce methane. There are several thousand in operation in Germany. It is one of the better methods of reducing greenhouse gas emissions. Bio-gas is a known technology that Germans would be thrilled to explain.

    A solar shade does not need to be positioned over the arctic. Ocean temperatures effect the amount of ice that accumulates. Tropical glaciers are important too.

    Center below(sunward) Lagrange point 1. Place 2,450 million of them over the arctic and antarctic. Make the other 100 million tethers. Tilting some of the shades 45° cuts the light blocked by 29% but could give you a lot of thrust so tethers would not need to be very strong. A fancier version would block the infra-red but let red and blue light through for plant growth.

    If we are limited to current rocket technology and manufacturing practice then deploying the sun shades would add a lot of greenhouse gasses. You can loft hydrogen filled balloons over the arctic without using a rocket.

    Deploying 6 billion solar panels on roof tops should be much easier. Just because something can be done within the laws of physics does not mean that it is a good idea.
     
  11. Mar 13, 2018 #10

    mfb

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    Whatever you put close to L1 has a half shadow larger than Earth. Shadowing all of Earth a bit is the only reasonable option there. Things "below"/"above" are above some point that is typically not over the Arctic/Antarctic due to axial tilt, and they are attracted towards L1. Shift them sidewards to fix it and you get torque. It is not that easy. Halo orbits around L1 to shadow all of Earth would work, but you are still left with ridiculous areas to cover.
     
  12. Mar 14, 2018 #11

    sophiecentaur

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    I keep telling people to paint all the desert regions white (roofs and roads too). That would be by far the cheapest solution to blocking the Sun's rays and it wouldn't matter if the painters 'missed a bit'.
     
  13. Mar 14, 2018 #12

    mfb

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    And the first time a bit of wind comes the paint gets covered by darker dust.
    Meanwhile heating costs go up for houses and driving could become more dangerous.

    If it would be that easy, we would do it.
     
  14. Mar 14, 2018 #13

    stefan r

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    And exterminate how many species?

    Or goes airborne and spreads the toxic mess. Chokes the only streams near the desert.

    There have been proposals to use trimethyl aluminum as aviation fuel. The alumina particles in chemtrails will block sunlight. You could also use H2S (rotten egg odor) to add sulfates in the upper atmosphere. Sulfates reflect UV out and do not block much infra-red.

    Ways to disrupt the climate in the Arctic include a dam across the Bering straights, arctic heat exchangers, spraying liquid salt water over the top of the ice sheet in winter. In the tropics you can spray salt water from sailboat masts to seed clouds. They even invented a rotating spiral sail for this purpose.

    There are also proposals to dump rust in the oceans and create red tides and algae blooms. The dead diatoms carry some carbon to the deeper ocean.
     
  15. Mar 15, 2018 #14

    JMz

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    I think the relevant science here is not physics but sociology.
     
  16. Mar 15, 2018 #15

    sophiecentaur

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    If we don't do something, there will be extinctions anyway.
    Exposed rocks have hardly changed for thousands of years and non-toxic paint would obviously be chosen.
    That objection could apply to any measure that's taken. If the painting system is effective enough to increase the cost of house heating and put ice on roads then clearly it would need less paint. Changing back to the status quo would be much easier with an Earth based solution.
    No doubt about that. Strange that wearing thicker jumpers and walking more are such unattractive measures.
     
  17. Mar 15, 2018 #16

    JMz

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    Not strange if you're a billionaire who would lose a great deal of money from abandoning coal and can afford lobbying & public advertising to make all alternatives seem as unattractive as possible.
     
  18. Mar 15, 2018 #17

    stefan r

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    Rocks exposed by retreating glaciers do not have much living on them yet. The topical glaciers get a lot of sunlight.

    Do you prefer trimethylaluminum or hydrogen sulfide? We can do a bit of both. There is also the cheap and lazy option of not removing sulfur from petroleum. The link claims that not using ultra low sulfer jet fuel kills about 80 people per year in the United States.

    Billionaires can make a lot of money selling high efficiency infrastructure. There is a lot of lobbying for lower electricity rates. If we were serious about reducing CO2 emissions we could simply tell electricity companies to make profits. Allow stockholders to sue for lost dividends.

    The low hanging fruit is vegan (not Alpha Lyrae). Dairy farmers are not billionaires. Choice of food is something you normally have complete control over. You can decide to ignore advertising.
     
  19. Mar 16, 2018 #18

    sophiecentaur

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    Raising taxes on fuel would be better value for us, rather than the wealthy.
    Politicians have a serious problem (ahhh). The solution to all this is to Consume Less but what sort of an economy would that lead to, when growth is paramount.
     
  20. Mar 16, 2018 #19

    stefan r

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    That statement is not physicsy. We can measure biodiversity, top soil, biochemical oxygen demand, water table levels, ice coverage.
     
  21. Mar 16, 2018 #20

    sophiecentaur

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    Not "physicsy", perhaps; it sociological / economy driven. Eliminating the cause of a problem is surely better than repairing the results. My mother used (annoyingly) to say "Prevention is better than Cure.".
     
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