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    Crew Tether Spin - With Final Stage - On Routine Mission To ISS - First Human Test Of Artificial Gravity?
    By Robert Walker | May 19th 2014 10:05 PM | 7 comments | Print | E-mail | Track Comments

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    Centrifugal weight creation (what should we call it? There's an internet-word-inventing-opportuinty here!) is an untested pioneering science/technology. It's over-mature and thus free to take for dedicated geniuses like Joe Carroll and yourself on your spare time outside of multi-billion dollar bureaucracies.

    In the paper of Joe you link to:
    http://spaceshowclassroom.files.wordpress.com/2011/05/designconceptsfora...

    He develops the detail of "airbeams" (inflatable tubes, hoses). I think that airbeams are largely unknown to the public and need more attention in this context. I don't know anything about this kind of physics, but it seems intuitive to me that an airbeam would be both more rigid than a wire cable, and more flexibile than a lattice framework. And the trade-off should be possible to regulate dynamically by changing the air pressure inside the airbeam. Seems to be good! However, in his paper Joe Carroll writes:

    Page 10: "beyond some length it doesn’t make sense."
    And he suggests that they should be complemented by cables.

    I'd like to know more about the plus and minus of airbeams:
    - What gas pressure would they need in space? Sea level Earth pressure as I think is assumed in the paper isn't obviously optimal to me.
    - Would the gas pressure shift along the airbeam since the "simulated gravity" shifts along it? From zero gravity to Moon, Mars or even Earth gravity at different stations along it.

    I'd suggest a 100 mm (4 inch) or so thick airbeam with regulated pressure as radial "tether". And then elevator cabins for transporting payloads or crews between stations along that tether. Trying to combine stabilizing gas pressure and airbeam diameter on the one hand, with transportation requirements on the other hand, might be like trying to kill two birds with one stone, although they sit in different trees. I just want to raise that question.

    robertinventor
    Okay that's an interesting question. Sounds a good idea, that it might be stronger, but way too technical for me. Will you be listening to his webinar? It might be a good question to raise on the show, if not answered before then.
    I think loss of atmospheric pressure in the middle won't be an issue though. That only happens in a space habitat when you have kilometers of air under Earth normal atmospheric pressure. 

    It does happen in an O'Neil cylinder - and is partly why they are so heavy and need to be massively engineered - much of the weight of an O'Neil cylinder is  the atmosphere because of course you have ten tons per square meter of outward atomspheric pressure in full g - and so - if you provide that pressure just by rotating you need to have ten tons worth of atmosphere above it. So needs to be engineered, to withstand all that atmosphere as well as the land and the 4.5 tons per square meter of radiation shielding.

    However you do need kilometers of atmosphere for it to be an issue.

    Air has a density of 1.225 kg / m3. So even a 1 km radius tether can only contain enough air to supply 1.225 tons / square meter pressure difference between the centre and perimeter. In the Stanford torus and all the smaller habitats, then the air pressure is got mainly just by containing the air under pressure.

    When you transfer from one part to the other though of, say, a 600 meter radius tether assembly, you'd notice the change of pressure, like going in an airplane up to a height of 1 km and then down again. Pressurized cabins might be an idea within a large tether for passenger comfort during the transit.

    If it's only 25 meters or so, doubt if even that is needed, that would be like going up a lift to a height of 25 meters, you'd notice it still perhaps, as some do in lifts, but not a big issue.
    I never realized how many more variables were to be considered when designing artificial (centrifugal) gravity. However, since childhood I always wondered why most authors "whined" about bone depletion etc. during interplanetary travel as I was even then convinced that this could easily be prevented by using e.g. a rotating hub and spoke construction, obviously assembled in space, to do the journey. And I actually am still wondering why the space station was not equally designed that way. One could still do any zero-gravity experiments in the hub but have the sleeping, training, eating, sleeping and living quarters in the outer ring at exactly 1g.

    robertinventor
    Yes indeed my thoughts also. Yes indeed is of course compatible with a zero gravity lab in the hub,

    The hub and spoke idea is a rather massive construction, the problem there is  depends on what spin rates we can withstand. If we can only withstand 1 rpm, then it has to be a kilometers scale construction for full g, If it has to be that big, then seems likely we'd start with tethered spacecraft - which could later on be joined together with other spacecraft tethered to same c of g. to make a ring habitat as it expands.

    But if we can withstand higher spin rates - especially e.g. in a sleeping and eating region of the habitat then you just go there to sleep and to eat and to exercise, spend rest of your day in zero g - and that might be enough. If so then might be able to have much smaller designs such as the Nautilus X with its centrifuge sleeping compartment for instance.



    Or for even higher spin rates, then there's my idea of an individual centrifuge sleeping "hammock" for each astronaut, where they spend minutes, or hours a day, at whatever spin rate they find comfortable, which would at least improve their health and permit longer missions if perhaps not eliminate them altogether (though who can tell perhaps it would even be a complete solution especially for astronauts able to withstand high spin rates).

    The thing is, reason we need to do experiments to find out, that basically nobody really knows. Is easy to calculate how much artificial gravity you get for particular designs, and what the spin rate is. But the human body is far too complex to predict what the spin tolerances are or what the health effect of it is, except by trying it out to see what happens.

    Depending on the answers, we might need slow spin rates and kilometers long tethers, or might do just fine with Nautilus X type sleeping modules or smaller.

    Hfarmer
    It seems almost criminal that we have not invested more in something this basic for our astronauts and cosmonauts (..and Taikonauts in China). If there is a reason, it is because no one had real confidence in a tether lasting long in a space environment.  One precise micro meteor hit and the space craft are flying off on a tangent.  
    Science advances as much by mistakes as by plans.
    robertinventor
    Right yes, I wonder if that's part of it. If so, turns out it's not as much of an issue as they might have thought.

    TIPS with a 4 km tether lasted for 10 years from 1996 to 2006 so that shows it can be done.
    Chances of tether break during the 2 day experiment, and with a broad seat belt type tether (so a dust sized micrometeorite wouldn't break it) must be minute.

    And - if it does break - you lose gravity - but the crew can continue of course for months, and probably for a year or more in zero g if necessary with regular exercise, reasonably healthy as for the ISS. And both components have pretty much the same trajectory still, just differing by a few meters per second, so if you have some spare fuel, you can just go and collect it and join them together again.

    Then with a longer mission - well you can use Joe Carroll's idea of air beams - meters diameter air pressurized crawl tubes joining them together - or the Hoy tether, both designed so that if you have micro-meteorites they just create a hole in the tether system, and don't break it.

    Or, just have multiple tethers.

    The tethers don't weigh much compared with the total mass of a human mission with supplies, life support etc - so in a mission you could, e.g. have four tethers joining the craft together, and then have spares on board, so if one of them breaks you replace it, hard to see micro-meteorites or space debris destroying all 4 before you have a chance to fix it.





    Hfarmer
    I never thought about it in those ways.  
    Let's hope that this time we as a species have the political will to make these things a reality.  So much of what we would need to explore the space of the inner solar system with humans, it seems, isn't a matter of making new technology.  We had the technology then just got bored with space. 
    Science advances as much by mistakes as by plans.

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