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Aerospace The Space Hose

  1. Sep 12, 2010 #1
    Hi !

    I was pointed to this forum to get some help and technical advice and verification of a new kind of low cost Space Tower: the Space Hose.

    In a nutshell it is about using a lightweight hose made from PE foil which is blown trough from the bottom and is using the frictional forces of the flowing air to produce continuous lift for supporting the weight of the hose.

    It was designed as an alternative approach to solving the N-prize problem which is about putting a 9,99 gram satellite into space for 9 orbits and winning
    £ 9999,99 when staying within the £ 999,99 budget. Because of the "geostationary" orbit a space tower offers it would mean keeping the tower upright for a total of 9 days.

    You can find a brief presentation including most of my poor math in the attached PDF file.

    I'm aware that this approach is not a very realistic one due to the huge stability problems when going for a single hose, but the math showed that it could be feasable to support a 100km hose and the needed raw material and energy consumption would be within the N-prize budget, hence I think it is worth sharing with you.

    By using plain air at a reasonable blowing speed as the medium for continuously transfering the frictional force to the hose it overcomes most of the limitations of the existing inflatable space tower and the space fountain concept.A head diffusor is making the air blowing out sidewards on top with only a small downward momentum to support the payload and prevent tearing the hose.

    Have fun reading the slides and input is welcome because I'm pretty sure that I must have done something fundamentally wrong in my math!

    gutemine

    PS: Sorry, for the bad graphics and the funny comments in the slides - I had to compress heavily to get below the 256k limit of N-prize the forum for attachments and the N prize spirit which originates from the halfbakery is also about the entertaining value of potential solutions
     

    Attached Files:

    Last edited: Sep 12, 2010
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  3. Sep 12, 2010 #2

    russ_watters

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    Geostationary orbit is about 23,000 miles, not 100km. I don't think having a payload sit on top of a tower for 9 days would qualify as being "in orbit".
     
  4. Sep 12, 2010 #3
    The top of any tower is always 'geostationary' in the pure sense of the wording :-)

    But you are right, this is not what is understood as geostationary orbit in the general sense.
    I added "" around the "geostationary" to prevent further misunderstandings, thanks for pointing this out !

    I checked with the N-prize owner and he confirmed that if the SAT it would stay in 100km height being outside of the "launch device" for 9 days and hence would have circled the earth (center) 9x this would count as orbiting and hence be within the rules.

    Remember the N-prize is also about original ideas to achive the over all goal within the budget and weight limit. So my question to him was the other way around - if a 'geostationary' orbit in 100km height would be also accepted, and the answer was yes.

    gutemine

    PS: English is not my mother language, so I hereby excuse for typos and not 100% perfect wordings. But I'm more concerned about the math and physics in the proposal.
     
    Last edited: Sep 12, 2010
  5. Sep 12, 2010 #4

    DaveC426913

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    Sorry, I am confused now.

    How do you get the satellite to stay at 100km for 9 days once it has detached from the launch device? It will not circle the Earth at all. It will fall straight back down.

    To circle the Earth at 100km, it will need to be given a sideways velocity component of somehwer in the neighbourhood of 17,000mph (orbital velocity).
     
  6. Sep 12, 2010 #5
    Sorry for the confusion, but ask a bouncing ball in a fountain - he knows the answer.

    And 'outside' doesn't always mean 'detached'.

    And the slides also contain some math about blowing out at orbital speed with a de Laval nozzle - so maybe even this would be possible.

    Expansion of 1m³ air from the ground to 100Pa in 100km already gives an amazing expansion power as the used ideal gas formular would suggest.

    But this is a follow up problem - I'm more concerned about all the things I have done wrong in my friction power/pressure calculations.
     
    Last edited: Sep 12, 2010
  7. Sep 12, 2010 #6

    DaveC426913

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    OK, so it's still in the grips of the launch device, just suspended on air instead of anything solid. Might want to check with the N-prize rules on that one.

    Blowing out - at 17,000mph? I think that will "blow out" all his hard work on calculations for material strengths.

    And it better be more than "possible". This idea is dead in the water without this (major) component. Getting to 100km is a trivial feat compared to achieving 17,000mph velocity.

    So far, you've pushed the car out of the garage. Now your theorist is saying "it might be possible to put an engine in it to get it moving". You're a loooong way from winning any races.
     
    Last edited: Sep 12, 2010
  8. Sep 12, 2010 #7
    The slides are already including that blowing out that fast is unrealistic for such a weak structure.

    But this is not planned either - the slides suggest that you would need to change hose diameter to better prevent things like hypersonic flows ;-)

    But this is one of the things I failed to fully understand. Because of the decreasing pressure with increasing height the air would expand and flow faster until at some place (without diameter change) the flow would be breaking the sound barrier - so this hose would work as a kind of "fixed diameter de Laval nozzle" ?
     
  9. Sep 12, 2010 #8

    DaveC426913

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    OK so you're back to a novel method for making stationary tower, with your satellite simply resting on top.

    Might want to check with the rules on that.
     
  10. Sep 12, 2010 #9
    I can check the rules once more :-)

    BUT the primary question is would the tower work ?

    At least for the first few km the friction force calculation should be pretty accurate to balance the hose's weight - so there would be 'only' the stability problem remaining ?

    The classic space tether works with the centrifugal force of the counterweight at the top - would a downwards blowing diffusor at only 100km (if it is stabilized against sideward movements) work as a sustitute to generate the stabilizing pull force ?

    The Inflatable space tower people already have put the fixes for the stability problem(s) in their patent - see the straw pack comment in the slides, and the suggested Dyneema strings strengthening.
     
  11. Sep 12, 2010 #10

    DaveC426913

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    No need.


    The space hose has no legs unless they get that "blow out" working.
     
  12. Sep 12, 2010 #11
    Why ? You are still orbiting the planet at 100km height if you are on top of such a structure - which would be quite an achievment.

    And I'm not so sure about instability at very fast flow rates either - as long as the diffusor provides a surpressure the hose should be pretty stable even if the flow inside would be pretty fast (but with low denseness)

    Wouldn't an elastic hose suggest that the pressure inside (besides friction and the diffusor) is always the same then outside ?

    But this compexity of the problem is why I asked for help and advice ... so thanks for your patience with me !
     
    Last edited: Sep 12, 2010
  13. Sep 12, 2010 #12

    russ_watters

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    Based on the logic the OP is currently using, my car, sitting in my garage, qualifies for the prize.
     
  14. Sep 12, 2010 #13

    russ_watters

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    You need to google the definition of "orbit".
     
  15. Sep 12, 2010 #14
    If your garage would be 100km above sea level - yes !

    But you are getting now the spirit of the N-prize - it is about achieving something very likely to be impossible with a very unusual approach. And it only is not allowing ovieously cheating (asking your space shuttle astronaut friend to take the N-SAT on his next trip and float it in the shuttle for 9 orbits - then you share the prize money)

    The other participants so far just try the ordinary things (balloons, rockets, combination of both...) so I went for the impossible and tried to solve the space tower problem :-)

    So back to the original question - can a hose hold it's own weight just from the friction force of blowing air trough it and what happens if it goes to space (which starts at 100km) ?

    BTW - the 100km in my slides are only because of the N-prize origin of the idea. In my understanding the friction force of flowing air holding the structure should work also up to 36.000 km - BUT because of the very weak pressure there the hose would probably become instable or collapse (or would a diffusor work in this case also to recover at least a small pressure surpluss of 100Pa?).

    Wikipedia says about orbit: Orbit is the gravitationally curved path of one object around a point or another body. I'm missing the word speed in this definition ...
     
    Last edited: Sep 12, 2010
  16. Sep 12, 2010 #15

    russ_watters

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    A particular altitude is not part of the definition of an "orbit".
    Well certainly a hose can hold itslef up based on air pressure and friction inside. That's what this is:

    https://www.youtube.com/watch?v=iQWq9XjT8mY

    ....but can it be scaled-up to 100 km? I think that's just a pracitcal problem: I doubt any material can stand up to the required pressure at the bottom.

    No, you're missing the word "tower". If gravity dictates the curvature of the path, then a tower can't be dictating the path.

    Then the speed is what you need to shape the "gravitatinoally curved path" so it doesn't intersect with the ground. Note, this path need not be circular and the winner of this contest will not likely use a circular orbit but an elliptical one.
     
    Last edited: Sep 12, 2010
  17. Sep 12, 2010 #16

    russ_watters

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    By the way, if you can find the weight and strength of the material you want to use, it isn't difficult to calculate the pressure and airflow requirements. For instructional purposes, I can certainly help you with that.
     
  18. Sep 12, 2010 #17

    DaveC426913

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    gutemine, this is not an orbit. Every mathematically-able person on this board will agree. And I'll bet my paycheque that the N-prize judges will agree as well.

    No need to take my word for it. Ask them.
     
  19. Sep 13, 2010 #18
    Thanks for all your input!

    Regarding the petrol station advertising wiggle device. This is intentionally desinged to wiggle - the diameter of the hose is reduced upwards to increase the speed of the airflow which reduces the airpressure until the outside air can balance this and hence the hose is folding. This stopped flow then causes the pressure to increase until it blows up again. So this is designed as a kind of strange upward pendulum.

    My design is not this way. If you add a diffusor on top you can create a pressure surplus which holds the whole thing stable and by blowing downwards you get a stabilizing pull.

    In the halfbakery where the same problem was pointed out (but without the entertaining video) I suggested a simple experiment to understand the difference:

    Take a condom and put it over an adhesive strip tape roll and then blow trough the hole of the roll upwards. This gives a nice upright position :-)

    But you now have the problem of the inflatable space tower - pressure will increase dramatically with height, and you end up with expensive kevlar balloons to hold the pressure (but is is not that worse - so a big thumbs up for their idea!)

    Then you do the same after cutting away with a scissor the small repository piece at the top. Blow again - you have to blow faster, but it still works to hold the upright position. The remainder on the top works as a pretty bad diffusor. This is what the space hose would be (even when in our experiment the pressure increase of the diffisor does the job, not the friction - but you cann't buy that long condoms to verify) - so the experiment is cheating a little bit.

    If you then cut away the entire head so that the opening at the top has the same diameter then the rest of the hose/condom you will fail - no matter how hard you blow. The Bernoulli effect is aginst us.

    As soon as somewhere in the hose/condom the diameter shows a small imperfection making it smaller, then the flow speed will have to be slightly higher, which means at that place the pressure will drop within the hose and as soon as this happens the athmosperhic pressure will win and the hose will collapse at that place. The air then still flows but it would be totally instable even when friction gives still the upward lift (then you really have a space flag not willing to stay upright). Hence a small pressure surpluss is a must, but this is the way an upright hose should work. The space tether people are sugegsting a counterweight for generating the stabilyzing pull - in my case the diffsor produces the pressure surpluss and by blowing downwards also the needed pull.

    PS: I have to enter a meeting now, but I will try to answer the other questions no later then evening

    gutemine
     
  20. Sep 13, 2010 #19
    gutemine, I read through you posts and slides. Your proposal meets the N-prize rules. In summary, the object rides the moving column of air to the 100 km point, where it exits, and is thus outside, but remains attached. Technically, it's in geostationary orbit. Nine days later it's completed 9 orbits.

    I do wish people would stop focusing on the rules and respond to your question of whether or not it's feasible. I'm an aero guy, and your numbers look ok to me, but it's been decades since I crunched fluid flows.

    My concern is the stability of column in turbulent flow. http://www.youtube.com/watch?v=L4ujpHqbxiI"shows what usually happens, although your dynamics are somewhat different (higher pressure, a diffuser/thruster at the top...) Obviously the column of air will loose pressure as it rises, just as does the atmosphere.

    Also, I don't recall your final numbers on internal pressure, but if we assume it's at twice ambient pressure all the way to the top, however, your 10" column of air will itself weigh 2,309 lbs, though half will be supported by ambient, which leaves us with 1,154 lbs of additional mass to support. That'll be supported by the increased internal pressure, of course, but the bag will have to support 2 ATM along its entire length.

    I'd say give it a trial run with perhaps a 500' column and see how it behaves.
     
    Last edited by a moderator: Apr 25, 2017
  21. Sep 13, 2010 #20

    russ_watters

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    No, "technically", it is sitting on top of a tower. It is not in orbit.
     
  22. Sep 13, 2010 #21

    russ_watters

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    No, "technically", it is sitting on top of a tower. It is not in orbit.

    When something is in orbit, there is no external force holding it up - there is only gravity pulling it down.
     
    Last edited: Sep 13, 2010
  23. Sep 13, 2010 #22
    Maybe let's use a neutral example to end the discussion about orbit:

    For thousands of years mankind accepted the rule that water is not able to flow uphill. Then Achimedes invented his screw. You could argument that now the water is pumped, but it definitely is a continuous upwards flow. So maybe Achimedes would not have gotten any prize money either, but that wouldn't have made his invention one inch smaller.

    Regarding the air pressure weight - that's the good thing about pneumatics - the weigth of the air is not a problem (if there is not pressure surplus) because the hydrostatic pressure is the same inside and outside the hose if there is no air flow. Which means there is nothing the hose needs to balance with its strength. Which is especially true if the hose is open on the other end (=top). On sea level air has a hydrostatic pressure of approx 100000N/m² which would make even Atlas crack if he would have to hold it on his shoulders. But there is no problem with this, because our body is under the same pressure and feels pretty comfortable with that. A hose has the same pressure relief, so you may only need to hold the surpressure of the resistance pressure 'loss' - but I'm not even sure about this, because it is a flexible hose and not a fixed pipe.

    The slides contain also the worst case pressure needed if the hose is closed and all the weigth at the top (about 0,6 bar) which is nothing modern materials would not be able to hold (not the thin PE foil, I agree, but the suggested Dyneema string srengthening like the Polyamid in your garden hose should be sufficient). The formular to calculate the needed strength of the walls of a tank is pretty simple and easy to use. And the diameter is not the optimization point - you get linear force increase, but also linear weight increase when the pressure and wall thickness is the same.

    The 10" were only to make it within the N-prize budget, a real space hose for doing something usefull would be either bigger or a straw pack of such hoses (BTW I would prefere the later)

    Maybe I should ask the question on my math more generic:

    If I blow trough a very long hose from 1 bar into vaccum (and are ignoring friction), what pressure will the hose (not a fixed wall pipe) have ?

    I already know that speed on the vacuum side will not be infinite (I think it is about 740m/sec because of ideal gas law in case of normal room temperature in the vacuum, real case calculation at -90 degree Celsius is in the slides)

    Then you make the hose go upwards, and the hydrostatic pressure adds, but gets balanced from outside as already described.

    Then your add friction and what pressure do you get then ?

    gutemine

    PS: If I have a rocket with enough fuel to continuously blow also downwards I can fly around earth as slow as I want at any height - and you want to tell me that this is suddenly not an orbit ? If yes, then this is OK with me - no problem from my side !

    PPS: An electron is also orbiting the atom core, and the orbital 'speed' is determined by the electromagnetic forces (and some quantum mechanics so it is not really speed) and not the gravitational one. This is why lots of orbit definitions even lack the word gravitation

    The N-prize rules are asking for the 100km height to reach 'space' - in general you are right, otherwise cyling earth with a bicycle 9x would also get you the prize money, or simply waiting for 9 days. - BTW I liked the space garage approach. And thanks for the offered help on the strength calculation - as soon as we agree on the pressure gradient in the hose I will have to re-do that.
     
    Last edited: Sep 13, 2010
  24. Sep 13, 2010 #23

    DaveC426913

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    Yeah, mug where are you getting this from? It is not in orbit at all.

    By your logic, I could sit in my basement, suspending a pingpong ball using my vacuum cleaner, and claim, not only that it is in orbit, but that it will orbit the Earth every 24 hours.
    By your logic, a http://eastmanind.com/eastmancommercial/HOVERMOWER/tabid/187/Default.aspx" [Broken], which rides on a cushion of air, is in orbit.


    That's ridiculous.
     
    Last edited by a moderator: May 4, 2017
  25. Sep 13, 2010 #24

    DaveC426913

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    Correct. That is not an orbit.

    See above examples of other comparable setpups that are also not orbits.

    And the N-prize judges will agree. I guarantee it.




    No it isn't.

    Your idea does not meet the criteria for orbit. Ask the judges at N-prize.

    Do this before putting any more time into your proposal.
     
    Last edited: Sep 13, 2010
  26. Sep 13, 2010 #25
    Well, I already checkd with Paul (who IS the 'jury' - because he invented the prize and took care of the funding). He agreed that my proposal meets the spirit of the competition and I would be allowed to partizipate with this approach. And yes, I have sent him the slides and he said the space hose would qualify as a launch device to space!

    He sent me the forms already to officially join - I just would need to fill them out, sign them and send back to officially participate. That doesn't mean that I could make and win the prize money - but the other competitors have pretty the same problem. If their broadcasting device fails and they could not proove the 9 orbits they would not get their prize money either - even if their N-SAT would perfectly orbit infinitely.

    With the planned approach and materials I probably could do a 1-2km 'test flight' within a few weeks - 90% of the other partitcipants have not even an idea when they could do their first test flight. And if it would make only a few hundred meters - where is the problem - most of the home-brewn rockets have the same first launch (if they are lucky and make a lift-off at all)

    I'm not planning to cheat and ask your for permission - I'm simply creative in solving the puzzle, and try to have fun while doing so.
    I'm also trying to be honest and open minded by sharing my (bad) math and (weird) assumptions and ask clever people for feedback if and what I have done (awfully) wrong - to prevent missing something and waste all our time,

    If I'm doing this already - then I'm simply sorry.

    gutemine

    PS: In your basement you could at least claim that you are orbiting the sun.

    PPS: I just checked the orbit definition at the NASA Homepage (which in my understanding are pretty competent in this field):

    An orbit is a regular, repeating path that one object in space (!) takes around another one.
    And according to the NASA definition space starts at 100km above surface.

    http://www.nasa.gov/audience/forstudents/5-8/features/orbit_feature_5-8.html

    And yes, later their explaination gets lost with orbital speed, and gravitational forces (which is OK with me) - but that doesn't change the basic words of their own definition. If I would follow your argument even a space elevator 36000 km (or even 2x) long with a geostationary counterweight would not reach orbit either because it is still connected to the planet (and the first 100km would move identical to my proposal).
     
    Last edited: Sep 13, 2010
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