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#1
Sep1210, 06:07 AM

P: 59

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 Nprize 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 Nprize 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 Nprize the forum for attachments and the N prize spirit which originates from the halfbakery is also about the entertaining value of potential solutions 


#2
Sep1210, 09:36 AM

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#3
Sep1210, 09:55 AM

P: 59

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 Nprize 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 Nprize 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. 


#4
Sep1210, 10:11 AM

P: 15,319

The Space Hose
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). 


#5
Sep1210, 10:13 AM

P: 59

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. 


#6
Sep1210, 10:19 AM

P: 15,319

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. 


#7
Sep1210, 10:27 AM

P: 59

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" ? 


#8
Sep1210, 10:30 AM

P: 15,319

Might want to check with the rules on that. 


#9
Sep1210, 10:35 AM

P: 59

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. 


#10
Sep1210, 10:39 AM

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#11
Sep1210, 10:44 AM

P: 59

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 ! 


#12
Sep1210, 11:38 AM

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#13
Sep1210, 11:38 AM

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#14
Sep1210, 11:54 AM

P: 59

But you are getting now the spirit of the Nprize  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 NSAT 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 Nprize 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?). 


#15
Sep1210, 08:31 PM

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P: 22,248

....but can it be scaledup 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. 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. 


#16
Sep1210, 08:46 PM

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#17
Sep1210, 10:19 PM

P: 15,319

No need to take my word for it. Ask them. 


#18
Sep1310, 03:52 AM

P: 59

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 


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