The Space Hose

JaredJames

Thank you Paul, your insight is much appreciated.

I have quoted this small section and highlighted what I believe to be an important factor that cannot be overlooked and some consideration given to before dedicating yourself to your 'space hose'.

The satellite must orbit independently I think is the key, so the hose must be the launcher. This means you need to attain orbital velocity or hold a ballistic trajectory with altitude > 100km for a period of nine days (although I wouldn't class that as an orbit, it would seem to suffice here).

gutemine

I'm aware of this inherent limitation which I don't see as a problem and I don't see this as a threat or a roadblock either - I see this as an opportunity.

I already explained that it is not such a bad idea to solve the height and speed problem individually - the ballloon and rocket guys actually try the same - only 70km lower where it is much more difficult because the 70km remain also.

Hence the disadvantage of the hose actually still is an advantage in my opinion. You have the needed height and lots of air to work with on the remaining part of the problem. Which is exactly what you do as a partizipating N-prize team - hoping to succeed.

Nobody really commented so far on problem that the ideal gas formular would actually SUGGEST that the gas there already should blow out at (almost) orbital speed - the slides contain already the math and I already explained that this even would be even logically to some extent.

The slides already say unrealistic - but WHY and what is the CORRECT speed we would face there ?

And No is a comment, but I hoped for more ;-)

PS: Sorry for the capital letters - I don't want to be impolite, and I would also accept a 'we don't know' - if you help me finding somebody who does.

gutemine

N-Prize

Hi again all,

Sorry, I've been trying to sleep off a monster cold (well, it's "man flu", and we all know how serious that can be....). I'm also up to my ears in epinephrine, paracetamol and every other substance available, so apologies if my answers are as fuzzy as my head.

As far as the physics of the space hose goes, I wish I could help more, but my physics falls wayyyy short of being able to make a useful contribution. I've also tried to track down physicists who might be able to help, but with no real luck. (I'm a biologist, oddly enough.)

But as to the topic of viability/legality etc under the current rules - all your points are well taken. And yes, I can see many valid objections to broadening "orbit" to include something sitting atop a space hose. That still leaves the option of rewording the rules to demand that something stays up there by means of orbit "or other means". I do reserve the right to make such changes, but in this case I would seek the opinions of the existing teams.

My big mistake was in giving a positive opinion on the "legality" of the space hose before thinking out the consequences - for which I apologise.

If plans can move towards using the space hose as a launch platform for a free-orbiting satellite, that would solve many problems and would be a stunning outcome! (The kinetic energy of a 20g mass orbiting at 100km, incidentally, is about the same as the energy available from a teaspoon of petrol - which you doubtless already know but which always amazes me.)

As regards budgets, I will have to re-read the rules carefully to see how the hose, used as a "platform", would count. You may find that you can play with more than £999.99, especially if the hose can be wound in and re-deployed (what goes up should come down, right?). But let me think more on this before putting my foot in it again.

Yours,
Paul

JaredJames

Despite my previous comments regarding the legal side of things, I'm actually quite interested in whether or not such a system could work (if not on a realistic scale, at least for the N-Prize).

I am currently trying to look at stability issues with the hose, I'm not sure if you've quoted any before, but what sort of dimensions are you looking at using for the hose?

As I said previously, without a good support structure a constant diameter tube extended 100km vertically would be extremely unstable. Could you provide those numbers plus a reference for this material you want to use for the hose?

gutemine

If you look at the slides you have most of the numbers with which I started my calculations.

The 10" choosen diameter was just to have a commercially available dimension as a starting point and to be able to do a few km 'test launches' without manufacturing any special. If you want to launch something beyond an N-SAT probably bigger dimensions would be better.

The wind pressure calculation for the first 15km (beyond this jet streams are over and pressure is already pretty low) is already in the thread (I think 1-2 pages up) with a 50km 'breeze' as an example. You will find also the stagnation pressure of the hose under such a wind there. If you calculate the WORST case - eg whole force als pull on the bottom of the hose you get the 1800N/mm² - normal PE has only 20-30N/mm² but Dyneema has 3000-4000N/mm² tearing strength. And because the dimension of the foil is so low a single 8mm Dyneema string can hold this. I would prefere 3-4 strings with 4mm² to balance better and prevent spiralling of the hose.

See this as a kind of huge sail - hight tech sails are nowaday available from woven Dyneema and the strings to hold it are also Dyneema ones. And this on sea with rain, saltwater, low temperatures. The sail area of the space hose is not so much bigger (as calculated already above) but a cylinder has a pretty good friction coefficient if blown from the side (I used 0,1 - a sail is 1 or biger because it is desinged to catch windforce)

A hose under a reasonable pull force is like a giant spring or better a rubber band (with huge damping because of the air filling and light pressure surpluss) so it is not such a bad device to withstand forces - because it is small, so the forces are limited. And you still could use the straw pack approach that the inflatable space tower people suggest. PE can be flexible up to 10% before tearing apart, but we need much less in this case if you have a few Dyneema strings taking the pull force. The Pravda picture approach copied into the slides is not that bad from the enigineering perspective.

And as I already outlined - bowing is WELCOME for a hose pulled from the top, because it is a pretty flexible structure and should not be harmed. Worst case is the top going down a few km if the wind is heavy.

Finally the good thing about windforce is that it is a pretty continuous force and not a punctual one. So you can use existing engineering formulars to calculate the caused tension - I simply asumed the worst that the entire force is taken from the bottom as pull - which is still holdable

But please check and do your own math - EVERY input is welcome and valuable. And if we can verify the strength and stability part the penumatic one can wait (the slides actually suggest to ask an engineer AND a physics)

gutemine

DaveC426913

Yes, though let's note that the space hose is in every way equivalent to a standard-issue space tower. The fact that the last inch or so of the space hose is gaseous rather than solid is irrelevant to the rules.

i.e. as soon as you allow the space hose, the door is open for any space tower.


And once the door is open for space towers, you might as well just drop the whole "reaching orbital speed" requirement altogether. Any entrant who has a choice of winning the prize by building a tower rather than building an orbital launch platform, is going to build the tower.



Seems to me one solution could be to rewrite the rules to include multiple trips rather than just the one, then set the cost to cover the total. That way, entrants might come up with ingenious ways to re-use components to keep costs down in bulk. But that might be whole other contest...

gutemine

well, we/Paul could simply make an NT-prize to build a 100km Tower within the budget able to lift at least 9,99 gram - then the disussion would be over ;-)

The reason why Paul created the prize was to enforce creativity and not demotivate it by the prize rules. So I simply decided to take myself this freedom and asked him if it meets the spirit.

There was no intention from my side to cheat, use a loophole or something, or rewrite the orbit definition (but there is still some room for interpretation - but let's NOT start this discussion again)

PS: If I would actually win I would donate the money to a children care organisation anyway.

gutemine

DaveC426913

Pretty much, yep.

Unfortunately, that is the almost inevitable outcome if they accept the space-hose as an entry. (Because the rules will need to be rewritten to eliminate the word 'orbit'.)

Good lord, no one thinks you were trying to cheat.

In fact, it is your responsibility as an entrant to push the rules as hard as you can. The challenge set out by the N-prize is huge; it will not be won without some very creative thinking such as this.

Or perhaps the local space agency?

gutemine

Look, I've read the Inflatable Space Tower patents and also their papers and presentation at the space elevator conference.

They spent quite some money and time on patenting it, but they still missed the point that air provides an easier method of producing lift then filling inflatables with helium (which runs out of buoyancy too early) or build them huge to withstand the pressure. So the N-prize limit was exactly the driver to TRY to avoid this problem - If it works we owe Paul a lot - just by pushing people into the desert and let them dig for water where nobody tried before.

I personally decided just to have fun and find out if it works but make the space hose idea public so that it is not patentable by anyone anymore !

And I'm not looking for fortune and fame either - so don't think that I try to market or sell you the space hose idea. I just like it (like my other children) and want it to prosper.

PS: And as I already said - if somebody is willing to try it out - I'll bring the beer.

gutemine

mugaliens

No, they won't. The N-Prize organizers have already spoken on this matter (you can't have missed this fact, as it's been mentioned several times in this thread).

You continue to confuse the difference between free-floating orbit and anchored orbit. To illustrate, let's take the example of an equitorially-anchored (tethered) space station at 42,164 m semi-major axis with a space-tether counter-weight of x kg at y km distant (immaterial to my point). Is it in "orbit" according to your definition? Certainly. In fact, according to your definition, it's in geosynchronous orbit. Mine too..

Let's move the counterweight out a bit while moving the space station in just one foot. According to your definition, it's no longer in "orbit."

Phooey!

Put simply, the N-Prize organizers came up with their own definition of "orbit" and have defendend their position, along with the funds. If you'd like to come up with your own definition, just start your own competition and front your own funds. :)

Put simply, your definition involves only that of a free-wheeling, totally untethered body. Meanwhile, the N-Prize folks have already ruled gutamines entry complied with their rules. They don't want anything "attached," but they've already ruled that balancing on a column of air is not "attached."

So who are you really, Dave? Are you the N-Prize coordinator himself? If so, please put up. If not, I've had it up to hear with your attempts to usurp the response of the N-Prize coordinators in terms of denouncing his idea based on your very narrow concept of the term "orbit."

Good-day.

- Mugs

gutemine

well, the real problem with all orbit definitions is that they were not specified with any tower/elevator construct in mind. Some contain gravtiy and/or speed - some do not, etc.

If you build the classical 72.000km space tower with a counterweight asteroid at the end then only about 1 inch in the middle (which would not even need to be the mass center) would actually be in orbit if you hammer the definitions in stone - because only this inch would rotate exactly with the obital speed at 36000km of 7,something km/sec.

The part below would be too slow, and the part above would be too fast and actually fly away without the tether or the tower.

BTW if there would be people having to stand on the counter weight asteroide, they would need to do this on the earth facing side - or they would be in big problems (calculate the acceleration then and then decide if it is a comfortable space)

My suggested 100km Space hose would have the same speed profile then the first 100km of the 72000km Space Elevator - so where is the point not to accept it as an achievment (in case it would work) and an approach worth discussing and analyzing.

The nice thing about a real orbit is that you are weightlessness - but this is not a must to be in space, and can be also a pain - so why thinking bad about avoiding it !

So can we please keep this orbit discussion aside for the moment - belive me if such a tower is really built the orbit definitions will be adapted, optimized or what so ever - and that's also what Paul suggested - which I think is a pretty clever approach to maybe get the wanted results of his N-prize competition to find an ultra cheap way to space and discuss the solution later (with or without prize money paid out is not even the point).

gutemine

DaveC426913

I think you're missing the point here. The launch system is not constrained by any but the broadest terms (such as budget). Nobody cares what the launch system does.

The 72,000km tall space elevator is only the launch system for the satellite. The point of the 72,000km tall space tower is that is has the ability to launch the satellite. Which is all the N-prize cares about.

DaveC426913

Because it's not "a way to space". Sitting on top of a very tall tower is not the same thing as being in space, just like pushing your car out into the driveway is not the same thing as putting an engine in it and driving it to the racetrack.

What advantages specifically (other than access to partial vacuum) are conferred from being at the top of a tall tower?


Orbit is not about weightlessness. Orbit is
1] freedom to roam over the Earth as needed, fuel free
2] the doorway to leaving Earth altogether.

gutemine

Space is a location - not dependent on the speed !

I'm in space if I'm 70.000km away from earth and don't have any speed at all. Then I' will spend the next hours/days to fall back to earth - but I'm definitely in space!

If you are in Paris it doesn't make a difference if you are on top of Eiffel tower, in a cab or a TGV entering Gare del'Est or sitting at the Seine and eating a baguette.

If you are in London (and have not even passed the Channel) you are definitely not in Paris !

This starts to become almost a fight comparable to geocentric vs. holocentric. If you are standing still compared to earth and are 100km high above you still orbit the Sun at amazing speed, and together with the sun you orbit the milkieway at another pretty high speed.

BTW Einstein spent quite a time of his life to explain that motion/time and speed dramatically depend on the observing point.

If I would follow this argument landing on the moon would have been a waste of time and the real achievment would have been Apollo 8 which orbited the first time the moon (something the Russians achived before if I remember right)

And orbit is also a lock-in as stiting on a tower - it costs fuel and time and needs acceleration to change height, direction,... try to make a polar orbit out of an equatorial - then you will know.

I have now written already 3 times that if air flow friction works to lift and keep a tower up to 100km it would work also for 36000km - and then you would have your orbital speed too.

Let's try it from the human view point - as a current space torist I have to pay about 20-30 Millon $ to see the earth from 350km (=ISS) from space (orbiting, I know). Do you think the people paid for the orbiting part/velocity - or for the view ?

If a space hose could offer a launch vehicle beeing able to bring you to space (as a loation !) for an infinitely time (if you stay on top) with a much smaller budget you think this is something nobody would care ?

If you can read everywhere that the current space elevators and towers have a problem because of no material supporting them, and you then find a way where a continuous support reliefs this material problem - then this is useless, because somebody planns to build only a 100km prototype ?

Maybe I simply misunderstand your point and apologize if my reply sounds impolite, but I really have a porblem understanding why this part is so important for trying out something and get some proove of concept by competing in a Prize which will get nobody rich ?

gutemine

JaredJames

If you were to tether a space station, it is classed as in geosynchronous orbit so long as it maintains orbital velocity and holds it's position above the earth.

By having the counterweight, you shift the CoG to a point central to the both units. It is this point that must remain at the geosynchronous orbit altitude (36000km) and the velocity must be that of a geosynchronous orbit

If you think of it, the tethered weight would be travelling far slower than the station due to having a shorter orbital period (height within 36000km and station outside of). It is the point at 36000km that needs to be at geosynchronous orbital velocity and the CoG of the two counteracting objects.

Even if you forget geosynchronous orbit, as long as both units move as one, they would require the correct orbital velocity for whatever altitude you set them at. If you don't overcome gravity with a velocity greater than that of geosynchronous, you will fall to earth (when orbit < 36000km) and if your velocity is greater than that of geosynchronous you will slingshot away (for an orbit > 36000km). The lower altitude object travels slower than required orbital velocity and the higher object travels faster than required orbital velocity. They counteract each other and provide a stable orbit, with a point central to both (the effective CoG) travelling at the correct orbital velocity for the altitude it is holding.

You cannot separate the two elements because they function as one. Individually, if you cut the tether, without the counterweight, the station would require a different velocity in order to maintain it's altitude and position over the earth.

When it comes to 100km, there is no such thing as free floating orbit. If you do not maintain the required orbital velocity around earth, the satellite will be pulled towards the planet. Holding something on top of a tower, you have simply extended the earths surface to that altitude and placed something on top. Not an orbit by any means.

Anyway, I think this point has been hammered into the ground now and we should perhaps concentrate on the physics of the device???

EDIT: sorry for so many corrections, completely misread your post the first time.

gutemine

I like this sentence :-)

Did you have already some progress on (re-)checking the structural strength needed ?

I already shared all the data and calculation I have on this subject - which doesn't look that bad in my understanding, but at the moment it is just patched together out of classical engineering formulars and some assumptions.

If PE foil combined with Dyneema can hold all possible stresses (pressure AND pull) put onto the structure because of it's strange diameter to length to thickness to weight ratio (hopefully my English teacher will never see this sentence) this would be already some kind of confirmation to proceed with this concept.

As the slides say - I hate to wait for carbon nano tubes !

On the other hand if the physics would not work to provide the lift force and handle the gas flow this would be still only half of the lunch.

So we would need urgently somebody also beeing able to put some light on the suggested gas dynamics - If nobody here can help out on this - what would you suggest ?

gutemine

JaredJames

I have the dimensions from your slides, can you provide me with a link to the exact materials you plan to use (or provide me with some datasheets on them) so I can be sure I'm looking at the right stuff?