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# 9 Kilometers of Balloons

For measuring "as the crow flies"
 (0) [vote for, against]

Several months ago some News was made by a Physics Experiment, in which the results indicated that neutrinos might be able to travel faster than the speed of light.

But one thing the experimental result depends on is an accurate measurement of the distance between the source of the neutrinos and the detector. They happen to be about 730 kilometers apart, but the experiment requires parts-per-million accuracy of both the distance measurement and the travel-time measurement.

This Idea will focus on making a more accurate distance measurement. Currently the satellite-based Global Positioning System was used to make a measurement that may be wrong by as much as 20 centimeters. This is considered acceptable because a millionth of 730 kilometers is 73 centimeters. But who says we have to be satisfied with that?

Now, you might use laser beams to make distance measurements (we know the distance to the Moon down to a few millimeters, if I recall right, thanks to laser reflectors put there by astronauts). However, here on Earth the atmosphere tends to interfere with long-distance laser measurements. It also directly affects the speed of light, and does so irregularly (density variations in the air). Thus we need a better way!

So, let us start with some fairly stiff and tough plastic, like polycarbonate. Now imagine a large sheet of it, like you go to the lumber yard to get a large sheet of plywood. Now imagine lots of these sheets, equipped with a (formed as part of the plastic) latching system so that the sheets can be connected to make bigger sheets.

Now imagine a secondary latching system so that we can also create an "X" pattern for some of these plastic sheets. That is, the "X" is the edge-on view of the connected sheets. In an office building, such an "X" might form some of the walls of 4 adjacent cubicles.

Now imagine that all these sheets are full of fairly large holes, say 5-10 centimeters in a nice regular hexagonal patterm. This will reduce the weight of the sheets substantially, and allow wind to blow through the holes, yet let the plastic retain most of its strength and rigidity.

Now imagine that some of these large holey plastic sheets have attachment points for cables or ropes. I'll get back to those momentarily.

Finally, we want the dimensions of our "X" pattern to be about 10 meters on each "arm" of the "X". So, 20m long and 20m wide. Now we start attaching sheets to each other, building a nice long 9-kilometer length. This length is somewhat arbitrary, and I'm actually guessing how long we can make it work for this purpose, given the stiffness of a 20-meter "X".

Whatever length we end up using, we MARK it --the whole length!-- like we mark an ordinary ruler. Thus we now have a 9-kilometer measuring stick. We could use it to precisely measure the width of a large town in one step.

We now attach balloons all along the length of our measuring stick, to loft the whole thing somewhat above the trees and various buildings (they do tend to just be in the way, sometimes). Since the ballons are unmanned, they can filled with hydrogen and thus be smaller.

It could be difficult to hold this measuring stick still, the wind is almost always blowing above treetop level. But what you can do, as an alternative, is to anchor one end with guy wires, and let the other end swing past the place on the ground you want to measure.

Now shine a laser beam up from the ground, and record which mark it hits, on the measuring stick, as the wind blows the balloons by, overhead. Do the same thing at the anchored end, of course; we want the stick to simultaneously/momentarily be above both places, so that we can accurately find the distance between them.

All you have to do, now, is repeat this along, say, a Great Circle Route, to accurately find longer distances between two points --such as the relevant locations of that Physics Experiment.

 — Vernon, Jan 08 2012

Neutrino experiment http://en.wikipedia...ht_neutrino_anomaly
As mentioned in the main text. [Vernon, Jan 08 2012]

Polycarbonate properties http://en.wikipedia.../wiki/Polycarbonate
Some relevant info. [Vernon, Jan 08 2012]

Marking a Great Circle Route 8-Kilometer_20_22Tower_22_20Balloon
Something hinted-at in the main text, fleshed-out. [Vernon, Jan 08 2012]

Notice which way this structure is NOT flexing --from side to side, against the (10-meter?) width of the roadway. [Vernon, Jan 09 2012]

And what makes you think that this marking stick will be more accurate than 73 cm over its whole distance? Errors in measuring when marking out the distance points will certainly add up, and the result will likely be no more (or even less) accurate as the GPS measurement for a massive increase in price!
 — Hive_Mind, Jan 08 2012

Ah, but this idea has the advantage of being complex and difficult to implement. This more than offsets problems such as (for instance) the coefficient of thermal expansion of polycarbonate (a 1°C temperature change will change its length by about 60ppm).
 — MaxwellBuchanan, Jan 08 2012

 [MaxwellBuchanan], duh, you are saying that the temperature of the measuring stick can't be taken, and the measurment appropriately adjusted?

[Hive Mind], in general, any source of error that can be identified can also be compensated. Be more specific, please.
 — Vernon, Jan 08 2012

 Firstly, there is, as [MB] mentioned, thermal expansion. Or is there also a complex system of thermoprobes, refrigerating systems, and heating elements such that the stick is constantly maintained at the exact temperature it was originally marked at, regardless of weather, cloud conditions, time of day, or season? Even a minute change in temperature over 9 km could result in significant error.

 Secondly, there is whatever system you're using to mark the ruler- if the width between centimeter markings has an error of so much as .01%, this would add up to a relatively vast error over the full 9-km length- and for that matter, there is error inherent in the dimensions of the polycarbonate sheets, just as when you order lumber from a lumberyard it's never /exactly/ the dimensions you ordered. One would have to have the polycarbonate very precisely machined, and all that would likely be ruined as the joints between sheets added length or flexed.

 Furthermore, polycarbonate can bend and/or stretch, making the dimensions of the Uberruler and the positions of the markings significantly variable over the full 9 km.

There's more, but these are the most obvious.
 — Hive_Mind, Jan 08 2012

 [vernon], duh, I'm merely pointing out that your measurement device will require several thousand points along the polycarbonate structure to have their temperature measured to within some fraction of a degree. Clearly, this added complication is only a bonus!

 As an added extra, you'll also want to measure the moisture content of the polycarbonate (like many plastics, polycarbonate shrinks and swells very slightly depending on moisture), and to make some sort of allowance for its gradual loss of plasticiser and residual monomer over time (which cause it to shrink) at all points.

 Of course, you'd also need to monitor any longitudinal forces acting on the structure. Polycarbonate has a pretty low Young's modulus, about 2Gpa. So, if the cross-sectional area of the "chain" were, 100cm^2, then a longitudinal force of 1kgf will stretch or compress the entire structure by something like a metre.

 Fortunately, though, you don't need to worry about this effect too much, because it will be dominated by variations in ambient pressure. Atmospheric pressure varies commonly by, what, a percent, and polycarbonate is not entirely incompressible. So, variations in ambient pressure on your 700km ruler will change its length by a tiny fraction of a percent - maybe a few metres overall.

 Even this, though, is not something you need to worry about yet, because a far bigger problem will be rippling. Your 700km structure will behave pretty much like a 7m length of videotape, rippliness wise, so you'll have to wait for a pretty calm day (windspeed, say, less than 0.1km/hr over the entire length of the structure; no thermals or anything else).

 Oh, but wait. What if one of the balloons is a tiny bit more bouyant than the next? (For example, what if, yesterday, the weather in the middle of the structure was a bit warmer, and the residual heat means that the middle balloons have a bit more lift?) That's a pisser. Still, more measurements can be made to correct for that.

All in all, [vernon], I think that, practicality-wise, this idea of yours is right up there with all your other ones.
 — MaxwellBuchanan, Jan 08 2012

I'll one-up you all and do 10 kilos of balloons!
 — RayfordSteele, Jan 09 2012

Hang on, doesn't space distort due to gravity and so given that we have two very massy objects rotating then any attempt to get an absolute measurement of any distance between two points in that area is not going to work that well. Or I am being thicker than normal?
 — not_morrison_rm, Jan 09 2012

 Could be, because I was going to ask the same question, just not as well.

If gravity warps space would the position of the closest large gravitational attraction not warp a circular LHC into an eliptical LHC?
 — 2 fries shy of a happy meal, Jan 09 2012

 [Hive Mind], the measurement markings are to be added after the thing has been fully assembled, and while sitting on the ground (all you need is a 9km straightaway).

 [MaxwellBuchanan], I think the temperature problem is not quite as great as you make it out to be. First, polycarbonate is a HARD plastic (can be harder than aluminum if I recall right), and harder substances tend to conduct heat better than softer substances. We especially WON'T be wanting this made with "plasticizers" or "water content". Also, the sheets from which this measuring stick would be constructed aren't intended to be so thick that they take a long time to adjust to an external air-temperature change.

 Another factor is that, above the ground, there is no shade other than clouds. Air temperatures AT the ground can vary far more widely than they do at 500 meters of altitude. (This isn't to say the temperatures can't vary up there; we know that various ground features can produce thermal updrafts. We simply want to avoid those.) So, if the weather is reasonably fair and clear, such that one end of it doesn't pass through, say, a cold-weather front, then we can have a reasonable expectation that all of this measuring stick will be the same temperature.

 By the way, where is it indicated that all the measurements need to be made within some limited time frame? Just pick some particular/suitable but moderately common weather conditions, and only make meaurements with this tool when those conditions exist. Which eliminates your air-pressure problem. There are times to hurry, and times to take your time.

 Next, where is a longitudinal force going to come from? Don't you know that very-similar balloons basically all travel together in the same wind at the same speed?

I will agree that rippling could be a problem, which is why I specified a 20-meter "X". Think "truss" in 2 dimensions, not just one. Across 9 kilometers it still might not be enough to prevent all ripples. On the other hand, again there is the fact that balloons tend to travel together. What is going to cause ripples, when we get to choose the weather in which it is deployed?
 — Vernon, Jan 09 2012

 So, [Vernon], you want to make this of a good heat conductor, but you also want to make it thick enough so that it takes a long time to adjust to changes in air temperature? Well, that covers both options then.

 And it's a good idea to leave out the plasticizers. You'll need a team on hand with plenty of glue, because plastics generally contain plasticizers for a good reason, but that will add immensely to the fun. And yes, of course you will make the plastic without water - that wasn't my point but hey.

 And yes, of course, you're right about the forces: it should be very straightforward to suspend a 700km structure weighing (quick calculation based on a 100cm^2 cross-section of plastic) a mere 70,000 tons with no lateral forces at all.

 Yes, this sounds like a wonderful idea, carefully thought out, rigorously researched, and presented with the skill and insight of a true engineer.

Go, bake - the world will be in your debt.
 — MaxwellBuchanan, Jan 09 2012

//harder substances tend to conduct heat better than softer substances// huh?
 — hippo, Jan 09 2012

 [MaxwelBuchanan], obviously you failed to read what I actuallly wrote: "the sheets from which this measuring stick would be constructed aren't intended to be so thick that they take a long time to adjust to an external air-temperature change" --how does that translate to (what you wrote) "you want to make it thick enough so that it takes a long time to adjust to changes in air temperature" ?

 Next, you ignore the Title of this Idea, which says we would be suspending this measuring stick all along its length with "9 Kilometers of Balloons". So how do you get "a 700km structure" ?

[hippo], look up diamond, the best solid heat conductor. It's so hard that it can conduct thermal vibrations as if they were sound vibrations. I expect various other hard materials to exhibit a similar effect (just not as strongly).
 — Vernon, Jan 09 2012

So all we need to start with is a 730km long diamond?
 — pocmloc, Jan 09 2012

 [Vernon] MB's point on moisture is that Polycarbonate just loves sucking up atmospheric moisture.

 Then there's the fact that you're right, balloons tend to move in a given air stream as a group. But each time this structure moves between wind columns (or part of it recieves a gust the rest doesn't) it's going to wiggle like crazy.

 There's also the fact that plastic creeps over time, and given the length of this, it doesn't take much creep to cause the entire thing to deform.

Finally there's the fact that this doesn't help with it's original stated goal because the distance in the experiment as cited is, I'm pretty sure, the straight line distance through the planet. Neutrinos are funny that way.
 — MechE, Jan 09 2012

 // aren't intended to be so thick that they take a long time to adjust to an external air-temperature change// Yep, misread that, my apologies (actually, the rate of thermal equilibration is pretty irrelevant - it'll be somewhere between minutes and a few hours; either way, you'll have to track the temperature and rate-of-change at multiple points and then calculate the thermal expansion of the big plastic ruler).

 I took 700km because that's the distance you're trying to measure to better than 20cm (which you tell me is the limit of GPS). Whether you do it in 9km steps or in one go, your glorious plastic ruler still has to be accurate to the same factor.

 Incidentally, while the metricians are maneuvering this ruler into place for each measurement, they could always try a gentle shove one time, and a few whacks with a big hammer the next. In that way, they will be able to settle fairly definitively the business of reactionless reactions. [vernon] - you could be in the ruining for not one but two Nobel prizes.

 As I've emphasised all along, I see the problems with this idea as being its chief merits - its flaws have a sort of Baroque beauty to them.

 The more flaws an invention has, the more chance you stand of solving at least one of them.

(Incidentally, if we know the distance to the moon to within a few millimetres by laser reflection, and if we assume that all of the errors therein are caused by the laser having to pass twice through a few tens of kilometres of turbulent atmosphere, then this strongly suggests that your 700km distance could be measured, laserwise, to a very few centimetres. We need to guard against this sort of thinking, before some smartarse makes your 700km measurement more accurately, more cheaply and with less polycarbonate than you propose, just to show off.)
 — MaxwellBuchanan, Jan 09 2012

I have a toasted bun waiting for "A Large Plastic Ruler to Give to the People Who Measured Neutrinos Travelling at FTL Speeds"
 — FlyingToaster, Jan 09 2012

What is the cumulative error of a quintillion laser photon lengths?
 — reensure, Jan 09 2012

Tiny.
 — MaxwellBuchanan, Jan 09 2012

 [MechE], okay, I didn't know that about polycarbonate. Ever since "Lexan" was first marketed, I thought it was fairly resistant to such things as humidity.

 Ummm, wouldn't a very hard plastic exhibit far less "creep over time" than a more-ordinary/softer plastic?

 Note I wrote an anno in the "8Km Tower" Idea about how, once you know an accurate Great Circle Route distance, you can use that to compute an appropriate "chord" distance. I know full well that neutrinos go straight through the Earth.

 [MaxwellBuchanan], if the weather conditions are fair-enough across the 9km distance, then all you have to do is hoist the ruler and wait. After it reaches a constant-enough temperature, make your length-adjustment calculation.

 It occurs to me that a minor modification of this Idea, putting a laser system on the ruler, would remove the need to mark the ruler, AND remove any worry about what its current length is, even if it has flexed from the perfectly-straight (just laser-measure the length between its end-points on-the-fly).

 If that same laser beam passes through a couple of splitters, which direct parts of the beam straight downward, then by receiving those beams at ground-level you now know how far apart two points are, on the ground. You could perhaps tie this with the use of modern surveying equipment, to connect the two laser-marked ground points with other (already known) points on the ground.

The preceding could simplify an attempt to measure a Great Circle Route, because you are no longer required to get the ruler directly in line with the GCR; it just has to provide ground-marks close enough for surveyors to connect them to the GCR.
 — Vernon, Jan 10 2012

//compute an appropriate "chord" distance// You know the earth is not spherical?
 — pocmloc, Jan 10 2012

 //wouldn't a very hard plastic exhibit far less "creep over time"//

 Not really. First off, what you're looking for is rigid, not hard, the two aren't really the same thing. And neither has a lot to do with creep, whch is more related to polymer chain length and cross-linking. Relatively soft rubber tires will not creep much at all because vulcanization cross-links it like crazy.

 Second, PC isn't particularly hard or rigid. What it really is is very amorphous. That means instead of a bullet impact shattering it and throwing most of the material away, it just gets stuck into it. (Picture the difference between punching glass and punching jello, the glass is sttronger, but the jello will still be intact after the punch). This exact trait makes creep worse.

Oh, and a note on the Tacoma Narrows bridge. It wasn't flexing in the direction of the road bed, but it was flexing because of wind loading in that direction.
 — MechE, Jan 10 2012

 // a minor modification of this Idea, putting a laser system on the ruler, would remove the need to mark the ruler, AND remove any worry about what its current length is, even if it has flexed from the perfectly-straight (just laser-measure the length between its end-points on-the-fly).//

 Aha! So, in other words, the best way to make the plastic-ruler-method work is to dispense with the plastic ruler and measure the distances by laser.

Brilliant. Absolutely brilliant. I wish I'd thought of that.
 — MaxwellBuchanan, Jan 10 2012

 Am I missing something major? Vernon's ideas are confusing but that I know of always based on solid science. This one seems like jibberish or am I missing what this idea even does.

 All it seems to even propose to do is measure the distance between two arbitrary points above the Earth. Even if it then could measure the distance from the ground to the ruler, you still don't have anything as you don't have the altitude of the ground from the center of the Earth. So even if you built the whole thing out of unobtainium and did a great circle measurement, you'd still have nothing as you don't know it follows a circle, so you won't know the distance of a chord, so the whole project is a waste.

What am I missing?
 — MisterQED, Jan 10 2012

You've missed the major impetus this would give to the balloon industry.
 — MaxwellBuchanan, Jan 10 2012

[MisterQED], a longer measuring stick means making fewer measurements (which of course are subject to error). Also, using an airborne stick means you can get line-of-sight much more easily, almost anywhere, than at ground-level.
 — Vernon, Jan 10 2012

Hey, nobody accuses me of being learned.
 — MaxwellBuchanan, Jan 10 2012

That's so true.
 — 8th of 7, Jan 10 2012

What about the step-mis-alignment problem? (I would do a sketch, if I could be bothered...)
As your ruler is only 9km long, you need to move it 9km to make your next measurement 'step'. To get an accurate measurement, the ruler needs to be in perfect alignment with how it was for the last step, in 5 dimensions no less. Which, for a ruler this big, will be virtually impossible...

[neutrinos shadow], see my last anno of Jan 9. It removes the need for end-to-end positioning. The height becomes basically irrelevant. And ground-surveying techniques can compensate for modest angles away from the desired GCR line.
 — Vernon, Jan 11 2012

 //The art of playing along for a jolly wheeze.// Well, maybe. I get the whole "hey wouldn't it be great to turn a measurable proportion of the Earths mass in to a mega-structure to do something that could be easier and better done with \$40 worth of string or something" fun, but isn't part of the whole "hullaballoon"ish fun that if it was built, it would work? Wouldn't this idea be funner if it was a long string connecting geostationary satellites? I realize the string would be many orders of magnitude longer, but the negation of gravity, the removal of sound and wind vibration and the added fun of accounting for solar wind, micrometeorites and the pressure of background microwave noise to create a TRUE mega-structure that has the added bonus of possibly being able to perform the mock task that it was created to perform as then you could gauge curvature? If it is all for fun, why worry about the moisture absorbency of materials?

Sigh, it saddens me that I have been here so long and it seem I have still have not decoded even the foundations of the humor and the place of engineering within it.
 — MisterQED, Jan 11 2012

I think "foundations" is a bit strong. More a couple of two-by-fours with some plastic sheeting under them.
 — MaxwellBuchanan, Jan 14 2012

[MisterQED] No, no, you're not missing anything - this idea is nonsense. Everyone knows this, it's just [Vernon]'s dogged attempts at ignoring everyone's objections that is keeping the twitching corpse of this idea alive.
 — hippo, Jan 15 2012

 [annotate]

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