h a l f b a k e r yYeah, I wish it made more sense too.
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This Idea could be applied at different scales. The particular scale under discussion here will involve the orbits of Earth and Mars. We want a fast way to move stuff between them, so...
The circumference of the Earth's orbit around the Sun is 939,887,974 kilometers (link). The orbit of Mars is
52.4% larger than that (link), about 1,432,000,000 kilometers in circumference.
That second link also indicates that the orbital velocity of Mars is about 80% that of Earth's.
Next, a "telescoping pointer" (link) consists of a set of nested tubes (usually 3 or 4 of them) all about the same length. For this Idea we need only 2 different sizes of tubing.
We want to construct a telescoping tube all the way around the Sun, a little larger than the Earth's orbit. If each section of the tube was only about 1 kilometer long, we would only need about a billion of them, connected end-to-end, to construct the **outer** tube.
At every connection place we have, inside the outer tube, a single nested tube that is 0.53 kilometers long (because of that 52.4% above).
We include appropriate power supplies, electronics, servo-motors, hydraulics, whatever, in order to ensure that, at any one of those connection places of the outer tube, a telescoping expansion can occur, which would expose the length of inner nested tubing.
This construct is pure hardware. There is no need for this tube-around-the-Sun to be pressurized for human habitation (not to mention that doing so would present a large headache in terms of preventing atmosphere leaks at the expansion joints). The Xpand-O ring is simply a tool. A quite-large tool.
After the ring is fully constructed, we can now use it to transfer stuff between Earth and Mars. So, for anyone leaving Earth, his or her space-ship travels a little way out from Earth's orbit, to the Xpand-O ring, and anchors itself. Okay, not quite so close. The ring has to be located farther than the Moon, so that the Moon doesn't collide with it. Assume a travel time of 4 days, to reach the Xpand-O ring.
Now **all** the telescoping expansion joints of the Xpand-O ring are signaled for activation. It will take perhaps 20 minutes for the electronic signal to propagate all the way around the ring to the far side of the Sun, but modern electronics and timers are plenty good enough to account for the delay, such that all the joints can, after that delay, expand simultaneously.
So, if every 1-kilometer length of the Xpand-O ring simultaneously telescopes to become 1.523 kilometers, a process that should only take a few hours, then, afterward, the entire Xpand-O Ring is now about the same circumference as Mars' orbit. The spaceship can now release its anchor and travel the short remaining distance to the Red Planet (and 2 more moons to avoid).
That total travel time of, say, 6 days, in the preceding description, assumes that the Earth and Mars are appropriately aligned during the transfer. When they are not so conveniently aligned, some additional stuff needs to be described (shortly).
Note that the mass of the entire Sun-girdling Xpand-O ring is so much more vast than that of the spaceship, that moving the extra mass of the spaceship, during either the expansion process or a Mars-to-Earth contraction process, is trivial.
Also note that due to the "pirouetting ballerina effect" (link), and the Law of Conservation of Angular Momentum, the orbiting velocity of the expanding ring automatically slows down as it enlarges. I will not say that it will slow down the exact amount needed to match the orbital velocity of Mars, because I haven't done the appropriate calculations.
However, even if the amount of slow-down is wrong, there is an easy way to correct for it, by the same stuff needed to deal with awkward planetary alignments.
Basically, we mount a maglev system on the Xpand-O ring. An appropriate design is needed to deal with the fact that the ring expands. One way to do it starts by giving each inner length of tubing a "taller" maglev track, than the outer tubing. This track is initially offset from the track on the outer tubing.
The outer tubing also has slots to accommodate the inner-tubing's track. When the Xpand-O ring is in the "contracted" position, the inner-tubing maglev track occupies those slots, and is not in the way of the outer-tubing maglev track, which is perfectly aligned and usable by itself.
When the ring is expanded, each piece of inner-tubing maglev track clears the slots, and each piece of inner-tubing can be rotated, relative to the outer tubing, so that all the sections of maglev track line up perfectly.
Now our spaceship can electromagnetically travel along the maglev track, accelerating to a hundred thousand miles per **minute** if necessary, in order to traverse sufficient circumference of the Xpand-O ring, to deal with the problem of awkward planetary alignments. (Total travel time should never exceed two weeks.) And of course the spaceship can match orbital velocity with the planet, before detaching from the maglev track for final approach.
Circumference of Earth's Orbit
http://sse.jpl.nasa...cfm?Object1=Jupiter
As mentioned in the main text [Vernon, Mar 21 2012]
Some planetary orbital comparisons
http://www.sjsu.edu...watkins/orbital.htm
As mentioned in the main text (see Mars data) [Vernon, Mar 21 2012]
Telescoping Pointers
http://www.nextag.c...pointer/stores-html
As mentioned in the main text [Vernon, Mar 21 2012]
Pirouetting Ballerinas
Ballerina_20Wrist_20Weights
As mentioned in the main text [Vernon, Mar 21 2012]
Natural Gee-forces above the Sun
Planet_20Stellar
Some information relevant to an annotation [Vernon, Mar 21 2012]
An Earthly use for Vacuum Welding
3D_20Printing_20in_20a_20Vacuum
Relevant to some annotations, for anyone interested [Vernon, Mar 23 2012]
[link]
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// If each section of the tube was only about 1 kilometer
long, we would only need about a billion of them // |
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Well, that sounds do-able. |
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This is pure, unadulterated insanity. I wish I could come up
with stuff like this. [+] |
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Other than the unobtanium needed to build this structure, I really can't see anything inherently wrong with this. |
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You'd need something (solar sails, ion engines?) to correct the orbit over time, and your travel time might be a little longer because most likely you'd want to tilt it from the ecliptic a bit to minimize orbital interference and problems with eccentric orbits. [+] |
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Corrections could be made very slowly by varing the
current applied to the maglev tracks. The ideal
arrangement would be to have eight or more tracks
running down the interior walls of the tube; changing the
magnetic force of one track would alter the field profile of
the entire arrangment and cause the tube to bend. I'm not
sure, but I think the lowest-voltage track would always be
on the inside of the curve. I'll need an actual physicist to
verify that part for me. |
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[MechE], why is unobtanium needed? The starting situation describes it as basically having about the same orbital velocity as the Earth. There are no significant stresses on it when the whole Xpand-O ring is simply orbiting the Sun. And there is nothing technically unusual about the expansion process --yes, it "lifts" against the Solar gravity well, but the starting point, in terms of Gees, is (let's see, 1Gee at 6million miles from Sun, 1/4Gee at 12 million miles from Sun...) about 1/241Gee at 94million miles from Sun. |
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What needs to be computed is the amount of stress, in terms of revolutionary velocity of Ring around Sun, after expansion is done, as a result of the slow-down due to Angular Momentum Conservation, compared to natural orbital velocity at that same distance from Sun (about Mars-orbital distance). If ordinary materials can't handle that much stress, then, yes, unobtanium would be needed. |
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But until the calcs are done, I don't know that it is right for you to claim right-off-the-bat that this Idea is technically impractical. Do note that one way to reduce the stress is to build it, partly expanded, in a Solar orbit half-way between Earth and Mars. Then it would contract down to Earth's orbit, acquiring velocity (perhaps ending with a value different from Earth's), and it could expand up to Mars' orbit, losing velocity (perhaps ending with a value different from Mars') --but in either case the total stress should be about half that of the original scenario. |
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I will agree that trying to run a maglev at 100,000 miles per minute on such a ring --despite its size-- will be associated with another whole category of stress, and perhaps I have overestimated the maximum practical velocity. But, hey, if we are willing to take 9 months in a Hohmann ellipse transfer orbit, to get between Mars and Earth, anything less than that should be acceptable. (Not to mention that we could exclude expansions and contractions of the ring at times when the two planets are too-awkwardly aligned.) |
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At the risk of being dragged into the street and shot, I'm
suggesting graphene laminate. |
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Mind=BLown. Seems so simple, would this actually work? |
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Sweet. This one I get.
Expanding the ring a bit farther, the asteroid belt should contain enough raw material for something of this magnitude once you'd shrunk/refined it to smaller than the orbit of Mars... it's all nicely spread out and everything. |
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Item one, thermal expansion issues. Item two,
total quantity of material. Item three, expanding
the ring will result in some pretty nasty loading at
each joint (figure the hoop stress of the
expansion, not the lifting, this is probably the
biggest). Item
four, vacuum welding. Item five, sealing and
joining under the above conditions. Item six,
transport of material into position. |
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I'm not trying to say it's impossible, just pretty
sure that you're going to be at the upper limits of
current materials science, and far above the limits
of current orbital engineering. As I said, I like the
idea, I just am reasonably certain that those
stress calculations are going to prove scary. |
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// Item four, vacuum welding // |
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Not an issue. Several techniques are baked but not widely-
known (because they have extremely limited applications).
Examples: particle beam welding, high-amperage laser
welding, point excitation welding, resistance insert
welding. |
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// you're going to be at the upper limits of current
materials science, and far above the limits of current
orbital engineering // |
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In other words, well within Halfbakery tolerances. |
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If you're going from Earth's orbit to Mars' orbit in a few hours there is no way around the acceleration forces you would encounter. You are still moving a long distance in a short time, after all. Wouldn't it take more energy to expand all of these joints than it would just to accelerate the ship at the same rate with a rocket? Like Mech said, those stress calculations are going to be scary. |
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[DIYMatt], that's an excellent point, and thank you. If you had a 1Gee constant-acceleration spaceship, you could go from Earth to Mars in about 3 days, depending on their relative orbital alignment. (You would accelerate for half the distance and then decelerate during the other half.) Therefore to do it in just a few hours will require a much more stressful acceleration, which I neglected to think about. Obviously, therefore, the Xpand-O ring must be resized rather more slowly than indicated in the main text. (For unmanned cargo pods, though....) |
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Regarding vacuum welding, it is possible that [MechE] was more concerned about accidental welding than deliberate welding. In the vacuum of space two metal surfaces tend to lose a thin coating of gas that semi-attaches to them when in an atmosphere. And without that gas layer between them, simple contact of metal objects can equal "welding". Which means that deliberate vacuum welding is very easy. But I think I read somewhere that the accidental-welding problem can mostly be solved with graphite as a gas-replacement substance, to be applied to vulnerable metal surfaces. |
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Very large space-construction projects always require enormous quantities of materiel. That's why we need mines on Mercury, with solar-powered electromagnetic launchers, to send metal mined from the planetary core (Iwhich is quite large and much easier to get at than Earth's) to anywhere we need it, in the Solar System... |
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So how many ships would you need to transport
before this would pay off? |
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As has been discussed in other ideas of orbital arches, I think we have an arch-in-compression issue. Your description certainly leads me to think that the telescoping sections are "pushing" out, somewhat against solar gravity. Maybe I misread. |
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So my counteridea is this. Have the whole hoop in tension, ie spinning (just) slightly faster than a necessary to counter solar gravity. Not a lot at all, because you're essentially going for a orbit just faster than the orbit radius would dictate, so that distributed tension would keep the orbit stable. Kind of like a caternary. |
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The main bit is that you could maintain/moderate rotational velocity via actuated angled mirrors distributed about the ring, like a couple billion solar sails. This structure is then somewhat more stable, also able flex and wend about the uneven gravity field of an interplanetary orbit, in fact the length of each segment would likely be dynamically changed to keep stability high and stress low. |
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...Anyhoo, when transitioning from high to low or low to high orbit, you just command the mirrors to angle their elves to increase or decrease rotational speed, coordinated with extension or retraction of the hoop segments. This will better let you match orbital speeds and gets away from your troubling ("a" weighs a lot less than "b" so we won't worry about it) issue, along with some other troubling physics issues. This gives the flexibility and control to do whatever you want, let the rocket surgeons work out the minutae. |
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Also gives you all the power you could imagine for linear accelerators, etc. |
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In support of previous, I fear you're missing the concept of stable orbital speed. |
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Mars, whilst it's year is longer that Earth's, actually has higher orbital velocity. You need to add orbital speed as you expand the ring otherwise you'll lag, and also fall out of "orbit", placing the ring in compresion. Since there is no structure that can possibly maintain compresison over these distances, you're doomed. Hence why I beleive a ring under moderate tension (does not need to be much at all) is better, and this is done by having an orbital speed slightly above neutral, and adding/removing orbital speed as you transition up/down. |
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//Mars, whilst it's year is longer that Earth's, actually has higher orbital velocity.// Not quite; assuming a circular orbit, orbital velocity is inversely proportional to the square root of radius, so Mars does move more slowly than Earth. But for constant angular momentum, velocity is inversely proportional to radius, so it will indeed be in compression when expanded to Mars's orbital distance. |
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Roger that, chalk it up to me being distracted. Big mistake but, can't beleive I got it arse about. Still, the ability to control speed works the other way too - slow down or speed up, using the mirrors/sails. |
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// Item four, vacuum welding // |
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As Vernon said, I meant the accidental type. Welding in orbit isn't difficult, preventing it from happening on a large, semi-static (that is, it sits in one palce for a while, then has to move) structure can be problematic. |
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[spidermother], based on what you wrote, if I assume an initial orbital radius of 1 arbitrary unit, and an orbital velocity of 1 (appropriate but different) arbitrary unit, and then double the radius, then at the new radius the appropriate orbital velocity would be 1/4 the original value, but in terms of conserving angular momentum the velocity would need to be 1/2 the initial value. |
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So an initially-orbiting ring that expands to double its initial size would be revolving at twice the actual orbital speed, at the new size. Which should put the double-size ring under tension, not compression. Unless I missed something? |
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Regardless of which way (expansion or contraction) lies compression, I think we need to avoid that. Such a large-but-skinny object under compression would be subject to the Uncertainty Principle and could be expected to buckle as a result. So, if we can have tension by expanding, the initial size should be at Earth's orbit. If we can have tension by contracting the ring, the initial size should be at Mars' orbit. All that remains is to figure the actual amount of tension, and whether or not ordinary materials can handle it. |
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Note that if we can't get to Mars with just one Xpand-O ring, we could nest several of them in-between Earth and Mars, and the spaceship would transfer between a just-expanded ring and an about-to-expand ring when going to Mars, or transfer between a just-contracted ring and an about-to-contract ring, when going to Earth. |
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Have you thought about how to get past the asteroid belt while expanding or contracting? I have no idea how dense it is. If you tacked the position of all significant asteroids could you time the expansion of the ring so it misses them all, or are there so many asteroids that it is unlikely that there will every be a time when this ring could pass through without hitting some? I guess that's yet another reason to use the asteroids in the construction process. |
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//double the radius, then at the new radius the appropriate orbital velocity would be 1/4 the original value, but in terms of conserving angular momentum the velocity would need to be 1/2 the initial value// |
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No, you've squared where you should have taken the square root. If you quadruple the radius, then at the new radius the appropriate orbital velocity would be 1/2 the original value, but in terms of conserving angular momentum the velocity would need to be 1/4 the initial value. |
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[spidermother], OK, yes, I somehow missed seeing the word "root" in what you previously wrote. So this simply means, as I previously wrote, that we need to construct the Xpand-O ring so that when it is expanded, it possesses proper orbital velocity while it is also near Mars' orbit. And when it is contracted it will be under tension. |
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Which means the appropriate figures are roughly, if Mars orbits at 80% of Earth's velocity, and the contraction factor is the inverse of that 1.5 expansion factor previously described, then the contracted ring will be moving at about 0.8*1.5=1.2 times Earth's orbital velocity. |
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As a matter of practicality, it could still be built near Earth's orbit, at orbital velocity. After being built, we would want to spin it up to give it appropriate tension, before expanding it. |
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I'm aware that that Larry Niven's "RingWorld" must be spun up to something like 42 times Earth's orbital velocity, in order that its Sun-facing side experiences 1Gee, and as a result it has to be made of unobtanium. |
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For a mere 1.2 times Earth's orbital velocity, though, ordinary steel might be strong enough to hold an Xpand-O ring together.... |
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[scad mientist], the asteroid belt is not a factor, since it is located between Mars and Jupiter, not between Mars and Earth. Some few asteroids ("Earth grazers") will have to be eliminated, of course, before this can be built. They are not a problem if we have the tech to actually build an Xpand-O ring. |
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Being a welder, I hope it's evident why I assumed you
meant deliberate welding in a vacuum; now that I've gone
off and read more about it, this vacuum-welding phenom
interests me. Ima study it and try to come up with some
halfbaked solutions. Thanks guys! |
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<later> helpful link, [Vernon]. Although it actually seems
to be a useful process, for some reason my brain is
chewing on vacuum-welding prevention (beyond methods
already in use). It may be the first fully-serious 'bake I've
done in a long time. |
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Whether or not this would actually work, or is in any way feasible, I love it. |
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So, um. This this thing will, um, do stuff? Have you
developed the anti- asteroid shield this thing might
need? Or are we using nano healing stress materials?
What does this thing do again? I'm going back into my
cave...( man, Farmer John clock were nice. ) |
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It's like a clock, 'cause it goes around. Only it's rooly big. And it gets even bigger, when you want it to. And when it gets bigger, you hold on to it, and it takes you somewhere. In space. |
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//And when it gets bigger, you hold on to it, and it
takes you somewhere. |
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Man, if I had a dime everytime I heard this... |
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Well, it turns out that every vacuum-welding preventative
that I can come up with is basically a poor facsimile of
PTFE. I guess I'm not as brilliant as I thought I was. |
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I haven't read all the annos diligently, so forgive
me if I cover trodden ground. When dealing with
unimaginable largeness, I find it useful to reduce it
to more manageable terms. |
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Imagine 2 poles 1 km long, attached so that they
can extend anywhere from 1-2km. This can be
powered by a solar motor and stuff, but the forces
required to overcome inertia to accelerate and
then decelerate are quite large, even if the poles
are very thin and made of something light. |
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Then assume a billionish of them, but not
attached, just near each other. Will lengthening
each of them change their orbit in the same way
that putting your arms and legs out on an office
chair changes your speed of rotation? If so, is this
enough to change the orbit in any significant way
to the extent required? If so, the stresses are
manageable and more importantly, the entire ring
becomes pointless, because you just need a
section of the ring of sufficient mass that when
you attach your capsule to it and extend the
section, the orbit will change. |
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If not, then it's not possible because each section
will need to exert extra force on the next section,
accumulating with each section, so you would not
need equal sections, but instead huge sections
near the capsule and proportionally tiny sections
on the opposite side. |
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Discuss, as my certificate for winning the school
discus once said (which has never had a usable
double meaning until now). |
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// solar motor and stuff // // billionish // |
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A 'baker after my own heart. The idea is what's important. |
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[Alterother] Re: You question as to my state of inebriation in another idea entirely. |
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Only a few minutes has passed, so clearly I am still,
but in that thread, in years to come, should anyone
stumble upon it, your comment will seem somewhat
assumedly inappropriate. And in this thread, I will
seem all-the-more endrunkened. |
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Don't worry, I don't mind. |
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[marklar], the annotations contain some corrections to certain points of the main text, so you probably do need to read through them. At the end of you might be surprised to notice that expanding this ring should be relatively easy, since it is under tension in the contracted state, and that tension will tend to assist the expansion of the ring. Which of course means that contracting it will be more difficult, since the contraction process will have to fight increasing tension. |
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Anyway, neither of those situations is like what you described. |
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I suspect that expanding the ring will be as hard as getting out of a crevasse by pushing outwards on the sloped walls. |
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The planet Mercury weighs 3.3x10^23 tonnes. If this ring weighs 1000 tonnes/km (when expanded) this gives us a weight of 1.4x10^12 tonnes, so mining a tiny fraction of the planet should give you enough stuff to make this from. |
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//Mercury... so mining a tiny fraction of the planet should give you enough stuff to make this from// |
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Wouldn't it be better to do Mars? Then you could let the Sun's gravity pull the components into place, as opposed to Mercury, where you'd have to drag each and every piece up a gravity well. |
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Hard cheese on the Martians, I admit, but the three-legged wallahs have it coming, in my opinion <falls asleep with copy of the The Telegraph over his face> |
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In re-reading this old Idea, it occurs to me that it is more
time-efficient to always run the maglev system when the
ring is in the fully-contracted state. That is, if Mars and
Earth are on opposite sides of the Sun, it is a much shorter
distance to maglev half-way around Earth's orbit than Mars'
orbit. So, no need for maglev track mounted on the inner
tubes of the overall Xpand-O Ring, and all the associated
complexity of doing that can be eliminated. |
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[Vernon], I haven't quite got my head around all the maths & physics involved, but I suspect you will need to be running the maglev shuttle at both orbits; as your Ring is also rotating, at a greater rate than orbital velocity, to maintain tension. |
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[neutrinos shadow], remember that the time it takes to
expand the ring will be known in advance. So, a vessel can
maglev along the minimized ring to whatever location is
appropriate, such that after the expansion, throughout
which process the ring was rotating at known rates, Mars
will be the shortest distance away. |
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