enigma, re: your technical problems mentioned in post #5, would any or all of these also apply to a skyhook?
Government Labs don't usually write stuff that is BS though. If it involves physics breaking stuff they have to show that physics, as it was understood up to that point, isn't correct. This, as far as I know, hasn't happened yet.LunchBox said:...
(Psst... just because the people work for a place who's name ends in "national laboratory" doesn't mean they have a direct pipeline to the wisdom of the ages. In fact, they are just as likely to be wrong as anyone else... I know... I work with these people from time to time.)
Isn't it? I've always found vibrations to be an interesting topic. The numbers were for comparison. Now, in the 'articles' you link, the authors stress how only a spindly, lightweight structure will be needed. Spindly, lightweight structures have extremely small bending (EI) stiffnesses. The Sears Tower is practically rigid compared with a 'space fountain' structure. Pick your favorite 'space fountain' design (as the articles you linked surprisingly had no structure sizing) and perform a sinusoidal gust loading along the height... I imagine the tip displacement value will astonish you.
Ok... I'll explain. The gust loading will not be even over the side area of the structure facing the wind. This difference in loading along the windward face will create a torque on the structure. And spindly structures have even lower torsional (GJ) stiffnesses than bending stiffnesses.
No... they just fail to say anything useful...
I'll assume you meant 'your' and not 'you are'. I saw no 'math' in your Wikipedia article and the only technical publication linked from there was on a 'launch loop', not a 'space fountain'. The wonderful catch-all in the Wikipedia article really means that the problems were manageable within the scope of the universe we occupy, not that the problems were practically solvable, or that they were economically practical. I would ABSOLUTELY LOVE to see that analysis done by Roderick Hyde. If you have it, please send me a link or a pdf. Also, always remember Akin's Law of Spacecraft Design Number 17
No... I didn't say that they were science fiction. In fact, I am a huge proponent of rail gun technology. As soon as it becomes economically feasible, I think the military should put those bad boys on EVERYTHING. However, what I was referring to was the atmospheric drag that will suck momentum from these projectiles. Not only that, but the projectiles will need to be ferromagnetic in order to be redirected at the top and bottom of the tower. The atmospheric drag on a projectile traveling at Mach 6+ will cause tremendous heating and could exceed the Curie temperature of the material making it no longer ferromagnetic. Also, the velocity of the returning projectiles will will be limited by the terminal velocity of the projectile profile. All these losses will add up to necessitate a tremendous energy expenditure to bring the projectiles back up to speed at the bottom of the 'space fountain'.
Now look, maybe I started a little harsh, but I'm sick and tired of people thinking you can get to space easily by climbing successively taller trees. My goal it not to stifle creativity... far from it. However, I think a little realism and practicality needs to be brought into every discussion. Oh and I was serious about wanting to see that analysis...
It goes to geostationary orbit, which is about 22,200 miles high.Ki Man said:if this is about 200 miles high
There exists a variety of space-elevator conceptions. There are speculation links at the bottom of this page...KI Man said:how quickly will we be traveling to get up this thing.
Usually, no. Occasionally? Yes. Just because you have PhD after your name does not mean you can't make mistakes or overlook certain aspects of a problem. That's why designs are always done in groups. In this case, the idea has so many critical engineering details neglected as to be worthless. Where is the report? All I've seen is a non-technical Wikipedia article.SkepticJ said:Government Labs don't usually write stuff that is BS though.
Link works fine for me. Links to the website of University of Maryland's Space Systems lab director Dr. Dave Akin. Law #17 states:Neither did your non-functioning "link". You might want to go back and fix that, because I can't be privy to the "debunking" of "crap" concept space fountains.
Something which is absolutely true. I have read many technical journals with blatant errors that got overlooked.Dave Akin said:17. The fact that an analysis appears in print has no relationship to the likelihood of its being correct.
Lunchbox and Ki Man are not the same person.Even if you're not one and the same,
It is proposing a pump which drains the air (and keeps the air drained) out of a pipe _200 miles long_?!? Amazing what is trivially attainable when you just wave the magic "engineers can do anything... and easily" wand.Vacuum pipes, which the streams travel through, make this a non-issue. No air, no drag.
I see a grand total of zero linked technical papers in this thread, or the one which I seperated this discussion out of.I guess I'll have to say everything that the linked papers say before you get it
Ribbon-type space elevators do not need to be anchored on the equator. They can be anchored anywhere, including the poles.SkepticJ said:Another advantage to space fountains is they need not be built on the equator. One could build one at the North Pole if they wanted to
Ki Man said:meh, ignore what i said before i was drunk or something (not literally)
how fast are we talking? how high is it going to be (estimate) and how big is the elevator going to have to be (like how wide is it going to need to be at most and what kind of things are going to need to be carried up by the elevator carts.)?
Until the asteroid falls out of the sky blowing the Arctic ice sheet or Antarctica a new crater. It's the centripital force of the asteroid on the end that holds the ribbon tight. Other places as well have a problem, because geosynchronous orbit can only happen above the equator.hitssquad said:Ribbon-type space elevators do not need to be anchored on the equator. They can be anchored anywhere, including the poles.
enigma said:Usually, no. Occasionally? Yes. Just because you have PhD after your name does not mean you can't make mistakes or overlook certain aspects of a problem. That's why designs are always done in groups. In this case, the idea has so many critical engineering details neglected as to be worthless. Where is the report? All I've seen is a non-technical Wikipedia article.
Link works fine for me. Links to the website of University of Maryland's Space Systems lab director Dr. Dave Akin. Law #17 states:.......
It is proposing a pump which drains the air (and keeps the air drained) out of a pipe _200 miles long_?!? Amazing what is trivially attainable when you just wave the magic "engineers can do anything... and easily" wand.
It can happen anywhere, if you have a ribbon. If the ribbon were anchored at a pole, it would not align with Earth's axis.SkepticJ said:because geosynchronous orbit can only happen above the equator.
You are not correct here. What would hold the system up (keep it all from falling to the ground) is the orbital impetus. That is not sufficient, however. Anywhere other than in a synchronous orbit, the 'ribbon' would wrap itself around the Earth like a maypole, and this means that it must be in a synchronous orbit. To complicate matters, however is the tremendous weight of the assembly that would be 'hanging down' from that orbit. To compensate, an equal weight would have to pull 'up' from that synchronous orbit point, extending it a great deal upward, beyond synchronous. Then, that lower part would attempt to run itself ahead of rest if it is not anchored to the ground (ie, the lower the orbit of any part, the faster it will travel).hitssquad said:Ribbon-type space elevators do not need to be anchored on the equator. They can be anchored anywhere, including the poles.
I have an idea here (or, more correctly, my 14 beers and I have an idea). Let's just solidly anchor a bucky cable between Earth and the moon. Since the moon is already tide-locked with one face toward us, it's only the orbital period that presents a problem. Linking them with a non-elastic cable will eventually slow down the moon's orbital period, and to some extent the Earth's rotational one, until the moon is geosynchronous. Then all we have to do is climb up the cable like monkeys in space suits.blimkie said:Well KI Man, I also think a new station would be handy, i say on the moon.
Have you analyzed the engineering details of proposed space elevators to see if these issues are addressed? If not, you might want to check out something like the book https://www.amazon.com/exec/obidos/tg/detail/-/0974651710/104-0895070-5136740&tag=pfamazon01-20 by Bradley Edwards, which apparently contains a lot of detailed analysis of such engineering issues. Here's a collection of references, some available online:Kenneth Mann said:Then, the complications are just so great as to stagger the mind. The part that extends below synchronous wants to pull itself ahead in orbit, so even if it is anchored below, the lateral distortion forces would be incredible. Next, the weight of that part hanging down would be enormous. Not even the much ballyhooed nanotube structures would have anywhere the near the tensile strength to handle the needs of a structure this tall hanging down (I don't believe; --- maybe some super-super-super-nanotubes of the distant future will be able to). Then, there is the equal "weight" of the counterbalancing part pulling up, and its 'lateral backward' pull in orbit on the assembly. All in all, I just don't see it being done in the near future. Finally, I just don't see how you would handle the tendency of the upper part (beyond synchronous) to wrap itself around. You can't anchor that part.
The dynamics of the elevator, in general, are fairly straightforward but to ensure proper operation we need to examine the details of the elevator dynamics.
In 1975, Jerome Pearson published a technical article that included the a discussion on the natural frequency of the space elevator. Pearson found that the natural frequency depended on the taper ratio of the cable and in some cases would be near the critical 12 and 24 hour periods that could be problematic. Pearson also stated an ugly equation for calculating the shape of the cable as a function of the material strength, planetary mass, and planetary rotation speed.
We have taken Pearson’s original equation and attempted to simplify it into a more usable and intuitive form. However, this equation does not simplify well and like Pearson we have resorted to an analytical solution. In our case, however, we have ready access to spreadsheets that easily handle these types of calculations. We have composed a set of spreadsheets that produce ribbon profiles, tension levels, linear velocities, counterweight mass and total system mass. This spreadsheet is designed to handle different planetary bodies, rotation rates and applications.
Another spreadsheet we have composed is similar but for elevators with their anchors located off the equator. In this case the ribbon is found to sag toward the equatorial plane but remain entirely on the side as the anchor. This sag in the ribbon is due to the non-axial pull of gravity on the ribbon. The magnitude of the sag depends on the planetary rotation, planetary gravity and mass to tension ratio of the ribbon. In the case of a Martian cable, where anchoring the cable off the equator would allow it to avoid the moons this calculation is critically important. In the Martian case the cable extends parallel to the equatorial plane with only a 3 km sag back toward the equatorial plane when the cable is moved 900 km from the equator. This simple reanchoring of the cable would allow us to avoid any difficulties with the Martian moons.
What these and the dynamics work discussed below imply is that from a system stability and operations it is possible to move the anchor tens of degrees off of the equator if other factors (weather) permit.
In addition to the spreadsheets that we have assembled, David Lang has conducted computer simulations on the dynamics of the system. The code Lang is using was originally designed for modeling the ProSEDs experiment. Lang has modified it to examine the elevator scenario. The results from these simulations show that the elevator is dynamically stable for a large range of perturbations. The natural frequencies were found to be 7 hours for in-plane (orbital plane) oscillations and 24 hours for out-of-plan oscillations. The out-of-plane number is misleadinghowever. For any elevator or geosynchronous satellite a 24 hour period is found for the out-of plane because that simply implies an inclined orbit. For determining the stability, Lang gave the system various angular deviations, initial velocities and also quickly reeled in some length of the ribbon at the anchor. At some limit in each of these cases the elevator becomes unstable. What was found was that angles of tens of degrees were required to create a catastrophic failure. (The energy required to move the counterweight this far is equivalent to that required to lift 3000 loaded semi trailers kilometers into the air.) It was also found that reeling in 3000 km of ribbon in 6 hours will create a catastrophic failure. Each of these perturbations is well beyond any we expect to encounter. The events leading up to any of these are easily avoidable.
Lang also suggested that we consider a pulse type of movement for avoidance of orbital objects rather than a translational as we have been proposing. The difference is that in the pulse situation the anchor station is moved one kilometer and moved back to its starting position. This will send a wave up the ribbon to avoid an orbital object. The pulse will reflect off the counterweight and return to the anchor where an inverse pulse maneuver is conducted to eliminate the pulse. The result is a quiet system. In our proposal the anchor would be moved and remain there. This would send a long pulse that could oscillate up and down the ribbon for some time. Simultaneous pulses and a complex movement of the ribbon would result. This is a simplified explanation of a complex operation and response but the point is that there are operations that still need optimization.
Along with the computer simulations we have conducted some hardware tests of various ribbon designs and damage scenarios. The tests included several sets of ribbons with parallel and diagonal fibers composed of plastic fibers and epoxies or tape sandwiches. The ribbons ranged from two to four feet in length and were placed under high tension loads.
In the ribbon tests we found much of what was expected and predicted by our models. In situations where there is continuous rigid connection between adjacent axial fibers, aligned or diagonal, high stress points are created at the edges of the damaged area. These high stress points tend to be the starting point for zipper type tears and greatly reduce the optimal strength of the ribbon. On the contrary, ribbons with non-rigid interconnects between fibers had minimal stress points and yielded at high tensions and larger damage. A full description of the optimal ribbon design is found in our book. Similar tests are now being arranged at Rutgers to explore the degradation that might occur. We have also started to set up ribbons close to what will most likely be the final design.
Yes.Kenneth Mann said:What would hold the system up (keep it all from falling to the ground) is the orbital impetus.hitssquad said:Ribbon-type space elevators do not need to be anchored on the equator. They can be anchored anywhere, including the poles.
Yes. That is why a synchronous orbit would be selected for the poles, just as for any other latitude at which ribbon-type space elevators might be anchored.Kenneth Mann said:Anywhere other than in a synchronous orbit, the 'ribbon' would wrap itself around the Earth like a maypole
All orbits MUST lie in a plane which intersects the center of mass of the massive body (in this case, the Earth). An object in orbit about the north pole must pass over the south pole (and vice versa). The ribbon connecting the other anchoring mass would be wrapped around the Earth due to the anchoring mass "orbiting" the Earth.Yes. That is why a synchronous orbit would be selected for the poles, just as for any other latitude at which ribbon-type space elevators might be anchored.