Japanese Space-Elevator Experiment next week

[kerbiloid]

Aka space rot(a/o)vator.

[KerikBalm]

2 hours ago, Cassel said:

Where can I see this train live? Ohh no one built it, I wonder why.

Because achieving a vacuum is difficult on Earth? because terrain curves and the Gs involved when travelling at that speed for minor changes in course due to terrain are significant.

If we use the logic "it hasn't been done yet", we can also apply it to the space elevator.

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Ok, the cable does not have to be made of magnets, this is probably the only thing that can work in this idea.

Yet you don't explain why its the only thing

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You do not understand many things, and you write as if this idea has already been implemented.

And you haven't provided a single example of one of these things. Don't go ad hominem here.

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If you're writing a cable, you mean a flexible metal cable

 

Not necessarily metal. They refer to cables for space elevators too, even if those must be carbon nanotubes.

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So in my opinion, this concept is impossible to implement. The cable orbits at an altitude of 300-400 km, at the moment when your trains begin to slow down, gravity pulls them down to Earth. When they reach a speed equal to 0 km/h to the surface of the planet, while still at the height of 300km, the orbiting cable must hold train and cargo. And it is not important here the mass of the entire cable that you carried into orbit, only the part that is in contact with the train. The cable is flexible, right, so how will it behave?

The "train" does not move relative to the earth at all, so what do you even mean about slowing down? the "train" is the station at the end of the spoke. Gravity is always pulling it down to the Earth, its prevented from coming down by being magnetically suspended on the ring.

The cable will be deflected by the station, also consider how much cable is going by by per second... hint: its well over 8 km of cable per second. Its not the mass of the cable per se, but the centrifugal force on the relevant section of cable. The cable is in tension, and the whole system is experiencing an upward force (in a rotating reference frame corresponding to Earth's rotation). Its similar to someone resting on a line fixed at two points:

 

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Maybe it's worth to do a simple experiment and put a ring in something that floats (and resembles a cable, string maybe?) on the water in the aquarium, spin the ring, and then add the force that is directed to the center of the ring (this would be the braking train). How will the ring (string) behave?

I don't know why you call it a braking train.... But one could make a model to demonstrate it. Your proposal to do an experiment is not an argument against the idea.

 

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Here you make a mistake, it is mass of the counterweight keeps it upright.

It it the centrifugal force that results from mass going at faster than orbital velocity (ie mass above GSO) that keeps it upright. I haven't made a mistake at all.

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In your example, at the moment of braking the train you would have to add a counterweight that pulls the train and cargo up and to prevent deformation of part of the ring.
Flexible/elastic cable - no. Telescopic rigid construction - yes.

The ring itself is a "counterweight" by virtue of it not being massless, and moving faster than orbital velocity. Deformation of the ring near the stations is fine.

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Is this a joke? So, bringing the cargo into orbit and the fact that the train stopped in relation to Earth, and later repelled itself from the cable, do you think it will not change the orbit of the flexible ring and it will still be in the same orbit?

The shape of the ring deforms, but it will keep returning to the same position. Space ladders/elevators also have their "orbit" altered when payload is going up and down, and return to the initial position due to centrifugal force.

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In my opinion, there will be a change in the cable's orbit, something similar to the tehter's orbit in the image below.

Deformation would happen, but skyhooks like that are fundamentally different, and must expend propellant to return to the initial position. The orbital ring can use its connection to earth to return to its initial state.

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In the case of space-elevator, you can connect the cable with segments, even starting from the Earth. Only you would have to start with a very light construction, you do not have to reach the GSO in first step, but at the end of cable you would have to put a vehicle with an ion engine that would move a little faster than the cable in a given orbit and would pull the cable behind it.

This would not work. If your cable isn't past GSO, its not in tension, and it falls to the Earth. If you put an engine on the end to move the end in space fast enough to go faster than orbital velocity, then you wrap the cable around the Earth and it comes crashing down in a fraction of an orbital period. If you direct your thrust towards earth for direct lift... that's obscene amounts of thrust and dV for just 1 day of operation, and if you've got torchships like that, getting to orbit is trivial. An ion engine won't do it.

This comment you just made displays such a fundamental flaw in understanding... I'm actually a little shocked

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The next stage is the addition of further fragments of cables up to GSO and counterweight. If the cable is thin as a climbing rope, the counterweight does not have to be large.

You're not attaching anything up to GSO, because there's no  way to support any of it until you get to GSO. Even a cable as thin as a climbing rope, that is 35,000km long, is going to need a significan "counterweight".. and here's a hint, the closer to GSO you put it, the more massive it must be, so you won't be attaching any countermass to the end until you're well past GSO.

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The next step is to pull up the next connections and appropriate counterweight on the GSO.
I know that you imagine a space-elevator as one big cable, but for safety there can be many cables.

Multiple cables doesn't give much redundancy if the cables can barely sustain their own mass.... which currently they can't (even the nano scale nanotubes aren't strong enough to lift a 2nd cable of equal mass. "Bootstrapping" would be a very slow process adding small strands at a time)

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Over time, as better materials will be created, you can always pull cables with a larger cross-section using this small infrastructure.

If we had better materials, the elevator concept would be more appealing, but better materials on the ground wont help an initial cable that can barely lift its own mass (but when we talk a roughly 40,000 km long cable, payloads of a few tons are easy... a 2nd 40,000 km long cable is another story)

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But I see that you completely ignore the fact that in your idea when you pull up a cargo from the surface of the planet you also need a counterweight or some force that will keep your train in orbit.

*sigh" for the nth time, the "train" is not in orbit, the ring has mass, and all the "counterweight" does is supply centrifugal force to keep the line taught.

[Cassel]

19 minutes ago, KerikBalm said:

And you haven't provided a single example of one of these things. Don't go ad hominem here.

No one has built such a structure, but you write as if the subject has been so well researched and used in practice for years.
You started ad hominem.
Check the topic of this thread again. I found your idea interesting, but the fact that you ignore the basic problem makes this conversation pointless and offtopic.

As for the concept of the orbiting ring, it is an interesting idea to travel on orbit using only electricity, but I do not see how it could work transporting cargo from planet to orbit. Without a space-elevator, we must use more traditional methods.

[Bill Phil]

8 hours ago, KerikBalm said:

Yea, one of those would be cool too, they were after all initially called "Partial Orbital Ring System (PORS)". Somehow it seems harder to keep in operation to me, and the raising and lowering of the loop when not in operation also seems a bit sketchy to me, but maybe it is better than a full on orbital ring.

The Sahara desert seems like a good place to put one, it could be solar powered, and I'm sure the local countries could be enticed into allowing the construction (it would bring a lot of money and economic benefits)... but at 2000 km long, it would involve multiple African nations. The political consequences of control of it would be... interesting to say the least.

The idea was to put one in the Pacific...

[KerikBalm]

4 hours ago, Cassel said:

No one has built such a structure, but you write as if the subject has been so well researched and used in practice for years.

No one has built a space elevator and no one has built an orbital ring.

Both have had significant theoretical study however. Based on the theoretical studies, it seems to me that an orbital ring is much more attractive.

The physics would work, and would not require extremely high tensile strength materials (I was wrong about steel for Earth though, it seems Kevlar would be sufficient though) enough has been studied to know this.

To be sure, there would still be a massive amount of technical challenges to solve. It would be over 40,000 km in circumference, it would by far be the largest structure mankind has ever built. It would not be a trivial thing to put into practice...

Yet its on the same scale as a >35,000 km space elevator... so in both cases we're talking about a megastructure many times bigger than anything ever built, and they both come with massive technical challenges to solve.

Based on my understanding, the orbital ring has less challenges to solve/its challenges are more readily solvable.

So compare them:

size: its about the same

Material strength required: Elevator requires about 10x that of a ring

Construction:

Elevator: must have all its cable lofted to GSO (or manufactured there from material of an unspecified source, perhaps an asteroid), then the cable is lowered/extended/unspoolled while a counterweight is raised. The raising and lowering parts need active stabilization (ie, thrusters) until anchored

Ring: can be built on Earth, and then spun up to lift the whole thing, joints and/or elasticity must be built in as it raises to a higher altitude

Maintenance: The Space elevator is passively stable, the ring requires constant power input

Redundancy: the ring is easier to build in redundancy because the required strengths are much lower, leaving much bigger margins

stability when lifting payload: the elevator will sway and oscillate as payload goes up (requiring careful scheduling of the payload to go up and down at appropriate times to dampen oscillation rather than exacerbate it), the ring will deform and decelerate (but can be spun back up).

Safety: when a megastructure under massive load goes boom, its not a good thing, but an orbital ring seems like it would be much less likely to be catastrophic, compared to an elevator's cable breaking at anything over a few hundred km high (if it breaks above GSO, but below the counterweight, the structure still comes crashing down).

Payload considerations: payload ascent speed on an elevator is limited by many factors (climber power supply and heat dissipation, oscillation in the ladder, etc)... the same is true of a ring, but the distance to climb up on a ring is only a few hundred KM, on an elevator its 35,000 km, and one has to go slowly through the van allen belts. The elevator must be close to the equator, whereas a ring could be put at any inclination, allowing any point on earth to be served by a ring. Once the ring is built, it would be relatively easy to add on new stations, an elevator will only ever serve one location.

All together, the advantages of a ring seem to outweigh those of an elevator... so I think efforts should be spend solving the technical problems of building a "ring" instead of trying to work out the technical problems to build an "elevator"

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As for the concept of the orbiting ring, it is an interesting idea to travel on orbit using only electricity, but I do not see how it could work transporting cargo from planet to orbit. Without a space-elevator, we must use more traditional methods.

Well, physicists smarter than you or I in that field have studied it and concluded its feasible... not easy to build, no, nothing on that scale would be.

[Cassel]

12 hours ago, KerikBalm said:

No one has built a space elevator and no one has built an orbital ring.

Therefore, the claim that it is real and that it will definitely work is a mistake.

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Both have had significant theoretical study however. Based on the theoretical studies, it seems to me that an orbital ring is much more attractive.

The physics would work, and would not require extremely high tensile strength materials (I was wrong about steel for Earth though, it seems Kevlar would be sufficient though) enough has been studied to know this.
 

No scientist ever said "my idea works only on paper, I do not want your money".
 

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To be sure, there would still be a massive amount of technical challenges to solve.
 

At this point, we can agree.

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Ring: can be built on Earth, and then spun up to lift the whole thing, joints and/or elasticity must be built in as it raises to a higher altitude

This will not happen. If it was to be built it will first be tested on the Moon or Mars. Nobody will let you put a cable over 10 countries that can cut skyscrapers.
 

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Safety: when a megastructure under massive load goes boom, its not a good thing, but an orbital ring seems like it would be much less likely to be catastrophic, compared to an elevator's cable breaking at anything over a few hundred km high (if it breaks above GSO, but below the counterweight, the structure still comes crashing down).
 

I disagree here. The cable from the space elevator can be attached to an artificial island in the middle of the Pacific, even if it falls no city will suffer. As for the ring, this is a threat to every country that this ring will be above.

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Well, physicists smarter than you or I in that field have studied it and concluded its feasible... not easy to build, no, nothing on that scale would be.

Right :-) if they build it, they will show that they are smarter than me, so far you can write anything you want on paper, but that does not mean that it is possible to implement.

Edited September 14, 2018 by Cassel

[KerikBalm]

3 hours ago, Cassel said:

Therefore, the claim that it is real and that it will definitely work is a mistake.

I don't think I made such a claim in those words.

I do claim that an orbiting ring would work IF:

The ring were of sufficient strength, spinning at sufficient speed, stabilized by tethers, with stations capable of resting "on" (or close to as in the case of magnetic suspension) which are capable of accelerating or decelerating the ring. The specifics of how the stations work (eg maglev), or how it would be built (expandable joints? elasticity, built on earth and spun up) I'm not sure of, and just mentioning possibilities.

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No scientist ever said "my idea works only on paper, I do not want your money".

But its classical physics, which is very well understood. Nothing down at the weird quantum level, or dealing with relativistic effects. I'd wager that if you were to ask people with a PhD in Physics, you'd get over 99% agreeing that the principle is sound, even if the specific technical challenges of each component are difficult.

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This will not happen. If it was to be built it will first be tested on the Moon or Mars. Nobody will let you put a cable over 10 countries that can cut skyscrapers.

It would be fairly easy to avoid having the cable be far from cities, since it can be placed at any inclination (example, over the atlantic ocean, across sibera, over the pacific, and cutting across the australian outback). The only things that would fall are the stations and their few hundred km cables, since you'd only need 2 (lets say 4 for redundancy), that's really easy to avoid. Again, the ring, once up, would not come down and "cut skyscrapers"... thats a problem for a space elevator

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I disagree here. The cable from the space elevator can be attached to an artificial island in the middle of the Pacific, even if it falls no city will suffer. As for the ring, this is a threat to every country that this ring will be above.

For the nth time, it would not fall straight down. Every section of the elevator would have a velocity greater than surface velocity (getting closer to surface velocity as you get closer to the surface), as it falls, the top of the cable will accelerate forward relative to the surface. a break at GSO means you're going to have 35,000 km of cable falling down on earth, over a very wide area.

A little tidbit... about 66% of the way up to GSO, you can release payloads into a highly eliptical orbit with their PE just above earth's atmosphere. These orbits will have an orbital period close to 12 hours instead of 24 for a GSO orbit (going from around 12 to 24 as you get closer to the GSO point)... that is is they aren't being pulled radially inward by the cable under them.

The cable will not fall straight down from a space elevator. The tip of it will fall down several thousand km east of the anchor point (again, for a GSO break). I haven't done the math here, but there's the potential (assuming the cable stays intact after the initial break), for the cable to fall down and nearly encircle the earth with its line of destruction.

Space elevators are pretty darn dangerous if they fail.

With a ring, everything except the stations and the "short" (few hundred km) cables is going at or above orbital velocity... which means its in no immediate danger of coming down.

With an elevator, you have 10's of thousands of km of cable that is all suborbital. Everything below a break is coming down... that is very dangerous.

Edited September 14, 2018 by KerikBalm