[HN Gopher] Magnetically levitated space elevator to low-earth o...
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Magnetically levitated space elevator to low-earth orbit [pdf]
(2001)
Author : fosk
Score : 60 points
Date : 2024-08-02 20:03 UTC (2 hours ago)
(HTM) web link (publications.anl.gov)
(TXT) w3m dump (publications.anl.gov)
| buildbot wrote:
| Cooling a 200km loop with liquid helium sounds more than
| moderately difficult!
|
| Neat idea but not particularly possible given current material
| science as always seems to be the case with space elevators.
| eppp wrote:
| How cold would the pipe be in space if it was shaded? Wouldnt
| that cut the energy needed by a bit?
| perihelions wrote:
| It's more or less impossible to shade a space elevator
| because the (hot, radiant) earth spans a full hemisphere of
| its field of view and the sun wanders most of the opposite
| one.
|
| No way to passively reach cryogenic temperatures--let alone
| the _deep_ -cryogenic ones demanded by high current-density
| superconductors.
| punnerud wrote:
| What about using Starship or similar to move the coolant up,
| then let it "fall" down?
|
| Once you have the elevator operated some of the transportation
| could be used for refueling coolant.
|
| And you start it from space and gradually lower it down to
| earth.
| ben_w wrote:
| I don't know why you think that would help?
|
| If we could build this at all, we could build it on the
| ground, then just switch it on (gradually) and it would
| float, and if we needed to get consumables up, they can be
| pulled up on a winch like any other payload to space.
|
| But also, I don't know why you think Starship is the right
| category for a solution; the structure in this paper is 200
| _kilo_ meters in size (it says altitude, but for magnetic
| repulsion the best separation distance is a constant factor
| of the size before your get performance issues), whereas a
| fully stacked Starship is about 0.12 - 0.15. It would be like
| trying to refuel a 747 in flight with an personal selfie
| drone.
| punnerud wrote:
| The Starship was only for moving coolant, not as part of
| the elevator.
|
| I was thinking you probably have to have extra payload to
| stop the end. And that it then would be better to start
| from the top, than from bottom
| ben_w wrote:
| I can't visualise what you're trying to suggest. "Stop
| the end"?
| IncreasePosts wrote:
| (2001). I'm curious what has changed in this space since then.
| hinkley wrote:
| I believe the test tether someone took up burned itself to a
| crisp. The magnetic flux it experienced from the earth was much
| more intense than their math predicted. That's the last I
| heard.
| dredmorbius wrote:
| Do you have any idea which mission that was?
|
| Wikipedia has a listing, if that helps:
| <https://en.wikipedia.org/wiki/Space_tether_missions>
| throw310822 wrote:
| TSS-1R mission, 1996
|
| "TSS-1R was deployed (over a period of five hours) to 19.7
| km (12.2 mi) when the tether broke. The break was
| attributed to an electrical discharge through a broken
| place in the insulation."
|
| "Measured currents on the tether far exceeded predictions
| of previous numerical models by up to a factor of three"
| PaulHoule wrote:
| How is this different from
| https://en.wikipedia.org/wiki/Launch_loop ?
| marcosdumay wrote:
| There's no dynamic exchange of forces between moving objects on
| this one, just some current flowing through wires.
| datadrivenangel wrote:
| The Launch loop uses the momentum of a rotating cable to keep
| the system up. This space elevator uses super conducting
| magnets to levitate against the earths magnetic field.
|
| It's like a gyroscopic force versus an electromagnet: they're
| both forces, but one is caused by mechanical movement versus
| the other which is caused by magnet fields.
| ben_w wrote:
| This is supported by long-range magnetic pressure over the
| entire structure, with some (but not all) of that pressure
| coming from Earth's own field, and has no moving parts (other
| than the charge carriers).
|
| A launch loop could be short-range magnetic or electric
| pressure between the cable and the sheath, Earth's field is not
| important and it would also work on a body with no magnetic
| field, and it mostly functions by being a very big moving part
| surrounded by a vacuum chamber.
| JumpCrisscross wrote:
| NbTi has a critical temperature below 10K and generate fields of
| around 10 T [1]. The paper contemplates a 2T field.
|
| Could CeOFeAs permit cooling with hydrogen [2][3]?
|
| [1] https://en.m.wikipedia.org/wiki/Niobium%E2%80%93titanium
|
| [2]
| https://www.sciencedirect.com/science/article/abs/pii/S09214...
|
| [3] https://en.m.wikipedia.org/wiki/High-
| temperature_superconduc...
| al_borland wrote:
| I seem to remember reading about this in Popular Science around
| that time. Of all the things I saw in that magazine, the space
| elevator made of carbon nanotubes was always the one that stuck
| with me. Though I seem to remember PopSci taking about harnessing
| an asteroid, or something, and putting it geosynchronous orbit,
| as a means to create the top anchor point.
|
| 25 years later, it seems just as far fetched.
| worldsayshi wrote:
| Although we have come much further with carbon nanomaterial. I
| wonder how close we are to achieving continuous fabric.
| stretchwithme wrote:
| How is the elevator car in a space elevator accelerated
| horizontally? That's what reaching orbit is, right? Horizontal
| acceleration?
|
| The car starts out on the ground at 465m/s. It has to accelerate
| to 11,068 km/h.
|
| What makes it accelerate? The cable, without any force applied to
| it anywhere? Or is there a rocket on that car?
|
| To put mass into orbit, you have to accelerate that mass. And do
| it without decelerating the elevator.
|
| There are no free lunches.
| JumpCrisscross wrote:
| > _How is the elevator car in a space elevator accelerated
| horizontally?_
|
| Momentum transfer from the cable, which is attached to an
| orbiting counterweight.
|
| In this design, some of that momentum would be borrowed from
| the Earth's rotation via the cable's coupling to its magnetic
| field. In general one boosts the counterweight directly or,
| more practically, by sending things down [1].
|
| [1] https://space.stackexchange.com/questions/22447/how-will-
| the...
| schiffern wrote:
| This paper's design has no orbiting counterweight, and only
| reaches an altitude of 200 km.
|
| A launch loop can harvest energy and momentum from the rotor
| to accelerate payloads, but I don't see any such mechanism
| here.
| JumpCrisscross wrote:
| > _This paper 's design has no orbiting counterweight_
|
| Which is why I say I "in this design, some of that momentum
| would be borrowed from the Earth's rotation via the cable's
| coupling to its magnetic field." The cable is an
| electrostatic counterweight because we're using
| electromagnetism, not the comparably weak gravitation.
| Benjammer wrote:
| One thing with a space elevator that makes it so much more
| efficient than rockets is precisely because you don't
| necessarily need the payload itself to supply this horizontal
| acceleration. The space elevator is attached to the ground at
| one end, and the other is way up in orbit. There must be forces
| in play _already_ for the entire thing to stay standing, before
| you get to any concept of a payload/car. Part of the idea of
| building the elevator in the first place is to solve for these
| orbital forces in a generalized way independent of the payloads
| themselves. It's like strapping various sized rockets to your
| various specific payloads, versus building a generalized model
| of a rocket ship, and then just putting the various payloads
| inside the generalized rocket ship. Space elevator is a further
| evolution of the concept. You don't even need to use the rocket
| ship abstraction anymore. You're generalizing/abstracting the
| orbital transition itself into the structure of the elevator,
| and then just send things up and down it. The payload now only
| needs to worry about moving along the elevator, the elevator
| itself has already "solved" for the orbital horizontal
| acceleration by nature of its structure existing in the first
| place.
|
| In terms specifically of mass/energy conservation, as the other
| reply said, energy is borrowed from either the earth's rotation
| and/or kinetic energy from a counterweight at the end of the
| elevator up in orbit.
| lionkor wrote:
| Or, you know, use a rocket...? I dont see an issue with Hydrogen
| Oxygen rocket propellants at all.
| mlyle wrote:
| The annoying things with propellants is that you need to use
| them to lift more propellants. The rocket equation is not kind.
|
| Coming up with some way that lets us waste more mass will push
| aerospace away from such an exotic set of technologies towards
| more mainstream use. It is only the fact that space flight is
| barely possible that makes it so hard.
| JumpCrisscross wrote:
| > _dont see an issue with Hydrogen Oxygen rocket propellants at
| all_
|
| There isn't a reusable cryogenic rocket.
| codesnik wrote:
| somewhat related concepts: Space fountain and and Launch loop
|
| https://en.wikipedia.org/wiki/Space_fountain
|
| https://en.wikipedia.org/wiki/Launch_loop
| spacebacon wrote:
| Several prompts later ...
|
| The gap between current material science and the required
| advancements for constructing a magnetically levitated space
| elevator is significant. Let's break down the key areas where
| advancements are needed and assess the current state compared to
| the required state:
|
| 1. Superconducting Materials Current State:
|
| NbTi Superconductors: NbTi (Niobium-Titanium) superconductors are
| among the most common, with critical temperatures around 9-10 K.
| They are widely used in MRI machines and particle accelerators.
| NbTi can sustain high current densities and generate substantial
| magnetic fields, but only at very low temperatures maintained by
| complex and costly cryogenic systems. Required State:
|
| Higher Temperature Superconductors: For a space elevator,
| superconductors that can operate at higher temperatures would
| reduce the need for extensive cryogenic cooling, thus making the
| system more practical and less costly. Currently, high-
| temperature superconductors (HTS) exist (like YBCO - Yttrium
| Barium Copper Oxide), which can operate above 77 K (the boiling
| point of liquid nitrogen), but they are not yet produced in long,
| high-quality, and affordable lengths suitable for large-scale
| engineering projects. Gap Analysis:
|
| The primary challenge is to develop superconductors that can
| operate at higher temperatures with sufficient current densities
| and stability. The current material science has not yet achieved
| a commercially viable production of long-length HTS with
| consistent quality and performance required for such
| applications. 2. Carbon Nanotubes and Advanced Fibers Current
| State:
|
| Carbon Nanotubes (CNTs): CNTs are known for their extraordinary
| tensile strength and low density, making them ideal candidates
| for space elevator cables. However, the production of long,
| defect-free CNTs with consistent properties remains a significant
| challenge. Current production techniques yield short lengths with
| varying qualities, and scaling up these methods while maintaining
| material integrity is difficult. Required State:
|
| Mass Production of High-Quality CNTs: For a space elevator,
| extremely long CNTs or similarly strong materials are required to
| construct a cable that can withstand the enormous stresses
| involved. These materials must be lightweight yet possess ultra-
| high tensile strength and stability over long periods. Gap
| Analysis:
|
| The major hurdle is the ability to produce continuous lengths of
| high-quality CNTs or alternative advanced fibers at a commercial
| scale. The technology for producing and manipulating these
| materials at the necessary scale is still in its infancy. 3.
| Structural Materials and Stability Current State:
|
| Composite Materials: Current composite materials, including
| carbon fiber composites, offer high strength-to-weight ratios.
| However, they are not yet capable of withstanding the specific
| stress and environmental conditions required for a space
| elevator, particularly in terms of radiation resistance and
| thermal stability. Required State:
|
| Advanced Composites and Alloys: Materials need to be developed
| that can endure the harsh conditions of space, including
| temperature extremes, radiation, and micrometeorite impacts,
| while maintaining structural integrity over potentially very long
| periods. Gap Analysis:
|
| Development is needed in creating materials that not only provide
| the necessary strength and durability but also can be
| manufactured and maintained at a reasonable cost. Improvements in
| radiation shielding and thermal management materials are also
| required. 4. Cooling and Power Systems Current State:
|
| Cryogenic Cooling: Current cryogenic systems can maintain
| superconductors at low temperatures, but they are heavy, complex,
| and energy-intensive. They are impractical for continuous, large-
| scale applications like a space elevator. Required State:
|
| Efficient Cooling Solutions: More efficient and lightweight
| cooling systems are required to maintain superconductors at
| operational temperatures without prohibitive power consumption.
| Alternatively, development of superconductors that operate at
| higher temperatures, requiring less intensive cooling, would be
| beneficial. Gap Analysis:
|
| Significant innovation is needed in both cooling technology and
| power systems to make a space elevator feasible. The challenge is
| to achieve efficient, reliable, and cost-effective solutions that
| can be integrated into the elevator structure. Summary The gap
| between current capabilities and the required advancements is
| substantial. While we have foundational materials and
| technologies, such as NbTi superconductors and carbon nanotubes,
| they are not yet developed to the extent necessary for practical
| use in a space elevator. Advances in high-temperature
| superconductors, scalable production of high-quality carbon
| nanotubes, and the development of lightweight yet strong
| structural materials are critical.
|
| Material science must progress significantly in these areas to
| move closer to realizing the concept of a magnetically levitated
| space elevator. This will require substantial research,
| development, and potentially novel breakthroughs in materials
| engineering and related technologies. The timeline for achieving
| these advancements is uncertain, and it could span several
| decades.
| JumpCrisscross wrote:
| > _major hurdle is the ability to produce continuous lengths of
| high-quality CNTs_
|
| What is an intermediate market for medium-length high-quality
| CNTs?
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