I'm as excited about the theoretical concept of a space elevator as anyone. But the problem remains that no one can produce a cable even close to strong enough. This article has a good description of the material science problem: http://www.spaceward.org/elevator-when. Basically, we would need to find a material that is at least 10x, probably 25x as strong as any cable today.
Carbon Nanotubes are theoretically strong enough, but no one knows how to manufacture them. The longest carbon nanotube tether that has ever been manufactured is only a few inches long, a millimeter in width, and not particularly strong due to imperfections in the manufacturing process.
Obayashi is planning a 10m cable. Even building a 10m cable made of carbon nanotubes would require a Nobel Prize worthy breakthrough.
Reminds me of Ono Sendai making wetwire jacks to the internet.
Most I've read on the subject (this article included) are very thin on details, or point out the great scientific hurdles and breakthroughs that still need to be overcome / made.
This article made me think of the publicity stunt some years ago to build a mountain of 3,560 feet high in The Netherlands for $432 billion. The stunt was taken seriously and became world news:
If this is indeed a PR stunt I wonder if it would reflect positively or negatively on Obayashi? Would be like proposing an unrealistic, probably under-priced project. Of course they don't say when it can be realized..
There is better stuff like the orbital ring which looks very expensive but actually feasible with current technology.
So, not really. It's a highly regulated industry, but this is not the bottleneck.
On the not-so-bright side, we'll have to develop new metallurgy and other industrial processes based on local chemistry.
Where would the counterweight have to be for one end to be in high Earth atmosphere, balancing atmospheric drag with lift and gravity? My math tells me the end would be traveling at a relatively tame 260 kph.
A huge advantage is that a hook at the far lunar Lagrange 2 would be very close to escape velocity (e.g. asteroids or GEO).
A steel cable would have far too low a strength to weight ratio to work in a space elevator.
The part you quoted refers to the material that might be used for a 96,000 kilometer cable.
At Earth's equator (zero altitude - i.e., on the ground), an object moves spinward at about 0.46 km/sec. In geosynchronous orbit, an object has to move at about 3.07 km/sec.
A space elevator car ascending from stationary on the equator to a terminal at geo altitude would require a tangential (lateral) ∆V of 2.61 km/sec. This is in addition to the energy needed for ∆ altitude-related potential energy change. Am I thinking about this right?
The faster the ascent, the greater the lateral reaction force on the elevator because ∆V/time increases. Has anybody done that model? I didn't find anything in a brief search.
The lateral ∆V also suggests it could get windy on ascent because the atmosphere rotates with the earth on a macroscopic basis. Maybe later tonight, I'll calculate lateral wind velocity as F(altitude) and see if I can fold in pressure drop to get wind pressures as F(altitude).
I would love to see even a prototype attempt in my lifetime.
Angular momentum is given by
L = I * ω
where I is the moment of inertia and ω is the angular velocity. Let's assume that we put the internet (https://m.youtube.com/watch?v=iDbyYGrswtg) into the elevator and ship it off to space. Let's also say that the internet has a mass m and is of negligible diameter compared to Earth's radius. Clearly, its angular velocity ω will stay constant, assuming that the space elevator was built perfectly straight and perpendicular to Earth. However, the internet's moment of inertia I = m r^2 will not stay the same but increase quadratically with its radial position r and its angular moment will thus have to increase, as well. If you take the initial radius to be Earth's radius (~6,300km) and the final radius to be the geostationary orbit (~36,000km), the quadratic dependence will give you an enormous difference in angular momentum which will have to be accounted for by some torque that we apply to the internet.
It doesn't matter where this torque comes from--for instance we could imagine the internet to have some kind of jet propulsion engine, where the emitted gas's angular momentum would exactly match the internet's change in angular momentum, so that total angular momentum is conserved.
Moreover, it could actually be a small torque, provided that we move the internet at a small velocity in the perpendicular direction. (Recall that the change in angular momentum is given by the integral of the torque over time, so the smaller we want the torque to be, the slower we have to move the internet and the longer it will take the internet to reach its final position.)
Now what happens if we don't provide said torque? Recall that I assumed earlier that the angular velocity ω of Earth and the elevator (and thus the internet) be constant. If we don't provide the mentioned torque, moving the internet upward will increase the moment of inertia of the system Earth + space elevator + internet due to more mass being located farther away from the axis of rotation. By conservation of angular momentum L = I ω, the entire system's angular velocity then has to decrease, similar to a figure skater stretching out her arms while rotating in order to slow down. All this assumes, however, that the space elevator's cable is completely rigid in the lateral direction and doesn't move under the effective torque it will feel as the internet moves upward. In practice, however, this will not be the case unless further measures are taken which counter the effective torque on the cable and keep the cable perfectly perpendicular to Earth. (Only then Earth's rotation will actually slow down under the backreaction.) This seems somewhat difficult to achieve, though, and I think the better way would indeed be to equip the internet with a jet propulsion engine which provides the necessary angular momentum.
[EDIT] Made the part about backreaction on Earth and stability of the space elevator a bit clearer.
silly, the Internet doesn't weigh anything! ;-)
That's from 2011. It probably weighs at least one watermelon by now, given Netflix etc.
When the payload detaches from the elevator, the angular momentum of the Earth about the sun does decrease (some of the AM goes with the payload) but the mass of the Earth also decreases, and the angular velocity of the Earth about the Sun doesn't change.
It does if your spaceship escapes from Earth in a prograde direction (equivalent to Earth throwing a ball forward, causing a retrograde reaction upon the Earth). This type of escape trajectory is necessary to reach any destination farther from the Sun (Mars, asteroids, etc). It's a tiny change obviously, but it's non-zero.
Note that returning from Mars/asteroids and aerobraking should add angular momentum, speeding up the Earth and at least partly counteracting this effect.
Those are separate from the disconnect I was talking about; I meant a gentle disconnect after which the spacecraft remains in orbit.
The system is not connected to Earth, so it doesn't change the planet's orbit.
Seems like that would negate the lateral problems, but maybe I'm just introducing a twisting one instead...?
A space elevator would reach at least 36,000km to hit geostationary orbit ( https://en.wikipedia.org/wiki/Geostationary_orbit ). Most designs are even longer, to provide a counterweight.
No known material could support a tower that tall (towers need compressive strength; elevators need tensile strength). It would need to rely on 'active support' or 'dynamic structures', like a space fountain ( http://www.orbitalvector.com/Orbital%20Travel/Space%20Founta... )
We can get to about 9km using stone by climbing Mount Everest.
Edit: And bowed, basically in equilibrium with lateral forces.
It comes from the cable needing to support itself, not unlike the rocket equation that comes from the rocket having to propel its own fuel.
Honestly that's my favorite Sci-Fi novel series of all time. Just give Red Mars a try and I prosome you won't be able to put it down.
... the destruction of the space elevator by a terrorist organisation and the consequent destruction on the surface of Mars as the cable, released from its counterweight, wrapped itself around the planet... I’m not sure it’s a great example :-)
But I liked in the book, how it did not actually took sides, but just showed the implications of what violent struggle/war for independency on mars means for different sides.
And mainly from the perspective of Nadia, the engineer who build things. And she sees everything just gets destroyed and smashed.
(I got moved a bit by the memory)
I loved the trilogy, though.
Whooooa. Let's think about this for a second. Eight days means people need to sleep (and not just sitting up in a chair, no matter how comfy). At 1m x 2m per bed that would be a 15m x 4m space even without aisles to walk between the beds or down the middle or any sort of privacy separators. Also, a bathroom and actual washing facilities of some sort are mandatory, and a kitchen with at least minimal food-prep capabilities (even if it's mostly pre-made); modern airplane galleys only need to deal with trips in the tens of hours.
18m x 17.2m is really really not a lot of space for all that.
I can’t see how one would read that other than as each car holding 30 people.
You would need an extra comma to make it six cars holding 30 people in total:
”Obayashi envisages a space elevator using six oval-shaped cars, each measuring 18m x 7.2m, holding 30 people, connected by a cable”
Having 30 people in one car including gear, provisions and sharing sanitation seems absurdly small if not logistically impossible
it might be interesting to see what type of personality tests them use before allowing anyone to actually board one of these should they ever come into existence.
Tube beds could be close packed, and people could sleep in shifts. Also, one can survive just fine with just a washcloth and towel, and a source of warm water.
For efficiency you'd want to go higher. There'd be a point much higher than 300 km where detethering would put you into a highly elliptical orbit where the periapsis is 300 km. Then you'd just have to burn retrograde to circularize. Off hand I'm not sure what the math for that would be but it should be pretty simple algebra.
An inflatable "house" is conceptually completely possible.
Airplanes have to be small because of air resistance. Space stations have no such constraints.
The mathematical argument of 2D vs 3D still holds.
We don't understand ourselves or our bodies anywhere near as well as we can understand or advance materials science. My money is on new cables before reliable stasis.
On the other hand, we can successfully freeze and thaw bunny kidneys.
From the article: Shizuoka University and contractor Obayashi aim to launch two small (10 sq cm) satellites connected by a 10m steel cable from the International Space Station.
I don't see any ways in which this is a space elevator related experiment.
Hmmm...is that 30 people/car or 30 people/6 cars?
You will be enclosed with them on 18m x 7.2m, that's 120m², for 8 days!
The former case would sound like torture, in the latter case it could be done comfortably, though, but it would still require some good nerves by the travellers...
In spacecraft, Soyuz is about 6 m³ for three astronauts for two days. Apollo was 6 m³ for three astronauts for two weeks. The Japanese proposal is spacious in comparison.
At what point does the 20 year amortized cost of a system involving a space fountain or launch loop acting as the 1st stage of a vastly simplified and downscaled rocket break-even with some small multiple of the 20 year amortized cost of a space elevator? I suspect that this multiple might be small enough that economies of scale and optimizations of other systems could keep space elevators out of the picture forever.
Maybe the same thing will happen here? The system you've described could open the Solar System for us, and time + advancements in in-space manufacturing could eventually lead to people building space elevators as an alternative.
(Also, Earth is not a good place to get the experience in building space elevators. The Moon is much better, and probably Mars would be a good candidate later on.)
You could apply the same principle and weave a bootlace from them, but the limits of current technology would render that an exceedingly expensive bootlace.
Ripstop cloth is a mix of plastics and line giving a fexible cloth that is very very strong. Its also airtight so you can inflate it (for a time - its not 100% without a bladder)
Inflatables wings. Hulls.
Same goes for titanium wedding rings...
Fyi, the military has a specific way to lace boots so the laces can most easily be cut to remove the boot.
A nanotube suspension bridge would be pretty amazing to see.
But it’s amusing to think of it the other way: any society technologically advanced enough to have invented the shoelace will inevitably invent the space elevator.
(Though note that this is not one long nanotube, but a macroscale fiber made by extruding micron-scale CNTs in a special way so that they align.)
The elevator is by far the least interesting idea of these novels which center about a future where we have uplifted (given sapience) monkeys and dolphins. We are also trying to survive in an unkind universe where Earth is a third world political power that is making religious fanatics angry.
That aside, how might adversaries disrupt such an expensive and precarious venture? Seems a very hard to defend machine.
It will take decades of R&D, but someone might as well start on the bits we can do now, like a system for climbing the tether (which this is, and it's being done purely in space).
The most dangerous part would be slowly dropping the cable; lower it to the point where it could be pulled into a magnetic clamp -- without destroying everything in its path.
None of this should be construed as an endorsement of space elevators, though. They will never happen on Earth as it exists now. Over and above the material science, you have to clean out LEO of all satellites before you even start construction. It’s just a really dumb idea all around.
You build an orbital ring above the altitude of the LEO satellites, use non-synchronous skyhooks to pick up payloads from inside the atmosphere at an altitude that can be efficiently served by aeroplanes, and then fling them the rest of the way to geosynchronous or interplanetary transfer orbits by accelerating them along the ring.
A satellite impacting the tether will definitely "stop" it, in that it will, at the very least, melt an impact crater into it if the cable is wide enough to not be cut. It is unlikely that the cable will be that wide. I feel like a broken record, lately, but the dominant concerns of impact modeling at orbital velocities are (a) mass and (b) energy. Everything traveling at 8 km/s effectively splashes into whatever solid object it hits, both because the room temperature shear resistance of the materials involved is orders of magnitude less than the shears involved, and also because the kinetic energy is dumped into thermal energy, melting or vaporizing the materials involved. One tends to get results like: (https://www.esa.int/spaceinimages/Images/2009/02/Hyperveloci...) That link notes that pressures of 365 GPa are reached, and typical yield stresses of theoretical nanotube cables are around 100 GPa.
A carbon nanotube cable is unlikely to be more than an inch or two across at LEO. You need that kind of strength to beat the space-elevator-equivalent of the rocket equation, which governs the taper needed to get the cable to even support its own mass in Earth's gravitational field.
Anyone here remember that thread and can link it back here? Thanks
* If would need to be the most precisely engineered thing we've every produced just to stand a chance of being good enough.
* Because of that, it will be particularly sensitive to wear and tear. How the maintenance would work is an open question.
* It will probably attract terrorists like crazy.
* It needs to never get struck by lightning. It is a particularly attractive lightning rod.
* It generally should avoid bad weather. Whatever it is attached to on Earth needs to be able to move. When moving it you have to avoid not only the bad weather but everything in space, too.
* If the cable breaks, bad things could happen. Bad things can range from burning up in the atmosphere to it whipping around in space damaging satellites, or anything else.
> It needs to never get struck by lightning. It is a particularly attractive lightning rod.
Haven't buildings solved this problem with lightning rods?
On another note, I am personally fascinated by space elevators which is why I am somewhat interested in going back to the moon where we can build a space elevator with today's tech, avoid all of these problems, and have a large body of resources to build/fuel spaceships with.
The only thing I can think of is that all that energy unloaded into cable at once might ablate some of it, causing it to no longer be able to handle the tension.
Once you figure out how to make them en masse, now you have to figure out how to secure the strands into a bundle.
Less of a challenge than warp drive, but still...quite hard.
That's a colorful quote from a NYT editorial in the 1920s arguing that getting rockets into space would not only be impossible, but obviously so. When Musk announced his intentions to autonomously land and rapidly reuse rockets it was mostly dismissed. Certainly companies, full of world class engineers, that had been launching rockets since before he was born probably knew a bit more about what is or not possible than some programmer with an undergrad in physics and negligible real life aerospace experience, right? Then it became, 'We've looked into it already, of course. It's perhaps theoretically possible, but it's a complete waste of money and in way economical.' Then it became, 'Shit we're a decade behind technologically!'
There are a practically infinite number of ways for why any given nontrivial thing might not be possible, and quite a bit fewer ways that it can be possible. So it's generally quite easy to formulate compelling and intelligent arguments against the viability of something (not that my little paraphrasings above were intended to be intelligent). But these arguments are not necessarily as meaningful, or productive, as they might seem. Think of how much of our technology today would have seemed impossible, or extreme long-term future tech, not that long ago -- even to those most qualified to make such judgement. This of course does not mean anything is possible, but it does mean we'd likely be a much more backwards civilization if not for the headstrong visionaries among us doing what conventional knowledge told us ought not be able to be done.
He has other videos on ways we could get into space more cheaply, including by space elevators (which he basically doesn't think are feasible).
"And overall, such a tower is a diabolical invention. Rotating in equatorial plane it will knock off everything it encounters. And since any satellite orbit intersect the equatorial plane, sooner or later all satellites with orbit lower than the tower height will be knocked down. At the base of the tower will lay remnants of almost the whole cosmonautics."
I'd assume this closes naive discussions about space elevator, at least until the proponents will explain what they are going to do with the problem of hitting satellites. Yet I see this problem again and again with hardly any progress in this area...
as the cable offers resistance to the planet's atmosphere, and as the planet's atmosphere is active/changing, the "thing orbiting" would still have to have an excellent aerodynamic shape to survive the planet's atmospheric effects, right? (as e.g. the lower part of its cable would probably soon or later be "pushed" by winds therefore initially speeding up the counterweight but lowering its altitude - and/or later after some iterations of push/pull generating maybe a slingshot-effect, sending it into a potentially full crash-course towards the atmosphere/planet's ground).
E.g. as soon as the cable has headwind (in the opposite way of the planet's rotation) the cable would slack off, the thing in orbit would slow down & lower its altitude (how much? Would it anyway have to always skim the upper atmosphere?) => then as soon as the cable gets tailwind the opposite would happen, with relative slingshot-effect.
Just fantasizing here..
Patents should be allowed only for something that exists / can be demonstrated (which would ensure that patents are something somebody invested in, and therefore at least believed in).
It would be nice to see even a metre long demo, which I imagine might be possible as something like a student project (4 coil guns exchanging ball bearings).
In summary, if the cable breaks at the base, the elevator will fly harmlessly into space. If it breaks at the counterweight, a large portion of the cable (several thousand miles long) will collide with the Earth’s equator.
The space elevator would become a space whip. I wonder whether this has a use case, like getting hardened unmanned space probes to speeds required for interstellar missions, or just much faster missions to other planets in the solar system.
Assuming a catastrophic break near the upper end of the cable (before the counterweight), there's not much you can do to keep it from coming down.
The travel pods, likewise, can always have rockets on them whose sole purpose is to get the passengers to safely. Yes, it means you’re taking up more mass than you strictly need to, but the great thing about a space elevator is that the mass is no longer a hyper-critical parameter.
But yes, no rails here.
And just a cable falling could be a significant disaster by itself.
Will the station at the end of the tether still need a rocket to deal with the additional mass? Is the fact that this rocket only has to go up once the core advantage?
Wouldn't the load going up the elevator pull the tether to one side?
There are more reasons to build a space elevator, but that's a big one. It really would be far more energetically efficient.
To get near 100% efficiency, it follows from the kinetic energy formula and conservation of momentum the body you're pushing against must have a much larger mass than you.
So discounted exotic phenomena, the only way to travel efficiently through space is to push off a very large mass, departing at full velocity, or in the case of near-Earth travel, simply push Earth.
The space elevator is essentially an elaborate staircase. It is in a stable equilibrium, and climbing it doesn't steal energy from the counterweight (which in fact doesn't move in fact because it is in constant tension); you're just pushing Earth away.
In the grand scheme of things the very low efficiency of maybe 10% (in my guesstimation) to LEO isn't so bad (not even the maybe ~5% interplanetary efficiency); especially considering the costs of space systems in general in comparisson to fuel cost. This small fuel cost makes reusable rockets quite an attractive option near term (as noted by SpaceX).
But long term, that's quite a steep inefficiency. If we were to endeavor large scale colonization or exploration of exoplanetary resources it seems to me either a kinetic launch system or at least a space elevator variant would be a necessity.
 Derivation: M1 v1=M2 v2 => v1^2 = (M2/M1)^2 v2^2;
M1 v1^2 + M2 v2^2 = E => M2^2/M1 v2^2 + M2 v2^2 = E;
M2 v2^2 (1+M2/M1) = E => K2 = E/(1+M2/M1).
As M1->infinity, all the kinetic energy goes to K2 and none to K1 (which is why you don't give Earth any meaningful energy by walking).
The tyranny of the rocket equation! The energy use of a rocket isn't just "how much energy is needed to have that kinetic energy and that potential energy", but also includes the energy needed to lift and accelerate the fuel used to provide that energy, as well as the fuel needed to provide that energy, as well as the ... and so on.
Think of it like holding a rope tight between your arms and putting a robot that moves on it but ends up not exerting enough force to cause it to slack. Your arms (earth/space teather and the in space counterweight) and the object being moved would keep the same overall motion between all 3 objects (your body would just turn).
The space elevator is similar except earth is way more massive than the object being moved so nothing really changes. Also, due to gravity, you have to expend extra energy to move from the bigger object (earth) to a smaller object (space elevator counterweight), aka, the minimum energy cost of moving things out of gravity wells.
The rocket equation is about reaction mass that is carried by the thing expelling it. It does not apply to climbing a rope, nor does it apply to the flight of a helicopter.
Regarding pulling the satellite down,
Pulling down on the weight at the end is something we have to do anyway to keep it from flying out away from earth.
Maybe the required energy would be sucked out of the earth's rotation, but that seams insane.
As you climb the cable, the force of gravity pulling you back to earth decreases, and the centrifugal force pulling you away from earth increases. The difference between these two is the force you need to provide to climb the cable.
I believe you are correct for tethers much shorter than geosynchronous orbit. Below geosynchronous orbit, the force of gravity is higher than the centrifugal force. Therefore, an object climbing a space elevator will have to provide energy equal to the integral of the difference between the centrifugal force and the gravitational force across the distance traveled. The remaining energy (the remaining gravitational potential and the kinetic energy of the orbit) will be leeched from the orbiting counterweight (requiring the counterweight to have a rocket to maintain orbit, as you suggested)
For tethers that extend beyond geosynchronous orbit, it is possible to for no energy to be removed from the counterweight (instead, all the non-climbing energy will be taken from the rotation of the earth). Imagine that we place a counterweight on a tether beyond geosynchronous orbit. This counterweight and the earth it form an orbiting two body system. The tether will be under tension (the force necessary to keep the counterweight in synchronous orbit) -- let's call that force T. A climber that scales the tether will exert some force T_1 on the counterweight, pulling it towards the earth. However, as long as T_1 is less than T, the counterweight will remain where it is. The force of the table on the earth will become T_2 = T - T_1. In other words, a portion of the force necessary to keep the counterweight in orbit will now be applied by the climber instead of by earth. The energy that the climber must apply is the same as before, but the counterweight is not affected. The remaining energy, by process of elimination, must come from the rotation of the earth.
Geosynchronous orbit is 42 km from the center of the earth while the ISS orbits 7k km from the center of the earth. I expect the experiments are being done at the ISS for convenience rather than from a plan to build a space elevator to the ISS. The article also cites speed and distance numbers that imply reaching a geosynchronous orbit.
To answer your questions more directly: 1) below geosynchronous orbit, yes. 2) No, the ability to extract energy from the earth's rotation is the main advantage. 3) Yes, but for a counterweight beyond geosynchronous orbit, the tension on the tether will pull it vertical.
The ISS will almost certainly be decommissioned by 2030 anyway, and we're not going to have a space elevator by then. There'll still be other stuff in LEO that we want to get to though.
Why the tether needs to be 36,000km long wasn't mentioned.
The ISS circles the Earth every 92 minutes. If we dropped a cable from the ISS (or another satellite at the same height), the anchoring point (e.g. something like a floating oil platform) would also have to circle the Earth roughly every 92 minutes. That's not feasible.
Satellites at 36,000km circle the Earth every 24 hours, which is the same speed that the Earth rotates. If the satellite is orbiting around the equator, going the same direction as the Earth's rotation, then we would not have to move the anchor (the Earth's rotation would do it for us)
What kind of music are they going to play on the way up???
There would be multiple elevators on the continents of the planets that were tethered to orbital platforms.
They didn't seem to survive the covenant well
> Obayashi envisages a space elevator using six oval-shaped cars, each measuring 18m x 7.2m holding 30 people, connected by a cable from a platform on the sea to a satellite at 36,000 kilometers above Earth.
36000 km is GEO, so it would be near the equator, away from land and safe from quakes.
These early cable experiments are important, but someone should also be working on the composing an 8 day Elevator Muzak score that won't drive you insane.
3.4x10^7/(500)^2 = a m/sec2
For an 8min20sec flip time. 20+g if you really want the 8min.
Also, it makes the need for muzak nonexistant because all your passengers are dead and can't hear it anyway. Seems to me that defeats the purpose of trying to time the trip to coincide with the length of a particular song.
It just wasn't really that good.
We should probably treat it more like commercial air travel than compressive-structure elevator rides.
0: 200kph*8day/8min/2min => 67.981081 gravity
It looks like 6 Gs is about as much as is feasible for an extended period of time.
Any pointers to 6 Gs as being tolerable, for how long? Tnx.
10 Gs for 1 minute is lethal.
I don't think you'd get actual paste, but yes, 8-minute space elevator rides aren't looking very physically possible.
Geostationary orbit is 35,786km above the equator, so 8 days feels a fair approximation.
Why would it be "zero-g" you're not in orbit?
It is possible to crack a joke here and get it upvoted, but it's hard to pull it off. I even once had a joke upvoted by quite a lot,* like 50 points or something, but most jokes are downvoted not because humor is forbidden, but because insubstantive comments are discouraged.
Some humor is downvoted for being uncivil because a lot of humor is basically poking fun at people or mocking them. A lot of humor is not nice at all. HN tries to meet a very high bar for civility.
* Under my old handle and it hit 59 points:
At any rate, way better than "harumph! HN hates fun!"
It’s just a culture thing. HN tends to be more news and factually focused than reddit/Twitter/etc. People here just prefer to stay on topic, especially since humor is very different between people and can be very hit or miss.
If you want constant acceleration, you need to maintain constant force. A higher-velocity vehicle applies that force across a greater distance per unit time, and therefore requires more power.
Accelerating 1 metric ton at 1g requires 9800 N. So at peak velocity (18 km/s), that's 180 megawatts per ton, which is more than 700 times the power to mass ratio of a Tesla P100D.
So, there's surely a safe speed limit built into the materials being used? It's probably faster than the speed they're starting out with, but I kinda assume it can't be fast enough to shorten the trip to hours from days.
As an aside, moving people is probably not the most profitable use of the thing for the foreseeable future, as cool as that sounds. Getting a satellite into orbit for a tenth the cost is revolutionary (though they mention the cost compared to the shuttle, which is much more expensive than rocket transport...so they may be cherry-picking numbers to make this seem more revolutionary than it is).
Anyway, I can't think of how they could accelerate much beyond the fastest non-maglev train speeds without tearing apart the cable and car, but I may be underestimating the strength of carbon nanotubes, and whatever other component materials they're using. Perhaps there's a materials nerd here who knows.