I always enjoy Neal's pages. I found planes at high altitude very interesting, didn't know we could fly that high!
replies(1):
Regarding actual space elevators though, while they're not sci-fi to the extent of something like FTL travel - ie. they're technically not physically impossible - they're still pretty firmly in the realm of sci-fi. We don't have anything close to a cable that could sustain its own weight, let alone that of whatever is being elevated. Plus, how do you stabilize the cable and lifter in the atmosphere?
A space elevator on the moon is much more feasible: less gravity, slow rotation, no atmosphere, less dangerous debris. But it's also much less useful.
Re playing this gem https://neal.fun/stimulation-clicker/
If anything, "evolution" filters out disadvantages (eg: can't survive because your neck's too short and that pesky giraffe is eating all the leaves you could reach).
Evolution kills what doesn't work.
* Jeez, Everest is tall
* They got a plane to 17km in 1938!
* There was a paper airplane flight at 35km
The slow rotation is a minus, it means you've got to string the tether up to L1 instead of "just" up to geo/luna-stationary orbit. A lunar space elevator needs to be at least 56000 km long, more than 20000 km longer than the one to earth.
> But it's also much less useful.
Yeah, especially because all the things that make lunar space elevators a little more attainable also make lunar mass drivers a lot more attainable. Why ride in an elevator for a week if you also can just be fired from a cannon?
1) How do you attach the climber to the cable without affecting its structural integrity? By squeezing it really hard? A material that's optimized for longitudinal tension strength is probably not very tolerant of lateral compression.
2) How do you provide power to the climber? A regular electric cable can't support its own weight, so either you have to attach it to the climbing cable, or you have to make it from the same material.
3) Is it even worth it? The climber needs to cover a distance of ~36,000 km, so even at 200 km/h it takes 7.5 days from the bottom to geosynchronous orbit. How many climbers and what payload can the cable support at the same time? Refer to issue #1 regarding limits in speed and mass per climber.
The throughput in tonnes/day is absolutely abysmal in relation to the immense upfront infrastructure cost per elevator. Compare this to SpaceX's Starship, which is getting closer and closer to fully reusable 100 tonnes to orbit in minutes. Space elevators will stay science fiction forever, not because they're infeasible, but because they're useless.
Non-SI legacy units have been grandfathered in and 'accepted for common use', but ICAO recommends that SI units should be used[1] (eventually). China and quite the majority of the ex-USSR, for instance, use metre flight levels[2].
There have been at least two aviation accidents and incidents relating to unit mis-conversions. This is two too many. As an SI absolutist, everyone should switch to SI or units purely derived from SI (so domain-specific stuff like parsecs, electronvolts, and binary prefixes, if appropriately symbolled are OK). It is an internationally-recognised, and nearly universal standard that permeates every aspect of human lives.
[1]: https://aerosavvy.com/wp-content/uploads/2014/08/an05_cons.p...
[2]: https://en.wikipedia.org/wiki/Flight_level#People's_Republic...
To get into a very low earth orbit from an equatorial launch pad at sea level you need about 9.2km/s of Delta-V
To get there from a 100km tall tower, you need about 8km/s of delta-V - about 85%.
Think about how much scrolling there was to get to 100km.
To get to the ISS you'd need to scroll 4 times further. Starlink and Hubble are another 100km beyond that.
You start having radiation problems if you spend too much time above 600km.
Aside from Apollo, the highest a human has been is about 1400km - 14 times more scrolling than this page.
To get to GEO would require scrolling over 25 times further than even that.
This is especially true considering that you don't need something that barely holds - you need something that you know will hold up to many times more weight than it needs to, so that it can be safe: the potential energy such a thing would store would be enough to dig into hundreds of meters of rock all around the world, if it ever crashed. So, you have to ensure there is no realistic chance of it ever crashing. It also has to be highly non-fragile in other ways, so that a madman with a bomb or a freak collision with an airplane or a meteor (especially likely in the thin upper layers of the atmosphere) won't bring it all down.
This combination of properties may well be completely impossible to actually achieve in a material. Even if there is no obvious basic law of physics that it would break, that doesn't mean that it wouldn't break other, harder to touch, derived laws.
> As particles from the sun hit the atmosphere, they excite the atoms in the air. These excited atoms start to glow, creating brilliant displays of light called auroras.
The process is a bit more nuanced than that. The modern mainstream understanding is that the growing pressure of the solar wind makes the tail of the magnetosphere "contract" (sort of pushing it inwards from the sides), which leads to reconnection of magnetic field lines. Once the reconnection occurs, the magnetic field lines that remain bound to the geomagnetic dipole accelerate the particles on them towards the Earth => they slam into the atmosphere, exciting the atoms and generating the aurora.
Snipping off just the first few kilometers is not catastrophically destructive yet, and cutting it down further up would require multistage rocket designs, sophisticated steering/targeting and potentially significant yield (you'd need to cut unobtainium, after all...). If you can build a space elevator, you can defend against those.
You better thoroughly inspect what cargo you put on the elevator itself, of course.
https://foundation.fandom.com/wiki/Bombing_of_the_Star_Bridg...
It’s about as devastating as you would expect.
A terrorist attack on a space elevator is a pivotal plot point in Blue Mars by Kim Stanley Robinson, which IMHO is a better work in basically every way than Asimov's magnum opus.
My favorite is probably https://neal.fun/infinite-craft/
This type of interactive learning experience reminds me of how fun it was to browse Encarta back in the day. It was full of interesting facts, presented in fun interactive ways. As much as I love that we have Wikipedia today, a static web page with text and limited multimedia is far less engaging and conducive to learning.
I think that Neal Agarwal and Bartosz Ciechanowski should be sponsored by the Wikimedia Foundation to create similar experiences on Wikipedia. That would do so much to facilitate learning for students of all ages.
Kármán said that it's about this height where the aerodynamic lift and inertia being dominant are reversed.
I believe there are other services that will also give you virtual cards, I'm not familiar with them off hand.
Beautiful work though.
I think it's the first episode of season 2 or 3, not the first season. I remember someone else mentioning it, but I've only seen season 1 and don't recall that either.
Amazing work, as always. I love neal.fun
Edit: also good to know that paper airplanes have officially beat the SR-71, F-104 or X-43B with altitude record.
But for what purpose? You just want to float around in a elevator carriage, aren't you going somewhere when you go with a space elevator?
Pure payload capsules with no passengers wouldn't need this.
The argument for space elevators is that there's a pretty strong limit on how much payload can be launched by rockets due to injection of water into the upper atmosphere. Starship could arguably reach this limit with plausible projected growth rates in traffic.
Rotating cables ("rotavators") on the moon seem much more practical than full space elevators.
https://en.wikipedia.org/wiki/Momentum_exchange_tether#Rotov...
Conceptually I get, it's like being in a cold room that showers hot sparks on you from above occasionally...
...but I feel that the definition of temperature has been abused here slightly
Unironically oughtta work better than that stuff with the barleycorns and fortnights.
"Most grandkids" is good but not catchy.
Or Idiocracy "evolution began to favor those who reproduced the most".
...that is, until a satellite will hit the cable above. Space elevator is built in the equatorial plane, all satellites cross it, so eventually every satellite is going to collide with the cable. For this reason the space elevator is incompatible with existing spaceflight, that's why even with nanotubes it's unlikely to be built.
Is inherently incomplete. Not necessarily because they're needed to explain it, but they do need to be brought up at any time possible because they're cool.
But yes, a space elevator would be difficult to defend in World War III.
I do understand that this is one those generic ones (I saw it many times) which the original creator of the website just slapped on.
Most engineers would bring up a lot more issues than just finding a strong cable. Also, most attempts with e.g. carbon nanotubes have been abandoned ages ago https://www.newscientist.com/article/2093356-carbon-nanotube....
- We don't have a good ascent mechanism other than rockets - and then we might just use rockets without building an elevator. - We don't have a good (and safe) descent mechanism. - Maintenance? Protection from space debris? Protection from oscillations? Ground-protection if the elevator collapses?
This is dyson-sphere level of fiction. We can do back-of-the-napkin calcualtions on how things would work, but the practicalities make it completely impossible or impractical.
When the ICBMs go up, early warning radars notice them right away and you still have time to act. Leaders can make it to helicopters and basement bunkers, bomber squadrons can scramble, missile silos can already be empty when hit, road mobile ICBM launchers can still relocate.
But with a large enough number of MRBMs, your opponent might get ideas. They might start thinking about getting away with a decapitation strike.
The military space elevator is more like an ICBM in this case. There will be ample warning when somebody drops something from geostationary orbit (and also when somebody drops something from lower up).
This site does use buymeacoffee.com, which appears to be a dedicated payment platform. Its transaction fee is apparently 5%, which is steeper, but better for these small donations because of the lack of a fixed fee.
In most cases, 100km is less than the distance between sizeable metropolitan areas. It's a day long bike ride. Air runs out less than a bus ride across town. A 15k jog/hike would put you in the stratosphere. Those jet aircraft that seem so high are closer than that. Closer than your friends house or the local stadium probably.
Look at a map or globe with that in mind and everything feels so thin!
Then again, when doing mega structures, a launch loop is more plausible.
The elevators were developed for cheap space travel but unsurprisingly centralized the world's economic development around the owner countries. ie the other countries became increasingly reliant on them and the world segmented into (three) blocs. But the owner countries became increasingly protective / paranoid, leading to cold-war era developments where each of them secretly researched fancy space weapons and stockpiled more and more military assets around the elevators.
So some of the attacks were by poorer countries lashing out. Some attacks were to expose the military assets being hidden in the elevator (outlawed by intl treaty). Though most were probably just excuses to show things like giant robots vs death star.
You look to be right:
https://www.kimstanleyrobinson.info/content/space-elevator
And I'm not the only one to notice the cross-reference:
https://www.reddit.com/r/kimstanleyrobinson/comments/pv6zh9/...
Not to mention, securing the cargo would be an extremely difficult task in itself, especially when one of the main thinga you'd like to raise through the space elevators is rocket fuel.
nah, thats the simple part. getting up there efficiently is the difficulty. once we're up, its just a matter of force over time to create a nice orbit.
The faster you go, the more friction you face, and the more heat and vibration your equipment must endure.
Going slower reduce friction and stress but use more energy just negating gravity. Slow rocket is inefficient rocket.
So we wanna leave the atmosphere as soon as possible, but not so fast that the rocket melts or engines collapse. Prefferably just below the sound barrier.
once we're up, its pretty chill... until you wanna go down again. Slow rocket is alive rocket.
Edit: actually, "almost all species" is not right. Maybe "almost all interesting species"... which is admittedly too subjective a take.
If you like factory games and space elevators, then try Satisfactory!
https://en.wikipedia.org/wiki/Galactic_Center_filament
https://science.nasa.gov/asset/webb/milky-way-center-meerkat...
Now, I have no idea how practical it is to build one (Angela Collier has a video saying it's kinda ridiculous), but it's a cool idea.
https://www.youtube.com/watch?v=Z5aHMB4Tje4
Also since rockets have moved away from hydrolox, it would be nice to have a greener launching system.
It depends what you mean by "up there". ChatGpt tells me you'd free fall from 1000 km to 100km in about 8 minutes. It also did the math that you'd need 1.65G of sideways thrust to reach orbital speed. That's quite a bit of force for spacecraft sized objects.
If you have an actual space elevator, sure, you can go to close to geosynchronous altitude and by that time you'd have enormous sideways velocity just by being dragged sideways by space elevator and indeed it would be easy to propel yourself to orbit (above a certain altitude my intuition tells me you could let go of the rope and while you'd end up on an eliptise you'd still be in orbit)
After the first book, he then goes to explore all the questions that it brought up. The question of identity (to me) seems like the most reoccurring question.
Btw, there's a new book in the series. The Shattering Peace was released in September.
In terms of hardness, it probably on par with Expanse, so mostly technobabble with the magical tech only used when it's convenient for the plot. The abuse of "psychohistory" is particularly egregious. There's so many scenes where it's visualized a hologram of scribbles and they zoom in on more squiggles while divining the future.
But again it's pretty, so if you're okay with drama in space, it's maybe a 8/10.
For example, each short story almost completely changes the cast (of course, with some descendants of characters appearing occasionally), as befits a saga that spans centuries. No producer was willing to run with that (as they didn't believe the audience smart enough to follow it would be big enough for the show to make a profit), so they introduced cryonics, clones, sorta-AIs (including robots out of their original context) to have some sort of continuing cast.
Also, the books have a quaint 1940s (NOT 1950s as people usually say it) atmosphere, with excitement about "atomic" energy (changed to "nuclear" in the 1950s publication), distant descendents of the slide rule, and generally weird-sounding math and science, that the show totally drops in favor of a "contemporary" feel.
And btw, the space elevator scene is lifted from Brin's Foundation's Triumph where it is described as a "future" event, part of Trantor's fall, predicted by Seldon's early team and trickled down to the general population.
Being pedantic, this should be "there isn't enough oxygen for sustained human life". An acclimatised climber can survive tens of hours.
You know what does make way more sense and is way more achievable? Orbital rings [1].
Basically, put some copper wire in space, orbit it at ~8km/s, run a current through it and then you can reset structures on top of it (magnetically) and those structures are fixed to the Earth's surface. You can technically run a cable from 100-150km up to the surface and run a gondola into LEO. This would transform both Earth transport and interplanetary travel. You accelerate something on the inside (Earthside) of the ring at ~2G, like with a maglev train, and you have enough velocity to escape the Solar System.
There are other concepts like space fountains, orbital rings and sky hooks that seem more doable -- especially the sky hook seems close to do-able, especially on the Moon.
I wish directors were brave enough to kill off characters if it serves the plot. I get that there's IRL reasons that make it difficult (like contracts, scheduling, etc) but each new season accumulates more subplots to the point it's like a 30 minute episode is really a compilation of 3x 10-minute shows.
This bugs me in multiple-protagonist books too. Just feels like an excuse to pad the page count with introductions and cliff hangers every POV switch.
I think separated from that there's a good enough show in there.
Question: Why does the Douglas Skyrocket have its undercarriage down at 25km?
Unsolicited feedback: It would be nice to be able to click on an item and see some more information. Perhaps just a hyperlink to a wikipedia entry.
He did. The elevator music!
What's the best way to pull yourself directly vertical along a cable for 22,000 miles?
What's the best way to descend 22,000 miles quickly, but also with a braking mechanism that isn't going to require a heat shield?
Some sort of slow cable car going at 10mph even is going to take 2200 hours... 1000mph is going to take 22 hours still. That's a full day to orbit even going REALLY fast. And getting up to 1000mph vertically, for a sustained 22 hours... that's not an easy feat.
And if the goal is just to get up past the karman line and use the elevator as a stage 1 for a rocket launch and detaching from the elevator while suborbital is fine, then it's a one way trip, and still need to re-enter the old fashion way.
The scale of space makes all of the problems far more complicated (edit: not just the cable strength issue, but traversing the cable)
You trusted an LLM to do the maths when it is just s = 5t^2?
Brother Dawn: How often do we make this choice?
Demerzel: You always make this choice.
The next day’s hearings were entirely different. Hari Seldon and Gaal Dornick were alone with the Commission. They were seated at a table together, with scarcely a separation between the five judges and the two accused. They were even offered cigars from a box of iridescent plastic which had the appearance of water, endlessly flowing. The eyes were fooled into seeing the motion although the fingers reported it to be hard and dry.
In a recent re-reading of the series, I started having difficult with it in Second Foundation... and forced myself to finish Foundation's Edge. The amount of psionic ability and the... for lack of a better word "preaching" with the monologues was very much a science fiction of a different time.
Foundation (the TV series) had to do updates for modern audiences and media. I'm not sure if trying to remain perfectly faithful to the books would represent them well.
Foundation is a soft sci-fi about interactions between individuals and history and society. Trying to maintain the incidental harder parts of the written works that modern audiences expect to be somewhat consistent of far future technology with the 1950s lens on them would be quaint and a bit off-putting to people expecting future tech.
He threw his cigar away and looked up at the outstretched Galaxy. “Back to oil and coal, are they?” he murmured—and what the rest of his thoughts were he kept to himself.
[1] https://en.wikipedia.org/wiki/List_of_birds_by_flight_height...
[2] https://web.archive.org/web/20131011012320/http://blogs.bu.e...
What at joy it'd be to fully experience life, not just a sanitized productized version, and have the safety net of perfect medicine to cure what ails ya.
If you account for various inefficiencies like taking it slow in the lower atmosphere Ant whatnot, it still should be in the matter of hours. So totally feasible and even comfortable.
Of course, that would require a page 420 times longer, and I don't know if a browser would even support it.
Factorio, Dyson Sphere Program, Captain of Industry...loved them all. Satisfactory? Just wasn't for me.
That "last mile" bit is going to entail independent propulsion anyway. Getting to the altitude if the ISS is a mere 10 hour trip at a sedately 40kph which isn't unpleasant even for humans, but the ISS orbits at nearly 29000kph (as will you if you let go of the space elevator at that altitude) and the velocities are only half as scary at the far end, so your rendezvous anywhere other than one specific point in geo is going to be complicated. But you've saved the fuel costs of escaping the earth's atmosphere that's rather significantly more than the fuel costs of other bits of your satellite mission, including reentry. (At least until the costs of building and maintaining and protecting the elevator are factored in, but who knows what unobtanium costs?)
I just had to look that up. Absolutely incredible.
(Translation: yes, once as a kid).
Even more, your delta v required is still huge. I can't be bothered to run the numbers right now but most of the delta v is in the orbital velocity, not in the altitude.
Energy to reach LEO velocity ~ (1/2 * 1kg * (8km/s)^2) ~ 32MJ
Eh. Going up is easy. A Frenchman, a sheep, duck, and rooster solved the whole ‘up’ thing over two centuries ago.
But going DOWN? That’s far more difficult. What wonders may lie beneath our feet: vast caverns, ore, underground oceans… hard to get to though.
I do always have to object to comments like "space elevators are possible," "scientists have studied" and "would save money".
It's a fun thought experiment, nothing more (for now). You can do some calculus to estimate the necessary strength-to-weight ratio based on centripetal and gravitational forces. Single carbon fibers seem to meet this optimistic criteria.
But there are many forces left out. Many practicalitites left unconsidered. Why? Because there is no scientific community that believes it's vaguely achievable with near-future technology. It's simply not worth investing the outrageous resources required to do a vaguely useful viability analysis.
I don't think this is true
> Apple Pay does not cause additional fees for users and merchants.[1]
Of course you would be looking at a constant acceleration, not just a 1000km/hour trip. You'd probably be able to do the journey in a couple of hours with a reasonable acceleration and a rotating cabin (say 1.1g, meaning acceleration would slowly increase from about 0.1g at the surface, then after the flip point you'd decelerate at 1.1g). Even then sideways acceleration wouldn't be noticable (and your cabin could gimbal to just add it to vertical acceleration)
That's the other crazy thing. A space elevator takes forever at elevator, or car, or even plane speeds. But with constant acceleration/decelleration you can have a trip in airplane style seats with cabin crew serving you caviar // scratchcards (depending on class of cabin). Your peak vertical speed would be in the region of 8km/second - way above Earth's escape velocity, but you wouldn't even notice the acceleration/deceleration. You'd slow down in under 15 minutes.
Or you wouldn't and you'd depart Earth at 8km/s, twice the escape velocity.
(If you really wanted a fast departure you'd accelerate at say 1.2g and get upto 30km/s, twice the speed of New Horizons. 1.2g would probably mean you'd have the seatbelt on for the whole 40 minute trip)
You could launch cargo to Mars at say 5G, which would get it there in between 10 and 45 days depending where it is. Obviously you'd have a problem slowing down when you got there.
Space elevators only (theoretically) work because the entire structure is in tension. And the only material we currently know of that can handle the tensile forces is carbon fiber.
/s
This means that half-way after 58 minutes, the climber is traveling at 0.3 * 9.81 m/s² * 60 * 58 ~= 10.2 km/s ~= 36,720 km/h (!!!) relative to the cable. A tiny imperfection or wobble is going to make the climber crash into the cable, destroying both.
A climber with a mass of 10 tonnes requires 10^4 kg * 1.3 * 9.81 m/s² ~= 127.5 kN of force to accelerate at 1.3 g. At the ~56 minute mark, the climber reaches a speed of ~9,888 m/s. This means it requires a power output of 127.5 kN * 9888 m/s = 1.26 GW (!!!) to achieve this acceleration, plus overhead for the power electronics and transmission. Even at a voltage of 1 kV, that's around 1,500,000 A (!!!) of current that you have to transmit and invert.
If you have a way to reliably transfer that amount of power without touching the cable which is moving at 10 km/s relative speed, or with touching but without immediately melting the cable or the collector, let me know :-)
> So totally feasible
lol no
Maybe the Isp could be increased by mixing in some helium, but helium is very expensive.
They’re both acceleration. At high thrust, virtually equivalent.
They’re not obviously wrong.
A lot of the cable is moving at escape and orbital velocities. Tensile strength is all that holds it together.
If, as the cable fails, you sever the parts above from below around escape velocity, you’ll significantly reduce the length of cable that will ever hit the surface.
The issue, I think, is more about balancing drag and air intake at appropriate atmospheric densities for different speeds. An SR-71 Blackbird could fly at 85,000 feet continuously, and a MiG-25 set what I believe is still the air-breathing record max altitude by pulling a "zoom climb" (accelerating in higher-density air that the engines could use effectively, then pulling the stick back and coasting up through rarefied air too thin for the engines) to 38km or 123,000 feet.
Most experimental hypersonic aircraft use rockets because that's what works.
So either fire a rocket in space to circularize the orbit or reach more than Earth’s escape velocity 25,020 mph (11.186 km/s, 40,270 km/h) ~ Mach 32.6, due to some drag in air to thin for any kind of air breathing engine to work.
X-30 was aiming far lower ~Mach 20. Nuclear could make it more realistic than any form of chemical combustion. It might be physically possible using Hydrogen but you’re talking generating extreme thrust at vastly more extreme conditions than the space shuttle’s retry.
On Earth.
Zylon or M5 [1] could build an elevator on Mars. Kevlar on the Moon.
To drive this home, it’s estimated we could build a lunar space elevator for less than what Bechtel fleeced NASA for a mobile SLS launcher [2][3].
[1] https://en.wikipedia.org/wiki/M5_fiber
[2] https://opsjournal.org/DocumentLibrary/Uploads/The_Lunar_Spa...
[3] https://oig.nasa.gov/wp-content/uploads/2024/02/IG-22-012.pd...
Projects are massively expensive, including a lot spent on "looking expensive", but the writing cannot be as expertly crafted because the high expense means upper management craves purpose and control and meddles with things, and the giant "target" audience means you can't do anything interesting.
Surface area is 5x10^8 km^2. So it it 'only' the first ~2m of the crust (~6m if you don't count ocean).
Estimate for a standard classroom globe at 13" in diameter (I'm seeing a rnage of 12-14 inches as typical). I'm reporting in inches because that is what came up first and most of the globes are for sale in the US. Mixing units here, but, it works out.
But, in meters, the diameter of the Earth is 12,742,000 m on average. if we use the 'Karman line' as defining the edge of what the atmosphere is, that is 100,000 meters. Solving for X ... (13" / 12742000 m)=(X / 100,000 m). gives us an atmosphere thickness of approximately 0.1". -----
Paper glued to the globe would have a thickness of maybe, 0.004" (thin paper) to 0.012" (like a card stock paper).... so that analogy is off by an order of magnitude or more.
Even if you use the mesosphere as the definition for the top of the atmosphere, that is still 85,000 meters and thus similar.
People can check the numbers I used.
* Perhaps the analogy should go more like: the thickness of the cardboard sphere the globe is made out of is about the thickness of the atmosphere. Because, having completely destroyed a globe once in my youth, I remember the cardboard shell being approximately a tenth of an inch thick. But, that's maybe not a great reference for the analogy because not everyone has cut apart a classroom globe....
Another comment talks about atmosphere being a 1 mm layer on a grapefruit... so definition of atmosphere extents might be different in these two anecdotes.
(edit: I submitted this comment two minutes after another comment did the math on the globe/paper layer version...)
Once you're in space, force over distance until your fuel runs out.
90% of the atmosphere is below 16 km.
16 km * (12" / Earth diameter) :: https://www.wolframalpha.com/input?i=16+km+*+%2812%22+%2F+Ea...
0.015 inches, 0.38 mm
... and tossing sheets of paper into that ( https://www.wolframalpha.com/input?i=thickness+of+paper ) ...
16 km * (12" / Earth diameter) / thickness of paper :: https://www.wolframalpha.com/input?i=16+km+*+%2812%22+%2F+Ea...
4
Note that that's copy paper rather than card stock...
Adjusting this to 5.6km (the 50% atmosphere amount) ...
5.6 km * (12" / Earth diameter) / thickness of paper :: https://www.wolframalpha.com/input?i=5.6+km+*+%2812%22+%2F+E...
1
So it's a matter of selecting the proper globe, proper paper, and proper threshold for the atmosphere.
This is essentially what Scaled Composites and Virgin Galactic were trying to do with their cargo plane system, only you don’t have to worry about the ignition timing because you’re not in free fall.
https://en.wikipedia.org/wiki/List_of_birds_by_flight_height...
I don't know of any launch sites significantly above sea-level, the marginal performance increase wouldn't be worth the logistical nightmare. It's easier to fly up a 747 than build a launch facility on top of a mountain.
<https://neal.fun/size-of-space/>
There are a few sites which let you scroll through the solar system, from the Sun or Earth IIRC. Here's one:
<https://onotherplanets.com/solarwalk>
Ah, and "If the Moon Were Only One Pixel", which is what I'd had in mind, shared by @stared <https://news.ycombinator.com/item?id=45641839>:
<https://joshworth.com/dev/pixelspace/pixelspace_solarsystem....> (2014)
(HN discussions: <https://news.ycombinator.com/item?id=44266828> (4 months ago), <https://news.ycombinator.com/item?id=21735528> (6 years ago) <https://news.ycombinator.com/item?id=32936581> (3 years ago).
I think this thread would also be loved by the nerdy folks at https://Reddit.com/r/theydidthemath
A maglev train is several centimeters from the rail; if someone made the carbon nanostructures (the only known material strong enough are atomically precise carbon nanotubes or graphene, but the entire length has to be atomically precise you can't splice together the shorter tubes we can build today) this badly wrong, the cable didn't survive construction.
> Even at a voltage of 1 kV, that's around 1,500,000 A
Why on earth would you do one kilovolt? We already have megavolt powerlines. That reduces the current needed to 1500 A. 1500 A on a powerline is… by necessity, standard for a power station.
We even already have superconductor cables and tapes that do 1500 A, they're a few square millimeters cross section.
> Above GEO, the centrifugal force is stronger than gravity, causing objects attached to the cable there to pull upward on it. [...] On the cable below geostationary orbit, downward gravity would be greater than the upward centrifugal force, so the apparent gravity would pull objects attached to the cable downward.
So, without defensive countermeasures, the Space Elevator would indeed whip around the Earth.
But honestly, if I were designing such a thing, it would have break points, and maybe even a whinch at the base, to pull the line in. I'd also build it over water, and not over a population centre.
But I'm only a software engineer– it's likely a lot more challenging than this.
No maglev train I ever heard of travels at 36,000 km/h. This is about two orders of magnitude faster.
> We already have megavolt powerlines.
That's transmission over long distances, but you need to handle and transform all that power in a relatively small enclosure. Have you seen the length of isolators on high-voltage powerlines? What do you think is going to happen to your circuit if you have an electrical potential difference of 1 MV over a few centimeters?
Yes, you can handle large voltages with the right power electronics, but you need the space to do so. For comparison, light rail typically uses around 1 kV, while mainline trains use something like 15 kV. But a train is also 10 to 100 times as heavy as the 10t climber in my calculation, so you need to multiply the power (and therefore the electric current) by 10 to 100 as well.
This was part of the Plot of Halo: ODST, where fragments of the space elevator collapsed onto New Mombasa.
[1] https://en.wikipedia.org/wiki/Mario_Pezzi_(aviator)
[2] https://static.thisdayinaviation.com/wp-content/uploads/tdia...
[3] https://www.enricopezzi.it/fam_pezzi/mario_pezzi/images/MP_1...
[4] https://www.reddit.com/media?url=https%3A%2F%2Fi.redd.it%2F4...
The highest jet record is 37km in MiG-25. The scramjet record is 33km. I found source that says the limit is 40km at Mach 15.
... and the source document for the numbers was based on a paper that is fairly easy to find given the proper keywords in google search... https://pubmed.ncbi.nlm.nih.gov/1648028/ (and I learned that methane more rare in flatus than not).
> There is an art, it says, or rather, a knack to flying. The knack lies in learning how to throw yourself at the ground and miss.
You're not going sideways - you're actively falling continuously, but somehow missing the ground for the entire length of your orbit.
The other French method included two dogs, a bunch of chicken, and a very large cannon, which had quite a bit more showmanship.
There's no theoretical limitation on how fast an air breathing jet can move. You just have to redesign everything every few mach numbers, and deal with the atmospheric drag.
The NASA X-43A hit Mach 9.6 as an air breathing engine (test used a rocket at lower speeds for cost reasons) which in theory should be capable of ~65 km assuming it could survive a similar maneuver. Actual limits are heavily influenced by how much thrust you can generate while slowing down etc not just max velocity.
So yea no actually built air breathing aircraft can hit space, but it’s within the realm of possibility.
You think the problem is the speed itself, and not the fact that trains are close to sea level and at that speed would immediately explode from compressing the air in front of them so hard it can't get out of the way before superheating to plasma, i.e. what we see on rocket re-entry only much much worse because the air at the altitude of peak re-entry heating is 0.00004% the density at sea level?
> What do you think is going to happen to your circuit if you have an electrical potential difference of 1 MV over a few centimeters?
1) In space? Very little. Pylons that you see around the countryside aren't running in a vacuum, their isolators are irrelevant.
2) Why "a few centimetres"? You've pulled the 10 tons mass out of thin air, likewise that it's supposed to use "one kilovolt" potential differences, and now also that the electromagnets have to be "a few centimetres" in size? Were you taking that number from what I said about the gap between the train and the rails? Obviously you scale the size of your EM source to whatever works for your other constraints. And, for that matter, the peak velocity of the cargo container, peak acceleration, mass, dimensions, everything.
> For comparison, light rail typically uses around 1 kV, while mainline trains use something like 15 kV.
Hang on a minute. I was already wondering this on your previous comment, but now it matters: do you think the climber itself needs to internally route any of this power at all?
What you need for this is switches and coils on one side, a Halbach array on the other. Coils aren't that heavy, especially if they're superconducting. Halbach array on the cargo pod, all the rest on the tether.
Right now, the hardest part is — by a huge margin — making the tether. Like, "nobody could do it today for any money" hard. But if we could make the tether, then actually making things go up it is really not a big deal, it's of a complexity that overlaps with a science faire project.
(Also, I grew up with 25kV, but British train engineering is hardly worth taking inspiration from for other rail systems, let alone a space elevator).
Twice.
Because the only known material strong enough at the time was diamond, and diamond doesn’t ablate much when falling through atmosphere.
One of the early space elevator research companies specifically designed a cable that was made by stacking successive layers of material both to slowly increase carrying capacity by building the tether in iterative layers, and hoping it would ablate or at least reach a quick terminal velocity in the case of catastrophic failure.
It is undoubtedly the case that the senior staff on that project were familiar with the Mars trilogy.
What’s the downrange safety cone look like for space launch sites around the world? A little S curve in your insertion orbit would certainly waste a bit of delta V. But not all orbits are equatorial anyway.
I don't have a science background. But how does this work? If you can't feel it, how would you measure it?
Space boggles my mind I love it!
This all changes in outer space, where 0.01g is a valid propulsion mechanism for long duration missions.
Compensate the slight loss of ISP by using aerospiked rotating detonation engines...
On the planetary scale, humans are tiny. We're more or less equivalent to bacteria.
Our entire civilisation is a skin rash.
Basically, I would have thought that any momentum that can be imparted to the rocket before it has to rely on its self propulsion would be a huge help. Not talking about eliminating self propulsion, just an assist so the rocket could carry a larger payload or be smaller or whatever.
IE like a variation on Jules Verne's big gun for throwing the payload up there but engineered to be plausible and having the rocket still be self propelled. And safe.
But we don't seem to do this. So why?
Edit: First part of video [0]. Apparently it's not completely dumb. Just stupid-hard/impossible to do practically at the size required for big rockets and payloads. But small ones might work. Maybe.
Chuckers are the optimal large scale solution for airless bodies, but they're horizontal. You spread the acceleration out over a very long distance so you don't need a super beefy spacecraft and your humans won't turn to goo. Basically, a maglev train except it has track above as well as below and it doesn't have a maximum speed. Wrap one around the lunar equator and it can eject anywhere from sundiver to interstellar escape with human-tolerable acceleration.
But it was the optimum solution because that engine had a long burn to take it to L2. Hauling less engine to L2 was worth more than the loss of the engine not being powerful enough to fight gravity.
Build towers around the equator. Build a ring around the equator on those towers. Build a ring inside the ring, maglev supports. Evacuate the ring, spin the inner ring above orbital velocity. The objective is to generate as much outward force as the weight of the entire assembly including the towers.
Do it again, on top of the first one. Keep doing it until you reach synchronous orbit. If you want to go higher the inner ring is not moving, exerting downward force countering the outward force of the rest of it being above orbital velocity.
Forces:
1) Compression on the towers. Note that this goes to zero as tower height goes to zero.
2) The outward force on the ring exists across the whole ring, but the downward force of supporting the towers only exists where there is a tower. Your ring needs to be stiff enough to counter this. But, again, note that this force goes to zero as the space between towers goes to zero.
3) Maintaining a very hard vacuum in the structure.
We know how to do #3, the others must have answers. Thus it can be built.
Nothing else is feasible with current technology, the taper of the cables is highly dependent on the strength of the material (in tension, an elevator is based on always pulling out as the upper end isn't hooked to anything.) You need much better than anything we can currently do before the taper blows up so badly you can't build it.
Would powering the cable permanently, with a power station at the bottom and a constant feed of water for super-heated steam thrusters work? Just throwing scifi at it. I'm just curious why it has to be one component or why the weight can't be supported by propulsion. I'm guessing the TL;DR is the numbers just don't work out?
Orbital rings--only if you have elevators. Remember, the Ringworld is unstable. So is every other planetary ring.
I do not recall numbers on hooks so I will not address them.
The Moon has a whole different set of problems. There is no synchronous orbit, elevators must go above synchronous orbit, so the normal version can't exist. Nor can anything stand up to be yanked around by the Earth.
But there are two cases that avoid the yanking problem: pointed towards and pointed away from Earth. Current cables are good enough for a useful Earth-pointing cable. The free end dips below synchronous orbit, but it's moving very slowly. You do what people think rockets do--go up. It takes a lot less energy to catch the cable than it does to even reach orbit.
How to have such a cable in an environment with geosynchronous satellites is another matter...
There's also another interesting cable situation. Cable on Mars? Iffy--and those two moons would be a major problem. But flip the problem over--put the cables on the moons. The low end dips into the atmosphere at aircraft-type speeds. The cables can toss to each other. The high end can capture/eject to Earth or the asteroid belt.
Just because it's moving below circular orbital speed doesn't mean the periapsis is in the atmosphere.
And it's why we have been so worried about Russian nukes--they have used liquid fueled birds, they can't be held ready to launch. Such birds are pretty much only useful for a first strike as they won't be able to launch them once incoming missiles are detected unless they're being held at launch ready (and they can't do that for too long.)
Climbing the cable is a nightmare, especially as it gets thicker as you go up. Thus do not climb the cable! Rather, when the cable is built a whole bunch of anchors are built into it. You are not climbing the cable, you are climbing a track on the side of the cable. The cable's job is to support the track plus any load on it.
If you inflate a 18cm diameter head to the size of our planet, a 75um hair would be about 5km wide - which is about the average depth of our oceans.
It's one hair, not a whole head of hair!
Breakdown voltage is pressure dependent, not a constant.
Your figure is for (eyeballing a graph) approximately 2e-2 torr and 150 torr, less between, rapidly increasing with harder vacuum. The extreme limit even in a perfect vacuum is ~1.32e18 volts per meter due to pair production.
For a sense of "perfect" vacuum: if I used Wolfram Alpha right just now, the mean free path of particles at the Kármán line is about 15 cm, becomes hundreds of meters at 200km.
Though this assumes a free floating measurement, the practical results from https://en.wikipedia.org/wiki/Wake_Shield_Facility would also matter here.
> And you're operating this in space where you have ionizing radiation. Free electrons with a big voltage differential?
Mm.
Possibly. But see previous about mean free paths, not much actual stuff up there. From an (admittedly quick) perusal of the literature, the particle density of the Van Allen belts is order-of 1e4-1e5 per cubic meter, so the entire mass of the structure is only order-of a kilogram: https://www.wolframalpha.com/input?i=%284%2F3%29π%282%5E3-1%...
If this is an important constraint, this would actually be a good use for a some-mega-amps current, regardless of voltage drop between supply and return paths due to load. Or, same effect, coil the wires. And they'd already necessarily be coiled to do anything useful: Use the current itself to magnetically shield everything from the Van Allen belts.
Superconductors would only need a few square centimetres cross section to carry mega-amps, given their critical current limit at liquid nitrogen temperatures can be kilo-amps per mm^2.
But once you're talking about a 36,000 km long superconducting wire with a mega-amp current, you could also do a whole bunch of other fun stuff; lying them in concentric circular rings in the Sahara would give you a very silly, but effective, magnetic catapult. (This will upset a lot of people, and likely a lot of animals, so don't do that on Earth).
From what I've seen nobody currently directly launches more than 4.9 tons direct to GEO (Vulcan Centaur VC4). Starship is supposed do 27 to GTO (not GEO) when finished, but it's not finished.
If a space elevator lasts long enough to amortise the construction costs (nobody knows, what with them not being buildable yet), they would represent an improvement on launch costs relative to current methods, even if you were limited to 10 tons at a time and each GEO being a 2 hour trip.
I made a pikachu face when they returned the first image.
https://news.ycombinator.com/item?id=45646741
Ascending the elevator will produce 0.002g of horizontal acceleration throughout the trip.
And I don't understand the connection to the Van Allen belts--I'm talking about sunlight knocking electrons off your conductors.
I didn't say you did with that parenthesis, that was to indicate I was being very approximate with the pressures that correspond to your stated breakdown voltage: https://www.accuglassproducts.com/air-dielectric-strength-vs...
> I went looking for the dielectric strength of vacuum and I found a chart with values for a bunch of different things including vacuum.
That's even more wrong than looking up the value of acceleration due to gravity and applying "9.8m/s/s" to the full length of a structure several times Earth's radius (which was also being done in these comments).
Think critically: when you're reducing pressure, at what point does it become "a vacuum"? Answer: there is no hard cut-off point.
(Extra fun: https://en.wikipedia.org/wiki/Paschen%27s_law)
> And I don't understand the connection to the Van Allen belts
You mentioned free electrons. The thing Van Allen belts are, is fast-moving charged particles captured by Earth's magnetic field.
> I'm talking about sunlight knocking electrons off your conductors.
Very easy to defend against photoelectric emission.
Just to re-iterate, if you're lifting something up with a magnetic field, it's non-contact. You can hide the conductors behind any thin non-magnetic barrier you want and it still works.
Say, Selenium, with a work function of 5.9 eV. Tiny percentage of the solar flux is above that.
Even just shading them from the sunlight would work. Like, a sun-shade held off to one side.
Also, you could just have the return line inside the tether: If the supply is on the outside, return on the inside, you can even use the structure of the tether itself as shielding — coaxial voltage differential, so the voltage difference between supply and return lines due to load creates negligible external electrical field.
Honestly, this feels like you've just decided it won't work and are deliberately choosing the worst possible design to fit that conclusion. Extra weird as "but we can't actually build carbon nanotubes longer than 55 cm yet" is a great deal more important than all the stuff I've listed that we can do.
After the rocket is clear, activate compressors inside of the blimp and return it to base for re-use.
The base would need to be enormous and I'm sure the power draw would be insane, but being able to break the elevator cable into smaller lines and take the weight off of any individual strand might make it a touch more plausible without currently non-existent technologies.
