Submitted by Sorin61 t3_z5v1h4 in technology
Comments
danielravennest t1_ixyqy6k wrote
The classic space elevator - tied to the ground and stretching beyond synchronous orbit - became obsolete in 1986 when Hans Moravec invented a better one, the orbital skyhook.
This is a rotating cable in orbit that picks you up at the low point and throws you higher at the high point. It can be 50 times shorter, and built from today's carbon fiber. Transit time is much shorter, around 15 minutes.
The cable knocks off about half the energy to reach orbit. The rest is supplied by a single-stage rocket similar to the Falcon 9 first stage that flies and lands today.
The economic problem, rather than technical one, is there isn't enough traffic to space to justify a 1250 km cable in orbit. Nobody would build a bridge or airport to use once a week, which is about how often we launch rockets. A skyhook is similar - expensive to build, but cheap to use once you have it. So you need lots of traffic to justify building it.
YaAbsolyutnoNikto t1_ixz09ih wrote
Whilst I follow what you’re saying, what about induced demand here?
No wonder we launch so few rockets - they are freaking expensive.
If we could bring the costs down, more initiatives would follow.
Not building it because there’s not enough demand is like not building train tracks and trains because “nobody uses them” (no shit, they don’t exist).
danielravennest t1_ixz0u5w wrote
Demand for transportation already existed before railroads. It was handled by horses and wagons on land, and sailing ships on the water.
What I am hoping is the SpaceX Starship will induce demand by lowering cost to orbit. Once the demand exists, people will look for ways to satisfy it even cheaper.
SIGMA920 t1_ixzzkkw wrote
> What I am hoping is the SpaceX Starship will induce demand by lowering cost to orbit. Once the demand exists, people will look for ways to satisfy it even cheaper.
Isn't it already doing that?
4onen t1_iy01vof wrote
The SpaceX Falcon 9 and Falcon Heavy are. The SpaceX Starship has yet to successfully fly a stacked configuration.
SIGMA920 t1_iy02k9d wrote
Ah, even so costs are going down so that's hopeful.
[deleted] t1_iy02n00 wrote
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SBBurzmali t1_iy1sglg wrote
Not really, there's lots of talk about prices going down, "One tenth the price by 202X" and all that, but launch prices are still pretty much the same as they have been.
lookmeat t1_iy1t7lg wrote
Most rockets make it to LEO, no need for more. We'll probably still have Leo rockets and then use skyhooks to move into upper orbit where moving by rockets. The thing is we rarely need to do this right now. Maybe once Artemis puts a lunar station, and there's incentive to mine or something in the moon, it might make sense to bake a skyhook bridge from LEO into Lunar orbit. But that is going to take a while, we might see it in our lifetime, but not anytime soon.
ahfoo t1_ixysf3e wrote
There are dozens of alternatives. The skyhook is a cool concept but you also can have a "virtual" space elevator which is simply a beam of concentrated energy such as laser or microwave beam that a vehicle "climbs" by utilizing the energy in the beam. In this case the elevator is not a physical cable but a beam of energy.
This virtual space elevator concept happens to be a perfect fit for beamed energy from geosynchronous orbit which, in turn, would be much easier to put in place from a lunar base than to launch from the Earth. So you start with a lunar base, make a beamed energy station in GEO from orbiting slabs of lunar bedrock and then you have your virtual space elevator at the same time.
There are other approaches as well and they can all be mixed together. It's beyond doubt that going into orbit will be as common as crossing the ocean in a jetliner today. It will be something that ordinary people will do on vacation just as they might fly from the US to Europe today. When you think about it, crossing an ocean is an astounding thing to do but it's no big deal and going into orbit or the moon and beyond will be the same in time. Like everybody else, I wish that time was a little bit closer than it seems to be though.
arcosapphire t1_ixz37yi wrote
Can you explain the propulsion involved in the virtual elevator?
Getting energy is all well and good, but that doesn't let you apply force. The only non-propulsive method we have for space travel is the light sail, but the force involved is way too small for getting to orbit, so it can't be that.
There are two unconventional ways we have to apply non-chemical energy sources to propulsion: nuclear engines and ion thrusters. Nuclear engines are right out because they don't involve an external energy source. So that leaves us with ion thrusters, which still need propellant (often something like xenon). They can use external power for the energy to accelerate the propellant, but their thrust levels are also extremely low (too low for getting to orbit) and they still need propellant.
So...what alternative mechanism are you proposing? Since no existing method will work for this.
Exsanguinatus t1_ixzmyms wrote
There's actually a laser lift mechanism I've seen employed by small scale test craft. It involves firing a laser at the reflective bottom of a specially shaped craft. I believe it actually ignited the air under it causing propulsion, but it's been a long time since I saw it.
The proof of concept actually worked but the power increase needed for anything at scale was quite high. Also, the laser was not cohesive enough after atmospheric scattering to provide lift to a significant height during the PoC phase.
I'm not 100% sure if this is what the previous post is referring to, and it's possible that the technology has advanced since I first heard of it which was at least a decade back.
a-priori t1_ixzhulv wrote
Another one are plasma jets, which use microwaves to turn compressed gasses into plasma and extract thrust from that. These can be air breathing in the atmosphere and use stored gasses in vacuum.
There’s a prototype microwave plasma jet that’s proposed as an alternative for airplanes because it has similar power density (factoring in battery weight) to turbojets.
https://aip.scitation.org/doi/10.1063/5.0005814
If you could power these by beamed power, and switch from air breathing to stored gasses when in a vacuum, then it could be a viable lifting engine.
quettil t1_iy13t8q wrote
> Can you explain the propulsion involved in the virtual elevator?
Fire up particles. Particles bounce of payload. Newton's third law of motion means the payload goes up. It's called a space fountain.
arcosapphire t1_iy144mt wrote
Except they were saying the beam came from above (lunar or GEO).
bannacct56 t1_ixz2wrq wrote
The problem with carbon fiber is not the strength, it's strong enough but we do not yet know how to braid glue, stick these pieces together so they do not unravel. A
4onen t1_iy02jyw wrote
Partially true. If we could manufacture 100km single-crystal graphene (e.g. carbon fiber but sheets) then that would be sufficiently strong, and to prevent unravelling you could literally use something as weak and heavy as scotch tape to hold different ribbons of the graphene together. More ribbons, more tape, bigger and stronger cable.
The problem is the single-crystal manufacturing, which we can't do. Without it, we need a high-tensile-strength glue to hold the strands we can manufacture together. No such glue exists, especially not one that could connect via polar and/or van-der-walls bonds to the graphene.
Ergo, no space elevator, yet.
dagbiker t1_ixzc0nh wrote
It also wouldn't be a total disaster if it broke. If a tension wire breaks at the speeds and velocities it would need to travel half the wire would hit the earth with enough energy to be as powerful as a bomb.
Look at videos of people trying to move their cars using rope that snaps. It's not good. And that's assuming the counterweight doesn't fall back to earth.
If the sky hook fails it will wodnt be good. But at least it won't devistate as much of the world.
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De-Hond t1_iy0u41r wrote
>genetically engineering goats to produce spider silk?
What? And also how many tonnes of this spidermilk would he need? How many goats would he need?
Gingerbread-Cake t1_iy1bazn wrote
It was a while back; https://phys.org/news/2010-05-scientists-goats-spider-silk.html
But apparently still going; https://backyardgoats.iamcountryside.com/kids-corner/the-spectacular-spider-goats/
It’s apparently strong enough to build a space elevator out of. Now for the power supply issue…..
DutchieTalking t1_iy1uo6o wrote
I have no doubt that most people think of a space elevator as "so sci-fi it's only possible in movies or maybe thousands of years into the future". At which point it might not be as sci-fi as they think.
deltib t1_iy28old wrote
Don't we already have animals that produce spider silk? What's so special about goat spider silk?
Gingerbread-Cake t1_iy2ftcq wrote
Probably because goats can make more of it, stands to reason. That’s all I’ve got. I wasn’t one of the investors.
mocha-only t1_ixy5fay wrote
This reads like an essay from a grade 11 student who procrastinated.
PhaedrusC t1_ixy6xlg wrote
I don't think it is quite that bad, but I will agree that it is a bit light-weight and rather lean on engineering data.
pickleer t1_ixy9obx wrote
PopSci and PopMech have always been just that one step away from "Scientists hate this one trick that will shock the world" clickbait sensationalism. I had to take them off my regular website perusal list long ago.
sector3011 t1_ixyarnx wrote
Popular Mechanics reads like propaganda nowadays. Many articles heaping praise on the military.
MonoMcFlury t1_ixyg7ii wrote
Do you have any alternative recommendations?
pickleer t1_ixzaguy wrote
MonoMcFlury t1_iy464oq wrote
Thx. There's so much to check out!
pickleer t1_iy4l9v5 wrote
Way back in the day, google had a homepage you could set up for yourself. You could fill it with feeds and links and apps. Cell phones wound up looking like what you could do on this thing. They killed it, so I migrated all my links to an online spreadsheet. They're easy to set up and a wayyy easier way to keep and sort all your bookmarks and daily destinations. FWTW
WexfordHo t1_ixzaodr wrote
It’s what Scientific American used to be, before SciAm turned into another popsci dung heap.
MonoMcFlury t1_iy46bcu wrote
Ty. Gonna look into it.
ahfoo t1_ixyryew wrote
You can go straight to the source and read academic journals directly. It's great for your vocabulary and you get a sense of what is really going on. While many journals are paywalled, there are plenty with open access policies:
https://en.wikipedia.org/wiki/List_of_open-access_journals
Here is another collection:
Directory of Open Access Journals sorted by Science topics in English only
And yes, in many cases they are illustrated.
MonoMcFlury t1_iy468wt wrote
Good advice. Will have some reading to do! Thanks!
rdizzy1223 t1_ixz6dy7 wrote
You can just use something like sci-hub.
[deleted] t1_ixyus5t wrote
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Chalky_Cupcake t1_ixy7f0w wrote
>My wife and I crossed paths with Colin again in 2014. “How is that space elevator going?” he asked.
(7 years after first meeting Colin and discussing space elevators)
Colin: How is that cable material coming along?
Me: I’ve told you, that’s not my thing.
....
"Look bro i told you 7 years ago the cable part isn't my thing can you get off it already? jeez"
Tigger3-groton t1_ixyugvu wrote
The discussion seems designed to be read by a general, non-technical audience.
Timebomb_42 t1_ixybj1e wrote
"We are still at least 10 years away from a material solution"
Aka: With current technology we couldn't make it even given infinite money and resources. Come back when graphene gets out of the lab.
Still pretty sci-fi, only maybe possible near term on a lower gravity body, like on the moon. But even that is still very far out from becoming economically and practically feasible instead of just technically possible.
wordswontcomeout t1_ixylfas wrote
Graphene is out of the lab and be used extensively by a lot of private companies in battery tech and coating industries.
MartianSands t1_ixyoda9 wrote
Yeah, but not for bulk materials like this. It was touted as a super-strong material when it first hit the news, along with all it's other properties, but that's failed to materialise yet because we've had trouble making anything larger than flakes of it.
SpecificAstronaut69 t1_ixz1apo wrote
Yeah, I've got a earbuds with graphene-coated drivers.
The graphene performs the important task of them being able to say, hey, there's graphene in them in the marketing material.
danielravennest t1_ixyrabi wrote
Right. Atomically perfect carbon fiber would be extremely strong, but no manufactured product is like that. Even if it were perfect in the factory, handling and exposure to the space environment would damage it.
Twister_Robotics t1_iy03i2b wrote
No. With infinite money you could make it with the reinforced concrete. IIRC they did the numbers for that in the original paper on a space elevator. It's just completely impractical.
We could build one with current technology, just not cheaply enough to make it a reasonable investment.
fitzroy95 t1_ixy5muh wrote
Space elevators are largely a matter of engineering nowadays.
Yes, the materials aren't there yet, but they are getting closer every year.
Climbers are largely solved, basic design is largely solved, materials for the cable is the sole remaining barrier. And thats a not insignificant barrier atm, but its getting closer every year
TheImmortalLS t1_ixy6xy9 wrote
If a material strong enough to hold existed, we would have other tech instead. Such strong materials can improve compression ratios, improve engine efficiency via less moving weight, tank warfare would be dramatically different, etc.
Space elevators are built along the premise there is a material strong enough to anchor; everything else in its design is trivial. We are probably 100+ years away from a material, maybe 30 if a world war breaks out soon
sector3011 t1_ixy7cmq wrote
It still doesn't solve the problem of elevators getting hit by debris be it space rock or junk. There is no way to avoid this since the elevator is stationary.
dgriffith t1_ixyh54v wrote
They can be stationary but flexy.
If you can build a cable for a 40Mm long space elevator, then bending said cable sufficiently to avoid space debris by a few kilometres should also be doable.
You'd end up with waves travelling up and down the cable as it oscillates due to natural resonance anyway, you could probably augment or dampen that resonance as needed to ensure the cable avoids the big stuff along its entire length. These waves would be basically unnoticeable to cars riding the cable due to the sheer scale of things.
NinjaFenrir77 t1_ixyagh5 wrote
That’s a problem, but not one that will prevent space elevators from being built/used. The chances of this happening are relatively small, and the damage being much less impactful than the impact of having an operational space elevator.
[deleted] t1_ixyanti wrote
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TomSwirly t1_ixyg485 wrote
> The chances of this happening are relatively small,
Can we see the math?
> and the damage being much less impactful than the impact of having an operational space elevator.
Having a 35,000km structure collapse onto the Earth sounds pretty darn "impactful".
NinjaFenrir77 t1_ixyib4o wrote
There’s not a lot of math to show until we start talking specifics of the elevator and know the materials we are working with. In general, space is pretty empty.
Are you taking about the orbiting station? Because that won’t crash into Earth, it will fly away (slowly) because it is orbiting faster than it should to have a stable orbit in order to balance out the elevator cable. A few thrusters can help it stay in a stable orbit if the cable breaks.
The cable itself isn’t a huge threat. It could potentially kill some people if it landed on them, but the scenario of it whipping into the Earth at supersonic speeds isn’t going to happen due to wind resistance and basic safety precautions.
Harabeck t1_ixz6vua wrote
> Having a 35,000km structure collapse onto the Earth sounds pretty darn "impactful".
I might damage your roof, and it'd be a huge pain in the ass, but it's not like it'd be a tower that crushes everything beneath it.
TheImmortalLS t1_ixz9z4v wrote
It’s the same probability as ISS getting hit, +/- a bit since the iss can go up and down. Maybe a space elevator can dodge a bit too.
drysart t1_iy1p5nu wrote
Of all the practical problems facing a space elevator, dealing with debris is by far the easiest of them.
You don't run one cable from the ground up to orbit; you run several of them parallel to each other, spaced far enough apart from each other that no piece of debris could sever more than a certain amount of them at once. And at regular intervals down the cables, they'd be linked to each other such that if any subset of cables gets severed, the remaining cables would continue to hold the entire structure upright.
How many cables you'd need and how far apart they'd need to be would need to decided upon by dedicated research into the nature of the debris problem -- how much debris, how big it can be, etc. And then you just engineer in redundancy for the unavoidable failures to reduce their impact into being a bothersome maintenance task to repair/replace severed cables rather than a complete catastrophic disaster collapse.
jherico t1_ixy6u3z wrote
> Yes, the materials aren't there yet, but they are getting closer every year.
The Moon is getting further away every year too but I'm not going to invest in any company whose business plan involves solving the "missing moon" problem.
TomSwirly t1_ixyesgy wrote
> Space elevators are largely a matter of engineering nowadays.
We are talking about a structure that is over 35,000km tall.
The tallest structure to date is less than 1km tall.
In the last 200 years, the tallest structure height has increased by less than 3% per year, on average, so we would expect to be able to build a 35,000km structure in about 400 years.
EDIT: I was wrong - the center of gravity of the structure has to be 35,000km tall. That means that the structure has to be higher than that.
IvorTheEngine t1_ixyl204 wrote
That's a false equivalence though, as towers are compressive structures (that buckle before the material fails), while a space elevator could be in tension. A 1km tower is hard, but we regularly hang cables 1km down to the seabed, or for suspension bridges.
danielravennest t1_ixyspk5 wrote
There is a figure of merit for materials, which is the breaking strength divided by the weight per meter. This gives the maximum length/height at which it fails under its own weight.
Best available carbon fiber is 385 km scale height. But nobody engineers a structure at the failing point. With a reasonable 2.4 factor of safety, you get a 160 km vertical cable as the maximum dangle.
Towers need epoxy to stabilize the fibers in compression, so the maximum erection height is less than that.
IvorTheEngine t1_iy0wqzt wrote
The next logical step in most discussions about space elevators is that you can taper them.
However, you're right, it's still not practical with even the best current materials, even if it's hair-thin at the ground, it would need to be impossibly large at the orbital end.
danielravennest t1_iy3gpkl wrote
This is why I mention the Skyhook elsewhere in these comments. It tapers from the center outwards rather than top to bottom. Also the stress ramps from center to tip linearly. So compared to a stationary vertical cable the total stress is 1/4 as much.
For example, a 587 km radius (twice that in total length) skyhook moving 2400 m/s at the tip at 1 g acceleration sees 294 g-km of total stress. A safe stress I showed above is 160 g-km, so the cable needs to taper by 6.27x in area from center to tip. This is fairly reasonable.
To avoid atmospheric drag, you place the tip when vertical at 200 km, and thus the center at 787 km. Orbit velocity is 7464 m/s at that height. The tip moves 2400 m/s counter to orbit at the low point, or 5064 m/s. The equator moves 465 m/s, so the tip moves 4599 m/s relative to the ground. That's the speed a rocket needs to match velocity. That can easily be done with a single stage.
IvorTheEngine t1_iy3jal4 wrote
I love the idea of a skyhook - they seemed like an idea that could only work on paper, until Space-X started landing boosters on barges.
I can see how you could visit it, then it drops you off when you go home, but if you use it to launch things into orbit, doesn't it lose energy?
I've seen proposals where it flings things to the moon or mars, and recovers energy by catching incoming mining products - but could you use it just to put things in orbit?
danielravennest t1_iy3l1yy wrote
If traffic to a Skyhook is "unbalanced" (more mass going in one direction than the other) the orbit will change. You can make it up over time with electric propulsion. Since electric propulsion is at least ten time more efficient than rocket fuel, you still come out ahead.
In Earth orbit you can potentially react against the magnetic field by running a current through the ionosphere. That uses almost no fuels, just a little gas to make plasma contact.
LiliNotACult t1_ixya63p wrote
I wish that I lived in the same make believe place where people like this live. Apparently they don't have terrorists nor suicidal mad men. Also, good luck if it ever actually comes down.
Kalibos t1_ixydk67 wrote
There's a great sequence in the show Foundation showing a terrorist attack on a space elevator, incidentally.
Harabeck t1_ixz7haq wrote
It should be noted that the space elevator in Foundation is completely ridiculous. The cable structure would not need to be that utterly massive. A real elevator would use a cable or ribbon that would slow enough as it hit the atmosphere to be a nuisance that might kill a person if it hit them directly, but it wouldn't be leveling swathes if city.
LiliNotACult t1_iy353h6 wrote
I don't know man a few thousand tons in free fall can do some nifty things.
NinjaFenrir77 t1_ixyaqmv wrote
“The biggest danger of space elevators is the risk of homicidal insanity from sharing the trip with other for hours while listening to elevator music.” -Isaac Arthur
Lord_Parbr t1_ixy8dqi wrote
The idea of something tethered to Earth and extending out into space, especially if it’s tethered on that end to something in orbit triggers my anxiety, and it doesn’t even exist yet
grat_is_not_nice t1_ixy9zl1 wrote
It is actually tethered to a counterweight that is beyond geosynchronous orbit. The center of mass of the entire elevator system is at about geosynchronous orbit level.
In Arthur C Clarke's The Fountains Of Paradise, a space construction engineer dies after stepping off the counterweight, because it is not in orbit. If you step off something in orbit, you stay in the same orbit and rescue is trivial. If you are not in a stable orbit, you are going to have a completely different trajectory that will either end up hitting atmosphere or escaping (depending on the non-orbit you start from).
Lord_Parbr t1_ixybti1 wrote
It’s not so much the possibility of death that makes me anxious. It’s the idea of some massive structure that is extending from the Earth out into space. Just the very idea of a massive tube sticking out of the planet as it spins, however slowly. It’s completely irrational. I get the same feeling when I can hear 2 different songs playing at the same time
DGolden t1_ixyli1o wrote
> It’s not so much the possibility of death that makes me anxious.
I mean maybe it should? What happens when the damn thing breaks? whether by accident or terrorist attack, it could fail.
https://www.wired.com/story/what-happens-if-a-space-elevator-breaks/
> So, what's going on? Notice that the lower part of the cable just falls to Earth and probably causes some severe destruction. In this model, it wraps about a third of the way around the equator, even though its full length would almost make it all the way around the Earth, which has a circumference of 40,000 kilometers.
It may be that I actually qualified as an engineer a long time ago so was taught to be extremely pessimistic (or realistic, there are so many ways innocent-looking stuff can turn you into meaty chunks) about how damn near everything we make can suddenly fail and kill everyone, but I'm certainly very wary of the whole space elevator idea. It's cool, but also ... things go wrong. Would need a more detailed simulation than some back-of-the-envelope wired article, but still.
danielravennest t1_ixyryor wrote
I'm an actual space systems engineer. Any illustration you see of a single cable going up from Earth is wrong. Earth orbit is filled with artificial debris, and the rest of space has natural meteoroids. You see those as meteors at night as they hit the atmosphere and burn up.
So any large space structure will get hit by stuff. In fact, both the Space Shuttle and Space Station have taken hits, fortunately not a big one.
But a 60,000 km space elevator will have a lot of exposed area to take hits. At orbit speeds, everything turns to plasma and makes a crater. A big enough crater cuts the cable.
The only way to design something like this that lasts is to have many cable strands, and space out the strands so they can't all be cut at the same time. You can build it in segments with load sharing. Then impact damage (which WILL happen) means replacing one broken segment of one strand, which is a maintenance task.
Twister_Robotics t1_iy04ctm wrote
This is the way.
Not a single cable, more likely a truss like structure oriented vertically, with the load carrying members at the corners tied together diagonally to share the load in case of failure.
IvorTheEngine t1_ixyif7m wrote
In Red Mars a space elevator on Mars is sabotaged, and it is long enough to wrap right around the planet when it falls...
ScootysDad t1_ixyedl7 wrote
I don't see any new development in material science that can produce a 36,000km cable that an withstand the enormous tension, at least from the popsci environment. Any material science physicists here who can shed some light into this subject matter?
Gmn8piTmn t1_ixyptv2 wrote
So just that one tiny thing. Ergo not that sci-fi.
The article in a nutshell
unocoder1 t1_ixydvfn wrote
>To build it, we need a material whose specific strength is about 50 times higher than steel.
Ah, so it still has the same issues as it had 20 years ago. Ok then.
Gmn8piTmn t1_ixyq20i wrote
Yes but 20 years ago it was 20 years away so the breakthrough in material science should be riiiiight around the corner.
ObjectiveObserver420 t1_ixyiu1i wrote
Well that was the most pointless article I've read today
Twister_Robotics t1_iy04jpv wrote
You read the article?
Sir, this is a Reddit.
PM_Me_The_Surprise t1_ixykbvr wrote
Step 1: Produce 200 miles of a material that has the tensile strength to handle the load of 60 miles of weight and can also handle the wildly fluctuating temperature of space.
Step 2: Get it up there and in synchronous orbit.
Step 3: Unroll it
Step 4: Attach it to earth?
Yeah, this is really starting to sound like sci-fi to me. Especially that pesky step 1.
Gmn8piTmn t1_ixyqcit wrote
200 miles? No. At 200 miles you need to orbit at 25mach. Try 35.000 km
[deleted] t1_ixyw512 wrote
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PM_Me_The_Surprise t1_ixzem2q wrote
I was thinking this was more to do with getting things to the ISS or other low orbit needs, but I get what you're saying. That's a long fucking cable.
Gmn8piTmn t1_ixzh2dx wrote
It is but you can’t anchor one end of the cable at 250 miles because it will have to be moving compared to the ground at 28.000km/h (17.000+ mph) which means that you’d have a cable whipping around the earth at that speed. I mean the destruction would be monumental haha.
What you do is you anchor the cable at a geosynchronous orbit so it will be still compared to the earths surface at 35.000km away.
That’s a damn long cable lol.
axionic t1_ixyu4gu wrote
It would have to be a thing where it's about ISS height and you'd need a space plane traveling at Mach 15 to catch up with the ladder.
threehofive t1_ixyokrv wrote
Not even reading this because it is very far away. We might have the right carbon configuration for this and can even produce it in small amounts, but not even close to the scale we would need for an elevator.
danielravennest t1_ixyp47k wrote
What good is an article you can't read?
[deleted] t1_ixyap15 wrote
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unocoder1 t1_ixye6bj wrote
>This is still a lot of mass, because the cable is expected to be hundreds of tonnes.
Erm... maybe try billions of tonnes.
Gmn8piTmn t1_ixyq9rw wrote
That’s the whole point it won’t be billions of tons. Through magic advanced material technology it will be light.
unocoder1 t1_ixyrn6j wrote
Yeah, I just don't think that's realistic. If the cable is 100,000 km long and has a cross section of 1 square meter, it would weigh 122 million kg... if it were made of air. It would be almost a thousand times heavier if it was made of... water.
For 100,000 km cable to weigh "hundreds of tonnes", 1000 km should weigh tonnes and 1 km should weigh a few kilograms. I just cannot believe that will ever happen.
Gmn8piTmn t1_ixzixjj wrote
Yes that’s why I had the “magic” crossed. Because it’s completely unfeasible. Even if we could make a one continuous strand of carbon nanotube cable that would have to be absolutely perfect in all its length. And when I say perfect I mean to the atomic level. A single misplaced atom cuts the tensile strength at less than half.
And that’s for a 35.000km single walled continuous carbon nanotube.
The longest we’ve made was 55cm.
mtbaird5687 t1_ixyop0j wrote
I like how it's just a given that a space elevator is super safe and not risky...
QueenOfQuok t1_ixyqbfw wrote
How exactly are you supposed to get something away from Earth's atmosphere without accelerating it to Escape Velocity?
DBDude t1_ixzo7rn wrote
Let's say you want to jump to a ledge twenty feet up. It requires a lot of power to accelerate enough to overcome gravity to get that high, so much that nobody can do it.
Or you can just walk up the steps much more slowly. In the end your potential energy is still higher, and you are going marginally faster around the Earth due to your higher elevation.
axionic t1_ixytok7 wrote
Accelerate to orbital velocity, which requires half as much kinetic energy
Harabeck t1_ixz7zlt wrote
You do accelerate to orbital velocity using a space elevator, you just do it over ~35,000 miles and dozens of hours.
Martholomeow t1_ixyrngy wrote
I’m sure he’s a much better engineer than he is a writer
myne t1_ixywh7p wrote
Here's something I imagine: we build a steel belt around the planet to attach "satellites" and solar panels to, space elevators in central Africa, sth America, and Indonesia.
The only thing I'm unsure of is whether it is possible to build it "flat" on the ground and expand it outward by adding new segments until it reaches space, or if it must be built up there in the first place. I suspect it can't be built down here because it'd have to be the strongest self supporting structure ever built, and it would have to be held in the air, paradoxically by wires holding it down like bike spokes. Perhaps the smart way to build it is with spools of wow. Just feed the spool until it laps the planet, catch the end, and then keep adding wires until it turns into a rope.
LEO ~2000km. Earth radius ~6000km. 2pi8000=50,000km of wire for one lap. A decent size near solid rope would need a hell of a lot more than that.
But at some point, something like that is inevitable in my view.
evasiveswine t1_ixyxypm wrote
What happens if it falls down?
danielravennest t1_ixz1kcx wrote
Harabeck t1_ixz862r wrote
Kinda. It should be noted that the space elevator in Foundation is completely ridiculous. The cable structure would not need to be that utterly massive. A real elevator would use a cable or ribbon that would slow enough as it hit the atmosphere to be a nuisance that might kill a person if it hit them directly, but it wouldn't be leveling swathes if city.
Nice_Chest4335 t1_ixyz263 wrote
They talk about the fuel it takes for a rocket launch: what about the fuel or energy required for the vehicle or elevator to climb the massive distance till weightlessness?
danielravennest t1_ixz1sit wrote
In principle climbing the elevator takes the same energy as putting a payload in orbit with a rocket (33 MJ/kg). But the payload is only 2% of a rocket's weight. You eliminate the structure and fuel of the rocket stages below the payload.
DBDude t1_ixzolna wrote
Aside from what was mentioned, a big problem with rockets is gravity loss. They don't just have to accelerate to get to the speed they want, they also have to accelerate an extra 9.8 m/s2 to overcome gravity every second they're in the air. Think about it, just for a rocket to hover like a Falcon 9 requires 9.8 m/s2 of acceleration. That's a lot of wasted fuel.
[deleted] t1_ixz3gcd wrote
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bixtuelista t1_ixz9ilr wrote
Wouldn't you need continual thrust at the top to counteract pull from any atmospheric wind loading?
khendron t1_ixze2zi wrote
As much as a love the idea of a space elevator, we are nowhere close to making this happen. Even if we had strong enough materials, the logistics of constructing something that is 37,000 km in length (longer, actually) is way beyond our current capabilities.
And even if we had one built, the cost to maintain it would be an economic no go. Add to that the difficulty of designing a vehicle that can climb a 37,000 km structure in a reasonable amount of time while sustaining a liveable environment. Not to mention the danger posed by space junk, and every single satellite orbiting below geosynchronous orbit.
In other words, even if a space elevator was theoretically within our means, the practical challenges would be out of this world (pun intended).
hoehater t1_iy08w16 wrote
Beyond current capabilities? That’s one of the most daft things I’ve read in this thread.
If the materials we needed existed in sufficient quantities building such a structure would be relatively easy. We have factories that pump out literally BILLIONS OF MILES of fiber, rope, wire, pipes, tubing, etc.. 24x7 every single day.
DBDude t1_ixzmkkg wrote
The engineering was always sound, it's only matter of finding materials strong enough.
littleMAS t1_iy01rtb wrote
Assume there is material strong enough, it would become an unimaginably tall lightning rod. The ground potential differences are enormous, and the winds would create static charges that would keep the elevator in a constant state of fluctuating charge. Of course, someone would want to use it for terrestrial power generation, maybe putting a gigantic solar array at the end and bringing down petajoules of electricity. Just think of the impossibilities.
Cloudboy9001 t1_iy05zgr wrote
To substantially reduce cable taper--if we reach a point where mass produced graphene powder (but not solid graphene structures) is economical--an extremely strong material like carbon fiber or UHMW might be impregnated with graphene powder for enhanced strength (and other attributes such as creep resistance). Another means to keep cable taper reasonable may be to attach hydrogen balloons (perhaps with a helium liner) along the sides of the cable (that are capable, via telescoping arms perhaps, to fully or partially detach to permit vehicle travel).
The cable length might also be supported in space by nuclear or electric spacecraft pulling on it (being fueled or electrified via elevator cable) to further reduce taper and/or permit more/heavier traffic.
riding_steamer t1_iy1dm4y wrote
A space elevator sounds cool but imagine the insane amount of resources, time, and labor that will be used to build it. We would probably go extinct.
DENelson83 t1_iy1wsbz wrote
Yeah, those will never be a thing either.
The_Doc55 t1_iy618bg wrote
There is no material with the tensile strength to be able to handle this.
It would just topple over anyway, wind isn’t forgiving, you can’t have a solid foundation halfway up the sky.
Every action has an equal and opposite reaction.
Objects in motion stay in motion until acted upon by an outside force.
Given the above two rules, the elevator would rip the structure into shreds. We default back to the tensile strength part again. There is no material capable of holding itself up that high, as well as withstanding the force moment exerted by a high speed elevator.
Maybe instead of reading from a site called ScientificAmerican, consult an engineer.
nc1264 t1_ixy6if1 wrote
Arthur C Clarke has a great story about it. He invented the satellite so he should know. Not sure about the title
Echolife t1_ixy8xdg wrote
The Fountains of Paradise
Specialist_Peach4294 t1_ixy87ww wrote
My man Art was on point.
KenRen_97 t1_ixy9wl5 wrote
space elevators are less Sci fi then you think
Unfortunately They are a one way trip
[deleted] t1_ixyftdh wrote
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psValki t1_ixyvjpv wrote
Launch Loops and Orbital Rings can achieve the same thing using exotic materials such as "Steel" and "Aluminium".
Somesloguy t1_iy0bzn0 wrote
The energy required to set up the space elevator is more than it saves in propulsion later on.
QuestionableAI t1_ixy6fbf wrote
Stupid to the max for folks that get math.
BarfingOnYourFace t1_ixy7he8 wrote
Guy who wrote article: aerospace engineer and physics professor.
Guy who thinks it’s stupid to the max for people who get math: some random redditor
kopeezie t1_ixyh0fq wrote
We did the math with our professors at UPenn as a case study in mechanical engineering / material sciences. I can concur “stupid to the max”
TomSwirly t1_ixyf9dr wrote
Your argument by authority isn't a good one.
Neither you nor the original article did the math, so I will.
The tallest structure of any type ever built is less than 1km tall.
But a space elevator would be 35,000km tall.
Historically, the height of the tallest structure has grown by less than 3% a year, on average, so we should expect a space elevator in about 400 years.
The idea that we are going to build in our lifetimes some structure that is over 35,000 times taller than any structure built by man and which requires building materials that don't even exist today(*) - this idea is completely unrealistic.
Given that we as a society are obsessed by unreachable goals like this, but seem completely uninterested in the much more modest and much more critical goal of not destroying our ecosystem and our climate almost entirely, I doubt this will ever be accomplished.
You call me when we have built a structure that is even 10 km tall and then we can talk again.
(* - spider silk exists, but it is not a human building material, and not one building has been built with it.)
AzzaClazza t1_ixyk7sy wrote
I'd argue that's an invalid comparison. We don't build it up all the way, it's more like it's lowered to earth from orbit. We already lower things more than 10km into the ocean. Once the initial connection is made, it's a generation of building it up enough to support traffic. I don't think we'll ever see even the beginning of it but one day maybe. If we really expand into space it'll make economic sense.
Gmn8piTmn t1_ixyq5p3 wrote
So 34.990km to go. EzPz
friendlyfredditor t1_ixywdwg wrote
Here man...you don't have to do the math based on faulty assumptions.
[deleted] t1_ixyetot wrote
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blits202 t1_ixyc914 wrote
This is why we need to build a ladder to heaven. We cant be the last country in this race.
thecaptcaveman t1_ixyellr wrote
#secretspaceprogram
we don't need a space elevator. There are much better things to fly with.
Illustrious-Spare-30 t1_ixybp92 wrote
JESUS FUCKING CHRIST just build the goddamn thing already!
Gingerbread-Cake t1_ixyaoxn wrote
Until they build one, it is exactly as Sci-fi as I think. Hey whatever happened to that guy who was genetically engineering goats to produce spider silk? He mentioned using that to build a space elevator.