Podcasters: Paul Hill, Ralph Wilkins and Dr. Jenifer “Dr. Dust” Millard host.
Title : Awesome Astronomy: Awesome Astronomy – How Realistic is a Space Elevator?
Organization: Awesome Astronomy
Link : www.awesomeastronomy.com;
Description: An elevator into space – the science fiction future!
No more explosive rockets – ride an elevator into orbit and open up the solar system for human exploration. But is that realistic or are there just as many risks with the space elevator?
Damien Phillips, John Wildridge and Dustin Ruoff produce.
Bio: Awesome Astronomy explores the frontiers of science, space and our evolving understanding of the universe.
Join Paul, Ralph, & Jeni for informative and fun astronomy programmes dedicated to space and astronomy news and monthly podcast extras covering hot topics and special interviews in the world of science and astronomy.
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Transcript:
It’s the 365 Days of Astronomy podcast, coming in three, two, one… In this episode we’re going to talk about a topic that one of our viewers, Jonathan Zeller, asked us about in the comments of a recent show. So if you want to tell us your thoughts about this topic or suggest topics of your own, drop them in the comments section below and we’ll make a show about any of the ones we like.
So on to Jonathan’s topic, which is space elevators. What are they? Would they work?
And how likely are they? Stick around because as it turns out, for once, we actually know what we’re talking about in this topic. So here it is, the future, the ride into space that appears in the books of such science fiction luminaries as Robert Heinlein, Arthur C.
Clarke and Terry Pratchett. And they’ve appeared on our screens in Star Trek Voyager, the terrible 2019 Brad Pitt movie Ad Astra and the recent Apple TV series Foundation. Now Arthur C.
Clarke dreamt up satellites, personal computers and wireless communications, in short, the technological world we live in today. So are space elevators a good bet then? No, no, it’s really not.
Not in the next hundred years, if at all. But I’ll come on to that in a bit after we take a look at what space elevators entail. It’s a platform above the atmosphere with a cable stretched down to the Earth that a crawler can crawl up to get things into space without having to use dangerous and expensive rockets.
A bit like using a lift rather than the stairs, except that the platform in space needs to be quite a distance from Earth in order to remain directly over the bottom of the cable that’s attached to the Earth. This is known as geosynchronous orbit and it’s where certain remote sensing and communication satellites sit constantly over the same patch of Earth. Well, actually, in the case of a space elevator, it has to be in a more specific kind of orbit called a geostationary orbit, which is as far away as geosynchronous orbit, but lies on the plane of the equator.
The reason for this will become apparent in a minute when we look at disaster scenarios. But in order to get a platform to geosynchronous or geostationary orbit, it has to be placed, presumably by rockets, in space. Much higher than the International Space Station, a very achievable task.
But then it has to have a cable that drops down to a point on the equator where it can be tethered for a crawler to crawl up with people or cargo. But this space platform has to be 22,236 miles up. For reference, the tallest building in the world is half a mile high.
An airliner cruises around 6.5 miles. The International Space Station orbits 254 miles up in space. A space elevator platform would have to sit 87 times higher up in space, a tenth the weight of the moon.
And coming back to the reason why it has to be above the equator in geostationary orbit, if it were at a more loose or rakish geosynchronous angle, the cable would begin to slowly wrap around the earth, pulling the platform down. And more than 22,236 miles of high-strength cable that would cause global devastation on a scale that a recession, Brexit, a pandemic and a Russian invasion combined could only dream of. Now why did I say more than 22,236 miles of high-strength cable?
Well you don’t only need cable below the platform. That wouldn’t be stable. The crawler would pull the platform back towards earth, twisty-wrappy-hurty again.
So you need more cable going further out into space with a counterweight pulling the earth-to-platform cable taut through centrifugal forces. Now getting that much weight into space isn’t easy, especially when the space elevator isn’t built yet. So to simplify that, it’s been suggested we use just an asteroid that isn’t anywhere near where we need it to be.
Or if we wanted to build one on Mars, when one on earth’s a struggle enough, we could just use Phobos, one of Mars’s moons, as a counterweight. Idiots. Oh and I might have glossed over the strength of the cable a bit while I considered the other factors that are practically impossible for the next hundred years at least.
The cable would have to be more than 200 times stronger than steel, or be as wide as a football pitch if you were going to weave the full 22,236 miles from Kevlar. And if you say carbon nanotubes or graphene to me, you’d better be outside kicking distance. Nope.
New materials and material signs needed before we get this puppy. Oh and it needs to be tethered in the middle of the Pacific, the most inhospitable construction site on earth because any cable below the break point in the event of a snippety snap all comes down and everything above that drifts off into space. So you want the break to be very low down the cable and as far away from civilization as possible.
But let’s assume we’re a couple of hundred years in the future and you’ve got your platform launched into space and you’ve got your counterweight and you’ve got your 22,236 miles of cable tethered to the earth. Job done. When was the last time you drove 22,236 miles?
That’s New York to California and back four and a half times. And some wags will declare in an offhand way it might only take you a couple of days. Only if your crawler isn’t a crawler and it’s pulling its cargo up at the speed of an airliner.
Otherwise a more sedate but still unrealistic 100 miles an hour is still going to take over a week compared to seven hours for a rocket. Well we’re also possibly weeks away from the first test launch of SpaceX’s Starship and Musk is planning on that costing $50 per pound if you want to get to space. Even factoring in geostationary space rather than the piffling low earth orbit and a healthy margin for a megalomaniacal billionaire’s hubris when it comes to pricing even if that’s $500 or $5,000 per pound.
A big reusable spaceship that’s much quicker and you don’t need to get to the middle of the pacific before you can even begin your ascent starts sounding more reasonable and probably much cheaper. So disaster scenarios. Take your pick on this one.
Earthquakes, hurricanes, corrosion, erosion, sabotage, terrorism, sea vessel collision, natural degradation, mechanical failure, friction. Which do you want first? The cost of maintenance is going to be as high as the cost of building the thing and those costs go on forever.
So the cost of getting space isn’t likely to be any cheaper than conventional rockets. It could be far more expensive for the next few centuries at least. Then of course there is so much debris now in space from defunct satellites to bits of satellites that were blown up in military anti-satellite tests.
Ed White’s thermal glove that floated out of the hatch after the first ever American spacewalk in 1965. Sunita Williams’s camera that floated away in 2006 during a seven hour spacewalk. A spatula that Piers Sellers was using to test heat shield repairs on the shuttle.
All now travelling around the earth every 90 minutes in orbit at over 17,000 miles an hour. And if you say to me, well there are space litter pickers being invented now, again you’d better be out of distance. Debris from those satellite demolition tests means that spacecraft have to correct their courses on a regular basis to avoid getting hit by any number of those thousands of pieces of debris moving at hypersonic speeds.
Even the International Space Station has to manoeuvre out of the way from time to time because an impact from any of the pieces of debris in earth orbit larger than one centimetre could punch a catastrophic hole in it. And there are more than 900,000 of them to keep an eye on. On top of that there are thousands of large satellites observing earth, staring out into space, monitoring nuclear tests and companies like SpaceX, Amazon and OneWeb have plans for mega constellations of satellites that aim to put over 100,000 more satellites in earth orbit.
So it’s getting pretty damn congested up there. If satellites have to manoeuvre to dodge one another, a tether, motionless relative to those hypersonic washing machines, stands very little chance of not getting hit at some point. And damage to that cable brings us back to that twisty-wrappy-hurty scenario.
If the snap happens any more than a tenth the way up that cable, millions will die and multiple cities are going to be devastated as it snakes across continents. It’s such an incredible disaster scenario that I can’t even find a video to demonstrate this on this YouTube video. So will it happen eventually?
Well, possibly. Your guess is as good as ours. Material scientists will have to improve far beyond the current strength of modern wonder materials to make a cable that’s impervious to satellite collisions, corrosion, radiation and maintains its strength over its 22,000 mile length.
Currently the largest man-made objects in the world are the undersea communications cables that stretch from San Francisco to New Zealand and Japan. These are a marvel of engineering but they still don’t need the same incredible tensile strength. They don’t need to haul great weight and they don’t need to be guaranteed not to break or a few million people dying in the ensuing cataclysm.
It might surprise you to know that these important cables that network the globe get damaged all the time and are routinely repaired. And even they are only 5,000 miles long, a quarter of the length and a fraction of the strength a space elevator cable would need to be. So like teleporters and planet-destroying lasers, a space elevator’s a good science fiction staple but far beyond the technology for at least another hundred years, despite what some enterprising companies might say.
And who knows what technology we’ll invent in the next century that might make the space elevator look like a silly idea, just like the Star Trek communicator looked cool in the 60s but now seems far inferior to a modern mobile phone. We’ve found the Higgs boson, the particle that gives mass to objects, so could we soon find a way to manipulate gravity and make the ascent to space less dangerous and expensive? Maybe.
Who knows? We need to invent a car, not make a faster horse.
End of podcast:
365 Days of Astronomy
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