(The Silence of Ancient Light, continued)
Beyond the open door, intermittent lights flickered on after a moment to break the darkness, revealing an ovoid chamber a bit less than ten meters deep. Most of the chamber remained dark, and when most of the lights that hadn’t failed switched from their initial white to red, the chamber appeared darker still. Poles, spaced a few meters apart, extended from ceiling to floor. Set into the middle of the floor, a round window provided some extra illumination, sunlight reflected from the planet far below. Panels of controls and indicators lined the walls, many of them with circular gauges flashing maroon colors.
An alarm klaxon, accompanied by a red light flashing on and off in one-second intervals, sounded from deeper within the chamber, slightly offset from the alarm still sounding within the cab, creating an unsettling echo effect. More alarms sounded from further away, through open hatchways at either end of the chamber, deepening the insistent reverberation.
The hiss of moving air, pumped into the chamber from vents in the walls, underlay the alarm, though not competing with it for volume. That was the sound Anna heard when the door first opened, she realized, that and equalizing pressure between the cab and the station chamber. Nevertheless, it took a few moments more for her heart rate to settle back to a normal rhythm even after she realized they were not all about to be sucked out into space or suffocated in a vacuum.
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Chapter 10 begins!
Yes, we last left you with quite the cliffhanger. You thought they were all going to perish with silent screams into the vacuum of space, didn’t you? Well, probably you didn’t think that, because it would bring the story to quite the sudden end, and I’m sure it’s clear that we aren’t finished yet. There’s still time to get sucked out into space, though, but not quite yet.
You’ll note that the last scene ended with the explosive severing of the space elevator’s tether cable at the ground station. Since I posted that scene, of course, the new Apple TV+ show Foundation, based upon the seminal works by Isaac Asimov, premiered, and the pilot episode…
SPOILER ALERT! I’m about to discuss a very popular streaming show that has only recently aired, so if you have not yet watched it, and you plan to, I suggest you go and do so before continuing with this blog post!
The pilot episode also ends with the explosive severing of a space elevator tether cable, albeit at the top, near the orbiting space station level, not at the ground. I swear I had not seen this episode before writing my scene! Indeed, this particular dramatic event has been planned almost from the beginning of writing this story, a few years ago. And in any case, neither I nor Foundation can claim to be the first nor only fictional telling of a space elevator coming to such a dramatic demise.
In Foundation‘s episode, since the cut occurs near the top of the tether, at the geosynchronous orbit level, the tether falls back down to the planet (Trantor, in that case). We aren’t told how high up in orbit the station is, nor how large of a planet Trantor is (though we are told that it’s in fact a shell world, with many layers down in which people live, which is a fascinating concept I’ve seen explored in a few other places as well). However, we know from calculations that the station must be at or near geosynchronous height, and if Trantor has a density and mass anything like Earth’s, then that height is probably not too far off from the circumference of the planet.
In other words, as the tether falls, if it doesn’t burn up during atmospheric reentry, it will wrap itself completely around the planet, along the equator, causing massive damage as it does so. And, this is what we see happening, or at least what we are told happens.
Foundation got that right!
That’s not to say there aren’t other errors in the depiction. We don’t see evidence of a counterweight (with additional tether) extending beyond the station’s orbit, though to be clear I’m not sure it’s ruled out, either. Also, during the ride down the tether in the cab, we’re told the journey will take something like fourteen hours (I may have misremembered), which would mean it’s a very fast cab indeed. That’s not impossible, especially for a highly advanced civilization, of course, but a multi-day journey is likely more practical.
What else did they get right? The depiction of the planet from the orbiting station is spot on. Geosynchronous orbit is very high up, and from that altitude the planet is not going to loom close the way we see in images of Earth from the ISS. It will seem quite a bit smaller and farther away, though not as small and far as Earth seems in pictures taken during the Apollo missions to the Moon. As near as I can tell, it will look pretty much as Foundation depicts, so kudos to them for that, too!
Ok, enough blathering on about someone else’s story, for all it has that one similar element to my own. What is different here?
The tether from Kepler 62f is severed at the base, near ground level, not at the top. How will this change the outcome? In this case, the centrifugal force of the counterweight, which is a massive rock on its own tether about another 10,000 kilometers above the ring station, will exert an upward force on the entire tether, lifting it up out of the atmosphere, and at a minimum to a higher orbit, if not more. Needless to say, this is going to exert some significant shear forces upon the ring station itself.
Anna has already figured this out. She’s pretty sure the event will not be survivable. It’s time to evacuate, and quickly.
How quickly? Why doesn’t the break in the tether cause an immediate impact to the station?
The tether is under tension, and the break causes a shockwave of untensioning. That shock is going to travel its length, but it’s not instantaneous. In fact, much like the crack of a whip, the shockwave travels through the tether at the speed of sound, but more precisely, the speed of sound through the material of the tether. If the tether was made of steel, that would be about 5 kilometers per second (faster than through air), but the tether isn’t made of steel. The core is made of some sort of carbon nanotube, and surrounding that is a sheath of polycarbonate and composite materials, in efforts to provide lateral strength while maintaining low mass.
So how long before the shockwave hits the station? Anna makes a guess, but it’s only a guess. Our heroes have a small window of opportunity to escape, but they aren’t sure how small the window is, and furthermore, the means of escape appear to be very few. They don’t have any good options.
Read on, my friends, and find out what options they do have.