(The Silence of Ancient Light, continued)
The island rapidly dwindled with distance below them, the sparkling sea stretching away to distant horizons in all directions, while the sun hung low to the west in a blaze of fiery orange and pale yellow. Directly overhead, the sky quickly took on a deep blue tone, set against the now familiar pale turquoise to north and darkening east. Other mountainous island chains dotted the sea in the distance, tiny, as if on a relief map.
Acceleration pushed at them all floorwards, but only gently, and only for a few minutes. Ca-Tren squawked in surprise and wobbled on her feet, Laxmi and Jaci both squatted slightly and reached to the low furniture for support, while Anna held onto the main control console. After the initial rush, they all found their feet, and in less than five minutes the acceleration eased and the cabin assumed a constant, smooth, and noiseless velocity as it climbed the interior of the cable.
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Last week I mentioned I had one more scene ready to go, and here it is. What’s more, the next scene is already written, too, so you may fully expect that one next week. Wow, three scenes to be published with only a week between them? What is the world coming to? More to the point, will I be able to keep it up? That, my friends, is a bigger question.
Last week we left our heroes having just started the alien space elevator on its upward journey, as Anna whispered to herself, “Next stop, orbit.” So just how long will this ride take?
Remember, the other end of the ride is the ring station, which is at geostationary orbit, 41,000 kilometers above the ground. That’s pretty high up there. By contrast, back here at Earth the International Space Station orbits a mere 400 km high, so we are talking an altitude a hundred times greater. Why so high? Because this is the altitude at which the angular velocity of the planet’s rotation matches the required velocity to maintain a constant state of free fall, or in other words, a stable orbit. Remember, the greater the altitude, the less velocity is required to maintain orbit. At 400 km, the ISS zips along at about 17,000 miles per hour in order to stay in orbit, which is pretty fast. At 41,000 km, the ring station orbits at closer to 6,700 mph (3,000 meters per second), still really fast, but quite a bit slower than the ISS. And, it has to move at this speed, because this is how fast the elevator cable is moving at that height, since it must remain stationary with respect to the ground.
So, the elevator cab, or more precisely, the climber, has a long way to go. How fast it can climb the cable is determined by a number of factors, not least of which is not crushing the passengers with acceleration. In fact, in order to keep the ride comfortable, after the initial acceleration, the climber will maintain a consistent velocity, so it won’t impart any additional g-forces on the passengers beyond what the planet’s gravity provides.
Gravity doesn’t just fade away in orbit, by the way, at least not until you get much farther from the planet. In low orbit, where the ISS flies, the astronauts on board are still subject to about 90% of the gravity we feel here on the surface. The difference is that they are forever falling, with the station itself, but they are falling fast enough that they keep missing the earth and instead curve around it, endlessly (subject to a slight atmospheric drag and inevitable entropy).
So our elevator passengers feel gravity, and while it will eventually become somewhat less strong as they ascend, they won’t really notice, at least not at first. Instead, the higher up they climb, the faster they, and the climber, and the cable, are moving laterally in order to maintain rotation with the planet. They won’t be in free fall until they reach their destination, at geostationary altitude, but they will gradually feel lighter on their fee right up until that moment.
Ok, back to the speed of the climber’s ascent. We’ve established that it shouldn’t go so fast as to cause discomfort to the passengers, but it also shouldn’t go too fast or it might impart undue stress on the cable itself. The faster the climber moves, the more lateral force the cable must impart upon it to keep it rotating around the planet, which will tend to precess the cable westwards due to coriolis forces. Too much force, and the cable could break, and that would be bad.
We also don’t want to go so slowly, however, that the journey becomes impractical for how long it takes. We need a happy medium. How about as fast as high speed commuter train, or perhaps just a tad over that? This seems to be a good compromise, and we arrive at about 300 kph. That’s pretty fast, too, or it would be for an object on the ground. At 300 kph, the climber will reach the same altitude as the ISS in just about an hour and a half. That seems pretty good!
But remember, we’re going a hundred times higher than the ISS.
This journey is going to take about five days.
And that, my friends, is why the climber is stocked with a bar.