I've been debating whether or not I should use a ground-based spaceport for my sci-fi story or something much more cheaper as space elevator. Because my story involves large freighter spacecraft that carries tons of cargo and human passengers in cryo-stasis, it would be unrealistic for a ship like that to try and land on a celestial object. If it were to attempt to land on Earth, it would burn and break into pieces. So I thought of having a space elevator instead, but in the counterweight (where the opposite end is) of the elevator, I thought the space dock should be there. That's where the ships dock and unloads the cargo and gets passengers back to Earth. Would this be ideal or would be a ground-based spaceport be better. When we're talking big ships, I honestly believe a space elevator with a dock would be the best choice but I may be wrong.
There is nothing wrong with the space elevator concept for an SF story where you can assume that the necessary materials are available. Making the orbital end an actual docking station might be questionable if you are going to propose very large spaceships. If there was a collision, or a drag on the station due to an incomplete undocking, it might cause the entire structure to destabilise or the elevator cable to break. The most common alternative is what sailing ships have done through the ages when too large to physically dock, which is to employ smaller ships or boats to ferry cargo and passengers back and forth.
I like the space elevator space port, myself. It's a realistic concept you can do a lot with. But if the elevator concept is too tricky, a stationary orbiting spaceport where small shuttles go back and forth to the planet's surface and the larger vessels dock at the orbiter will also work. (Like @Bryan Romer also suggests.)
If you dock the spacecraft at the end of the elevator where the counterweight is located it might put the elevator out of balance. I suppose that would depend on the size of the spacecraft. I'm not sure how the numbers would work out. It's the point on the elevator in geosynchronous orbit, below the counterweight end, that is the neutral spot and the logical place for a docking site. There objects experience zero Gs so an arbitrary mass could be attached to the elevator without affecting anything. At the counterweight end there is a centrifugal force pointed away from the Earth. Any massive object attached to that end would tend to raise the elevator into space. Of course the elevator itself would be quite massive so I'm not sure a spacecraft, even a big one, would make much difference.
@GingerCoffee, @Peter C I've taken both of your ideas and mashed them into one. Space Elevator with space dock at geosynchronous orbit (isn't geostationary orbit the same thing?) Smaller ships ferry passengers and cargo to large freighters that are docked closby but not necessarily next to the dock itself. Freighters are also refueled by smaller spacecraft.
You're right "geostationary" is more correct. That's a geosynchronous orbit above the equator so that the object in orbit is always above the same point on the Earth. I think what you're proposing sounds good to me. I did some reading about space elevators because I'm thinking about using one in my next story. The main problem with them in reality, it seems to me, is that they have to be movable. If an elevator is stationary objects in lower orbits will eventually collide with the elevator at high speed causing destruction. Thus it is necessary to move the elevator out of the way of oncoming satellites and other debris. The proposals I've seen entail anchoring the bottom of the elevator to a floating platform at sea and then using rockets to move the entire elevator when necessary. It sounds pretty difficult.
Getting back to the counter weight part of the idea, I was at first confused by the terminology when I read the plans for these space elevators. To me, the counter weight is the thing that goes up when the elevator goes down and down when the elevator goes up. But space elevators need a different counterweight, one that counters the weight of the cables in addition to the anchor station that holds the cables in their geostationary orbit. http://www.weirdwarp.com/2009/02/lets-get-into-space/space-elevator2/ http://science.howstuffworks.com/space-elevator2.htm It made me think what is really needed are two counter weights, one that counters the weight of the cables, and one that counters the weight of the elevator car. So I picture two spaceports that are actually both elevator cars. One goes up as the other comes down. Ships dock, unload cargo then undock before the spaceports change positions.
The main problem with the space elevator is the cable. Geostationary orbit is 22,236 miles above sea level and a cable of that length would break under it's own weight. Spider-silk or some other advanced technology would be needed to make a cable that had an adequate strength to weight ratio. The space station at the top of the cable would need to be higher than geostationary orbit to act as a counter-weight holding the cable up. At 100 miles an hour, the lift would take about 10 days to make the trip. http://en.wikipedia.org/wiki/Geostationary_orbit
I've heard it said that our real life material science may provide cables of sufficient strength in the not-too-distant future. However, I don't have a reference for that. A space elevator on Mars would be easier because the rotation rate is similar to Earth and yet the gravitational field is weaker (thus geostationary orbit is lower and not as much cable is needed). The trip up the elevator would take less time too. However, you'd still have to worry about the elevator being hit by debris.
And what would the electromagnet be attached to? The discovery of carbon nanotubes was what started the space elevator speculating. However, Why we'll probably never build a space elevator But hey, it's sci-fi. Just invent some unobtainium.
