RSS
Home
All aboard the space elevator!
Print
Email
RSS
Subscribe
Companies like SpaceX and Ariane may be working toward practical, commercial solutions to human and robotic space travel. But some people are thinking further ahead. Way ahead:
The benefits of a fully realized elevator would make carrying people and goods into space cheaper, easier and safer than with rocket launches, proponents say, opening up a host of possibilities. Restaurants and hotels for space tourists. Wind turbines that provide energy by spinning 24 hours a day. A cheaper, easier and more environmentally friendly way to launch rockets.
The article credits legendary sci-fi writer Arthur C. Clarke with the concept. But pioneer Konstantin Tsiolkovsky had a most similar idea almost a century ago. The principle is simple: about 22,500 miles above the earth's equator is a spot called the geostationary point. Satellites in geostationary orbit take exactly one day to circle the earth. If they orbit in the same direction the earth rotates, they'll stay above the same spot. Many weather and communications satellites are in geosynch for this reason, seen in dynamic schematic to the left. 
So what if a really strong cable or other robust structure could be connected from the earth's surface to that distant point? With a little bit of a counter weight on the other side, such a device would literally connect the sky and ground. A sort of gondala to the heavens. Passengers or freight could just ride an elevator up to orbit instead of using the suite of exciting and expensive rockets.
In reality, it's not nearly that easy of course. For one thing, there's the huge weight of thousands of miles of whatever materiel is used to connect the two distant points. Then there's the tension required to keep the line taught. The two add up to a considerable force. There are no materials in existence right now that could take the strain. The closest is carbon-fiber nano-tube and engineers estimate it's too weak by a factor of 10 or so.
There's also some physical danger from this thing if its ever built. For starters, that's a lot of mass to have in near orbit or hanging, literally, by a thread, even if it's a very strong thread. The business end of the elevator is clocking along at almost 2 miles per second. 
Even while stationary, not in use, the whole contraption would be a hazard to aircraft and spacecraft where a collision with either one could be catastrophic (And would thus make an ideal target for terrorists or in the course of traditional warfare). When in use the forces roughly distribute themselves as shown in the illustration to the left. One whale of a resonance could be induced in that system, enough to make the dramatic Tacoma Bridge undulations and eventual collapse seem trivial. If the sag in the line pulls that cable and/or counter weight too far down or it gets out of whack, look out below!
It would be an interesting physics problem to determine under what circumstances various components would strike earth and what the kinetic energy transfer of the cable and counter weight might be if they did. But just looking at it and thinking of the velocities, altitudes and masses involved, it's a safe bet that if many, many tons of cable and counter weight are suddenly screaming in at orbital velocity, it might compare to an artificially created reenactment of the Cretaceous-Tertiary Impact that marked the demise of the dinosaurs.
It's worth noting that on certain moons and asteroids with relatively short rotations, i.e. days, this idea would work much better. For the dwarf planet Ceres, with a day of about nine hours and an escape velocity of only a few hundred meters per second -- and with little or no civilization to worry about below -- the stresses, strengths, and forces in play are all likewise greatly reduced to manageable levels even using technology available right now. Unfortunately, it wouldn't work well for our own moon; our familiar nightly companion is tidally locked. Its day is about one month long meaning its geosynchronous point is way, way far out, and there are other complications due to the earth-moon orbital geometry.
Nevertheless, it could work for earth, and there are a lot of benefits over conventional rockets, if the materials and safety issues can be worked out. That's still to be seen. But perhaps, one day, in the not too distant future, adults will ride to jobs into space just like they take a subway in a big city, while their young children are told a new twist on a favorite old story: Jack and the Beanstalk!
Related Articles:
Comments
