In order to make the idea of a space elevator work, some sort of "car" has to be designed. This
problem is much more difficult than it seems on the surface.
The picture above is of a "lifter prototype" built by Liftport Inc. It climbed a ribbon up the 290-foot
"Green" building at MIT. Although this effort should be commended, it is worth pointing out that
they failed to answer some of the fundamental issues with the climber.
The first issue is the power source for the climber. The Liftport prototype uses batteries to power
its ascent, which worked for a light load only going up 290 feet. However, with a several thousand
kilometer ascent, there is no known power source that is dense enough to power the climber all the way
up. One proposed answer is using ground-based lasers to focus on tuned solar panels on the climber.
This form of power transmission is far from perfected, and an ongoing source of research.
Some other issues that come into the design of such a lifter are its grappling method and any safety
devices that will be present. Holding onto a carbon nanotube tether will undoubtably be much
different than climbing that ribbon. However, these are engineering problems that are much closer to
being in our grasp.