The nanotube ribbon not only would have to stretch at least 22,000 miles (35,406 kilometers), it would also have to support an elevator car that might weigh 7 metric tons, plus a 13-ton payload, he said.

Space trash is another problem, since objects that collide with the ribbon could damage it. One proposal, presented at this year's conference, is to collect and remove trash from space using .

Another challenge is tying the elevator to a platform in the ocean that can be moved so the elevator can avoid collisions in space. That raises questions about how such a structure might react to being moved. No one knows exactly how the ribbon might oscillate when shifted at the base.

Scientists are researching space elevators as a way to dramatically decrease the cost of sending people and objects into space. It costs US$10,000 per kilogram to send a load into space using Delta and Atlas rockets, Laubscher said. A space elevator could transport loads at a cost of $3,000 per kg initially, with the cost quickly dropping to $300 per kg, he said.

He estimates that a space elevator will cost $1.5 billion in research and development and $18 billion to actually build. Subsequent elevators would cost less, with the second running around $7 billion.