You're working on several projects for NASA that use space tethers. How are these progressing?

Tethers have been a staple of science fiction technology for years, but you're working on them for real. What got you interested in them?

When I realized how powerful they were, despite their simplicity.

Tethers were neglected in the past because a single line or rope or cable presents a very large area to space debris -- it's literally bigger than a barn -- and is easily cut by space debris or meteorites. One 20-km long tether only lasted 3 days in space.

In 1992 I got a study contract from NASA to find a way to make a multi-line tether to replace the standard single-line tether. I felt that what was needed was to have an open tube -- like a net stocking on a showgirl -- where the lines were interconnected periodically, so that if a line was cut, other lines would take its place.

I knew, however, that if I pulled on the ends of the tube, it would collapse into a single line, which would be easily cut. I knew I was going to get the NASA contract, so I gave a lecture at the University of Washington to an aerospace engineering class about space tethers and told them that I was looking for computer help to simulate various ideas.

A few days later, then-student Robert P. Hoyt asked me to come see the computer simulation he had generated. He showed me the structure which I now call the Hoytether(TM). I had not signed the contract with NASA yet, and Hoyt had essentially written my final report!

He is now my partner, and runs the company.

Tethers offer opportunities ranging from handling individual satellites to rocketless travel between Earth and Mars. Are there fundamental differences between these applications, or are they simply the same principles applied at different scales?

They're basically the same principles at different scales.

There are, however, two kinds of tether, one uses conducting tethers and electrical currents running through the tethers to push on the magnetic field of Earth or Jupiter. This is a very powerful propellantless propulsion method, but it can only be used in low Earth orbit below 2000 kilometers or near Jupiter.

The other kind of tether uses strong polymers like Kevlar or Spectra and uses tether length pumping to change the energy in the tether. They both have their uses, and Tethers Unlimited has the patent on combining the two technologies.

What do you think space travel is going to look like over the next 20 years?

We will see rockets relegated to minor tasks, while most of space travel will be done using tether transport systems. There may be some use of solar sails in the solar system. For going to the stars, however, laser-pushed lightsails are the way to go.

What kind of future do you think humans have in space?

It's a promising future. Tethers will lower the cost of interplanetary travel, while laser pushed lightsails will let us leave the solar system and come back -- if we want to!