It sounds like 'Jack and the Beanstalk' but is an elevator reaching to space actually possible? Many writers have imagined such a device, mainly in science fiction, but NASA is seriously considering an extremely green alternative to environmentally toxic rocket fuel. Compared to dangerous, expensive and perchlorate-dependent rocket travel, taking an elevator into space, powered only by light, makes enough sense that NASA is considering offering a prize for the team that can show a way to do it.

The main ingredient of rocket fuel, perchlorate, is at the heart of a growing debate about the uses of the chemical. According to studies by U.S. Centers for Disease Control, perchlorate is showing up in water supplies across the country, putting the public at risk. If someone thinks that rocket travel is dangerous only for astronauts, think again.

A space elevator would eliminate the need for rocket fuel. As it stands now, plans call for a base tower approximately 50 km tall -- the cable would be tethered at the top and the bottom. To keep the cable structure from tumbling to Earth, it would be attached to a large counterbalance mass beyond geostationary orbit. An asteroid could be moved into place for that purpose.

The energy required to move a payload by space elevator from the ground to geostationary orbit could remain relatively low. Using today's energy costs, researchers figure a 12,000-kg Space Shuttle payload would cost no more than $17,700 for an elevator trip to GEO. A passenger with baggage at 150 kg might cost only $222! Today it costs around $10,000 per pound ($22,000 per kg). Potentially, the cost is only a few dollars per kg with an elevator. Of course, building the elevator will be costly and only makes sense if it gets heavy use by both passengers and payload, tourists and space dwellers.