Consultant Daniel MacDonald discusses aspects of a proposed space tower.
Consultant Daniel MacDonald discusses aspects of a proposed space tower. Gary Robbins

Ever since Arthur C. Clarke published "Fountains of Paradise" in 1979, scientists and science writers have been sketching out ideas for a space elevator. No one is close to building one. But the topic got an extended and mostly hopeful airing on Wednesday at UC San Diego's Qualcomm Institute, where scores of smarties gathered for day one of Starship Symposium, one of the opening events of the Clarke Center for Human Imagination.

Sci-fi writer Neal Stephenson took the stage and recounted his efforts, with others, to develop a rocket launch platform that would be 9.3 miles to 12.4 miles tall. The idea is being pursued because a rocket would face much less gravitational drag at those altitudes. It'd be quicker and easier to get into space.

Stephenson gave an interesting overview of the idea. But the most compelling insight came from his collaborators, notably Keith Hjelmstad, a professor of structural engineering at Arizona State University.


Hjelmstad said that building a structure that tall would be tough because "the design environment is highly uncertain. A fair amount of the tower exists in really cold temperatures. Building materials do some bad stuff at low temperatures. Those are not good conditions for workers. We might need robots."

Earlier, researchers figured that the upper reaches of such a tower would face winds up to 300 mph. That's been revised upward, to 460 mph. The revision has made it harder to figure out how to build a structure that could handle such loads.

"You need girth for stability," Hjelmstad said. "But you need to keep the amount of material small. Mt. Everest is a counter example."

He wasn't joking about girth. Hjelmstad said the base of a space tower would cover 11 square miles and that it would weigh about 430 million tons.

"The tower does seem to be possible," he said, "but there it sits, on the outskirts of feasibility."

Sci-fi star David Brin asks: Is there anybody out there?


The afternoon session is underway, but it's not proving to be as interesting as the lunch hour, when a Who's-Who of sci-writers brown-bagged it outside the Qualcomm Institute. With a turn of your head, you could see Gregory Benford, David Brin, Neal Stephenson and Vernor Vinge.

File photo of Vernor VingeWikipedia Commons

First up in the afternoon session is space consultant Patti Grace Smith, whose bland overview of the future of spaceflight is putting people to sleep. The table conversation at lunch was much more interesting: Why did director J.J. Abrams focus so much on Spock and Uhura's romantic relationship in "Star Trek Into Darkness?" Fair question.


Things are looking up. Geoff A. Landis is talking about nuclear-thermo rockets .... His opener: "I hope you're all familiar with the rocket equation." Geeks sit up in their chairs... "Pound force is not pound mass." Noted, and cool. But what about starships. Waiting ...

Landis ...

"A nuclear rocket could become the workhorse of the solar system."

"Can you go beyond the thermal limit?" Maybe. "You can operate a rocket on electricity .. But electric systems tend to be low thrust."

Artist's rendering of a manned base on Callisto. NASA

"A water-based economy for the solar system: Water is valuable for reaction mass, as well as for life support; Inner solar system is water-poor; Outer solar system is ice-rich."

He's talking about HOPE, the Human Outer Planet Mission. It would be a mapped trip to Callisto. "The first thing we'd do when we get there is tunnel under the ice and never look at anything ... It probably has a sub-surface ocean."

"We're also scouting it out for its resources. It is a source of enormous amounts of water."

Landis is talking about the technologies that could get us to the outer planet. Need to hear more about why we should go.

The total mission to/back from Callisto would be about five years.

He says the nuclear thermo rockets would be good for the outer planets, but probably couldn't get us to the stars. So it is not a starship.