January 2005

Toward a New Vision of Manned Spaceflight

Continued from page 3

By Mark Williams

During the 1960s, NASA declined to pursue either of two strategies that would have made manned spaceflight feasible in the long term. The first was development of von Braun's orbital platforms, where smaller modules lifted out of Earth's gravity could be assembled into larger space-going vessels. The second was the development of an alternative to chemical rockets.

Does NASA's new mission, as framed by the Bush administration, suggest that these lessons have been learned?

New Moon Rising: The Making of America's New Space Vision and the Remaking of NASA, by Frank Sietzen Jr. and Keith L. Cowing, is a book so rushed it seems unedited. Still, it sheds some light, and true believers have reason to be guardedly optimistic. Two major NASA projects, Constellation and Prometheus, will provide the technologies central to achieving the agency's new goals. Constellation will develop several models of the new Crew Exploration Vehicle: the first to carry astronauts into orbit around the earth, the second to travel to the lunar surface, and later versions to reach other planets. An essential part of von Braun's interplanetary strategy is being revived: CEVs may be assembled in Earth orbit. Meanwhile, Project Prometheus will develop a nuclear-powered electric propulsion system that could carry a spacecraft to destinations like Mars.

At first glance, it seems that the technologies that NASA once rejected are being reconsidered. But Freeman Dyson points out that the most important criterion for a nuclear electric propulsion system like that of Prometheus is the weight-to-power ratio, measured in kilograms per kilowatt. To substantially improve on existing chemical rocket systems, Dyson says, the system needs a ratio no greater than five kilograms per kilowatt. Unfortunately, in the current NASA proposal, the Prometheus system would have a ratio of 300 kilograms per kilowatt. "If Prometheus is funded," says Dyson, "it will set back progress in planetary exploring by 20 years. If we are serious about developing a nuclear system, we need a totally new kind of reactor, operating at much higher temperature than existing types." Developing that reactor, he says, will take a long time.

There are other problems. Most significantly, human beings may not be able to survive the levels of cosmic radiation pervading the solar system beyond Earth's magnetic field for the periods demanded by interplanetary missions. Even on the Russian Mir space station and the International Space Station -- both within the protective veil of Earth's magnetosphere -- weightlessness and radiation have been substantial hazards for astronauts and cosmonauts spending extended time in space. Exposure to cancer-causing cosmic radiation during a three- to five-year round trip to Mars would be equivalent to receiving 25,000 chest x-rays. The Apollo program's proposed tactic for dealing with solar flares -- which was to abort the mission and return to Earth -- will not be an option. Consequently, NASA researchers in Mountain View, CA, hope to use carbon nanotubes or other nanoparticles (see "Mitsubishi: Out Front in Nanotech,") to detect, diagnose, and treat the cancers and other health disorders inherent in manned spaceflight.

But for prolonged spaceflight, humans would probably require more radical biological enhancements. Future astronauts might differ significantly from their terrestrial kin. This is a long way from the vision of space travel for the masses that was promoted by Gene Kranz and Freeman Dyson. And as with the development of a new reactor, it might take a long time to create these demi-human space-farers. Concerning the future of human beings in space, a Kafka quote might apply: "There is infinite hope. But not for us."