Star Wars Does It Again

By Philip Elmer-DeWitt

In the eight years since it was founded, the Strategic Defense Initiative has poured $24 billion into various schemes for knocking down ballistic missiles, many of them dubious. But no Star Wars project seems more clearly -- or appropriately -- destined for the technological trash heap than the one that came to light last week. According to documents made public by the Federation of American Scientists for the express purpose of torpedoing the scheme, the Pentagon has for several years been secretly developing a new kind of booster rocket -- code-named Timberwind -- that would loft giant weapons into space on short notice. Its power source: an onboard nuclear reactor running at extremely high temperatures and spewing radioactive exhaust directly into the atmosphere.

The idea behind Timberwind is simple. Just pump liquid hydrogen through a small nuclear reactor heated to several thousand degrees Fahrenheit. The liquid hydrogen is instantly converted to hydrogen gas, which then blasts out of a nozzle. The resulting thrust is two to three times as great as that generated in conventional rocket engines by the explosive mixture of hydrogen and oxygen. Much larger payloads could thus be lifted into orbit.

That is the theory. In practice, it's more complicated. The reactors must be built of materials that are both lightweight and capable of withstanding extraordinary temperature changes, from several hundred degrees below zero to several thousand degrees above. To reduce the risk of fatal meltdowns, the uranium fuel must be packed in tiny particles coated with several layers of carbon alloy and carefully machined to very close tolerances. And because the fuel gives off "hot" -- meaning radioactive -- by-products, it is inevitable that the escaping gas will pick up some radioactivity on its way out.

These technological problems may be solvable. Timberwind proponents say cleanup systems could remove radioactive by-products before they are discharged into the air. Better still, the atomic engines would be handy on a manned mission to Mars. Nonetheless, the program's political problems may be insurmountable. The 1979 accident at Three Mile Island shook America's confidence in nuclear technology, and the Challenger explosion dramatically demonstrated the vulnerability of space launches. Not surprisingly, many scientists are bothered by the idea of putting these two technologies together. In 1989, antinuclear activists, protesting potential "Chernobyls in the skies," organized the first civil-disobedience demonstrations aimed at halting a U.S. space shot. Their target: NASA's Galileo spacecraft, an interplanetary scientific mission that used as its power source two | radioisotope thermoelectric generators fueled by plutonium. In October 1989, the Galileo launch went off without a hitch, despite the protests.

As nuclear devices go, Galileo's generators were relatively innocuous. Thermoelectric generators are battery-like gadgets that use natural radioactive decay in their fuel cells to produce electric power. Timberwind's engines, on the other hand, are true nuclear reactors that split atoms and generate heat, using the same chain reactions that power atom bombs. Although modern nuclear engineering has virtually eliminated the risk of explosions and meltdowns in such reactors, the problem of disposing of radioactive wastes has not gone away. Nor has the stigma attached to nuclear reactors in general. "If anybody tries launching a reactor-powered rocket," says Theodore Taylor, a veteran designer of nuclear devices, "past demonstrations will pale by comparison."

So why is the U.S. so interested in Timberwind? The reasons date back to the early 1970s, when NASA, with the Pentagon's blessing, decided to put the bulk of its research funds into the reusable space shuttle. Further development of conventional rocket boosters stalled. Now both agencies find themselves bumping into the limited payload capacities of the remaining rockets; NASA for hoisting its space station into orbit and the Pentagon for lifting its big directed-beam Star Wars weapons. The proposed nuclear-powered rockets would more than triple the payload of the U.S.'s most powerful booster, the Titan 4, from 20 tons to more than 70 tons.

Ironically, one of the projects killed in 1972 to make way for the space shuttle was Project Rover, a 17-year, $1.4 billion effort to develop nuclear- powered rockets. More than a dozen prototype engines were built and tested. The same work in today's dollars would cost $25 billion. But Rover was always viewed as a second-stage rocket that would be fired only after it was safely out of the earth's atmosphere. Launching a nuclear rocket from the ground was deemed to pose unacceptable health risks.

According to Steven Aftergood, a space expert at the Federation of American Scientists, project Timberwind is still at an early stage in its development. Fuel elements have been built and tested. Testing grounds have been selected in the Nevada desert. The Defense Science Board has given the project its seal of approval. And plans have been made to send a prototype rocket on a suborbital test flight over Antarctica and parts of New Zealand. All this was before the veil of secrecy had been lifted, however. Now that the word is out, and Congressmen have begun to stake out positions on either side of the issue, Timberwind is starting to look like another one of those wacky Star Wars projects that will never get off the ground.

With reporting by Bruce van Voorst/Washington