Nuclear Rocket?

Tony Hillerman, news editor of the Santa Fe New Mexican, was rifling through a stack of press handouts from Los Alamos Scientific Laboratory last week in the hope of finding something worth putting in the paper. One routine announcement noted that William F. Carlson of Bristol, Conn. had been hired for the new "N" Division, which, said the release, "is concerned with research and development of nuclear rocket propulsion."

This was indeed news. The Atomic Energy Commission had never announced that nuclear rockets were possible. Newsman Hillerman checked and provoked an official statement. Yes, said the AEC, two of its laboratories, Los Alamos and Livermore, are studying the "feasibility of nuclear propulsion for rockets."

Power Problem. The AEC did not say how feasible nuclear rockets look. Most scientific judgments about them have been pessimistic. Rocket motors develop their thrust by burning fuel with an oxidizer and expelling the products of combustion at high speed through a tail pipe. The energy of combustion is necessary to make the gases move fast, but the mass (weight) of the gases is also necessary. No mass, no thrust.

Nuclear fuel is a fine source of energy, one pound of U-235 producing as many calories as 1,500 tons of coal. A modest amount of U-235 could, so far as energy is concerned, propel a commodious space cruiser to the moon and back. But energy is not enough. A uranium-burning rocket motor would have no products of combustion to shoot out of its tail pipe, and without some massive material to jettison, the motor would have no thrust.

There are ways of getting around this failing of nuclear rockets. The most obvious is to take along a stock of material that can be gasified by the nuclear heat and shot out the tail at great speed. The trouble with this solution, of course, is that the weight of the material may make the nuclear rocket hardly more efficient than a chemically fueled one. In addition, a heavy shield must be carried to protect the crew from nuclear radiation.

Ionic Motor. More elaborate ways of using nuclear fuel in rockets have been dreamed up by the imaginative engineers who plan for space travel. One of their proposals is a nuclear reactor running a conventional electrical generator. The current from it ionizes atoms of some convenient element and expels them from the tail pipe. An "ionic motor" of this sort can run, theoretically, almost forever on a cupful of uranium.

Its thrust, however, would be comparatively small. It might be fine for cruising around the far reaches of the solar system, but it would not be strong enough to tear the spaceship out of the clutch of the earth's gravitation.

The AEC's scientists are not, presumably, thinking about space flight, which envisions a human crew that must not be subjected to radiation. Missiles, which are "uninhabited." should prove simpler to propel by nuclear power. With no crew, they will need no shield, and they can start on their journeys even more suddenly than artillery shells.

Knowledge of nuclear reactions has increased enormously in the last few years. Possibly AEC's scientists hope to develop an atomic explosive that exerts much of its force in one direction, as a "shaped charge" does. Such a charge might propel a missile without destroying it. The chances are, however, that the AEC rocketeers are using classified principles that laymen cannot even guess about.

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