that efforts of pure science, with no practical application for many decades, must be accompanied by the immediate application of science wherever possible to humanity's urgent problems.

I'm reporting on an apparent solution to the limits-to-growth-problem, based on fundamental facts of science that will never change: First, that while we search desperately for new energy resources here on Earth, a few thousand miles above our heads there streams by constantly night and day, a flood of high-intensity solar energy far greater than we could ever need.

Second, that already we know of materials resources, for large-scale industrial activities in space, thousands of times greater than we could ever obtain from the Earth without despoiling it completely. We spent, in today's dollars, $50 billion on the Apollo project. As a result we know that the lunar surface is one-third metals, usable for manufactured products, one-fifth silicon, ideal for solar cells and electronics, and more than 40 percent oxygen, essential in life support. I say we should use that knowledge, not throw it away or ignore it.

Already we know that there are special groups of asteroids, with orbits close to the Earth, that are rich not only in the minerals found on the Moon but also in the organic-chemistry elements needed for a complete industrial economy.

Last of three basic scientific facts, we know that the cost in energy to transport materials from the lunar surface into free space, where it can be used by a totally solar-powered industry, is less than onetwentieth as large as the energy cost to transport similar materials up from the Earth.

It makes sense to put at least a small fraction of our total national effort, perhaps one part in ten thousand of our Federal budget, into exploring over the next several years how we can use these basic scientific facts to break through the limits to growth and solve the urgent worldwide problems.

In addition to the eternal truths of science, there are facts of current events, that must be heeded in any practical program.

First, the Shuttle is the only vehicle system that will be operational for at least the next decade, and that can give us a toe-hold on the high frontier. If used efficiently, as an airline uses its aircraft, the Shuttle could transport a litle less than 2,000 tons of equipment per year into orbit.

Second, events are changing much too rapidly for us to foresee now just which industrial products in space will be the first to benefit from nonterestrial materials. Right now the idea of satellite solar power stations, in synchronous orbit where the sun always shines, beams down low-density microwave energy for conversion to ordinary electricity on Earth, looks like an ideal candidate. The need is great, and the demand can be estimated as a worldwide market of over $200 billion by the turn of the century. Clearly the use of materials already at the top of Earth's gravitational mountain could reduce transport costs by a large factor, as well as avoiding environmental impact questions that would be raised by the alternative of launching rockets through the atmosphere from Earth, with a total traffic that would be 2,000 times larger in tons per year than the shuttle traffic.

But it may be that by the time the high frontier is opened the satellite power concept will have hit engineering or environmental blocks, or during its development some other energy technology will have

become less expensive. It makes sense therefore to preserve generality in opening the nonterrestrial resources. By the time we have broken through the limits to growth, it will be clearer how first to exploit the breakthrough.

In the past 3 years there has been great progress in the scientific and engineering studies of the high frontier concept, and that progress is well documented, in proceedings of conferences published by the American Institute of Aeronautics and Astronautics, in publications of the Edison Electric Institute, and in a disarmingly slim volume with the technical articles from a 1976 NASA study. These articles have gone through the entire process of scientific peer review. Last summer, a study more than four times as large as this one was completed, and its results, in 16 peer-reviewed technical articles, will shortly be published by NASA.

To show you how much has been accomplished with very little, here are a few pictures of one special device that may be a key to reaching the high frontier within the limitations of the Shuttle. The device is a new type of electric motor called the mass-driver. First is a schematic of the mass driver. It takes in electric power, accelerates any sort of mass to a high speed, and then expells it [slide 1].

That mass if expelled in space provides a reaction force just like a rocket. If located on the lunar surface the machine could accelerate materials from the surface of the moon to free space.

A first working model has already been built by a group of student volunteers under the direction of Dr. Henry Kolm [slide 2].

The machine was demonstrated at several location, one of them the final briefing at our 1977 NASA-Ames study [slide 3].

The tests were entirely successful, and the model accelerated a pound of mass from zero to 85 miles per hour over a 6-foot length in onetenth of a second. A mass-driver reaction engine could be carried into orbit in sections, by the Shuttle, to an orbital workbench of a kind already studied by NASA-Johnson Space Center [slide 4].

With your permission, I would like to take 30 seconds to show you the operation of that model. You will have to watch carefully, and after the countdown occurs, don't blink your eye, because the acceleration takes less than a tenth of a second.

[Film demonstration.]

The reaction engine could be assembled as shown next [slide 5].