Engines for the cosmos: exploration of deep space requires systems of propulsion that can go the distance.

GALACTIC FORCES SPIRAL ACROSS THE COSMOS, fueled by nuclear fission and fusion, and atoms in plasmatic states churn in the constraints of gravitational forces and magnetic fields. In their wanderings, the galaxies spew light, radiation, atomic, and subatomic particles through the universe.

Throughout the ages of man, minds have wondered about visions of journeying through the stars. If humans and human devices from Earth are to go beyond the moon and journey into deep space, they must use the forces of the cosmos, such as ions, electrons, and energies generated from the manipulation of subatomic and atomic particles. Forms of electromagnetic waves, perhaps in the light or radio frequencies, must control deep space engines. We won't get far from Earth on our accustomed hydrocarbon fuels.

DEEP SPACE PROPULSION

Rocket propulsion to explore deep space has different requirements than launch propulsion on Earth, where high thrust is required to escape the planet's gravitational pull. Vehicles in deep space are only faintly affected by Earth's gravity. Consequently, high thrust engines are not required.

To explore the outer planets in a reasonable time, engines must generate either high exhaust velocity or high specific impulse. Specific impulse, abbreviated as [I.sub.sp], is a measure in seconds of propulsion system efficiency in converting fuel energy into momentum. Chemical propulsion can provide high thrust, but is limited in specific impulse (fewer than 500 seconds). The reason is that chemical propellants carry within their chemical composition all of the energy that can be generated, and current technology is about at the limit of the amount of energy that can be put into a chemical bond.

To achieve higher specific impulses, we must look to other energy sources, including fission and fusion. With the very high energies from these sources, subatomic particles of light gases can be manipulated to efficiently generate low thrust energy by using electron guns, electrical fields, magnetic fields, electric currents, lasers, radio waves, or combinations thereof.

This idea was shared by several early 20th-century chemical rocketeers. In 1947, Wernher von Braun asked Ernst Stuhlinger to research the concept of electric propulsion as written in Herman Oberth's book, Possibilities of Space Flight, published in 1929 in Berlin. As Stuhlinger recalls, von Braun said, "I wouldn't be a bit surprised if we flew to Mars electrically."