(The following description of an orbit is excerpted from the novel "Tom Swift and His Rocket Ship," Victor Appleton II, Grosset & Dunlap Publishers, New York, 1954, p. 115.)

"By the way, Tom, has that there rocket o' yours got a name?"

"Yes. It's going to be christened the STAR SPEAR. And she's practically ready for orbital flight."

"What does orbital mean?" Chow asked, wrinkling his brow.

"Orbital means a track," Tom replied. "A thing to go around onča more or less circular path."

Bud added, "A rocket in orbital flight is like a baseball swinging at the end of a string. The path of the ball in relation to your fist will be its orbit."

Chow doubled up his fist and swung his arm in a circle. "I get it. Go on."

"In the rocket we turn off the motors at a certain altitude," Tom said, "and keep on flying along our orbit."

"Hm," Chow grunted. "But after you turn off the motors, what's goin' to keep the lil ole rocket goin'?" The cook scratched his bald head. "Why don't she slow down an' tumble right back to the earth?"

"Its centrifugal force exactly balances the pull of the earth," Tom answered. "And there's no mass of air, as we know it here, to interfere with the rocket and slow it down."

"I sure can't figger that," Chow said. "An' you fellows better not count on it either. Take along enough gas to get back!"