“Cesium!" Understanding came to Hank Mahenili. Any informed engineer knew the importance of this element. "Just what is cesium, Dad? And what is it used for?" "Technically, son, its atomic number is 55, and its atomic weight is 132.91. Its use?" Mr. Brewster smiled. "I’ll tell you this, we’ll never get to the moon without it." "You mean it’s used in rocket propulsion?" Biff asked. "That’s right, Biff. It’s a high-thrust, long-life rocket propulsion fuel. Most costly." "More than gold?" Li asked eagerly. "Much more, Li. If you and Biff had about ten pounds of it between you, you’d have your education paid at any college you wanted to go to—M.I.T., Cal Tech—any of them." "Wow! Must be worth more than a thousand dollars a pound, then," Biff said, his voice filled with amazement.”