"A rocket was cheaper."
The source of the money required for the project was something Duran had overlooked. However, it was, he realized, one best postponed for the present. The important thing now was to regain his son's confidence.
"Did you design it?"
"Yeah. Well, I drew it up. Nothing very original about it. But it was a good little machine."
Duran noticed the boy's restless squirming, saw him perfunctorily place a hand to the baggy pocket of his jacket and quickly withdraw it, then arrived at a decision. Reaching into his own coat, Duran took out the pack of cigarettes, extending it to his son.
"Care for a cigarette?" he asked.
The youth looked at him doubtfully for an instant. Then he smiled his first smile that evening.
"Thanks, Dad," he responded, taking one and lighting it self-consciously. He added, "You've been out of town so much, I didn't think you knew I'd started—"
"I know, Rog," the man said, aware of a rising flood of self-condemnation. "Go on, son. About the rocket. What kind of fuel did you use?"
"Oh, nothing special. It had a liquid bi-propellant motor. We used ethanol and liquid oxygen. Pretty old-fashioned. But we didn't know how to get hold of the fancier stuff, and didn't have any way of synthesizing it. Then, at the last minute, we found that one of the valves feeding into the nozzle was clogged up. That's why we were late to class."