"It's absolutely baffling," Gordon continued. "Our first project was a simple one, with a tested rocket system. Actually, we used a modified Aerobee, a rocket of proven dependability. Nothing should have gone wrong. But when we fired, the rocket exploded at the top of the launcher. We investigated thoroughly, of course, and found someone had cleverly sabotaged the shoot."
"The what?" Barby asked.
"The shoot. When we launch a rocket we simply call it a shoot."
"Oh. Now I understand."
"Ask any questions you want. Well, we discovered that someone had rigged a steel bar at the top of the launching tower. It was spring-loaded and triggered to move right across the path of the rocket when we fired."
"What does spring-loaded mean?" Mrs. Brant asked.
"The bar was activated by a spring. The spring was under tension. The steel bar lay along one of the pieces of the frame, and was held by a latch. When the trigger withdrew the latch, the spring pushed the bar across the path of the rocket. That's what spring-loaded means in this case."
"Couldn't anyone have found the steel bar?" Scotty wanted to know.
"Yes, if anyone had looked for it. But once the launching tower was erected, there was no reason for anyone to go to the top for an inspection."
Scotty nodded his understanding.