hen you're not on a military project?" Scotty asked.

"Yes and no. The work is sponsored jointly by the Department of Defense
and some other agencies, including the National Science Foundation.
However, we are not working on military projects, in the sense that our
rockets are not weapons. They're for research purposes. Of course some
of the things we're doing will be valuable for military application
later, and so our test base is closed to the public and most of our work
has a high classification. Usually the work is secret, but sometimes
it's top secret. Is that clear?"

Scotty and the Brants agreed that it was.

"Very well. Since we operate under security, every person who works on
the base is fully investigated and cleared for top secret. This is an
important point. You know how thorough these investigations are. Once a
security check for top secret is completed, there is literally nothing
of importance that isn't known about a person. But in spite of the most
careful security work, there is someone on our base about whom we do not
know everything.

"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.

"To go on, as soon as we found the bar and the spring mechanism we knew
we'd b