A million worries flooded Pete Graham's brain. Was the cable strong enough? Would it snap under stress? Could the helicopter negotiate the powerful updrafts? A single gust of wind buffeting the helicopter far above, and the gleaming probe would be dashed against the rocks and lost forever.

Then there was the awful possibility that his baby might malfunction. During the deployment phase, he tried to keep this last, horrible notion as far from conscious thought as was humanly possible.

When the Virgil probe was settled to the rock floor of the crater, anxiety rang in Graham's ears. There was a single, horrifying moment after the cable was released when it looked as if Virgil might tip over. But to the scientist's relief, the probe caught itself. A jerky manipulation of one leg, and the giant mechanical spider oriented itself on the floor of the cavern. When the applause erupted in the trailer, Clark Beemer didn't join in. After ten minutes of seeing that thing crawling around in Popocatepetl, the PR man was checking his watch, bored.

The scientists instructed the probe to plant two stationary cameras on the floor of the cave to monitor its movements. Another head-mounted microcamera gave a bird's-eye view of Virgil's progress.

As it crawled around in semidarkness in the steaming cavern, the men in the trailer studied its every move. Clark Beemer couldn't believe how excited they all were.

"What is it for anyway?" Clark muttered as the scientific team studied the data coming in from Virgil. Pete Graham didn't lift his eyes from his computer screen. "Virgil is a planetary probe designed to exist in hostile environments. If it can endure the heat of a volcano, it can do the same thing on an alien world."

"Don't you have heat simulators at NASA?"

"Nothing like this," Graham explained. "And a natural environment, not an artificial one, is what Virgil will be facing. We need to test him under battlefield conditions."